DE102021116330A1 - joint prosthesis - Google Patents

Abstract

The invention relates to a joint prosthesis (1) intended for use in the human or animal body, having an at least partially spherical joint head (2) and a concave joint socket, the joint head (2) being connected to a shaft. The spherical shape results in three degrees of freedom of relative movement between the joint head (2) and the joint socket, which is overlaid with a further rotational degree of freedom of the joint head (2) about its axis (5), which is permanently connected to the shaft. As a result, a significant proportion of the movement and, above all, the acting load is transmitted wear-free by means of these radial bearings. The wear that occurs between the joint head (2) and the joint socket is significantly reduced due to the reduced load input.

Description

The invention relates to a joint prosthesis intended for use in the human or animal body, in particular a hip joint prosthesis, with an at least partially spherical joint head and with an at least partially concave joint socket, the joint head being connected to a shaft and the joint head being rotatable and/or rotatable in the joint socket. or is arranged pivotably. Furthermore, the invention relates to a joint head for such a joint prosthesis, in particular a hip joint prosthesis.

Such a joint prosthesis, in particular as an endoprosthesis, serves to replace the functions of the natural joint after a loss of function. The joint prosthesis is mainly used for severe degenerative diseases of the joints, for example hip arthrosis, and after hip injuries as an operative therapy to restore pain-free mobility. The pain caused by osteoarthritis can lead to protective postures, which then overload other joints and structures of the body and cause secondary diseases or secondary osteoarthritis. Depending on the severity of the damage, partial or total joint prostheses are used. The hip joint prosthesis is the most common endoprosthesis.

The hip joint represents the connection between the femoral head at the upper end of the thigh bone (femur) and the socket (acetabulum) of the hip bone and, like the shoulder joint, can be moved around three main axes. The three main movements are anteversion, retroversion and abduction, whereby the condyle is held in the hip socket by several ligaments.

It is known that a prosthetic joint wears out faster than a natural joint, especially if the body is subjected to incorrect loading. That is why it is important, especially with a joint prosthesis, to put strain on the body gently.

In many hip joint prostheses, both the inner joint of the socket component and the condyle portion of the femoral component are made of metal, such as a cast chrome-aluminum alloy. However, these metal-on-metal prostheses have largely been superseded by the use of a modified form of acetabular shell which has a metal outer shell and a polyethylene liner. Although such prostheses have been used in large numbers, the occurrence of undesired erosion of the shell and the release of debris into the surrounding tissue cannot be reliably estimated.

It has been suggested that this debris migrates out of the acetabular cup and can contact the bone, possibly leading to osteolysis which can ultimately result in bone resorption and possible loosening of the hip joint prosthesis.

From the DE 601 00 019 T2 a method for coating prosthesis parts is known in order to reduce roughness and unevenness and to achieve improved wear behavior.

the DE 442 30 20 A1 relates to a joint prosthesis, in particular a hip joint prosthesis with improved wear properties. For this purpose, the joint socket has a synovial fluid reservoir in its sliding surface assigned to the joint head, so that under load a friction-reducing sliding film is built up between the sliding surfaces by the synovial fluid being distributed in the sliding gap by pumping action and reducing wear and abrasion there.

In the DE 30 46 553 A1 a hip joint prosthesis is proposed in which both the joint ball and the hip socket itself are made of oxide ceramic material, in particular aluminum oxide, and the hip socket has a circular recess in the area of its opening, in which there is a ring made of bioinert, plastically deformable material in order to to avoid contact between the oxide-ceramic material of the acetabulum and the same material of the joint ball in the area of the socket opening.

In a hip joint implant according to the WO 2020/239 585 A1 the bearing shell can consist of an outer shell and an inner shell in order to achieve an additional degree of freedom and thus a reduction in wear and tear and greater mobility.

the DE 44 28 290 A1 describes a hip joint prosthesis, the outer geometry of the ball head and/or the calotte of the socket insert having a geometry that deviates from the spherical shape, as a result of which an enlarged fluid reservoir is produced so that sufficient synovial fluid is available.

The invention is based on the object of creating a joint prosthesis which significantly reduces signs of wear and the associated undesired material removal of the joint components. Furthermore lies the The object of the invention is to create a joint head suitable for this purpose for the joint prosthesis.

The first-mentioned object is achieved according to the invention with a joint prosthesis according to the features of claim 1. The further development of the invention can be found in the dependent claims.

