WO2025237893A1

WO2025237893A1 - Meniscus prosthesis for application in the lateral knee compartment

Info

Publication number: WO2025237893A1
Application number: PCT/EP2025/062882
Authority: WO
Inventors: Tony George VAN TIENEN; Thijmen STRUIK; Albert Jan van der Veen; Branco Siebren van Minnen; Antonius Christiaan VAN DER ZANDEN
Original assignee: Atro Medical Bv
Current assignee: Atro Medical Bv
Priority date: 2024-05-13
Filing date: 2025-05-12
Publication date: 2025-11-20
Anticipated expiration: 2026-11-13

Abstract

A prosthesis for application in a knee compartment comprises several sections. The first section (1) has a first fastening part (5) for securing the first section (1) to a bone surface. The curved second section (2) has a first end and a second end, the curved second section (2) in between the first end and the second end, wherein the first end of the curved second section is connected to the first section. The elongate third section has a third end and a fourth end on opposite ends of the elongate third section, wherein the third end of the elongate third section 3 is connected to the second end of the curved second section. The fourth section (4) having a second fastening part (6) for securing the fourth section (4) to a bone surface, wherein the fourth section is connected to the fourth end of the elongate third section.

Description

Meniscus prosthesis for application in the lateral knee compartment

FIELD OF THE INVENTION

The invention relates to a meniscus prosthesis, in particular a lateral meniscus prosthesis.

BACKGROUND OF THE INVENTION

The meniscus is a C-shaped construct in the knee joint that shares the vertical load of the femoral condyle with the cartilage of the tibia, thus enlarging the loaded area of the cartilage, and also acts as a sliding bearing to e.g. distribute lubricating synovial fluid through the joint. The native meniscus shows an anisotropic behaviour with respect to the tensile modulus, to withstand the hoop stress and compression between the femur and tibia bones forming the knee.

Earlier attempts to create a prosthesis to replace the meniscus follow this anisotropic design with flexible materials with comparable stiffness in compression but reinforced with fibers or stiff rings to approach the stiff elastic modulus of the native meniscus in circumferential direction.

WO 2023/126435 A1 discloses an arc-shaped meniscus prosthesis that comprises a first end having a first fastening part for securing the first end to a bone surface, and a second end having a second fastening part for securing the second end to a bone surface. A curved intermediate section connects the first end and the second end. The curved intermediate section is made of a single first biocompatible, non- resorbable material that has a tensile modulus of at most 160 MPa. The first material is isotropic with regard to the tensile modulus and the intermediate section is a monolithic piece of the first material.

Although the known meniscus prosthesis has mechanical properties mimicking the native meniscus with anatomical fit, there would be a demand for an improved meniscus prosthesis that has also has a mechanical fit during movement of the mammal joint, in particular the knee.

SUMMARY OF THE INVENTION

A prosthesis for application in a knee compartment, comprising a first section having a first fastening part for securing the first section to a bone surface; a curved second section having a first end and a second end, the curved second section in between the first end and the second end, wherein the first end of the curved second section is connected to the first section; an elongate third section having a third end and a fourth end on opposite ends of the elongate third section, wherein the third end of the elongate third section is connected to the second end of the curved second section; and a fourth section having a second fastening part for securing the fourth section to a bone surface, wherein the fourth section is connected to the fourth end of the elongate third section.

The elongate third section, in between the fastening part and the curved second section, provides improved mechanical freedom for the curved second section, so that the curved second section can move in response to knee kinematics, so that the prosthesis, in particular the curved second section, can provide support to the knee upon loading. The elongate third section provides motion freedom to the curved second section during movement of the leg, because the curved second section is not directly fixated to the bone. Moreover, the elongate third section allows to plan the location of the second fastening part in a place reachable during implantation, away from the curve covered by the curved section and away from the natural meniscus horn. This allows to obtain improved clinical results, because the locations along the curved section may be unsuitable for attaching an artificial fastening part. For example, there may be insufficient room for the second fastening part of e.g. a lateral meniscus in between the femur and the tibia at the anatomical location of the anterior fixation location. The elongate third section provides such a different location of the second fastening part. The elongate third section results in useful mechanical freedom, so that the prosthesis can still move through the knee compartment in response to knee kinematics as desired, and provide support to the knee joint.

The elongate third section may extend from the second end of the curved second section in tangential direction with respect to the curved second section. This may provide better mechanical support for the curved second section.

The curved second section may extend in between a segment of an inner circle having an inner radius and a segment of an outer circle having an outer radius, the inner circle and the outer circle being concentric. This approximate shape of an arc provides similarity to the natural meniscus and supports physiological loading of the prosthesis.

