WO2018165403A1

WO2018165403A1 - Hard-tissue stem implant comprising a bulk stem implant, a face, pillars for contacting a cancellous portion of a hard tissue, and slots, wherein the pillars are prearranged to match an underlying structure of the cancellous portion

Info

Publication number: WO2018165403A1
Application number: PCT/US2018/021503
Authority: WO
Inventors: George J. Picha; Grant Wesley PHILLIPS; Rachel Smith; James Price
Original assignee: Applied Medical Research Inc
Current assignee: Applied Medical Research Inc
Priority date: 2017-03-10
Filing date: 2018-03-08
Publication date: 2018-09-13
Anticipated expiration: 2019-09-10

Abstract

Hard-tissue stem implants are provided that comprise a bulk stem implant, a face, pillars, and slots. The pillars are for contacting a cancellous portion of a hard tissue, are distributed on the face, across an area of at least 80 mm², and extend distally therefrom. The pillars are prearranged to match an underlying structure of the cancellous portion of the hard tissue. The slots are to be occupied by the cancellous portion of the hard tissue. Methods of making and using hard-tissue stem implants are also provided.

Description

HARD-TISSUE STEM IMPLANT COMPRISING A BULK STEM IMPLANT, A FACE, PILLARS FOR CONTACTING A CANCELLOUS PORTION OF A HARD

TISSUE, AND SLOTS, WHEREIN THE PILLARS ARE PREARRANGED TO MATCH AN UNDERLYING STRUCTURE OF THE CANCELLOUS PORTION

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No.

62/469,738, filed March 10, 2017, the entire disclosure of which is hereby incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The invention relates to hard-tissue stem implants, and more particularly to hard-tissue stem implants that include a bulk stem implant, a face, pillars for contacting a cancellous portion of a hard tissue, and slots, wherein the pillars are prearranged to match an underlying structure of the cancellous portion of the hard tissue.

BACKGROUND OF THE INVENTION

[0003] Conventional hard-tissue implants include implants designed to promote ingrowth of hard tissue based on forming a tissue/implant interface in which the implant forms a continuous phase and the tissue forms a discontinuous phase, e.g. based on the implant having a concave and/or porous surface into which the hard tissue can grow, and designed to have add-on surface modifications, e.g. modifications added based on sintering.

[0004] For example, Van Kampen et al., U.S. Pat. No. 4,608,052, discloses an implant for use in a human body having an integral attachment surface adapted to permit ingrowth of living tissue. The implant surface is defined by a multiplicity of adjacent, generally concave surface parts having intersecting, generally aligned rims defining an inner attachment surface portion and by a multiplicity of spaced posts projecting from the inner attachment surface. Van Kampen also discloses that implants have been provided with porous surfaces, as described in U.S. Pat. Nos. 3,605, 123, 3,808,606, and 3,855,638.

[0005] Also for example, J.D. Bobyn et al, 150 Clinical Orthopaedics & Related Research 263 (1980), discloses that a pore size range of approximately 50 to 400 μπι provided an optimal or maximal fixation strength (17 MPa) in the shortest time period (8 weeks) with regard to cobalt-base alloy implants with powder-made porous surfaces.

Specifically, implants were fabricated based on coating cylindrical rods of cast cobalt-base alloy with cobalt base alloy powder in four particle size ranges. The particle size ranges were as follows: 25 to 45 μιη; 45 to 150 μιη; 150 to 300 μιη; and 300 to 840 μιη. The

corresponding pore size ranges of the particles were as follows: 20 to 50 μηι; 50 to 200 μιη; 200 to 400 μιη; and 400 to 800 μηι, respectively. The particles were then bonded to the rods based on sintering. All implants were manufactured to have a maximal diameter of 4.5 mm and a length of 9.0 mm. The implants were surgically inserted into holes in dog femurs and bone ingrowth was allowed to proceed. After varying periods of time (4, 8, or 12 weeks), the maximum force required to dislodge the implants was determined. Implants with a pore size lower than 50 μιη yielded relatively low fixation strengths at all time points, while implants with a pore size higher than 400 μπι exhibited relatively high scatter with regard to fixation strengths, thus indicating that a pore size range of approximately 50 to 400 μπι provided an optimal or maximal fixation strength.

[0006] Conventional hard-tissue implants also include implants having surface texturing, e.g. raised portions and indented portions, barbs, and/or pillars, to promote an interference fit between the implants and adjacent bone, to make it difficult to withdraw the implants from hard tissue, or to more effectively mechanically anchor at an early date or affix into adjoining hard tissue.

[0007] For example, Tuke et al., U.K. Pat. Appl. No. GB2181354A, discloses an orthopedic implant having at least one surface area, integral with the adjacent portion of the implant and adapted in use to contact bone. The surface area has a finely patterned conformation composed of a plurality of raised portions separated from each other by indented portions. The indented portions are of a width and depth to allow bone penetration thereinto in use to promote an interference fit between the implant and adjacent bone in the region of the patterned area.

[0008] Also for example, Amrich et al., U.S. Pat. No. 7,018,418, discloses implants having a textured surface with microrecesses such that the outer surface overhangs the microrecesses. In one embodiment, unidirectional barbs are produced in the surface that can be inserted into bone or tissue. The directional orientation of the barbs is intended to make it difficult to withdraw from the bone or tissue.

[0009] Also for example, Picha, U.S. Pat. No. 7,556,648, discloses a spinal implant, i.e. an implant for use in fusing and stabilizing adjoining spinal vertebrae, including a hollow, generally tubular shell having an exterior lateral surface, a leading end, and a trailing end. The exterior surface includes a plurality of pillars arranged in a non-helical array. Each pillar has a height of 100 to 4,500 μπι and a lateral dimension at the widest point of 100 to 4,500 μηι. The exterior surface also has a plurality of holes therethrough to permit bone ingrowth therethrough.

[0010] Unfortunately, interfaces of hard tissue and hard-tissue implants in which the hard tissue is in a discontinuous phase may be susceptible to stress shielding, resulting in resorption of affected hard tissue, e.g. bone resorption, over time. Also, addition of surface texturing to implants by sintering can result in the surface texturing occupying an excessive volume of corresponding hard tissue/implant interfaces, leaving insufficient space for hard tissue. In addition, spinal implants are designed to perform under conditions relevant to spine, i.e. compression, rotational shear, and vertical shear, with the compression being essentially constant, the rotational shear being intermittent, and the vertical shear being rare, rather than conditions relevant to other hard tissues such as long bone, maxillary bone, mandibular bone, and membranous bone, i.e. load bearing conditions, including compression and tension, varying across the hard tissue and across time, and intermittent rotational and vertical shear.

[0011] Picha et al., U.S. Pat. No. 8,771,354, discloses hard-tissue implants including a bulk implant, a face, pillars, and slots. The hard-tissue implant has a Young's modulus of elasticity of at least 10 GPa, has a ratio of (i) the sum of the volumes of the slots to (ii) the sum of the volumes of the pillars and the volumes of the slots of 0.40: 1 to 0.90: 1, does not comprise any part that is hollow, and does not comprise any non-pillar part extending to or beyond the distal ends of any of the pillars. The hard-tissue implants can provide immediate load transfer upon implantation and prevent stress shielding over time, thus promoting hard- tissue remodeling and growth at the site of implantation. The interface can have a continuous phase corresponding to the hard tissue and a discontinuous phase corresponding to the hard- tissue implant.

[0012] Nonetheless, there remains a need for hard-tissue implants that address the issues discussed above and that provide improvements. The hard-tissue stem implant disclosed herein is such an implant.

BRIEF SUMMARY OF THE INVENTION

[0013] A hard-tissue stem implant is provided that includes a bulk stem implant, a face, pillars, and slots. The bulk stem implant has a proximal end, a distal end, and an elongated stem body therebetween. The face is an exterior surface of the bulk stem implant. The pillars are for contacting a cancellous portion of a hard tissue. The pillars are distributed on the face, across an area of at least 80 mm², extend distally therefrom, and are prearranged to match an underlying structure of the cancellous portion of the hard tissue. Each pillar is integral to the bulk stem implant, has a distal end, has a transverse area of (100 x 100) to (10,000 x 10,000) μπι², and has a height of 100 to 10,000 μιη. The slots are to be occupied by the cancellous portion of the hard tissue. The slots are defined by the pillars. Each slot has a width of 100 to 10,000 μπι as measured along the shortest distance between adjacent pillars.

[0014] Also provided is a method of making a hard-tissue stem implant that, upon implantation into a hard tissue, provides immediate load transfer and prevents stress shielding. The hard-tissue stem implant is as described above. The method includes a step of (1) determining the underlying structure of the cancellous portion of the hard tissue. The method also includes a step of (2) designing the hard-tissue stem implant such that the pillars will be prearranged to match the underlying structure of the cancellous portion of the hard tissue. The method also includes a step of (3) making the hard-tissue stem implant.

[0015] Also provided is a method of use of a hard-tissue stem implant in a hard tissue of an individual in need thereof. The hard-tissue stem implant is as described above. The method includes a step of (1) selecting the hard-tissue stem implant such that the pillars are prearranged to match the underlying structure of the cancellous portion of the hard tissue. The method also includes a step of (2) implanting the hard-tissue stem implant in the hard- tissue of the individual.

