Patent Application
20230355399
The invention relates to a prosthesis for mammal. The invention relates in particular to a meniscus prosthesis for a stifle joint or knee joint of a mammal.
In mammals, such as dogs and humans, the stifle joint stability after (partial) rupture of the cranial cruciate ligament is reconstructed by surgical interventions. In dogs these include Tibial Plateau Leveling Osteotomy (TPLO), tibial tuberosity advancement (TTA), Triple Tibial Osteotomy (TTO), and intra-articular repair techniques and extra-articular repair techniques with autograft or synthetic materials. These existing techniques require invasive approaches with sawing bones and metal fixation plates.
There is a need for an improved less invasive treatment of knee problems related to joint instability in mammals.
A meniscus prosthesis is known from EP 3 116 448 B1 in the name of Atro Medical B.V., which discloses a meniscus prosthesis comprising an arc-shaped meniscus prosthesis body having a main portion comprising a reinforcing part and two end portions comprising fixation parts, wherein the main portion comprises a part made of a first biocompatible, non-resorbable material extending between the two end portions, wherein the reinforcing part and the fixation parts are made of a second biocompatible, non-resorbable material and wherein the reinforcing part extends between the fixation parts and wherein the fixation parts have a through hole. However, veterinary medicine presents different challenges than human medicine.
It is an object of the present invention to provide an improved prosthesis for a mammal. In order to address this concern, a prosthesis for a mammal is provided, the prosthesis comprising:
a prosthesis body with a dorsal surface and a ventral surface shaped to fit in a joint between a tibia and a femur so that the dorsal surface faces a distal end of the femur and the ventral surface faces a proximal end of the tibia; and
at least one fixation element (303) for fixing the prosthesis body to the tibia,
wherein the dorsal surface is inclined in a dorsal direction towards a caudal edge of the prosthesis body, to stabilize the stifle joint.
The inclination towards the caudal edge provides stabilization of the stifle joint, because it prevents the distal end of the femur from dislocating in caudal direction with respect to the proximal end of the tibia. The fixation element ensures that a force applied on the inclined caudal edge does not cause the prosthesis to slide over the tibia, thus further stabilizing the joint. Implantation of the prosthesis set forth may provide joint stability, may prevent progression of osteoarthritis, and/or may prevent secondary meniscus lesions and associated secondary interventions.
The dorsal surface may be inclined in the dorsal direction also towards a medial edge of the prosthesis body and/or towards a cranial edge of the prosthesis body. This helps to further stabilize the joint in the medial and/or cranial directions, respectively.
The dorsal surface may protrude in the dorsal direction more at the caudal edge of the prosthesis body than at the medial edge of the prosthesis body and the cranial edge of the prosthesis body. This is because the force exerted by the femur on the prosthesis may be largest in caudal direction. The more protrusion at the caudal edge helps to protect against in-plane movement of the femur with respect to the tibial plateau.
The prosthesis body may have a wedge shape wherein a thickness of the prosthesis body increases from a center of the prosthesis body towards the caudal edge, medial edge, and cranial edge. This may further reinforce the prosthesis body. In certain embodiments the prosthesis body can rest on the surface of the tibial plateau.
For example, the prosthesis is a medial meniscus prosthesis for a stifle joint. Stifle joints of quadrupeds may be vulnerable to instability, due to for example their body conformation, especially after (partial) cranial cruciate ligament rupture. The prosthesis may provide stability to the joint. Further, in certain embodiments, the prosthesis may halt or reduce the development of osteoarthritis and, optionally, related chronic lameness.
At least one of the at least one fixation elements may be located at a cranial end of the prosthesis body or at a cranial horn position of a corresponding native meniscus. These are examples of locations for a fixation element that are particularly well-suited to provide stability to the prosthesis and joint.
The at least one fixation element may comprise a through hole in the prosthesis body. This allows to fix the prosthesis body by means of an engaging element. For example, the fixation element may further comprise a screw, pin, cord or nail, to fit through the through hole.
The ventral surface of the prosthesis may be shaped to match a shape of a tibial plateau. This provides for a good fit of the prosthesis, directly on top of the tibial plateau, for example as a replacement of a removed meniscus.