The first fastening part may be located inside the outer circle and the second fastening part may be located outside the outer circle. This feature provides improved fastening positions and/or may improve flexibility properties of the prosthesis. The elongate third section may extend from the second end of the curved second section in tangential direction with respect to the inner circle and the outer circle. This may provide better mechanical support for the curved second section.

The length of the elongate third section and the fourth section together may be at least 0.5 times the outer radius and at most 3 times the outer radius, preferably at least equal to the outer radius and at most 2 times the outer radius, more preferably at least 1.1 times the outer radius and at most 2 times the outer radius, even more preferably at least 1 .5 times the outer radius and at most 2 times the outer radius, even more preferably at least 1 .6 times the outer radius and at most 1 .9 times the outer radius. This range may provide optimal mechanical support within the anatomical envelope. Also, this range may include parts of the tibia surface that are anatomically suitable to attach the fourth section.

The circle segment may have an angle, measured from a radius touching a transition between the first segment and the curved second segment to a radius touching a transition between the curved second segment and the elongate third segment. Said angle may be at least 135 degrees and at most 220 degrees, preferably at least 140 degrees and at most 210 degrees, more preferably at least 150 degrees and at most 200 degrees. This range may provide optimal mechanical support. Also, this range may include parts of the tibia surface that are anatomically suitable to attach the fourth section.

The elongate third section may be elastic. This elasticity may contribute to and dictate movability of the curved second section, as well as tension to pull the elongate third section in place.

The elongate third section may be made of a biocompatible, non-resorbable material that has a tensile modulus of at most 160 MPa as determined by ISO 527-1. This may provide appropriate elasticity characteristics to the third section for providing the desired mechanical behavior of the curved second section to adapt to knee kinematics.

The second curved section and the third curved section may be made of a single, homogeneous material. This not only may facilitate efficient manufacturing of the prosthesis, but it also may prevent failure due to circumferential overload resulting in tear and wear while the function of a supporting construct remains.

The second fastening part may be configured to rotatably secure the fourth section to the bone surface, so that the third section can rotate around an axis defined by the second fastening part when secured to the bone surface. This feature alternatively provides mechanical freedom to the curved second section, because the elongate third section may pivot around the second fastening part.

The first fastening part may be configured to rotatably secure the first section to the bone surface, so that the second section can rotate around an axis defined by the first fastening part when secured to the bone surface. This feature alternatively provides mechanical freedom to the curved second section, because the curved second section may pivot around the first fastening part. When both the first and second sections are rotatably secured to the bone surface, the prosthesis may have better mechanical freedom, in particular when (at least part of) the prosthesis is made of an elastic material.

The curved second section may have a cross section with a wedge shape, and the elongate third section may comprise a transition section in which a cross section of the elongate third section transitions from a more wedge shape towards the third end to a more rectangular shape with smoothened edges towards the fourth end (or towards the second fastening part). The wedge shape may be desirable for the curved second section to achieve the movement and support compressive loads within the knee. The rectangular shape may be desirable for good attachment properties and to support motion of the prosthesis via the elongate third section. Also, the transition between the wedge shape and the rectangular shape in the elongate fourth section may be a smooth transition to prevent interference with the surrounding tissues within the joint and to prevent potential failure of the prosthesis as a result of a weak spot introduced via a sudden transition. In a similar manner, transition between different cross section(s) may be incorporated to facilitate prothesis function while fixation locations differ from the anatomical positions of the native meniscus. The first fixation section may also comprise a smooth transition section in which a cross section of the first section transitions from a more wedge shape towards the curved second section to a more rectangular shape with smoothened edges towards the first fastening part.

The elongate third section may comprise a thread that extends from the third end of the elongate third section to the fourth end of the elongate third section. For example, the elongate third section may be a section of thread. The thread may be, for example, a suture or a wire. This has the advantage of enabling highly flexible on-the-spot selection of a suitable place on the bone to attach the second fastening part while loading of the prosthesis remains transduced via the fixation parts. Because the thread can pivot around the second fastening part, it can provide the desired mechanical freedom to the curved second section. The thread may be kept tensioned because the bone structures around the curved second section may provide a bias away from the second fastening part. The thread may be elastic or inelastic to achieve different mechanical properties of the prosthesis. A combination of different materials and structures may be used to provide in this mechanical freedom. Preferably, materials with a tensile modulus of a magnitude of at most the tensile modulus of the curved section is used to enable load distribution via the curved section upon joint loading.

The fourth section may comprise another segment of the same thread to provide in the biomechanical properties of the prosthesis. For example, the second attachment member is a segment of the thread. This allows efficient attachment during surgery by securing the thread to the bone.