According to the invention, a joint prosthesis is therefore provided in which the joint head is connected to the shaft so that it can rotate in particular about an axis or by means of a shaft. Contrary to the prejudice in the medical world that a pivot axis is not suitable for simulating the complex movement of human or animal joints, for example the hip joint, and therefore the use of such rotatable bodies was rejected as unsuitable, it has been shown that the inventive rotatable Rod end bearing contributes in an almost amazing way to a considerable reduction in friction and the associated abrasion. The invention is based on the finding that the necessary degrees of freedom of movement of the joint prosthesis are optimally suited by a superimposed movement, namely the joint head around the axis or on the shaft as the first axis of rotation on the one hand and the movement of the joint head in the joint socket on the other to realize desired degrees of freedom, which correspond to the known joint prostheses. According to the current state of knowledge, when the user walks or runs, for example, the relative movements mentioned are distributed significantly in favor of the rotary movement of the joint head about its own axis in relation to the superimposed movement of the joint head in the joint socket. In other words, the vast majority of the joint movement is ensured by the rotary movement of the joint head about its own axis. It is obvious that the wear and tear can be reduced to a very considerable extent as a result of the rotatable mounting of the joint head. The considerations of friction-reducing material pairings known from the prior art are thus almost obsolete, as is the use of special synovial fluids. Rather, harmless, body-compatible materials can be used, even if they have caused abrasion in joint prostheses in the past. It is to be expected that, according to the invention, more than two-thirds of the load during a complete movement cycle will be absorbed by the bearing of the joint head. It is particularly advantageous that the initial rolling movement during the transition from the standing position to walking or running, which leads to a particularly high load, is almost completely absorbed by the joint head bearing. It can be assumed with a probability bordering on certainty that the joint prosthesis according to the invention leads to a noticeable improvement in the sense of movement for the user, so that a health-promoting increased activity resulting therefrom will positively influence the general state of health. In addition, it is expected that the previous restrictions on user activities that apply to conventional joint prostheses in order to avoid damage to the joint prosthesis can be restricted or even lifted.

A particularly advantageous embodiment of the invention is achieved in that the joint head is arranged so that it can rotate freely through 360° without a stop or an angle limitation. Although there is no circumferential rotational movement within a movement cycle and a corresponding degree of freedom is therefore generally not required, it has been shown that the angular position of the joint head in the joint socket varies due to the superimposed movement and the contact surface is therefore not limited to certain circumferential sections of the joint head. Circumferential rotational mobility ensures that such a change in the relative position does not result in mobility being restricted.

A further, likewise particularly advantageous embodiment of the invention is achieved in that the articulated head and/or the shaft carrying the articulated head is arranged such that it can rotate by means of a plurality of radial bearings. Known bearings, for example roller or plain bearings, can be used here, the load capacity and service life of which can be predicted with a certain degree of reliability. Of course, such bearings can also be produced from body-compatible materials if a component of the joint prosthesis fails and particles are introduced into the tissue as a result. Furthermore, according to current knowledge, it is not necessary for synovial fluid to flow through the bearing surface, but this should not be ruled out according to the invention. By using roller bearings, the axial play can also be reduced to a minimum that is no longer noticeable to the user.

Another embodiment of the invention that is also particularly promising is also achieved in that the joint head can be fixed on the shaft or the axle against the restoring force of a radially deformable and/or displaceable fixing element, and that the Fixing element in the position of use of the joint prosthesis forms an undercut acting in the axial direction for fixing in a predetermined relative desired position of the joint head on the axle or shaft. Accordingly, for assembly, the joint head is merely pushed axially onto the axle with an assembly force that can be adjusted, for example, with the fixing means being moved into a position that is displaced radially inwards relative to the axle. After reaching the target position, the fixing means returns to the radially projecting position under the influence of the restoring force, for example a spring element, whereby the axial target position is fixed.

It has proven to be particularly expedient if the fixing force of the fixing element can be adjusted, so that the fixing force can be adapted to the maximum load to be expected. As a result, in the event of an excessive load, such as occurs in practice in an accident or a fall, the joint head can be separated in order to avoid further damage to the joint prosthesis or the adjacent bone structure. Furthermore, the fixing force can also be adjusted in such a way that the joint head cannot be separated without causing damage, in order to avoid an unintentional loosening of the connection.

A likewise particularly advantageous embodiment of the invention is achieved in that the joint head is sealed relative to the shaft or the axle by means of at least one sealing element to protect against penetrating and/or escaping substances, for example particles, so that damage to the bearing by bodily fluids is avoided in particular .

The joint head could be spherical. On the other hand, a variant of the invention is particularly practical, in which the joint head has a first maximum diameter in the frontal plane and a second maximum diameter in the sagittal plane, the first maximum diameter deviating from the second maximum diameter, so that the joint head has an elliptical or ellipsoidal shape, for example shape. As a result, the joint head can not only perform rotational movements in the joint socket, but can also be displaced translationally in one plane, which means that lateral forces in particular during abduction or adduction initially lead to a displacement of the joint head in the joint socket and not to an immediate introduction of force.

The joint head could consist of a metallic, a ceramic and/or a metal-ceramic material. On the other hand, it is particularly advantageous if the joint head has a plastic as a significant material component, which may also be deformable, so that the respectively acting contact surface is enlarged and the surface pressure is reduced.

The second-mentioned object of creating a joint head suitable for the joint prosthesis is achieved according to the invention in that the joint head has a radial bearing for an axis or a shaft supported by a radial bearing for fixing to the shaft.