[0016] Also provided is another hard-tissue stem implant. The other hard-tissue stem implant includes a bulk stem implant, a face, pillars, and slots. The bulk stem implant has a proximal end, a distal end, and an elongated stem body therebetween. The face is an exterior surface of the bulk stem implant. The pillars are for contacting a cancellous portion of a hard tissue. The pillars are distributed on the face, across an area of at least 80 mm², and extending distally therefrom. Each pillar is integral to the bulk stem implant, has a distal end, has a transverse area of (100 x 100) to (10,000 x 10,000) μπι², and has a height of 100 to 10,000 μπι. The slots are to be occupied by the cancellous portion of the hard tissue. The slots are defined by the pillars. Each slot has a width of 100 to 10,000 μπι as measured along the shortest distance between adjacent pillars. The hard-tissue stem implant has a Young's modulus of elasticity of at least 3 GPa. The hard-tissue stem implant also has a ratio of (i) the sum of the volumes of the slots to (ii) the sum of the volumes of the pillars and the volumes of the slots of 0.40 : 1 to 0.90 : 1. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] These and other features, aspects, and advantages of the present disclosure are better understood when the following detailed description is read with reference to the accompanying drawings, in which:

[0018] FIG. 1 is a perspective view of a hard-tissue stem implant corresponding to a femoral stem implant;

[0019] FIG. 2 is a perspective view of a hard-tissue stem implant corresponding to a humeral stem implant;

[0020] FIG. 3 is an illustration of a pattern defined by stress lines of human adult femur including a principal compressive group, a principal tensile group, a secondary compressive group, a secondary tensile group, and a greater trochanteric group;

[0021] FIG. 4 is an illustration of (A) a cancellous portion of a human adult femur and (B) a side view of a portion of a hard-tissue stem implant corresponding to a femoral stem implant including pillars prearranged to match an underlying structure of a cancellous portion of a human adult femur;

[0022] FIG. 5 is a schematic perspective view of a portion of a hard-tissue stem implant including pillars;

[0023] FIG. 6 is a schematic top plan view of a portion of a hard-tissue stem implant including pillars;

[0024] FIG. 7 is a schematic side elevational view of a portion of a hard-tissue stem implant including pillars;

[0025] FIG. 8A is a schematic perspective view of a pillar of a hard-tissue stem implant;

[0026] FIG. 8B is a schematic cross-sectional view of a pillar of a hard-tissue stem implant;

[0027] FIGS. 9A-E are schematic top plan views of portions of hard-tissue stem implant including pillars in which the circumference of the transverse area of the pillars thereof have (A) a square shape, (B) a rectangular shape, (C) a herringbone shape, (D) a circular shape, and (E) an oval shape;

[0028] FIG. 10 is a schematic perspective view of part of a portion of a hard-tissue stem implant including pillars.

[0029] FIG. 11 is a top view of the femoral stem implant of FIG. 1;

[0030] FIG. 12 is a bottom view of the femoral stem implant of FIG. 1;

[0031] FIG. 13 is a first side view of the femoral stem implant of FIG. 1; [0032] FIG. 14 is a second side view of the femoral stem implant of FIG. 1;

[0033] FIG. 15 is a sectional view of the femoral stem implant of FIG. 13; and

[0034] FIG. 16 is a third side view of the femoral stem implant of FIG. 1.

DETAILED DESCRIPTION

[0035] As set forth in the figures, example hard-tissue stem implants are provided. The hard-tissue stem implants provide advantages, including for example that the hard-tissue stem implants can promote hard-tissue remodeling and growth of the hard tissue at the site of implantation and that the interface of the hard-tissue stem implants and the hard tissue can withstand substantial yield/elongation and load before failure. Without wishing to be bound by theory, it is believed that these advantages are based on properties of the hard-tissue stem implants and the interface resulting from implantation thereof.

[0036] This is because the interface can have a continuous phase corresponding to the hard tissue and a discontinuous phase corresponding to the hard-tissue stem implant. The hard tissue can also make up at least 40% of the volume of the interface, and the product of the Young's modulus of elasticity of the hard tissue and the volume of the tissue and the product of the Young's modulus of elasticity of the implant and the volume of the pillars of the implant can be well matched. Thus, the interface can exhibit mechanical properties similar to those of the bulk hard tissue adjacent to the interface. Also, the pillars potentially may be pressed into the hard-tissue, potentially eliminating micro-motion and migration of the implant over time, accommodating torque, and/or eliminating the need for adhesives such as cement or grout to hold the implant in place. In addition, the hard-tissue stem implants may promote rich vascularization of the hard tissue of the interface, enhancing wound healing, providing nutritional support, accelerating healing, remodeling, and integration of the hard tissue, and limiting the potential for infection of the hard tissue. Rapid or immediate integration of the hard tissue into the space between the pillars of the hard-tissue stem implant may also prevent detrimental cellular reactions at the interface, such as formation of fibrous tissue, seroma, or thrombosis.

[0037] In some cases the pillars may initially penetrate the hard tissue, e.g. partially or completely, upon implantation of the hard-tissue stem implant. In such cases, the hard- tissue stem implants can provide immediate load transfer upon implantation and prevent stress shielding over time, thus promoting hard-tissue remodeling and growth at the site of implantation. Alternatively or additionally, in some cases the pillars may penetrate the hard tissue later, under physiological loading. Also alternatively or additionally, over time the hard tissue may grow in and around the pillars, thus occupying slots between the pillars, e.g. during healing.

[0038] It also is believed that the hard-tissue stem implants also provide further advantages in hard-tissue stem implant applications involving implantation into a cancellous portion of a hard tissue in particular, e.g. for femoral stem implants for hip replacement and/or humeral stem implants for shoulder replacement. Again without wishing to be bound by theory, it is believed that prearranging the pillars to match an underlying structure of the cancellous portion of the hard tissue allows for customizable design of the hard-tissue stem implants to meet local loading patterns and/or bone type, thus further promoting hard-tissue remodeling and growth at the site of implantation.

[0039] The interface resulting from implantation of the hard-tissue stem implant into the hard tissue will be, or can become, an interface that is continuous with respect to the hard tissue and discontinuous with respect to the hard-tissue stem implant, across an area of the face of the hard-tissue stem implant from which the pillars extend. Such an interface will further exhibit properties similar to those of the bulk hard tissue adjacent to the interface, e.g. high resilience to load. The result is that the interface following implantation of a hard-tissue stem implant into a hard tissue is surprisingly long-lasting and resilient to load.

[0040] As used herein, the term "hard-tissue stem implant" means an implant suitable for implantation into a cancellous portion of a hard tissue, and particularly into a medullary canal of the hard tissue. Hard-tissue stem implants include a stem, corresponding to a portion of the hard-tissue stem implant that is intended for implantation into the cancellous portion of the hard tissue, and that, following implantation, is located within the hard tissue. Exemplary hard-tissue stem implants include a femoral stem implant and a humeral stem implant.

Exemplary hard tissues suitable for implantation of the hard-tissue stem implants include femur and humerus.

[0041] As used herein, the term "pillar" means a projection that extends distally from a surface of a hard-tissue stem implant, e.g. from a face of the hard-tissue stem implant, that is not in direct physical contact with any other pillars or other parts of the implant other than the surface, and that is for contacting a cancellous portion of a hard tissue. Because a pillar is not in direct physical contact with any other pillars or other parts of the implant other than the surface, upon implantation no pillar forms a continuous phase within the resulting interface of the hard tissue and hard-tissue stem implant. A pillar can have a transverse area, i.e. an area of a cross-section taken relative to a vertical axis along which the pillar extends distally from the face of the implant, of, for example, (i) (100 μιη x 100 μιη) to (10,000 μιη x 10,000 μιη), i.e. 1.0 x 10⁴ μιη² to 1.0 x 10⁸ μιη², (ii) (200 μιη x 200 μιη) to (2,000 μιη x 2,000 μιη), i.e. 4.0 x 10⁴ μιη² to 4.0 x 10⁶ μιη², (iii) (250 μιη x 250 μιη) to (1,000 μιη x 1,000 μιη), i.e. 6.3 x 10⁴ μιη² to 1.0 x 10⁶ μιη², (iv) (300 μιη x 300 μιη) to (500 μιη x 500 μιη), i.e. 9 x 10⁴ μιη² to 2.5 x 10⁵ μιη², (v) (350 μιη x 350 μιη) to (450 μιη x 450 μιη), i.e. 1.2 x 10⁵ μιη² to 2.0 x 10⁵ μιη², or (vi) (395 μιη x 395 μιη) to (405 μιη x 405 μιη), i.e. 1.6 x 10⁵ μιη². Of note, the expression of transverse areas of pillars as squares of linear dimensions, e.g. (100 μιη x 100 μιη), here and throughout this application, is for purposes of convenience only and is not intended to limit any pillars so described to square shapes, square transverse areas, or square cross-sections. A pillar can have a pillar height, i.e. the height of the pillar from the face of the hard-tissue stem implant to the distal end of the pillar, of, for example, 100 to 10,000 μτη, 100 to 5,000 μιη, 200 to 2,500 μιη, 300 to 1,000 μιη, 400 to 600 μιη, 450 to 550 μιη, 490 to 510 μτη, or 500 μιη. A pillar can have a volume, i.e. product of pillar transverse area and pillar height, of, for example (i) (100 μιη x 100 μιη x 100 μιη) to (10,000 μιη x 10,000 μιη x 10,000 μιη), i.e. 1.0 x 10⁶ μιη³ to 1.0 x 10¹² μιη³, (ii) (200 μιη x 200 μιη x 100 μιη) to (2,000 μιη x 2,000 μιη x 5,000 μιη), i.e. 4.0 x 10⁶ μιη³ to 2.0 x 10¹⁰ μιη³, (iii) (250 μιη x 250 μιη x 200 μιη) to (1,000 μιη x 1,000 μιη x 2,500 μιη), i.e. 1.3 x 10⁷ μιη³ to 2.5 x 10⁹ μιη³, (iv) (300 μιη x 300 μιη x 300 μιη) to (500 μιη x 500 μιη x 1,000 μιη), i.e. 2.7 x 10⁷ μm³ to 2.5 x 10⁸ μm³, (v) (350 μιη x 350 μm x 400 μιη) to (450 μm x 450 μιη x 600 μιη), i.e. 4.9 x 10⁷ μιη³ to 1.2 x 10⁸ μιη³, or (vi) (395 μm x 395 μιη x 490 μιη) to (405 μm x 405 μιη x 510 μm), i.e. 7.7 x 10⁷ μπι³ to 8.4 x 10⁷ μιη³. A pillar can have, as seen from a top view, a square shape, a rectangular shape, a herringbone shape, a circular shape, or an oval shape, respectively, or alternatively can have other polygonal, curvilinear, or variable shapes.

[0042] As used herein, the term "slot" means the spaces between the pillars.

Accordingly, the pillars define the slots. The slots can have a slot height as defined by the pillars, of, for example, 100 to 10,000 μιη, 100 to 5,000 μιη, 200 to 2,500 μιη, 300 to 1,000 μπι, 400 to 600 μπι, 450 to 550 μπι, or 500 μπι. The slots can have a slot width as measured along the shortest distance between adjacent pillars of, for example, 100 to 10,000 μπι, 100 to 7,500 μιη, 100 to 3,000 μιη, 150 to 1,000 μιη, 175 to 450 μιη, 190 to 410 μιη, 190 to 210 μιη, or 390 to 410 μπι. The slots have a volume corresponding to the volume of the space between the pillars.