Alternatively, the ventral surface may be shaped to match a shape of a native meniscus on top of a tibial plateau. This provides for a good fit of the prosthesis, on top of the meniscus. This allows the prosthesis to be used, for example, to stabilize the joint after (partial) cruciate ligament rupture, if the meniscus is still relatively healthy. For example, the prosthesis may be implanted on top of a native meniscus, which may be intact or slightly injured, for example.
As mentioned before, the prosthesis may be configured to replace a stabilizing function of cruciate ligaments of the mammal. However, this is not a limitation. The prosthesis may also be used, for example, to enhance the stabilizing function of cruciate ligaments or to stabilize the joint in general.
The dorsal surface may comprise a rim at the caudal edge of the prosthesis body, wherein the rim is shaped to fit around and extend beyond at least part of an edge of the distal end of the femur, to provide a counter pressure to the distal end of the femur to protect the distal end of the femur from displacement in caudal direction.
According to another aspect of the invention provides the prosthesis set forth for use in a method of treating osteoarthritis. For example, by implanting the prosthesis, development of osteoarthritis may be halted or slowed down.
The person skilled in the art will understand that the features described above may be combined in any way deemed useful. Moreover, modifications and variations described in respect of the system may likewise be applied to the method and to the computer program product, and modifications and variations described in respect of the method may likewise be applied to the system and to the computer program product.
In the following, aspects of the invention will be elucidated by means of examples, with reference to the drawings. The drawings are diagrammatic and may not be drawn to scale. Throughout the drawings, similar items may be marked with the same reference numerals.
Certain exemplary embodiments will be described in greater detail, with reference to the accompanying drawings. The matters disclosed in the description, such as detailed construction and elements, are provided to assist in a comprehensive understanding of the exemplary embodiments. Accordingly, it is apparent that the exemplary embodiments can be carried out without those specifically defined matters. also, well-known operations or structures are not described in detail, since they would obscure the description with unnecessary detail.
Regarding humans, orientations include superior and inferior to indicate top and bottom, respectively. Expressions anterior and posterior may be used to denote front and back sides, respectively, as illustrated in
Throughout this disclosure, the terminology for quadrupeds is used. However, the same technology may be applied on prostheses for humans. In that case, the expression ‘dorsal’ may be replaced by ‘superior’; the expression ‘caudal’ may be replaced by ‘posterior’; the expression ‘ventral’ may be replaced by ‘inferior’, and the expression ‘cranial’ may be replaced by ‘anterior’. The expressions ‘lateral’ and ‘medial’ are used in the same way for quadrupeds and humans.
Certain embodiments of the present disclosure relate to the design of an implant which can stabilize and decrease pain in the stifle joint. Additionally or alternatively, the implant may help to halt or slow down the development of osteoarthritis secondary to joint instability and misfit of the joint structures. The stifle joint of certain animals, such as dogs and horses, corresponds to the knee joint in humans. The implant may combine the biomechanical functions of the Cranial Cruciate Ligament (CCL) and the medial meniscus. To that end, the implant may support rotational and translational stability of the femur with respect to the tibia. Further, the implant may distribute the loads imposed on the tibia by the femur in case of joint instability. Such joint instability may be due, for example, to an absent or malfunctioning native meniscus and/or CCL. The implant may comprise a caudal rim, which prevents the proximal tibia from shifting cranially with respect to the femur. This stabilizing function may be provided by the implant's asymmetric geometry. Moreover, the stiffness of the material of the implant can be used to further improve the stability. For example, by choosing a relatively stiff material for (certain regions of) the implant (e.g. stiffer than native meniscus tissue), in combination with the rim, shifting of the tibia with respect to the femur at the stifle joint may be reduced or eliminated. The implant may be fixed on the tibia on at least one location, preferably on the cranial (or anterior) edge of the tibia.
In certain embodiments, a prosthesis for a stifle joint of a mammal comprises a prosthesis body with two surfaces. The prosthesis has a complex shape with a dorsal surface and a ventral surface. When implanted in a stifle joint or knee joint, the dorsal surface may contact the femur, and the ventral surface may contact the tibial plateau. The prosthesis may be fixedly positioned by fixation element(s). The fixation elements may fix the prosthesis body to a bone adjacent to the ventral surface, in particular the tibia. For example, the prosthesis may be placed in a medial compartment of the stifle joint. For example, the prosthesis may be placed in the place of the medial meniscus or in addition to the medial meniscus.