The curved second section may be made of a single biocompatible, non- resorbable material that has a tensile modulus of at most 160 MPa as determined by ISO 527-1. This provides additional flexibility to the curved second section and may allow it to flex under the, compressive, loads exerted to it by the surrounding bone structures.

Advantageously, the curved second section and the elongate third section are formed together as a single piece of a single biocompatible, non-resorbable material that has a tensile modulus of at most 160 MPa as determined by ISO 527-1. This simplifies production and improves durability. Advantageously also the first section and the fourth section are formed together with the second curved section and the elongate third section to form the single piece of a single biocompatible, non-resorbable material that has a tensile modulus of at most 160 MPa as determined by ISO 527-1 .

According to another aspect, a method of manufacturing a prosthesis is provided. The method comprises attaching the thread to the second end of the curved second section of the prosthesis set forth. This method provides efficiency by allowing the thread to be added to the prosthesis body at any given time, to prepare for surgery.

According to another aspect, a method of implanting a prosthesis as set forth is provided. The method comprises posterior fixation of the first section and anterior fixation of the fourth section. Preferably the posterior fixation precedes the anterior fixation. Yet preferably, the prosthesis first section, curved second section, elongate third section, and fourth section are brought into the preferred position in the knee before posterior and anterior fixation.

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. BRIEF DESCRIPTION OF THE DRAWINGS

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.

Fig. 1 A shows aspects of the anatomy of a knee joint.

Fig. 1 B shows movement ranges of the natural lateral meniscus and medial meniscus.

Fig. 2 shows a lateral meniscus prosthesis.

Fig. 3A shows indications of cross sections of a meniscus prosthesis.

Fig. 3B shows a wedge-shaped cross section.

Fig. 3C shows a rectangular shaped cross section.

Fig. 3D shows a circular shaped cross section.

Fig. 4 shows several dimensions of a lateral meniscus prosthesis.

Fig. 5 shows the lateral meniscus prosthesis in an anatomical context.

Fig. 6A-F show alternative configurations of a meniscus prosthesis.

Fig. 7 shows several alternative configurations in an anatomical context.

DETAILED DESCRIPTION OF EMBODIMENTS

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.

Fig. 1A illustrates aspects of the anatomy of the tibia plateau part of a human knee joint (transversal plane). The drawing shows the tibia plateau 101 with the lateral meniscus 102, the medial meniscus 103, and the intermeniscal ligament 104. The lateral meniscus 102 is joined to the tibia plateau 101 at the anterior lateral horn 105 and the posterior lateral horn 106. The medial meniscus 103 is joined to the tibia plateau 101 at the anterior medial horn 107 and the posterior medial horn 108. The anterior cruciate ligament 109 and the posterior cruciate ligament 110 join the tibia to the femur.

The medial meniscus horns 107, 108 are further apart than the lateral meniscus horns 105, 106 and the outer rim of the medial meniscus covers a larger surface of the tibia plateau compared to the lateral meniscus. This results in larger (i.e. anterior- posterior) translation of the lateral meniscus over the tibia plateau compared to the medial meniscus. The lateral meniscus thus has different mechanical freedom than the medial meniscus.

Fig. 1 B shows the extend of movement of the menisci in a human knee. The anterior medial meniscus 103 displaces about 7 mm on average and about 3 mm on average at the posterior side. The lateral meniscus 102 displaces about 13 mm on average at the posterior side and about 10 mm on average at the anterior side.

The average anterior-posterior translation of the lateral meniscus (about 11 mm) is typically a factor 2-3 times the anterior-posterior translation the medial meniscus (5 mm).

Fig. 2 shows a top view of a lateral meniscus prosthesis 200. The prosthesis has a first section 1 having a first fastening part 5 for securing the first section 1 to a bone surface, such as the tibia plateau 101. The first section is connected to one end of a second section 2. This second section has a C-shape, or an arc-shape. Thus, it is curved. The cross section of the second section may have a wedge shape, with the thin end at the inner circular side and the thick end at the outer circular side. The other end of the second section is connected to one end of a third section 3. The third section 3 has an elongate shape and extends substantially linearly in a longitudinal direction tangentially to the second section. The third section may have any cross sectional shape, e.g. wedge or rectangular, oval or circular, or combinations thereof, and may have a transition from wedge shape to a rectangular shape, possibly via an oval or circular shape. The other end of the third section 3 is connected to the fourth section 4 having a second fastening part 6 for securing the fourth section 4 to the bone surface, such as the tibia plateau 101.