[0043] As used herein, the term "pore" refers to a void space of less than 1,000 μπι in size, i.e. having a diameter of less than 1,000 μπι, on or below a surface, e.g. the surface of a hard-tissue stem implant. Pores can occur in a material naturally, e.g. based on a natural porosity of the material, or can be introduced, e.g. by chemical or physical treatment. Pores can be continuous with respect to each other, based on being interconnected with each other below a surface, or pores can be discontinuous, based on not being interconnected with each other below a surface. Pores can be sufficiently large to allow for migration and proliferation of osteoblasts and mesenchymal cells. Accordingly, for example, a porous surface is a surface that includes void spaces of less than 1,000 μπι in size in the surface, whereas a non- porous surface is a surface that does not include such a void space.

[0044] As used herein, the term "interface resulting from implantation of the hard- tissue stem implant into a hard tissue," or more simply "interface," means the product of implantation wherein the pillars of the hard-tissue stem implant are contacting a hard tissue and the slots of the hard-tissue stem implant are occupied, partially or completely, by the hard tissue. The interface includes the pillars, hard tissue that occupies the slots of the hard-tissue stem implant, any remaining unoccupied space in the slots, any hard tissue that occupies any additional space between the face of the implant and a plane defined by the distal ends of the pillars, and any hard tissue that occupies any pores on the face or the pillars. Accordingly, the interface boundaries are the face of the hard-tissue stem implant, the internal surfaces of any pores on the face, and the bulk tissue surrounding interface.

[0045] In some example embodiments, e.g. immediately after implanting the hard- tissue stem implant with at least some penetration of the pillars into the cancellous portion of the hard tissue and/or after at least some remodeling and growth of the cancellous portion of the hard tissue to partially fill in space between the hard-tissue stem implant and the cancellous portion of the hard tissue, the pillars are contacting the cancellous portion of the hard tissue (e.g. at distal ends of the pillars), and the slots are partially occupied by the cancellous portion of the hard tissue. In other example embodiments, e.g. immediately after implanting the hard-tissue stem implant with extensive penetration of the pillars into the cancellous portion of the hard-tissue and/or after extensive remodeling and growth of the cancellous portion of the hard tissue to fill in all space between the hard-tissue stem implant and the cancellous portion of the hard tissue, the pillars are contacting the cancellous portion of the hard tissue (e.g. at distal ends and lateral surfaces of the pillars), and the slots are completely occupied by the cancellous portion of the hard tissue. In other example embodiments, the pillars contact the cancellous portion of the hard tissue over time, based on remodeling and growth of hard tissue in and around the pillars, e.g. during healing.

[0046] As used herein, the term "continuous," when used for example in reference to the hard-tissue of an interface, means that the hard tissue forms a single continuous phase, extending throughout and across the interface to each boundary of the interface. As used herein, the term "discontinuous," when used for example in reference to the hard-tissue stem implant of an interface, means that the hard-tissue stem implant does not form such a single continuous phase.

Hard-Tissue Stem Implant

[0047] Considering the features of an example hard-tissue stem implant in more detail, FIG. 1 and FIG. 2 provide illustrations in perspective view of example hard-tissue stem implants 100, corresponding to a femoral stem implant 1001 and a humeral stem implant 1002. Additional views of the femoral stem implant 1001 are shown in FIGS. 11-16.

[0048] As described in more detail below, the hard-tissue stem implant 100 can be made from one or more materials and/or hard tissues. The hard-tissue stem implant 100 can be made, for example, from one or more materials such as implantable-grade

polyaryletherketone that is essentially unfilled (such as implantable-grade

polyetheretherketone or implantable-grade polyetherketoneketone), titanium, stainless steel, cobalt-chromium alloy, titanium alloy (such as Ti-6A1-4V titanium alloy or Ti-6Al-7Nb titanium alloy), ceramic material (such as silicon nitride (Si3N4)), or implantable-grade composite material (such as implantable-grade polyaryletherketone with filler, implantable- grade polyetheretherketone with filler, implantable-grade polyetheretherketone with carbon fiber, or implantable-grade polyetheretherketone with hydroxyapatite). The hard-tissue stem implant 100 also can be made, for example, from one or more hard tissues such as a hard tissue obtained from a human or animal (such as autologous hard tissue, allogenic hard tissue, or xenogeneic hard tissue), human cartilage, animal cartilage, human bone, animal bone, cadaver bone, or cortical allograft. Such hard tissues obtained from a human or animal can also be treated, in advance of implantation, to decrease or eliminate the capacity of the hard tissue to elicit an immune response in an individual upon implantation into the individual. The hard-tissue stem implant 100 also can be made, for example, from one or more materials such as resin for rapid prototyping, SOMOS (R) NanoTool non-crystalline composite material, SOMOS (R) 9120 liquid photopolymer, SOMOS (R) Watershed XC 11122 resin, ACCURA (R) XTREME (TM) White 200 plastic, or ACCURA (R) 60) plastic. The hard- tissue stem implant 100 also can be made from further combinations of the above-noted materials and/or hard tissues.

[0049] As shown in FIG. 1 and FIG. 2, the hard-tissue stem implant 100 includes a bulk stem implant 110, a face 120, pillars 140, and slots 150. [0050] Considering the bulk stem implant 110 in more detail, the bulk stem implant 110 has a proximal end 113, a distal end 114, and an elongated stem body 115 therebetween.

[0051] As shown in FIG. 5, the bulk stem implant 110 forms the core of the hard- tissue stem implant 100. The bulk stem implant 110 can be made from one or more of the materials or hard tissues noted above with respect to the implant 100, e.g. one or more materials such as implantable-grade polyaryletherketone that is essentially unfilled (such as implantable-grade polyetheretherketone or implantable-grade polyetherketoneketone), titanium, stainless steel, cobalt-chromium alloy, titanium alloy (such as Ti-6A1-4V titanium alloy or Ti-6Al-7Nb titanium alloy), ceramic material (such as silicon nitride (Si3N4)), or implantable-grade composite material (such as implantable-grade polyaryletherketone with filler, implantable-grade polyetheretherketone with filler, implantable-grade

polyetheretherketone with carbon fiber, or implantable-grade polyetheretherketone with hydroxyapatite), or e.g. one or more hard tissues such as a hard tissue obtained from a human or animal (such as autologous hard tissue, allogenic hard tissue, or xenogeneic hard tissue), human cartilage, animal cartilage, human bone, animal bone, cadaver bone, or cortical allograft, or e.g. one or more materials such as resin for rapid prototyping, SOMOS (R) NanoTool non-crystalline composite material, SOMOS (R) 9120 liquid photopolymer, SOMOS (R) Watershed XC 11122 resin, ACCURA (R) XTREME (TM) White 200 plastic, or ACCURA (R) 60) plastic.

[0052] The bulk stem implant 110 can be porous or non-porous. For example, the bulk stem implant 110 can include one or more surfaces that are porous, and/or can be made from one or more materials that are porous. Such porous surfaces can include pores having diameters of, e.g. 1 to 900 μπι, 100 to 800 μπι, or 200 to 600 μπι. Also for example, the bulk stem implant 110 can include only surfaces that are non-porous, and/or can be made only from one or more materials that are non-porous.

[0053] Considering now the face 120 in more detail, as shown in FIG. 1 and FIG. 5, the face 120 of the hard-tissue stem implant 100 is an exterior surface of the bulk stem implant 110, having a total area 160. Of note, FIGS. 5-7 and FIG. 10 show only a portion of the hard-tissue stem implant 100, corresponding to a face 120, surrounded by an edge 130, shown separated from the hard-tissue stem implant 100 below and around the face 120. As shown in FIG. 5, the face 120 can be flat, i.e. have a flat contour. Alternatively, the face 120 can be cylindrical, i.e. have a cylindrical contour. As further alternatives, the face 120 can have other angular, curvilinear, and/or irregular contours. The face 120 can have a rectangular peripheral shape as seen from a top view, although other polygonal, curvilinear, or other shapes may be used in further examples.

[0054] As shown in FIG. 5, in some examples the face 120 can be defined by an edge 130. For example, the edge 130 can be a single continuous edge that defines the face 120. As shown in FIG. 5, the edge 130 and the pillars 140 closest to the edge 130 can define a peripheral border 122 of the face 120. As shown in FIG. 1, the hard-tissue stem implant can further include at least one additional exterior surface 124, the at least one additional exterior surface 124 being adjacent the face 120, and the face 120 being recessed relative to the at least one additional exterior surface 124. For example, as shown in FIG. 1, the edge 130 can define an intersection between the face 120 and the at least one additional exterior surface 124. In accordance with these examples, the edge 130 can include a raised wall 123 that extends above the face 120, such that the face 120 is recessed with respect to the raised wall 123. In other examples, the face 120 can be elevated with respect to the at least one additional exterior surface 124. In other examples, the face 120 may not be defined by an edge 130.

[0055] The face 120 can be porous, e.g. including pores having diameters of, e.g. 1 to 900 μπι, 100 to 800 μπι, or 200 to 600 μπι, or the face 120 can be non-porous.

[0056] The bulk stem implant 110 can include more than one face 120, e.g. two, three, four, five, or more faces 120.

[0057] Considering now the pillars 140 in more detail, the pillars 140 are for contacting a cancellous portion of a hard tissue. The hard tissue can be, for example, femur or humerus. The cancellous portion of the hard tissue can be, for example, a cancellous portion of proximal femur or a cancellous portion of proximal humerus. In some examples, the pillars 140 may contact a cancellous portion of a hard tissue immediately upon implantation, e.g. based on extending distally from a face 120 of the hard-tissue stem implant 100. In some examples, the pillars 140 may contact a cancellous portion of a hard tissue over time after implantation, e.g. based on remodeling and growth of a cancellous portion of a hard tissue to come in contact with pillars 140 for which distal ends 430 of the pillars 140 are recessed relative to a surrounding surface of the hard-tissue stem implant 100.