From the lateral side towards the periphery of the prosthesis, which corresponds with the medial, cranial and caudal sides of the joint, the height of the prosthesis in dorsal direction is gradually increasing. With this increment in height, or inclination of the dorsal surface of the prosthesis body in dorsal direction, a “grip portion” is created that provides grip to the adjacent bones, in particular the femur, and has the ability to restrain movement of femur and tibia within a physiologic range of motion of the joint. The combination of the improved grip thanks to the inclination and the fixation element(s) may lead to more stability in the stifle joint while maintaining a physiologic range of motion. The inclination of the dorsal surface of the prosthesis body, together with the fixation element(s), may protect the stifle against large stresses that may occur where the tibia and the femur are joined in the stifle joint. Furthermore, the inclination may prevent the femur from slipping away.
This implant design may be less invasive than existing procedures to stabilize the stifle joint after (partial) cranial cruciate ligament rupture. Moreover, the implant design may provide sufficient stabilization of the stifle joint. TPLO, TTA, and TTO involve bony cuts in the tibia near the stifle joint, or repositioning of the patella ligament attachment on the tibia to adapt the stifle joint biomechanics. In certain embodiments, such procedures may be avoided by the present prosthesis.
The dorsal surface of the prosthesis can have an increment in height in the dorso-ventral direction (i.e. sagittal plane), forming a grip portion of the prosthesis. The grip portion with the increment in height may be formed at least at the caudal end of the prosthesis body. The grip portion may be at the caudal end of the prosthesis body; this does not exclude increments of height in the ventro-dorsal direction at other portions of the periphery of the prosthesis, such as the medial and cranial ends of the prosthesis. The increment in height may be larger at the caudal end of the prosthesis than at the medial and cranial ends of the prosthesis, restricting the shift of the femur backwards, the common instability after CCL lesions. In this way, the femur may be supported by the grip portion and restrained in its movement within the physiologic and healthy range of motion.
In certain embodiments, the implant may comprise a C-shape, resembling the medial meniscus, with the inner edge being the lateral edge and the outer edge comprising the caudal, medial, and cranial edges. The height of the dorsal surface may be smaller at the inner edge of the C-shape (lateral edge) than at the outer edge of the C-shape (the caudal, medial, and cranial edges).
In certain embodiments, the outer edges extend further in the dorsoventral direction from the implant body than the inner part of the prosthesis. Moreover, the caudal edge of the dorsal surface may extend even further in the dorsoventral direction from the implant body than the cranial and medial edge. This way, the grip on the bones is largest in the direction where the largest shear stresses may occur. For example, this may prevent the medial femoral condyle to slide backwards on the tibia. This may occur after cranial cruciate ligament rupture in, for example, dogs and other quadrupeds, and causes instability of the joint. In humans, this problem may occur for example due to a rupture of the anterior cruciate ligament.
The grip portion may have a wedge shape. This way, by gradually incrementing in height further towards the cranial, lateral and caudal edge, sharp edges on the caudal surface may be avoided.
The fixation element may be located at a cranial end of the prosthesis body. When the maximum height of the grip portion is located at the caudal end, the forces exerted on the caudal end by the femur and on the cranial end by the tibia via the fixation element may keep the implant firmly in the correct place. However, the fixation element may be located anywhere on the prosthesis or prosthesis body. Moreover, the presence of one or more extra fixation elements is not excluded.
The thickness of the prosthesis body, measured as a distance between the dorsal surface and the ventral surface, may be greater at the edge of the prosthesis body, in particular the caudal, medial, and cranial edges (with the most pronounced increment in the caudal edge) than in the remainder of the prosthesis body.
The ventral surface of the prosthesis may be shaped to match a shape of the tibial plateau. This improves the fit of the prosthesis, in case for example the live meniscus is (at least partially) removed.
The ventral surface may be shaped to match a shape of a meniscus on top of the tibial plateau. This improves the fit of the prosthesis, when the prosthesis is implanted on top of the resident meniscus.