Such a condyle is basically also already suitable for replacing an existing condyle of a joint prosthesis inserted into the human or animal body, so that the advantages according to the invention are achieved simply by replacing the condyle, while the existing shaft and the existing joint socket can be retained unchanged.

• 1 eine Seitenansicht eines in einem Femur fixierten Gelenkkopfs einer erfindungsgemäßen Gelenkprothese;
• 2 eine geschnittene Darstellung des in 1 gezeigten Gelenkkopfs;
• 3 eine perspektivische Darstellung des in den 1 und 2 gezeigten Gelenkkopfs.

The invention permits various embodiments. To further clarify its basic principle, one of them is shown in the drawings and is described below. This is shown in a schematic representation in each case

• 1 a side view of a joint head fixed in a femur of a joint prosthesis according to the invention;
• 2 a cut representation of the in 1 shown rod end;
• 3 a perspective view of the 1 and 2 shown rod end.

A joint prosthesis 1 according to the invention, designed as a hip joint prosthesis, is described below with reference to FIG 1 until 3 explained in more detail. The joint prosthesis 1 has a spherical joint head 2, which is held in a joint socket, not shown. The joint socket is implanted in a pelvic bone (not shown) and a shaft 3 carrying the joint head is implanted in a femur 4 . The spherical shape results in three degrees of freedom of the relative movement between the joint head 2 and the joint socket and thus between the femur 4 and the pelvic bone. A further rotational degree of freedom of the joint head 2 about its axis 5 permanently connected to the shaft 3 is superimposed on these degrees of freedom of movement. The joint head 2 is mounted, for example, by means of radial bearings 6 designed as modified industrial bearings, which combine a very high mechanical load capacity with low rolling resistance, so that the movement of the joint head 2 during a movement cycle, for example when walking, preferably takes place around this radial bearing 6, so that a more substantial Part of the movement and especially the acting load is transmitted wear-free by means of this radial bearing 6. The compensation required to adapt to the instantaneous center of movement is achieved by the relative movement of the condyle 2 and the socket. Although this proportion is always present, it is a comparatively small proportion, so that the overall movement behavior is significantly improved. The wear that occurs between the joint head 2 and the joint socket is significantly reduced due to the reduced load input. The joint head 2 is mounted on the axle 5 against the restoring force of a fixing element 7 that can be displaced radially inward in the direction of the arrow F, which returns to the radially projecting position when the desired position is reached and thereby creates an undercut that acts in the axial direction for fixing in a predetermined relative desired position forms.

Reference List

1

joint prosthesis

2

rod end

3

shaft

4

femur

5

axis

6

radial bearing

7

fixing element

f

arrow direction

QUOTES INCLUDED IN DESCRIPTION

This list of the documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 60100019 T2 [0007]
• DE 4423020 A1 [0008]
• DE 3046553 A1 [0009]
• WO 2020239585 A1 [0010]
• DE 4428290 A1 [0011]

Claims (10)

A joint prosthesis (1), in particular a hip joint prosthesis, intended for use in the human or animal body, with an at least partially spherical joint head (2) and with an at least partially concave joint socket, the joint head (2) being connected to a shaft (3) and the joint head (2) is rotatably and/or pivotably arranged in the joint socket, characterized in that the joint head (2) is connected to the shaft (3) so that it can rotate in particular about an axis (5) or by means of a shaft. Joint prosthesis (1) after claim 1 , characterized in that the joint head (2) is arranged to be rotatable by 360°. Joint prosthesis (1) after claim 1 or 2 , characterized in that the joint head (2) and/or the shaft carrying the joint head (2) is rotatably arranged by means of a plurality of radial bearings (6). Joint prosthesis (1) according to at least one of the preceding claims, characterized in that the joint head (2) can be fixed on the shaft or the axle (5) against the restoring force of a radially deformable and/or displaceable fixing element (7), and that the fixing element (7) in the usage position of the joint prosthesis (1) forms an undercut acting in the axial direction for fixing the joint head (2) in a predetermined relative target position on the axle (5) or the shaft. Joint prosthesis (1) according to at least one of the preceding claims, characterized in that the fixing force of the fixing element (7) is adjustable. Joint prosthesis (1) according to at least one of the preceding claims, characterized in that the joint head (2) is detachably connected to the shaft (3). Joint prosthesis (1) according to at least one of the preceding claims, characterized in that the joint head (2) is sealed relative to the shaft or the axis (5) by means of at least one sealing element to protect against penetrating and/or escaping substances, for example particles. Joint prosthesis (1) according to at least one of the preceding claims, characterized in that the joint head (2) has a first maximum diameter in the frontal plane and a second maximum diameter in the sagittal plane, the first maximum diameter differing from the second maximum diameter. Joint prosthesis (1) according to at least one of the preceding claims, characterized in that the joint head (2) has a plastic material as a significant proportion. Joint head (2) for a joint prosthesis (1) according to at least one of the preceding claims, characterized in that the joint head (2) has a radial bearing (6) for an axle (5) or a shaft mounted by a radial bearing (6) for fixing has the shaft (3).

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