[0058] As shown in FIG. 6, the pillars 140 are distributed on the face 120 of the hard- tissue stem implant 100, across an area 170 of the face 120 of at least 80 mm². As shown in FIG. 1, the pillars 140 can be distributed on the face 120 of the hard-tissue stem implant 100 over a portion of the hard-tissue stem implant 100 that, following implantation, is located within the hard tissue, but not over another portion of the hard-tissue stem implant 100 that, following implantation, also is located within the hard tissue. Thus, the pillars 140 can be distributed on the face 120 of the hard-tissue stem implant 100 over only a portion of the stem of the hard-tissue stem implant 100. In other example embodiments, the pillars 140 can be distributed on the face 120 of the hard-tissue stem implant 100 over an entire portion of the hard-tissue stem implant 100 that, following implantation, is located within the hard tissue. Thus, the pillars 140 also can be distributed on the face 120 of the hard-tissue stem implant 100 over the entire stem of the hard-tissue stem implant 100.

[0059] As shown in FIG. 5 and FIG. 6, the pillars 140 can be distributed on the face 120 of the hard-tissue stem implant 100 such that none of the pillars 140 are located at an edge 130, i.e. the face 120 can have a peripheral border 122 that is not occupied by any pillars 140, resulting in the area 170 of the face 120 across which the pillars 140 are distributed being less than the total area 160 of the face 120. In other example embodiments the pillars 140 can be distributed on the face 120 of the hard-tissue stem implant 100 such that at least some of the pillars 140 are located at an edge 130, e.g. the area 170 of the face 120 across which the pillars 140 are distributed can be equal to the total area 160 of the face 120

[0060] As shown in FIG. 7, the pillars 140 extend distally from the face 120 of the hard-tissue stem implant 100. For example, the pillars 140 can extend distally along a vertical axis 410 from the face 120 of the hard-tissue stem implant 100. As shown, the pillars 140 can extend in a uniform direction, i.e. all pillars 140 extend distally at the same angle with respect to the face 120 and in the same direction. Also for example, some pillars 140 may extend distally at a different angle and/or in a different direction relative to other pillars 140, for example for a hard-tissue stem implant 100 for which the face 120 is not flat. As also shown, the pillars 140 can be perpendicular to the face 120, e.g. extending

perpendicularly from the face 120. Also for example, the pillars 140 can extend from the face 120 at other angles and/or varying angles.

[0061] The pillars 140 are prearranged to match an underlying structure of the cancellous portion of the hard tissue. Of note, although FIGS. 5-7, FIG. 9, FIG. 10, and FIG. 13 show pillars 140 in regular even arrays, this is for purposes of illustrating details about the pillars rather than details of distribution of the pillars. With reference to FIG. 3, which is an illustration of a pattern defined by stress lines (also termed Singh lines) of human adult femur including a principal compressive group, a principal tensile group, a secondary compressive group, a secondary tensile group, and a greater trochanteric group, a hard tissue that is load bearing and that includes a cancellous portion may tend to exhibit a pattern defined by stress lines in the cancellous portion. The trabeculae of the cancellous portion generally tend to be distributed along the stress lines, and shapes of the trabeculae generally tend to be defined by the stress lines.

[0062] With reference to FIG. 4, as noted the pillars 140 are prearranged to match an underlying structure of the cancellous portion of the hard tissue. In some examples, the pillars 140 are distributed along lines positioned and shaped like the stress lines. For example, the pillars 140 can be distributed along lines positioned and shaped like stress lines of the cancellous portion of the hard tissue at which the face 120 and the pillars 140

extending therefrom will be implanted. This can be seen in FIG. 4, in which the pillars are distributed along curved lines that are positioned and shaped like stress lines of a cancellous portion of a human adult femur. Accordingly, in some examples the pillars 140 are prearranged to match the underlying structure of the cancellous portion of the hard tissue based on being distributed in a pattern defined by stress lines of the hard-tissue corresponding to one or more of a principal compressive group, a principal tensile group, a secondary compressive group, a secondary tensile group, or a greater trochanteric group.

[0063] Also for example, the pillars 140 can be distributed on the face 120 of the hard-tissue stem implant 100 such that the pillars 140 are packed more densely on one area of the face 120 and less densely on another area of the face 120. Moreover, for a bulk stem implant 110 including more than one face 120 across which pillars 140 are distributed, the pillars 140 can be distributed differently on the various faces 120, e.g. in different regular patterns 310, in different irregular patterns, and/or packed at different densities.

[0064] As shown in FIG. 5, each pillar 140 is integral to the bulk stem implant 110, i.e. the pillars 140 and the bulk stem implant 110 are made from the same starting material, rather than, for example, the pillars 140 being an add-on to the bulk stem implant 110. Like the bulk stem implant 110, the pillars 140 can be porous, e.g. including pores having diameters of, e.g. 1 to 900 μπι, 100 to 800 μπι, or 200 to 600 μπι, or the pillars 140 can be non-porous.

[0065] As shown in FIG. 7, each pillar 140 has a distal end 430, corresponding to the distal-most portion of the pillar 140 relative to the face 120 of the hard-tissue stem implant 100. Each pillar 140 can have distal edges 432, corresponding to edges defining the distal end 430 of each pillar 140. Each pillar 140 can also have lateral edges 434, corresponding to edges of the lateral sides of each pillar 140. The distal edges 432 and/or the lateral edges 434 can be sharp, although other rounded, angular, smooth, and/or irregular edges may be used in further examples. [0066] With respect to dimensions of the pillars 140, as shown in FIG. 8A and FIG. 8B, each pillar 140 has a transverse area 510, i.e. an area of a cross-section taken relative to the vertical axis 410 along which the pillar 140 extends distally from the face 120, of, for example, (i) (100 μιη x 100 μιη) to (10,000 μιη x 10,000 μιη), i.e. 1.0 x 10⁴ μιη² to 1.0 x 10⁸ μιη², (ii) (200 μιη x 200 μιη) to (2,000 μιη x 2,000 μιη), i.e. 4.0 x 10⁴ μιη² to 4.0 x 10⁶ μιη², (iii) (250 μιη x 250 μιη) to (1,000 μιη x 1,000 μιη), i.e. 6.3 x 10⁴ μιη² to 1.0 x 10⁶ μm², (iv) (300 μm x 300 μιη) to (500 μιη x 500 μm), i.e. 9 x 10⁴ μm² to 2.5 x 10⁵ μm², (v) (350 μιη x 350 μm) to (450 μιη x 450 μιη), i.e. 1.2 x 10⁵ μιη² to 2.0 x 10⁵ μιη², or (vi) (395 μm x 395 μιη) to (405 μιη x 405 μm), i.e. 1.6 x 10⁵ μm². As shown in FIG. 7 and FIG. 8B, each pillar 140 has a pillar height 420, i.e. the height of the pillar 140 from the face 120 of the hard- tissue stem implant 100 to the distal end 430 of the pillar 140, of, for example, 100 to 10,000 μιη, 100 to 5,000 μιη, 200 to 2,500 μιη, 300 to 1,000 μιη, 400 to 600 μιη, 450 to 550 μιη, 490 to 510 μιη, or 500 μιη. As shown in FIG. 8A, each pillar 140 has a volume 520, i.e. product of pillar transverse area 510 and pillar height 420, of, for example (i) (100 μιη x 100 μιη x 100 μιη) to (10,000 μιη x 10,000 μιη x 10,000 μιη), i.e. 1.0 x 10⁶ μιη³ to 1.0 x 10¹² μιη³, (ii) (200 μιη x 200 μιη x 100 μιη) to (2,000 μιη x 2,000 μιη x 5,000 μιη), i.e. 4.0 x 10⁶ μιη³ to 2.0 x 10¹⁰ μιη³, (iii) (250 μιη x 250 μιη x 200 μιη) to (1,000 μιη x 1,000 μιη x 2,500 μιη), i.e. 1.3 x 10⁷ μιη³ to 2.5 x 10⁹ μm³, (iv) (300 μιη x 300 μm x 300 μιη) to (500 μιη x 500 μm x 1,000 μιη), i.e. 2.7 x 10⁷ μm³ to 2.5 x 10⁸ μm³, (v) (350 μm x 350 μιη x 400 μιη) to (450 μm x 450 μιη x 600 μm), i.e. 4.9 x 10⁷ μm³ to 1.2 x 10⁸ μm³, or (vi) (395 μιη x 395 μm x 490 μιη) to (405 μιη x 405 μm x 510 μm), i.e. 7.7 x 10⁷ μm³ to 8.4 x 10⁷ μm³. As shown in FIG. 1 and FIG. 5, the pillars 140 extending from the face 120 can, for example, all have identical dimensions, e.g. identical pillar transverse areas 510, pillars heights 420, and thus identical individual volumes. Alternatively, as shown in FIG. 3, one or more pillars 140 can have dimensions that differ from those of other pillars 140, such that the pillar transverse areas 510 and/or pillar heights 420, and thus volumes, of the one or more pillars 140 differ from those of the other pillars 140. As shown in FIG. 1, for a hard-tissue stem implant 100 that includes a raised wall 123, the pillar height 420 can be the same as a height of the raised wall 123, or alternatively the pillar height 420 can be less than, greater than, or variable with respect to, a height of the raised wall 123.

[0067] Turning to FIG. 9A to FIG. 9E, the pillars 140 can have, as seen from a top view, a square shape, a rectangular shape, a herringbone shape, a circular shape, or an oval shape, or alternatively can have other polygonal, curvilinear, or variable shapes. For example, in some embodiments all pillars 140 can have the same shape, e.g. a square shape, a rectangular shape, a herringbone shape, a circular shape, or an oval shape, as seen from a top view. Also for example, in some embodiments not all pillars 140 have the same shape as seen from a top view.

[0068] Also noted above, shapes of the trabeculae generally tend to be defined by the stress lines. In some examples, the pillars 140 are shaped similarly to trabeculae of the cancellous portion. For example, the pillars 140 can be shaped similarly to the trabeculae of the cancellous portion of the hard tissue at which the face 120 and the pillars 140 extending therefrom will be implanted. In some examples, one or more pillars 140 have dimensions that differ from those of other pillars 140, such that the pillar transverse areas 510 and/or pillar heights 420, and thus pillar volumes 520, of the one or more pillars 140 differ from those of the other pillars 140.