The dorsal surface may be shaped to match a shape of a distal end of the femur. The grip portion may comprise a rim, shaped to fit around at least part of an edge of the distal end of the femur, to provide a counter pressure to the distal end of the femur to protect it against shear stress with respect to the proximal end of the tibia.
The prosthesis may be configured to replace the function of cruciate ligaments of the mammal: protection against shear stress is primarily a task of the cruciate ligaments. The presented prosthesis may be used to provide that protection when the natural cruciate ligaments are damaged (e.g. partial or complete rupture). Certain embodiments comprise a polymer implant body with a concave-shaped upper surface on which the distal end of the femur is positioned and a bottom surface contacting the tibial plateau. The implant may be higher at the circumference than in the center and higher at the caudal side than the cranial side. The sagittal cross-section of the implant may be wedge-shaped from center to the peripheral rim. The meniscus implant may maintain its position on the tibial plateau by a fixation device.
In certain embodiments, the prosthesis body may be arc-shaped, e.g. resembling the shape of the meniscus. In that case, the center 230 of the prosthesis body may be at or near the lateral edge of the prosthesis body.
The edges of the anatomically shaped implant may provide a restriction to the spherical medial compartment of the distal femur. The wedge-shaped caudal edge of the implant levels the tibial plateau and limits the caudal drift of the femoral compartment. The implant may be fixed to the tibia in order to further prevent the femur from sliding down the tibia and/or dislocating from it. As such, the implant may replace the cranial cruciate ligament.
In certain embodiments, the anatomically shaped dorsal surface of the prosthesis body surrounds the medial stifle compartment of the distal femur and distributes contact stresses over the femoral and underlying tibia cartilage.
In certain embodiments, the anatomically shaped ventral surface of the implant adapts to the medial proximal tibia and distributes the contact stresses over the tibia cartilage.
The fixation device keeps the implant on its position on the tibia and consequently retains the cranial position of the femur on the tibia. This prevents translations that would otherwise lead to high shear stresses on cartilage of the stifle joint generating osteoarthritis or lead to frequent giving way, i.e. dislocation of the femur with respect to the tibia.
In certain embodiments, the flexibility of the implant provides conformity to the femoral and tibia cartilage surfaces in the stifle joint and, as such, transfer of forces from femur to the tibia. For example, the flexible implant may comprise a polymer.
The implant material properties may be chosen so that the implant material limits the movement of the femoral condyle.
A caudal, wedge-shaped cross-section of the implant, together with the optional fixation to the tibial plateau, provides sufficient limitation in freedom of movement of the femur with respect to the tibia. This creates a biomechanically stable stifle joint, even if the cranial cruciate ligament is absent (e.g. due to damage).
It will be understood that the location(s) of the fixation means, the number of fixation positions, and the method of fixation (e.g. screw, pin, adhesive, or otherwise) can be changed without changing the essence of the present disclosure. This applies to all the embodiments.
Further, it is observed that the fixation means may be included in the caudal part of the implant, e.g. as a peg that can be inserted in the tibia or an attachment point for a bone anchor or suture.
Reinforcement of the wedge-shaped caudal end of the implant may be provided in certain embodiments to better withstand the high shear forces between the distal end of the femur and the proximal end of the tibia. This reinforcement may be realized by using a different material or a higher density material near the wedge-shaped caudal end. The properties of the remaining portion of the implant may be selected, for example, to mimic the strength and stiffness of a native meniscus. In alternative embodiments, all of the implant body 302 may have the same strength, for example similar to the natural meniscus. However, it is also possible to use a different strength, for example stronger than a natural meniscus.
In certain embodiments, the shape of the implant does not follow the anatomical shape of the bones in detail. For example, the implant may be made of a geometrical ring-shape or horse-shoe shape. The wedge and fixation means may still be provided to withstand the shear forces between the distal end of the femur and the proximal end of the tibia.
It will be understood that, although the above examples are based on the stifle joint of a dog, a similar implant may be made for other mammals, in particular quadrupeds, such as horses and cats.