Fig. 3 shows several cross sections of the prosthesis 200. Fig. 3A shows the prosthesis 200. Fig. 3B illustrates a wedge shape, which occurs at least in the curved second section 2, and may occur in part of the third section 3. Fig. 3C illustrates a flat shape (rectangular with smooth edges), which may occur in the first section 1 and fourth section 4, as well as in part of the third section 3. A circular cross section, as shown in Fig. 3D and Fig. 6E, or e.g. an elliptical shape is also possible in the third section 3.

The illustrated prosthesis generally has a J-shape, although other configurations are also possible and described herein. The curved second section 2 may form e.g. an arc of about 180 degrees, or an arc in a range of 150 to 200 degrees. The first section 1 and fourth section 4 may be smaller, just long enough to provide sufficient strength for the fastening parts 5 and 6. For example, the elongate third section may be at least two or three times longer than each of the first section 1 and fourth section 4.

Fig. 4 shows the prosthesis 200. The figure illustrates that the curved second section 2 has an arc shape. For example, a cross section (e.g. the wedge shape illustrated in Fig. 3B) of the curved second section 2 extends in between a segment of an inner circle 401 having an inner radius and a segment of an outer circle 402 having an outer radius r, the inner circle and the outer circle being concentric. These circle segments may have an angle of a degrees. The elongate third section 3 may extend from the end of the curved second section 2 in tangential direction with respect to the inner circle 401 and/or the outer circle 402. That is, in certain embodiments the cross section of the elongate third section 3 substantially extends in between two parallel lines (not illustrated) that are tangential to the concentric circles 401 , 402.

As shown in Fig. 4, advantageously the first fastening part 5 of the first section 1 is located inside the outer circle 402, whereas the second fastening part 6 of the second section 2 is located outside the outer circle 402. Thus, a suitable fastening position may be designed for the second fastening part 6, away from the location of the natural meniscus horn 105.

The length of the elongate third section 3 and the fourth section 4 together (measured in a direction tangential to the inner circle 401 and/or the outer circle 402) may be preferably at least 0.5 times the outer radius r and at most 3 times the outer radius r. More preferably, the length I of the elongate third section 3 and the fourth section 4 together may be at least equal to the outer radius r and at most 2 times the outer radius r. Even more preferably, the length I of the elongate third section 3 and the fourth section 4 together may be at least 1.1 times the outer radius rand at most 2 times the outer radius r. Yet more preferably, the length I of the elongate third section 3 and the fourth section 4 together may be at least 1.5 times the outer radius r and at most 2 times the outer radius r. Even more preferably, the length I of the elongate third section 3 and the fourth section 4 together may be at least 1.6 times the outer radius r and at most 1.9 times the outer radius r. This way, elastic properties and attachment location of the fastening means may be improved.

When measured from a radius touching a transition between the first segment (1) and the curved second segment (2) to a radius touching a transition between the curved second segment (3) and the elongate third segment 3, the circle segment spanned by the curved second section 2 may have an angle a of at least 135 degrees and at most 220 degrees. Preferably, this angle a is at least 140 degrees and at most 210 degrees. More preferably, this angle a is at least 150 degrees and at most 200 degrees.

Fig. 5 shows the prosthesis 200 in place on a tibia surface 101. The first fastening part 5 is located at or near the posterior lateral horn 106 to provide for fixation at the anatomical position of the posterior lateral horn. The second fastening part 6 is located away from the anterior lateral horn 106. This allows for an easier fixation due to less interference with the anatomical structure while providing functional prosthesis movement during knee movement.

Fig. 6 shows several alternative embodiments of the prosthesis 200. The Figures 6A through 6D vary in the length of the elongate third section 3, and the angle a to cover anatomical variations of the human knee.

Fig. 6E shows an embodiment in which the cross section of the third section 3 is e.g. circular, as in Fig. 3D. The elongate fourth section 4 may comprise transition regions for a smooth transition from the wedge-shaped cross section of the curved second section 2 to the circular cross section and from the circular cross section to the rectangular cross section of the fourth section 4.

Fig. 6F shows an embodiment in which part of the elongate third section 3 comprises a thread 606, such as a suture. The third section 3 may comprise a further fastening part 603 located at the second end of the curved second section 2. The thread may be fastened to this further fastening part 603. Alternative manners to connect the thread to the prosthesis at the end of the curved second section 2 may be implemented, such as welding or molding. The thread may be elastic or inelastic. The flexibility of even an inelastic thread provides motion freedom to the curved second section 2 while exerted loads remain transferred via the prosthesis fixations. The thread may comprise the fourth section 4’. Alternatively, the fourth section 4’ may comprise a piece of the thread 606. Also the second fastening part 6’ may be or comprise a piece of the thread 606. Moreover, fastening means may be added such as a pin or a ring made of metal or a polymer, for example.