[0069] Considering now the slots 150 in more detail, the slots 150 are to be occupied by the cancellous portion of the hard tissue. For example, upon implantation of the hard- tissue stem implant 100 into a hard tissue, the hard tissue can immediately occupy all or part of the space corresponding to the slots 150. This can be accomplished, for example, by pressing the hard-tissue stem implant 100 into the hard tissue. Moreover, to the extent that the hard tissue does not, upon implantation, immediately occupy all of the space

corresponding to slots 150, the hard tissue can eventually occupy all or part of the space corresponding to the slots 150 based on remodeling and/or growth of the hard tissue over time.

[0070] As shown in FIG. 5, FIG. 6, and FIG. 7, the pillars 140 define the slots 150 therebetween, i.e. the slots 150 are the spaces between the pillars 140. Accordingly, as shown in FIG. 7, the slots 150 have a slot height 440 as defined by the pillars 140, of, for example, 100 to 10,000 μιη, 100 to 5,000 μιη, 200 to 2,500 μιη, 300 to 1,000 μιη, 400 to 600 μιη, 450 to 550 μιη, or 500 μιη. As shown in FIG. 9A to FIG. 9E, the slots 150 have a slot width 152 as measured along the shortest distance between adjacent pillars 140 of, for example, 100 to 10,000 μιη, 100 to 7,500 μιη, 100 to 3,000 μιη, 150 to 1,000 μιη, 175 to 450 μιη, 190 to 410 μιη, 190 to 210 μιη, or 390 to 410 μιη. The slots 150 have a volume 710 corresponding to the volume of the space between the pillars 140.

[0071] As shown in FIG. 1, in some examples, the bulk stem implant includes a connector 116 for a head implant, the connector 116 being located at the proximal end 113 of the bulk stem implant 110 or adjacent thereto. The head implant can be for, e.g., replacement of a femoral head or a humeral head. In some of these examples, the connector 116 includes one or more of a female connector 117 or a male connector 118. In this context, female connector means a connector that has a cavity for receiving a protrusion of a male connector. Male connector means a connector having a protrusion to be received by a cavity of a female connector. Thus, in some examples the connector 116 can be a female connector 117. In accordance with these examples, the bulk stem implant 110 has a cavity 119 at the proximal end 113 of the bulk stem implant 110, or adjacent thereto. Also for example, the connector 116 can be a male connector 118. In accordance with these examples, the bulk stem implant 110 includes a protrusion at the proximal end 113 of the bulk stem implant 110, or adjacent thereto.

[0072] In some examples the hard-tissue stem implant 100 has a Young's modulus of elasticity of at least 3 GPa, for example 18 to 230 GPa, 18 to 25 GPa, 100 to 110 GPa, 190 to 210 GPa, 200 to 230 GPa, 105 to 120 GPa, or 4 to 18 GPa. This can be based on the hard- tissue stem implant 100 being made of one or more of the materials and/or hard tissues recited above. Regarding the materials, the hard-tissue stem implant 100 can have a Young's modulus of elasticity of at least 3 GPa based on being made from, for example, (i) implantable-grade polyetheretherketone that is essentially unfilled, which has a Young's modulus of approximately 4 GPa, (ii) implantable-grade polyetheretherketone with filler, e.g. carbon-fiber-reinforced implantable-grade polyetheretherketone, which has a Young's modulus of elasticity of at least 18 GPa, (iii) titanium, which has a Young's modulus of elasticity of approximately 110 GPa, (iv) stainless steel, which has a Young's modulus of elasticity of approximately 200 GPa, (v) cobalt-chromium alloy, which has a Young's modulus of elasticity of greater than 200 GPa, or (vi) titanium alloy, which has a Young's modulus of elasticity of approximately 105-120 GPa, all as measured at 21° C. Regarding the hard tissues, the hard-tissue stem implant 100 can have a Young's modulus of elasticity of at least 3 GPa based on being made from, for example, a hard tissue obtained from a human or animal (such as autologous hard tissue, allogenic hard tissue, or xenogeneic hard tissue), human cartilage, animal cartilage, human bone, animal bone, cadaver bone, or cortical allograft, as such hard tissues obtained from a human or animal can have a Young's modulus of elasticity of, e.g. 4 to 18 GPa.

[0073] In some examples, the hard-tissue stem implant 100 has a ratio of (i) the sum of the volumes 710 of the slots 150 to (ii) the sum of the volumes 520 of the pillars 140 and the volumes 710 of the slots 150, of, for example, 0.40: 1 to 0.90: 1, 0.51 : 1 to 0.90: 1, 0.51 : 1 to 0.60: 1, or 0.70: 1 to 0.76: 1. Without wishing to be bound by theory, it is believed that this ratio determines the approximate percentages of cancellous portion of hard tissue and hard- tissue stem implant 100 that will occupy the interface following implantation of the hard- tissue stem implant 100, e.g. that upon pressing the implant 100 into the cancellous portion of the hard tissue, or upon remodeling and growth of the cancellous portion of the hard tissue following implantation, that the cancellous portion of the hard tissue will occupy all or essentially all of the space corresponding to the slots 150 of the hard-tissue stem implant 100.

[0074] More specifically, as shown in FIG. 10, for a hard-tissue stem implant 100 including a face 120 defined by an edge 130, the interface includes (i) the pillars 140, (ii) the slots 150 of the hard-tissue stem implant 100, which have a volume 710 and which, upon or following implantation, become occupied by the cancellous portion of the hard tissue, (iii) any additional space between the face 120 of the implant 100 and a plane 720 defined by the distal ends 430 of the pillars 140, e.g. the space between the peripheral border 122 of the face 120 that is not occupied by pillars 140 and the plane 720, which has a volume 730 and which also becomes occupied by the cancellous portion of the hard tissue, and (iv) any pores 740 on the face 120 or the pillars 140, which, depending on their size, may also become occupied by the cancellous portion of the hard tissue.

[0075] Accordingly, for example, a ratio of the sum of (i) the volumes 710 of the slots 150 to (ii) the sum of the volumes 520 of the pillars 140 and the volumes 710 of the slots 150 of 0.40: 1 would, following implantation of a hard-tissue stem implant 100 and subsequent remodeling and growth of hard tissue, wherein the implant 100 includes an edge 130 and for which pillars 140 are located at the edge 130, result in an interface that includes by volume 40% hard tissue and 60% hard-tissue stem implant 100, and more particularly 60% pillars 140 of the hard-tissue stem implant 100. Similarly, a ratio of (i) the sum of the volumes 710 of the slots 150 to (ii) the sum of the volumes 520 of the pillars 140 and the volumes 710 of the slots 150 of 0.40: 1 would, following implantation of a hard-tissue stem implant 100 and subsequent remodeling and growth of hard tissue, wherein the implant 100 includes an edge 130 and for which no pillars 140 are located at the edge 130, result in an interface that includes by volume more than 40% hard tissue and less than 60% hard-tissue stem implant 100, with the percentage of hard tissue increasing, and the percentage of hard-tissue stem implant 100 decreasing, with increasing distance between the peripheral-most pillars 140 and slots 150 and the edge 130 of the hard-tissue stem implant 100. By way of further examples, ratios of 0.51 : 1, 0.60: 1, 0.70: 1, 0.76: 1, and 0.90: 1, would result in interfaces that include, by volume, 51% hard tissue and 49% hard-tissue stem implant 100, 60% hard tissue and 40% hard-tissue stem implant 100, 70% hard tissue and 30% hard-tissue stem implant 100, 76% hard tissue and 24% hard-tissue stem implant 100, and 90% hard tissue and 10% hard-tissue stem implant, respectively, for a hard-tissue stem implant 100 wherein the implant 100 includes an edge 130 and for which pillars 140 are located at the edge 130. Moreover, the percentage of hard tissue would increase, and the percentage of hard-tissue stem implant 100 would decrease, with increasing distance between the peripheral -most pillars 140 and slots 150 and the edge 130 of the hard-tissue stem implant 100. It is further believed that by achieving an interface that is at least 40% hard tissue, but that has a sufficient amount of the hard-tissue stem implant 100 to provide support and to keep the implant 100 from migrating, that the interface will exhibit properties similar to those of the bulk hard tissue adjacent to the interface, e.g. high resilience to load.

[0076] Accordingly, in some examples the hard-tissue stem implant 100 has a Young's modulus of elasticity of at least 3 GPa, and has a ratio of (i) the sum of the volumes 710 of the slots 150 to (ii) the sum of the volumes 520 of the pillars 140 and the volumes 710 of the slots 150 of 0.40: 1 to 0.90: 1. For example, in some embodiments, the hard-tissue stem implant 100 has a Young's modulus of elasticity of at least 3 GPa, e.g. 18 to 230 GPa, 18 to 25 GPa, 100 to 110 GPa, 190 to 210 GPa, 200 to 230 GPa, 105 to 120 GPa, or 4 to 18 GPa, and has a ratio of (i) the sum of the volumes 710 of the slots 150 to (ii) the sum of the volumes 520 of the pillars 140 and the volumes 710 of the slots 150 of 0.40: 1 to 0.90: 1, e.g. 0.51 : 1 to 0.90: 1, 0.51 : 1 to 0.60: 1, or 0.70: 1 to 0.76: 1.

[0077] With reference to FIG. 1, the femoral stem implant 1001 exemplifies a hard- tissue stem implant 100 in which (i) the hard-tissue stem implant 100 further includes at least one additional exterior surface 124, the at least one additional exterior surface 124 is adjacent the face 120, and the face 120 is recessed relative to the at least one additional exterior surface 124, (ii) the pillars 140 extend in a uniform direction, (iii) the pillars 140 are perpendicular to the face 120, (iv) the bulk stem implant 110 includes a connector 116 for a head implant, the connector 116 being located at the proximal end 113 of the bulk stem implant 110 or adjacent thereto, and (v) the connector 116 is a female connector 117. FIGS. 11-16 show additional views of the femoral stem implant 1001.

[0078] With reference to FIG. 2, the humeral stem implant 1002 also exemplifies a hard-tissue stem implant 100 in which (i) the hard-tissue stem implant 100 further includes at least one additional exterior surface 124, the at least one additional exterior surface 124 is adjacent the face 120, and the face 120 is recessed relative to the at least one additional exterior surface 124, (ii) the pillars 140 extend in a uniform direction, (iii) the pillars 140 are perpendicular to the face 120, (iv) the bulk stem implant 110 includes a connector 116 for a head implant, the connector 116 being located at the proximal end 113 of the bulk stem implant 110 or adjacent thereto, and (v) the connector 116 is a female connector 117.