The material of the implant may allow sterilization. The material of the implant may be biocompatible. The material of the implant may be nontoxic and bio-inert. Suitable materials for the implant body include hydrogels, thermoplastic materials, polyurethanes, for example.
The height of a meniscus of an average dog (e.g. an average-weight Labrador) may be, for example, 4 mm. For example, for such a dog, an appropriate height of the grip portion of the meniscus prosthesis may be 5 mm or greater. This dimension is purely given by means of example only.
In a stifle joint of a mammal where there is a lesion of the cranial cruciate ligament, instability occurs in cranial/caudal direction. Embodiments of the present disclosure may provide a solution to reduce this instability. A rim at the caudal edge of the prosthesis body, wherein the rim may extend from the prosthesis body in dorsal direction, in combination with at least one fixation element for fixing the prosthesis body to a bone adjacent to the ventral surface of the prosthesis body may provide such a stabilizing effect. To this end, the rim may be higher than the caudal edge of the native meniscus of the mammal.
For example, the prosthesis may have an overall length measured in cranial-caudal direction, as indicated e.g. by line IV in
According to an aspect of the invention, a prosthesis for a mammal, comprises
a prosthesis body (302) with a dorsal surface (311) and a ventral surface (312) shaped to fit in a joint between a tibia and a femur so that the dorsal surface faces a distal end of the femur and the ventral surface faces a proximal end of the tibia; and
at least one fixation element (303) for fixing the prosthesis body (302) to the tibia (150),
wherein the dorsal surface (311) is inclined in a dorsal direction towards a caudal edge of the prosthesis body, to stabilize the stifle joint,
wherein the prosthesis has a length measured in cranial-caudal direction (IV, IX),
wherein the prosthesis has a caudal width (421, 721) measured in ventral-dorsal direction at the caudal edge (204, 604, 820), and
wherein a ratio defined by the caudal width divided by the length is at least 0.25, preferably at least 0.3, even more preferably 0.4.
According to another aspect of the invention, a prosthesis is provided for implantation in a joint between a tibia and a femur of a mammal so that a dorsal surface faces a distal end of the femur and a ventral surface faces a proximal end of the tibia, the prosthesis comprising
a prosthesis body (302) with the dorsal surface (311) and the ventral surface (312); and
at least one fixation element (303) for fixing the prosthesis body (302) to a bone adjacent to the ventral surface (150),
wherein the dorsal surface (311) is inclined in a dorsal direction towards a caudal edge of the prosthesis body, to stabilize the stifle joint,
wherein the prosthesis has a length measured in cranial-caudal direction (IV, IX),
wherein the prosthesis has a caudal width (421, 721) measured in ventral-dorsal direction at the caudal edge (204, 604, 820), and
wherein a ratio defined by the caudal width divided by the length is at least 0.25, preferably at least 0.3, even more preferably 0.4.
According to an aspect of the invention, a prosthesis is provided for implantation in a joint between a tibia and a femur of a mammal so that a dorsal surface faces a distal end of the femur and a ventral surface faces a proximal end of the tibia, the prosthesis comprising
a prosthesis body (302) with the dorsal surface (311) and the ventral surface (312); and
at least one fixation element (303) for fixing the prosthesis body (302) to a bone adjacent to the ventral surface (150),
wherein the dorsal surface (311) is inclined in a dorsal direction towards a caudal edge of the prosthesis body, to stabilize the stifle joint,
wherein the dorsal surface (311) comprises a rim at the caudal edge of the prosthesis body, wherein the rim is shaped to fit around and extend beyond at least part of an edge of the distal end of the femur, to provide a counter pressure to the distal end of the femur to protect the distal end of the femur from displacement from the proximal end of the tibia in caudal direction.
The examples and embodiments described herein serve to illustrate rather than limit the invention. The person skilled in the art will be able to design alternative embodiments without departing from the spirit and scope of the present disclosure, as defined by the appended claims and their equivalents. Reference signs placed in parentheses in the claims shall not be interpreted to limit the scope of the claims. Items described as separate entities in the claims or the description may be implemented as a single hardware or software item combining the features of the items described.
Certain aspects are disclosed in the following clauses.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20197283.3 | Sep 2020 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/NL2021/050548 | 9/9/2021 | WO |