Fig. 7 shows the anatomy superimposed by the different embodiments of the prosthesis shown in Figs. 6A through 6D. The illustration shows that the angle a and the length of the elongate third section 3 provide variations for the location of the second fastening part 6 on the tibia plateau 101.

In all configurations shown (Figs. 1-7), the four sections 1 ,2, 3, 4 may be integrally molded or otherwise formed from a single material. For example, the prosthesis comprising all the sections may be 3D printed. Other manufacturing methods are also possible. Moreover, the prosthesis surface may be provided with a coating. The material or materials of the prosthesis, as well as the shape of the prosthesis, determine its mechanical properties.

The prosthesis, in particular the elongate third section, may be elastic. For example, the elongate third section is made of a biocompatible, non-resorbable material that has a tensile modulus of at most 160 MPa as determined by ISO 527-1 . In certain embodiments, the entire prosthesis is made of such a material.

In certain embodiments, the first section 1 and the curved second section 2 are made of the biocompatible, non-resorbable material that has a tensile modulus of at most 160 MPa as determined by ISO 527-1. The elongated third section 3 and the fourth section 4 may have a smaller tensile modulus. However, rotation around the second fastening part 6 is then ensured by the fixation technique used (for example by a suture or a loose screw or snap-fit construction), or by implementing (at least a portion of) the third elongated section as a thread.

The second curved section and the third curved section may be made of a single, homogeneous material. Also, the first section and the fourth section may be made of this single, homogeneous material. These sections of the prosthesis may be created in one molding or 3D printing operation, for example.

The second fastening part may be configured to rotatably secure the fourth section to the bone surface, so that the third section can rotate around an axis defined by the second fastening part when secured to the bone surface. An example fastening part is the anchoring element known from WO 2015/057056. Another example fastening part is the snap-fit attachment known from WO 2019/125167. Another example fastening part is a through-hole, through which e.g. a suture can be drawn and the prosthesis can be attached to the bone using the suture.

A method of creating a prosthesis may employ the thread to implement the third section 3’. The method comprises attaching the thread 606 to the further fastening part 603 of the third section 3’. This may be by pulling the thread 606 through a through-hole of the further fastening part 603, for example, and creating a knot to secure the thread to the further fastening part.

Throughout this disclosure, ISO 527-1 may refer to ISO 527-1 :2019 edition 3, published in July 2019.

A method of implanting a prosthesis as set forth herein may be provided. The method comprises posterior fixation of the first section 1 and anterior fixation of the fourth section 4. Preferably the fastening parts 5 and 6 are employed, for example by means of a screw or pin or suture, if the fastening parts 5 and 6 are through-holes. Preferably the posterior fixation precedes the anterior fixation. Yet preferably, the prosthesis first section 1 , curved second section 2, elongate third section 3, and fourth section 4 are brought into the preferred position in the knee before posterior and anterior fixation. The whole process may be performed while keeping the femur and the tibia in fixed relationship to each other.

The curved second section 2 and/or the elongate third section 3 and/or the entire prosthesis, may be made of a single first biocompatible, non-resorbable material that has a tensile modulus of at most 160 MPa as determined by ISO 527-1. The first material may be isotropic with regard to the tensile modulus and the curved second section 2 may be a monolithic piece of the first material. The elongate third section 3 may be isotropic with regard to the tensile modulus and the curved second section 2 may be a monolithic piece of the first material. The curved second section 2 and the elongate third section 3 may together form a monolithic piece of the first material. Advantageously, the first material has a tensile modulus of less than 50 MPa measured according to ISO 527-1 , preferably less than 40 MPa measured according to ISO 527-1 , more preferably less than 15 MPa measured according to ISO 527-1.

The first material may have a tensile modulus between 0.1 MPa and 50 MPa measured according to ISO 527-1 , preferably between 5 MPa and 50 MPa measured according to ISO 527-1 , more preferably between 5 MPa and 40 MPa measured according to ISO 527-1 , even more preferably between 5 MPa and 15 MPa measured according to ISO 527-1.

The meniscus prosthesis as a whole may be stiff enough to, when secured to the bone surface at the first end and at the second end, prevent dislocation of the curved intermediate section upon joint loading.

The first section 1 may comprise a second biocompatible, non-resorbable material that has a tensile modulus of at least 100 MPa as determined by ISO 527-1 , and the fourth section 4 may comprise a third biocompatible, non-resorbable material that has a tensile modulus of at least 100 MPa as determined by ISO 527-1 , wherein the second material and the third material can be the same material or different materials.