[0079] With reference to FIG. 4, this figure illustrates pillars 140 of a hard-tissue stem implant 100 corresponding to a femoral stem implant 1001, wherein the pillars 140 are prearranged to match the underlying structure of the cancellous portion of the hard tissue based on being distributed in a pattern defined by stress lines of the hard-tissue corresponding to one or more of a principal compressive group, a principal tensile group, a secondary compressive group, a secondary tensile group, or a greater trochanteric group. The hard- tissue stem implant 100 of this figure corresponds to a femoral stem implant 1001 wherein one or more pillars 140 have dimensions that differ from those of other pillars 140, such that the pillar transverse areas 510 and/or pillar heights 420, and thus volumes, of the one or more pillars 140 differ from those of the other pillars 140.

Methods of Making Hard-tissue stem implants

[0080] Methods will now be described for making a hard-tissue stem implant that, upon implantation into a hard tissue, provides immediate load transfer and prevents stress shielding. The hard-tissue stem implant 100 is as described above.

[0081] The method includes a step of (1) determining the underlying structure of the cancellous portion of the hard tissue. As noted above, with reference to FIG. 3, a hard tissue that is load bearing and that includes a cancellous portion may tend to exhibit a pattern defined by stress lines in the cancellous portion. For example, a cancellous portion of human adult femur may exhibit a pattern of stress lines including a principal compressive group, a principal tensile group, a secondary compressive group, a secondary tensile group, and a greater trochanteric group. As also noted, the trabeculae of the cancellous portion generally tend to be distributed along the stress lines, and shapes of the trabeculae generally tend to be defined by the stress lines.

[0082] The hard tissue can be, for example, femur or humerus. The cancellous portion of the hard tissue can be, for example, a cancellous portion of proximal femur or a cancellous portion of proximal humerus.

[0083] In some examples, the hard tissue can correspond to a hard tissue of an individual in need of the hard-tissue stem implant 100, into which the hard-tissue stem implant 100 is intended to be implanted. Without wishing to be bound by theory, it is believed that determining the underlying structure of the cancellous portion of the hard tissue of an individual in this way allows for customizable design of a hard-tissue stem implant 100 to meet local loading patterns and/or bone type.

[0084] In some examples step (1) includes one or more of measuring bone mineral density of the cancellous portion of the hard tissue, conducting a computed tomography scan of the cancellous portion of the hard tissue, or conducting magnetic resonance imaging of the cancellous portion of the hard tissue. In some examples step (1) includes other approaches for determining the underlying structure of the cancellous portion of the hard tissue.

[0085] The method also includes a step of (2) designing the hard-tissue stem implant 100 such that the pillars 140 will be prearranged to match the underlying structure of the cancellous portion of the hard tissue. Again, this allows for customization. This step can be carried out, for example by determining the features of the hard-tissue stem implant 100 in view of the particular hard tissue that will be the object of implantation. The hard-tissue stem implant 100 can be, for example, a femoral stem implant 1001 or a humeral stem implant 1002. Features to be determined include the material from which the hard-tissue stem implant 100 will be made, the dimensions of the bulk stem implant 110 of the hard-tissue stem implant 100, the area 170 of the face 120 of the hard-tissue stem implant 100 across which pillars 140 will be distributed, and the number, distribution, size, and direction of extension of the pillars 140.

[0086] In some examples, the hard-tissue stem implant 100 can be designed such that the pillars 140 will distributed along lines positioned and shaped like the stress lines. In some examples, the hard-tissue stem implant 100 can be designed such that the pillars 140 can be distributed along lines positioned and shaped like stress lines of the cancellous portion of the hard tissue at which the face 120 and the pillars 140 extending therefrom will be implanted. In some examples the hard-tissue stem implant 100 can be designed such that the pillars 140 will be prearranged to match the underlying structure of the cancellous portion of the hard tissue based on being distributed in a pattern defined by stress lines of the hard-tissue corresponding to one or more of a principal compressive group, a principal tensile group, a secondary compressive group, a secondary tensile group, or a greater trochanteric group.

[0087] Also for example, the hard-tissue stem implant 100 can be designed such that the pillars 140 will be distributed on the face 120 of the hard-tissue stem implant 100 over a portion of the hard-tissue stem implant 100 that, following implantation, is located within the hard tissue, but not over another portion of the hard-tissue stem implant 100 that, following implantation, also is located within the hard tissue. In other examples, the hard-tissue stem implant 100 can be designed such that the pillars 140 will be distributed on the face 120 of the hard-tissue stem implant 100 over an entire portion of the hard-tissue stem implant 100 that, following implantation, is located within the hard tissue.

[0088] Also for example, the hard-tissue stem implant 100 can be designed such that the pillars 140 will be distributed on the face 120 of the hard-tissue stem implant 100 such that the pillars 140 are packed more densely on one area of the face 120 and less densely on another area of the face 120. Moreover, for a bulk stem implant 110 that will include more than one face 120 across which pillars 140 are distributed, the hard-tissue stem implant 100 can be designed such that the pillars 140 will be distributed differently on the various faces 120, e.g. in different regular patterns 310, in different irregular patterns, and/or packed at different densities.

[0089] The method also includes a step of (3) making the hard-tissue stem implant 100. This can be done in accordance with the design. The hard-tissue stem implant 100 can be made from one or more of the materials and/or hard tissues as described for the hard-tissue stem implant 100 above. The hard-tissue stem implant 100 can include the various example embodiments as disclosed above. Methods for making a hard-tissue stem implant 100 as disclosed herein include laser cutting, injection molding, 3D printing, and other fabrication methods that are known in the art.

[0090] In some examples, the method further includes, before step (3), a step (0) of designing the hard-tissue stem implant such that the ratio of (i) the product of (a) the Young's modulus of the hard-tissue stem implant and (b) the sum of the volumes of the pillars to (ii) the product of (a) the Young's modulus of the hard tissue and (b) the sum of the volumes of the slots will be 0.80: 1 to 3.8: 1, e.g. 0.90: 1 to 3.6: 1, 0.85: 1 to 1.6: 1, 0.92: 1 to 1.4: 1, 2.2: 1 to 3.7: 1, or 2.4: 1 to 3.5: l . Without wishing to be bound by theory, it is believed that by designing the hard-tissue stem implant 100 in this way the interface resulting from

implantation of the hard-tissue stem implant 100 will have a Young's modulus of elasticity similar to that of the bulk hard tissue adjacent to the interface, and again will exhibit properties similar to those of the bulk hard tissue adjacent to the interface, e.g. high resilience to load.

[0091] The Young's modulus of elasticity of the hard-tissue stem implant 100 can be extrapolated based on that of the materials and/or hard tissues from which the hard-tissue stem implant 100 is made, or determined experimentally. The Young's modulus of elasticity of the hard tissue can be determined, for example, based on previously determined values for hard tissue of that type or based on direct measurement. For example, it has been reported in the art that wet human femoral bone yields values for Young's modulus of elasticity, as determined by mechanical testing, as follows: Ei_ong 17 GPa, Et_ransv 11 5, and Etransv 11 5. See, e.g., Elastic anisotropy of bone, http://silver.neep.wisc.edu/~lakes/BME315N3.pdf (last accessed Dec. 8, 2010) (citing Reilly, D.T. & Burstein, A.H., The Elastic and Ultimate Properties of Compact Bone Tissue, 8 J. Biomechanics 393-405 (1975)). It has also been reported in the art that wet bovine femoral bone yields values for Young's modulus of elasticity, as determined by ultrasound, as follows: Ei_ong 22 GPa, Et_ransv 15, and Etransv 12. See, e.g., Elastic anisotropy of bone (citing Van Buskirk, W.C. & Ashman, R.B., The Elastic Moduli of Bone, in Mechanical Properties of Bone, Joint ASME-ASCE Applied Mechanics, Fluids Engineering and Bioengineering Conference, Boulder, CO, 1981). It has also been reported in the art that the stiffness of compact bone tissue varies with the type of bone, e.g. the Young's moduli of fibular bone and tibial bone are about 18% greater and 7% greater, respectively, than the Young's modulus of femoral bone. See, e.g., Elastic anisotropy of bone.

Methods of Using Hard-Tissue Stem Implants

[0092] Methods will now be described for use of a hard-tissue stem implant 100 in a hard tissue of an individual in need thereof. The hard-tissue stem implant 100 is as described above.

[0093] The method includes a step of (1) selecting the hard-tissue stem implant 100 such that the pillars 140 are prearranged to match the underlying structure of the cancellous portion of the hard tissue. This can be done as discussed above. The hard-tissue stem implant 100 can be, for example, a femoral stem implant 1001 or a humeral stem implant 1002. The hard tissue can be, for example, femur or humerus. The cancellous portion of the hard tissue can be, for example, a cancellous portion of proximal femur or a cancellous portion of proximal humerus.

[0094] In some examples, the hard tissue can correspond to a hard tissue of the individual in need of the hard-tissue stem implant 100. Again, this allows for customization.

[0095] In some examples step (1) includes one or more of measuring bone mineral density of the cancellous portion of the hard tissue, conducting a computed tomography scan of the cancellous portion of the hard tissue, or conducting magnetic resonance imaging of the cancellous portion of the hard tissue. In some examples step (1) includes other approaches for determining the underlying structure of the cancellous portion of the hard tissue.

[0096] The method also includes a step of (2) implanting the hard-tissue stem implant 100 in the hard tissue of the individual. Basic steps can include reaming the hard-tissue to size, broach and trial, and implanting the hard-tissue stem implant 100 into a medullary canal of the hard tissue.

[0097] The implanting can be done, for example, without rotation or twisting of the hard-tissue stem implant 100. The implanting can also be done, for example, without use of adhesives, e.g. cement or grout. The implanting can also be done, for example, without use of screws or plating mechanisms.

[0098] The implanting can include, for example, pressing the hard-tissue stem implant 100 into the cancellous portion of the hard tissue, thereby providing immediate load transfer and preventing stress shielding. The pressing can be, for example, by direct compression, mechanical compression, or tapping. Such pressing can include pressing the pillars 140 of the hard-tissue stem implant 100 into the cancellous portion of the hard tissue, such that the pillars 140 penetrate into the cancellous portion of the hard tissue, partially or completely. For example, the hard-tissue stem implant 100 can be pressed into the cancellous portion of the hard-tissue such that the pillars 140 penetrate the cancellous portion of the hard-tissue to a depth of, for example, 1 to 10,000 μιτι, 100 to 5,000 μιτι, 200 to 2,500 μιτι, 300 to 1,000 μιη, 400 to 600 μιη, 450 to 550 μιη, 490 to 510 μιη, or 500 μιη. Also for example, the hard-tissue stem implant 100 can be pressed into the cancellous portion of the hard-tissue such that pillars 140 penetrate the cancellous portion of the hard tissue to a depth, relative to the pillar height 420 of the pillars 140, of for example 25%, 50%, 75%, and 100% of the pillar height 420 of the pillars 140.

[0099] In some examples the method further includes, before step (2), a step (0) of selecting the hard-tissue stem implant such that the ratio of (i) the product of (a) the Young's modulus of the hard-tissue stem implant and (b) the sum of the volumes of the pillars to (ii) the product of (a) the Young's modulus of the hard tissue and (b) the sum of the volumes of the slots is 0.80: 1 to 3.8: 1. This can be done as discussed above.

[00100] In some embodiments, additional hard tissue can be added to the face 120 and/or the pillars 140 of the hard-tissue stem implant 100 prior to implanting. For example, shavings of hard-tissue of a patient, generated during preparation work including sawing or drilling of hard tissue of the patient, can be added. This may promote growth of tissue into slots 150 of the hard-tissue stem implant 100 following implantation.

[00101] Also in some embodiments, additional compositions can be added to the face 120 and/or the pillars 140 of the hard-tissue stem implant 100 prior to implanting. Such compositions include, for example, blood, one or more antibiotics, one or more osteogenic compounds, bone marrow aspirate, and/or surface chemistry for inducing early bone ingrowth. For example, the face 120 and/or the pillars 140 can be coated with one or more such compositions, with the pillars 140 retaining the compositions during implantation. This also may promote growth of tissue into slots 150 of the hard-tissue stem implant 100 following implantation.

Another Hard-Tissue Stem Implant

[00102] Also disclosed is another hard-tissue stem implant. The other hard- tissue stem implant includes a bulk stem implant, a face, pillars, and slots. The bulk stem implant has a proximal end, a distal end, and an elongated stem body therebetween. The face is an exterior surface of the bulk stem implant. The pillars are for contacting a cancellous portion of a hard tissue. The pillars are distributed on the face, across an area of at least 80 mm², and extend distally therefrom. Each pillar is integral to the bulk stem implant, has a distal end, has a transverse area of (100 x 100) to (10,000 x 10,000) μιη², and has a height of 100 to 10,000 μπι. The slots are to be occupied by the cancellous portion of the hard tissue, the slots being defined by the pillars and each slot having a width of 100 to 10,000 μπι as measured along the shortest distance between adjacent pillars, The other hard-tissue stem implant has a Young's modulus of elasticity of at least 3 GPa, and has a ratio of (i) the sum of the volumes of the slots to (ii) the sum of the volumes of the pillars and the volumes of the slots of 0.40: 1 to 0.90: 1.

[00103] In some examples, the pillars are prearranged to match an underlying structure of the cancellous portion of the hard tissue.

[00104] The other hard-tissue stem implant can include each of the various features discussed above regarding the hard-tissue stem implant 100. For example, the bulk stem implant can include a connector for a head implant, the connector being located at the proximal end of the bulk stem implant or adjacent thereto, and the connector can include one or more of a female connector or a male connector, among other features.

Exemplary Embodiments

[00105] The following are exemplary embodiments of the hard-tissue stem implant, the method of making the hard-tissue stem implant, and the method of use of the hard-tissue stem implant as disclosed herein.

[00106] Embodiment A: A hard-tissue stem implant comprising:

(a) a bulk stem implant having a proximal end, a distal end, and an elongated stem body therebetween;

(b) a face being an exterior surface of the bulk stem implant;

(c) pillars for contacting a cancellous portion of a hard tissue, the pillars being distributed on the face, across an area of at least 80 mm², extending distally therefrom, and being prearranged to match an underlying structure of the cancellous portion of the hard tissue, and each pillar being integral to the bulk stem implant, having a distal end, having a transverse area of (100 x 100) to (10,000 x 10,000) μιη², and having a height of 100 to 10,000 μιη; and

(d) slots to be occupied by the cancellous portion of the hard tissue, the slots being defined by the pillars and each slot having a width of 100 to 10,000 μπι as measured along the shortest distance between adjacent pillars.

[00107] Embodiment B: The hard-tissue stem implant of embodiment A, wherein the hard-tissue stem implant is made of one or more materials selected from implantable-grade polyaryletherketone that is essentially unfilled, implantable-grade polyetheretherketone, implantable-grade polyetherketoneketone, titanium, stainless steel, cobalt-chromium alloy, titanium alloy, Ti-6A1-4V titanium alloy, Ti-6Al-7Nb titanium alloy, ceramic material, silicon nitride (Si3N4), implantable-grade composite material, implantable- grade polyaryletherketone with filler, implantable-grade polyetheretherketone with filler, implantable-grade polyetheretherketone with carbon fiber, or implantable-grade

polyetheretherketone with hydroxyapatite.

[00108] Embodiment C: The hard-tissue stem implant of embodiment A, wherein the hard-tissue stem implant is made of one or more other hard tissues selected from human hard tissue, animal hard tissue, autologous hard tissue, allogenic hard tissue, xenogeneic hard tissue, human cartilage, animal cartilage, human bone, animal bone, cadaver bone, or cortical allograft.

[00109] Embodiment D: The hard-tissue stem implant of embodiment A, wherein the hard-tissue stem implant is made of one or more materials selected from resin for rapid prototyping, SOMOS (R) NanoTool non-crystalline composite material, SOMOS (R) 9120 liquid photopolymer, SOMOS (R) Watershed XC 11122 resin, ACCURA (R)

XTREME (TM) White 200 plastic, or ACCURA (R) 60) plastic.

[00110] Embodiment E: The hard-tissue stem implant of any of embodiments

A-D, wherein the face is flat.

[00111] Embodiment F: The hard-tissue stem implant of any of embodiments A-E, wherein the face has a cylindrical contour.

[00112] Embodiment G: The hard-tissue stem implant of any of embodiments

A-F, wherein the hard-tissue stem implant further comprises at least one additional exterior surface, the at least one additional exterior surface is adjacent the face, and the face is recessed relative to the at least one additional exterior surface.

[00113] Embodiment H: The hard-tissue stem implant of any of embodiments

A-G, wherein the pillars extend in a uniform direction.

[00114] Embodiment I: The hard-tissue stem implant of any of embodiments

A-H, wherein the pillars are perpendicular to the face.

[00115] Embodiment J: The hard-tissue stem implant of any of embodiments

A-I, wherein the transverse area of each pillar is (250 x 250) μιη² to (1,000 x 1,000) μιη².

[00116] Embodiment K: The hard-tissue stem implant of any of embodiments

A- J, wherein the height of each pillar is 200 to 2,500 μιη.

[00117] Embodiment L: The hard-tissue stem implant of any of embodiments

A-K, wherein the width of each slot is 200 to 2,500 μιη.

[00118] Embodiment M: The hard-tissue stem implant of any of embodiments

A-L, wherein the hard-tissue stem implant has a Young's modulus of elasticity of at least 3 GPa, and has a ratio of (i) the sum of the volumes of the slots to (ii) the sum of the volumes of the pillars and the volumes of the slots of 0.40: 1 to 0.90: 1.

[00119] Embodiment N: The hard-tissue stem implant of any of embodiments

A-M, wherein the pillars are prearranged to match the underlying structure of the cancellous portion of the hard tissue based on being distributed in a pattern defined by stress lines of the hard-tissue corresponding to one or more of a principal compressive group, a principal tensile group, a secondary compressive group, a secondary tensile group, or a greater trochanteric group.

[00120] Embodiment O: The hard-tissue stem implant of any of embodiments

A-N, wherein one or more pillars have dimensions that differ from those of other pillars, such that the transverse areas and/or heights, and thus volumes, of the one or more pillars differ from those of the other pillars.

[00121] Embodiment P: The hard-tissue stem implant of any of embodiments

A-O, wherein the bulk stem implant is non-porous.

[00122] Embodiment Q: The hard-tissue stem implant of any of embodiments

A-P, wherein the pillars are non-porous. [00123] Embodiment R: The hard-tissue stem implant of any of embodiments

A-Q, wherein the bulk stem implant comprises a connector for a head implant, the connector being located at the proximal end of the bulk stem implant or adjacent thereto.

[00124] Embodiment S: The hard-tissue stem implant of embodiment R, wherein the connector comprises one or more of a female connector or a male connector.

[00125] Embodiment T: The hard-tissue stem implant of any of embodiments

A-S, wherein the hard-tissue stem implant is selected from the group consisting of a femoral stem implant and a humeral stem implant.

[00126] Embodiment U: The hard-tissue stem implant of any of embodiments

A-T, wherein the pillars are distributed on the face of the hard-tissue stem implant over an entire portion of the hard-tissue stem implant that, following implantation, is located within the hard tissue.

[00127] Embodiment V: A method of making the hard-tissue stem implant of any of embodiments A-U, that, upon implantation into a hard tissue, provides immediate load transfer and prevents stress shielding, the method comprising steps of:

(1) determining the underlying structure of the cancellous portion of the hard tissue;

(2) designing the hard-tissue stem implant such that the pillars will be prearranged to match the underlying structure of the cancellous portion of the hard tissue; and

(3) making the hard-tissue stem implant.

[00128] Embodiment W: The method of embodiment V, wherein the hard tissue corresponds to a hard tissue of an individual in need of the hard-tissue stem implant, into which the hard-tissue stem implant is intended to be implanted

[00129] Embodiment X: The method of embodiment V or embodiment W, wherein step (1) comprises one or more of measuring bone mineral density of the cancellous portion of the hard tissue, conducting a computed tomography scan of the cancellous portion of the hard tissue, or conducting magnetic resonance imaging of the cancellous portion of the hard tissue.