The second material and the third material may each have a tensile modulus between 100 MPa and 3500 MPa measured according to ISO 527-1 , preferably between 100 MPa and 1000 MPa, more preferably between 100 MPa and 250 MPa, measured according to ISO-527-1.

The first section 1 of the meniscus prosthesis 200 may be made entirely of the second material. The fourth section 4 may be made entirely of the third material. The first section 1 may comprise a first protrusion made of the second material, wherein the first protrusion engages with a corresponding recess in the curved second section 2. The fourth section may comprise a second protrusion made of the third material, wherein the second protrusion engages with a corresponding recess in the elongate third section 3. Such protrusions are known from WO 2023/126435.

The curved second section 2 may comprise a third protrusion, wherein the third protrusion engages with a corresponding recess in the elongate third section 3, or alternatively the elongate third section 3 may comprise a fourth protrusion, wherein the fourth protrusion engages with a corresponding recess in the curved second section 2.

The first section 1 and/or the fourth section 4 may comprise a core made of the second material and a cushioning material that covers the core.

Alternatively, the first section 1 may be made of the first material and the fourth section 4 may also be made of the first material.

The transverse cross-sectional area of the curved second section 2 may be wedge-shaped, with a larger thickness at an outer circumference of the curved second section 2 than at an inner circumference of the curved second section 2.

The first material, the second material, and the third material each may comprise a thermoplastic material, preferably a polyurethane, more preferably a polycarbonate urethane.

The first fastening part 5 may comprise a first through-hole configured to receive a connector for securing the first section 1 to a bone. The second fastening part 6 may also comprise a second through-hole configured to receive a connector for securing the fourth section 4 to a bone.

The meniscus prosthesis may further comprise a suture extending through the first through-hole and a suture extending through the second through-hole.

The meniscus prosthesis may be manufactured by means of molding. For example, a method of manufacturing a meniscus prosthesis can comprise molding at least part of the first section 1 of the meniscus prosthesis, the at least part of the first section 1 having a first fastening part for securing the first end to a bone surface, and molding at least part of the fourth section 4 of the arc-shaped meniscus prosthesis, the at least part of the fourth section 4 having a second fastening part for securing the fourth section 4 to a bone surface. Next, the method may proceed by molding a component forming a curved second section 2 and an elongate third section 3, connecting the first section 1 to the fourth section 4, wherein the component is made of a first biocompatible, non-resorbable material that has a tensile modulus of at most 160 MPa as determined by ISO 527-1 . For example, the molding of the component is performed in such a way that the material of the curved second section 2 touches a part of the surface of the first section 1 , and the material of the elongate third section 3 touches a part of the surface of the fourth section 4, for example they touch the surface of a stub of the first section 1 and the fourth section 4, respectively. During the molding procedure these different materials will attach to each other at the touching surface. Optionally the curved second section 2 and the elongate third section 3 may be molded as separate components touching each other in the way described.

For example, the curved second section 2 of the meniscus prosthesis disclosed herein may have a geometry that corresponds to the geometry of at least part of the anatomic lateral knee meniscus.

Moreover, the meniscus prosthesis may be made mostly or entirely of a material that has a meniscus-like elastic modulus in compression, but with a much lower elastic modulus in circumferential direction.

The sections of the prosthesis may be non-resorbable. This helps to make the implant more durable, so that it can be optimally used as a permanent prosthesis. The material used for the middle sections 2, 3 and/or the end sections 1 , 4 may contain selfassembling monolayer end-groups. This helps to provide a film on the surface that improves comfort.

An advantage of the meniscus prosthesis disclosed herein is that chances of failure will decrease while the implant is allowed to be further pushed out of the joint, without exceeding the ultimate tensile strength of the material, while remaining in tight contact with the femur and tibia to fill the wedge shape joint space and fulfill its bearing and load distributing function. In case of high load, the load may be (partially) shifted from load on the implant to load on the cartilage. The position of the prosthesis within the joint cavity will be restored when loads are normalized after overloaded.

In certain embodiments, the meniscus prosthesis may have an end-section formed by the first section 1 and/or fourth section 4 that is stiffer than the larger portion of the meniscus prosthesis. This end-section may be made of a stiffer material, in order to strengthen the connection to the bone of the patient. Such an end-section may be present at both ends of the prosthesis. For example, the end-section may comprise a fastening part, such as a hole. The flexible sections 2, 3 in between the two end-sections 1 , 4 may be referred to as a middle section. Furthermore, the increased flexibility of the middle section allows this part of the implant to continuously follow the changing shape of the condyle during flexion. In certain embodiments, the end-section 1 , 4 may have a small stub that extends into the flexible material of the middle section 2, 3. This increases the tear strength in shear force conditions, so that the durability of the implant in the joint may be increased.