[00130] Embodiment Y: The method of any one of embodiment V-X, wherein the method further comprises, before step (3), a step (0) of designing the hard-tissue stem implant such that the ratio of (i) the product of (a) the Young's modulus of the hard-tissue stem implant and (b) the sum of the volumes of the pillars to (ii) the product of (a) the Young' s modulus of the hard tissue and (b) the sum of the volumes of the slots will be 0.80: 1 to 3.8: 1.

[00131] Embodiment Z: A method of use of the hard-tissue stem implant of any of embodiments A-U in a hard tissue of an individual in need thereof, the method comprising steps of:

(1) selecting the hard-tissue stem implant such that the pillars are prearranged to match the underlying structure of the cancellous portion of the hard tissue,

(2) implanting the hard-tissue stem implant in the hard-tissue of the individual.

[00132] Embodiment AA: The method of embodiment Z, wherein the hard tissue corresponds to a hard tissue of the individual.

[00133] Embodiment BB: The method of embodiment Z or embodiment AA, wherein step (1) comprises one or more of measuring bone mineral density of the cancellous portion of the hard tissue, conducting a computed tomography scan of the cancellous portion of the hard tissue, or conducting magnetic resonance imaging of the cancellous portion of the hard tissue.

[00134] Embodiment CC: The method of any one of embodiments Z-BB, wherein the method further comprises, before step (2), a step (0) of selecting the hard-tissue stem implant such that the ratio of (i) the product of (a) the Young's modulus of the hard- tissue stem implant and (b) the sum of the volumes of the pillars to (ii) the product of (a) the Young' s modulus of the hard tissue and (b) the sum of the volumes of the slots is 0.80: 1 to 3.8: 1.

[00135] Embodiment DD: A hard-tissue stem implant comprising:

(a) a bulk stem implant having a proximal end, a distal end, and an elongated stem body therebetween ;

(b) a face being an exterior surface of the bulk stem implant;

(c) pillars for contacting a cancellous portion of a hard tissue, the pillars being distributed on the face, across an area of at least 80 mm², and extending distally therefrom, and each pillar being integral to the bulk stem implant, having a distal end, having a transverse area of (100 x 100) to (10,000 x 10,000) μιη², and having a height of 100 to 10,000 μιη; and

(d) slots to be occupied by the cancellous portion of the hard tissue, the slots being defined by the pillars and each slot having a width of 100 to 10,000 μπι as measured along the shortest distance between adjacent pillars,

wherein the hard-tissue stem implant has a Young' s modulus of elasticity of at least 3 GPa, and has a ratio of (i) the sum of the volumes of the slots to (ii) the sum of the volumes of the pillars and the volumes of the slots of 0.40: 1 to 0.90: 1. [00136] Embodiment EE: The hard-tissue stem implant of embodiment DD, wherein the pillars are prearranged to match an underlying structure of the cancellous portion of the hard tissue.

[00137] Embodiment FF: The hard-tissue stem implant of embodiment DD or embodiment EE, wherein the bulk stem implant comprises a connector for a head implant, the connector being located at the proximal end of the bulk stem implant or adjacent thereto.

[00138] Embodiment GG: The hard-tissue stem implant of any one of embodiments DD-FF, wherein the connector comprises one or more of a female connector or a male connector.

[00139] It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit and scope of the claimed invention.

Claims

CLAIMS What is claimed is:

1. A hard-tissue stem implant comprising:

(b) a face being an exterior surface of the bulk stem implant;

2. The hard-tissue stem implant of claim 1, wherein the hard-tissue stem implant is made of one or more materials selected from implantable-grade polyaryletherketone that is essentially unfilled, implantable-grade polyetheretherketone, implantable-grade

polyetherketoneketone, titanium, stainless steel, cobalt-chromium alloy, titanium alloy, Ti- 6A1-4V titanium alloy, Ti-6Al-7Nb titanium alloy, ceramic material, silicon nitride (Si3N4), implantable-grade composite material, implantable-grade polyaryletherketone with filler, implantable-grade polyetheretherketone with filler, implantable-grade polyetheretherketone with carbon fiber, or implantable-grade polyetheretherketone with hydroxyapatite.

3. The hard-tissue stem implant of claim 1, wherein the hard-tissue stem implant is made of one or more other hard tissues selected from human hard tissue, animal hard tissue, autologous hard tissue, allogenic hard tissue, xenogeneic hard tissue, human cartilage, animal cartilage, human bone, animal bone, cadaver bone, or cortical allograft.

4. The hard-tissue stem implant of claim 1, wherein the hard-tissue stem implant is made of one or more materials selected from resin for rapid prototyping, SOMOS (R) NanoTool non-crystalline composite material, SOMOS (R) 9120 liquid photopolymer, SOMOS (R) Watershed XC 11122 resin, ACCURA (R) XTREME (TM) White 200 plastic, or ACCURA (R) 60) plastic.

5. The hard-tissue stem implant of claim 1, wherein the face is flat.

6. The hard-tissue stem implant of claim 1, wherein the face has a cylindrical contour.

7. The hard-tissue stem implant of claim 1, wherein the hard-tissue stem implant further comprises at least one additional exterior surface, the at least one additional exterior surface is adjacent the face, and the face is recessed relative to the at least one additional exterior surface.

8. The hard-tissue stem implant of claim 1, wherein the pillars extend in a uniform direction.

9. The hard-tissue stem implant of claim 1, wherein the pillars are perpendicular to the face.

10. The hard-tissue stem implant of claim 1, wherein the transverse area of each pillar is (250 x 250) μιη² to (1,000 x 1,000) μιη².

11. The hard-tissue stem implant of claim 1, wherein the height of each pillar is 200 to 2,500 μιη.

12. The hard-tissue stem implant of claim 1, wherein the width of each slot is 200 to 2,500 μιη.

13. The hard-tissue stem implant of claim 1, wherein the hard-tissue stem implant has a Young's modulus of elasticity of at least 3 GPa, and has a ratio of (i) the sum of the volumes of the slots to (ii) the sum of the volumes of the pillars and the volumes of the slots of 0.40: 1 to 0.90: 1.

14. The hard-tissue stem implant of claim 1, wherein the pillars are prearranged to match the underlying structure of the cancellous portion of the hard tissue based on being distributed in a pattern defined by stress lines of the hard-tissue corresponding to one or more of a principal compressive group, a principal tensile group, a secondary compressive group, a secondary tensile group, or a greater trochanteric group.

15. The hard-tissue stem implant of claim 1, wherein one or more pillars have dimensions that differ from those of other pillars, such that the transverse areas and/or heights, and thus volumes, of the one or more pillars differ from those of the other pillars.

16. The hard-tissue stem implant of claim 1, wherein the bulk stem implant is non-porous.

17. The hard-tissue stem implant of claim 1, wherein the pillars are non-porous.

18. The hard-tissue stem implant of claim 1, wherein the bulk stem implant comprises a connector for a head implant, the connector being located at the proximal end of the bulk stem implant or adjacent thereto.

19. The hard-tissue stem implant of claim 18, wherein the connector comprises one or more of a female connector or a male connector.

20. The hard-tissue stem implant of claim 1, wherein the hard-tissue stem implant is selected from the group consisting of a femoral stem implant and a humeral stem implant.

21. The hard-tissue stem implant of claim 1, wherein the pillars are distributed on the face of the hard-tissue stem implant over an entire portion of the hard-tissue stem implant that, following implantation, is located within the hard tissue.

22. A method of making the hard-tissue stem implant of claim 1, that, upon implantation into a hard tissue, provides immediate load transfer and prevents stress shielding, the method comprising steps of:

(2) designing the hard-tissue stem implant such that the pillars will be prearranged to match the underlying structure of the cancellous portion of the hard tissue; and (3) making the hard-tissue stem implant.

23. The method of claim 22, wherein the hard tissue corresponds to a hard tissue of an individual in need of the hard-tissue stem implant, into which the hard-tissue stem implant is intended to be implanted

24. The method of claim 22, wherein step (1) comprises one or more of measuring bone mineral density of the cancellous portion of the hard tissue, conducting a computed tomography scan of the cancellous portion of the hard tissue, or conducting magnetic resonance imaging of the cancellous portion of the hard tissue.

25. The method of claim 22, wherein the method further comprises, before step (3), a step (0) of designing the hard-tissue stem implant such that the ratio of (i) the product of (a) the Young's modulus of the hard-tissue stem implant and (b) the sum of the volumes of the pillars to (ii) the product of (a) the Young's modulus of the hard tissue and (b) the sum of the volumes of the slots will be 0.80: 1 to 3.8: 1.

26. A method of use of the hard-tissue stem implant of claim 1 in a hard tissue of an individual in need thereof, the method comprising steps of:

27. The method of claim 26, wherein the hard tissue corresponds to a hard tissue of the individual.

28. The method of claim 26, wherein step (1) comprises one or more of measuring bone mineral density of the cancellous portion of the hard tissue, conducting a computed tomography scan of the cancellous portion of the hard tissue, or conducting magnetic resonance imaging of the cancellous portion of the hard tissue.

29. The method of claim 26, wherein the method further comprises, before step (2), a step (0) of selecting the hard-tissue stem implant such that the ratio of (i) the product of (a) the Young's modulus of the hard-tissue stem implant and (b) the sum of the volumes of the pillars to (ii) the product of (a) the Young's modulus of the hard tissue and (b) the sum of the volumes of the slots is 0.80: 1 to 3.8: 1.

30. A hard-tissue stem implant comprising:

(b) a face being an exterior surface of the bulk stem implant;

wherein the hard-tissue stem implant has a Young's modulus of elasticity of at least 3 GPa, and has a ratio of (i) the sum of the volumes of the slots to (ii) the sum of the volumes of the pillars and the volumes of the slots of 0.40: 1 to 0.90: 1.

31. The hard-tissue stem implant of claim 30, wherein the pillars are prearranged to match an underlying structure of the cancellous portion of the hard tissue.

32. The hard-tissue stem implant of claim 30, wherein the bulk stem implant comprises a connector for a head implant, the connector being located at the proximal end of the bulk stem implant or adjacent thereto.

33. The hard-tissue stem implant of claim 30, wherein the connector comprises one or more of a female connector or a male connector.