The meniscus prosthesis may be connected to the bone with 2 screws, one for each end-section.

Failure of the prosthesis as a result of breakage may be prevented by providing a different location for the second fastening part 6, away from the natural meniscus horn. Since there is more space at the chosen location, the leg has more freedom to move without being hampered by the second fastening part, preventing overload of the device. Importantly, the additional flexibility provided by the elongate third section 3 allows the prosthesis, in particular the curved second section 2, to more accurately deform to follow the condyle during knee movements, to better provide the function of a meniscus. The implant has the function to take over the function of the resected native meniscus: In particular, to share the vertical load from the femoral condyle between the meniscus and the part of tibial cartilage which is in direct contact with the condyle, and to avoid the situation that the tibial cartilage carries all the load after the meniscus is surgically removed. Due to the anatomical variation in, and the different forms and sizes of a joint, the more flexible the implant, the more it can adapt to these differences by means of reversible deformation and/or permanent creep. This also contributes to the meniscus acting as a sliding bearing with the synovial fluid as lubricant. When the meniscus is dissected, the lubricant is no longer able to build up a pressurized fluid cushion at its contact area. The meniscus prostheses as disclosed herein were found to be highly suitable to take over this function from the meniscus.

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 defined in the following clauses.

1 . A prosthesis for application in a knee compartment, comprising a first section (1) having a first fastening part (5) for securing the first section (1) to a bone surface; a curved second section (2) having a first end (7) and a second end (8), the curved second section (2) in between the first end (7) and the second end (8), wherein the first end (7) of the curved second section (2) is connected to the first section (1); an elongate third section (3) having a third end (9) and a fourth end (10) on opposite ends of the elongate third section (3), wherein the third end (9) of the elongate third section (3) is connected to the second end (8) of the curved second section (2); and a fourth section (4) having a second fastening part (6) for securing the fourth section (4) to a bone surface, wherein the fourth section (4) is connected to the fourth end (10) of the elongate third section (3).

2. The prosthesis according to clause 1 , wherein the elongate third section (3) extends from the second end (8) of the curved second section (2) in tangential direction with respect to the curved second section (2).

3. The prosthesis according to any preceding clause, wherein the curved second section (2) has an arc shape, so that a cross section of the curved second section (2) extends in between a segment of an inner circle (401) having an inner radius and a segment of an outer circle (402) having an outer radius, the inner circle (401) and the outer circle (402) being concentric.

4. The prosthesis of clause 3, wherein the first fastening part 5 is inside the outer circle and the second fastening part 6 is outside the outer circle.

5. The prosthesis according to clause 3 or 4, wherein the elongate third section (3) extends from the second end (8) of the curved second section (2) in tangential direction with respect to the inner circle (401) and the outer circle (402).

6. The prosthesis according to any one of clauses 3 to 5, wherein a length I of the elongate third section (3) and the fourth section (4) together is, at least 0.5 times the outer radius and at most 3 times the outer radius, preferably at least equal to the outer radius and at most 2 times the outer radius, more preferably at least 1.1 times the outer radius and at most 2 times the outer radius, even more preferably at least 1.5 times the outer radius and at most 2 times the outer radius, even more preferably at least 1.6 times the outer radius and at most 1.9 times the outer radius.

7. The prosthesis according to any one of clauses 3 to 6, wherein the circle segment has an angle a, measured from a radius touching a transition between the first segment (1) and the curved second segment (2) to a radius touching a transition between the curved second segment (3) and the elongate third segment (3), of at least 135 degrees and at most 220 degrees, preferably at least 140 degrees and at most 210 degrees, more preferably at least 150 degrees and at most 200 degrees. 8. The prosthesis according to any preceding clause, wherein at least the elongate third section (3) is elastic.

9. The prosthesis according to any preceding clause, wherein the elongate third section (3) is made of a biocompatible, non-resorbable material that has a tensile modulus of at most 160 MPa as determined by ISO 527-1.

10. The prosthesis according to any preceding clause, wherein the curved second section (2) is made of a single biocompatible, non-resorbable material that has a tensile modulus of at most 160 MPa as determined by ISO 527-1.

11. The prosthesis according to any preceding clause, wherein the second curved section (2) and the third curved section (3) are made of a single, homogeneous material.

12. The prosthesis according to any preceding clause, wherein the second fastening part (6) is configured to rotatably secure the fourth section (4) to the bone surface, so that the third section (3) can pivot around an axis defined by the second fastening part (6) when secured to the bone surface.

13. The prosthesis according to any preceding clause, wherein the curved second section (2) has a cross section having a wedge shape, and the elongate third section (3) comprises a gradual transition section (301) in which at least one cross section of the elongate third section (3) transitions from a wedge shape towards the third end (9) to a rectangular shape with smoothened edges towards the fourth end (10).

14. The prosthesis according to any one of clauses 1, 3-4, and 6-13, wherein the elongate third section (3) comprises a segment of thread (606) that is connected to a further fastening part (603) at the third end (9) of the elongate third section (3) and to the fourth end (10) of the elongate third section.

15. A method of creating a prosthesis according to clause 12, comprising attaching the thread (606) to the further fastening part (603).

Claims

CLAIMS:

1 . A prosthesis for application in a knee compartment, comprising a first section (1) having a first fastening part (5) for securing the first section (1) to a bone surface; a curved second section (2) having a first end (7) and a second end (8), the curved second section (2) in between the first end (7) and the second end (8), wherein the first end (7) of the curved second section (2) is connected to the first section (1), wherein the curved second section (2) has an arc shape, so that a cross section of the curved second section (2) extends in between a segment of an inner circle (401) having an inner radius and a segment of an outer circle (402) having an outer radius, the inner circle (401) and the outer circle (402) being concentric; an elongate third section (3) having a third end (9) and a fourth end (10) on opposite ends of the elongate third section (3), wherein the third end (9) of the elongate third section (3) is connected to the second end (8) of the curved second section (2); and a fourth section (4) having a second fastening part (6) for securing the fourth section (4) to a bone surface, wherein the fourth section (4) is connected to the fourth end (10) of the elongate third section (3), wherein the first fastening part 5 is inside the outer circle and the second fastening part 6 is outside the outer circle.

2. The prosthesis according to claim 1 , wherein the elongate third section (3) extends from the second end (8) of the curved second section (2) in tangential direction with respect to the curved second section (2).

3. The prosthesis according to claim 1 , wherein the elongate third section (3) extends from the second end (8) of the curved second section (2) in tangential direction with respect to the inner circle (401) and the outer circle (402).

4. The prosthesis according to any one of claims 1 to 3, wherein a length I of the elongate third section (3) and the fourth section (4) together is, at least 0.5 times the outer radius and at most 3 times the outer radius, preferably at least equal to the outer radius and at most 2 times the outer radius, more preferably at least 1.1 times the outer radius and at most 2 times the outer radius, even more preferably at least 1 .5 times the outer radius and at most 2 times the outer radius, even more preferably at least 1.6 times the outer radius and at most 1 .9 times the outer radius.

5. The prosthesis according to any one of claims 1 to 4, wherein the circle segment has an angle a, measured from a radius touching a transition between the first segment (1) and the curved second segment (2) to a radius touching a transition between the curved second segment (3) and the elongate third segment (3), of at least 135 degrees and at most 220 degrees, preferably at least 140 degrees and at most 210 degrees, more preferably at least 150 degrees and at most 200 degrees.

6. The prosthesis according to any preceding claim, wherein at least the elongate third section (3) is elastic.

7. The prosthesis according to any preceding claim, wherein the elongate third section (3) is made of a biocompatible, non-resorbable material that has a tensile modulus of at most 160 MPa as determined by ISO 527-1.

8. The prosthesis according to any preceding claim, wherein the curved second section (2) is made of a single biocompatible, non-resorbable material that has a tensile modulus of at most 160 MPa as determined by ISO 527-1.

9. The prosthesis according to any preceding claim, wherein the second curved section (2) and the third curved section (3) are made of a single, homogeneous material.

10. The prosthesis according to any preceding claim, wherein the second fastening part (6) is configured to rotatably secure the fourth section (4) to the bone surface, so that the third section (3) can pivot around an axis defined by the second fastening part (6) when secured to the bone surface.

11 . The prosthesis according to any preceding claim, wherein the curved second section (2) has a cross section having a wedge shape, and the elongate third section (3) comprises a gradual transition section (301) in which at least one cross section of the elongate third section (3) transitions from a wedge shape towards the third end (9) to a rectangular shape with smoothened edges towards the fourth end (10).

12. The prosthesis according to any one of claims 1 to 11 , wherein the elongate third section (3) comprises a segment of thread (606) that is connected to a further fastening part (603) at the third end (9) of the elongate third section (3) and to the fourth end (10) of the elongate third section.

13. A method of creating a prosthesis according to claim 12, comprising attaching the thread (606) to the further fastening part (603).