MENISCUS PROSTHESIS

Abstract

The invention is directed to a meniscus prosthesis comprising an arc-shaped meniscus prosthesis body having a main portion (1) comprising a reinforcing part (2) and two end portions (1A, 1B) comprising fixation parts (2A, 2B), wherein the main portion (1) comprises a part made of a first biocompatible, non-resorbable material extending between the two end portions (1A, 1B), wherein the reinforcing part (2) and the fixation parts (2A, 2B) are made of a second biocompatible, non-resorbable material and wherein the reinforcing part (2) extends between the fixation parts (2A, 2B) and wherein the fixation parts (2A, 2B) have a through hole (3A, 3B), the first biocompatible, non-resorbable material has a tensile modulus of at most 100 MPa as determined by ISO 527-1 and the second biocompatible, non-resorbable material has a tensile modulus of at least 101 MPa as determined by ISO 527-1.

Claims

1-13. (canceled)

14. 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, the reinforcing part extending between the fixation parts, and the fixation parts have a through hole, wherein the main portion comprises a part made of a first biocompatible, non-resorbable material extending between the two end portions, the first biocompatible, non-resorbable material having a tensile modulus of at most 100 MPa as determined by ISO 527-1, and wherein the reinforcing part and the fixation parts are made of a second biocompatible, non-resorbable material, the second biocompatible, non-resorbable material having a tensile modulus of at least 101 MPa as determined by ISO 527-1.

15. The meniscus prosthesis according to claim 14, wherein the first biocompatible, non-resorbable material comprises a hydrogel and/or a thermoplastic material.

16. The meniscus prosthesis according to claim 14, wherein the first biocompatible, non-resorbable material comprises a polyurethane.

17. The meniscus prosthesis according to claim 14, wherein the second biocompatible non-resorbable material comprises a thermoplastic material.

18. The meniscus prosthesis according to claim 14, wherein the tensile modulus of the second material is at most 3500 MPa.

19. The meniscus prosthesis according to claim 16, wherein the tensile modulus of the second material is at most 3500 MPa.

20. The meniscus prosthesis according to claim 14, wherein the form of the prosthesis body resembles the form of a native meniscus.

21. The meniscus prosthesis according to claim 14, wherein the first biocompatible, non-resorbable material and/or the second biocompatible, non-resorbable material comprises a radiopaque additive.

22. The meniscus prosthesis according to claim 14, wherein the through hole has a first portion with a first diameter and a second portion with a second diameter larger than the first diameter.

23. A process for the production of the meniscus prosthesis according to claim 14, comprising the steps of: molding the second material to form the reinforcing part and the fixation parts; making the through hole in the fixation parts; and molding the first material to form the part of the main portion of the prosthesis body to enclose the reinforcing part and, optionally the fixation parts.

24. The process according to claim 23, wherein the reinforcing part and the fixation parts are molded as one piece.

25. The process according to claim 23, wherein the through holes are made through the fixation parts and the first material in the end portions.

26. A method for replacing the native meniscus of a human, comprising the step of implanting the meniscus prosthesis according to claim 14 into the knee joint of a human.

Description

[0058] The invention is further illustrated by FIGS. 1 and 2. The dotted lines represent parts of the meniscus prosthesis that are located inside the meniscus prosthesis.

[0059] FIG. 1 is a top view of the meniscus prosthesis and FIG. 2 is an isometric view of the meniscus prosthesis.

[0060] In the FIG. 1 is the main portion of the arc-shaped meniscus prosthesis body and 1A and 1B are the two end portions.

[0061] The reinforcing part is represented by 2 and the fixation parts by 2A and 2B. The fixation parts comprise the through holes 3A and 3B.

[0062] Although the invention has been described in detail for purposes of illustration, it is understood that such detail is solely for that purpose and variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined in the claims.

[0063] It is further noted that the invention relates to all possible combinations of features described herein, preferred in particular are those combinations of features that are present in the claims.

[0064] It is noted that the term comprising does not exclude the presence of other elements.

[0065] However, it is also to be understood that a description on a product comprising certain components also discloses a product consisting of these components. Similarly, it is also to be understood that a description on a process comprising certain steps also discloses a process consisting of these steps.

[0066] The invention will now be elucidated by way of the following examples without however being limited thereto.

EXAMPLES

Test Method

[0067] The tensile modulus was determined according to ISO 527-1. The test specimen used was a specimen with the dimensions of the 1 BA type according to ISO 527-2. The test specimen were stamped from injection molded 80802 mm plaques using a special die. The specimens were saturated at least 2 weeks in a physiological buffered salt solution with pH 7.4 at a temperature of 37 C. prior to tensile testing. The test atmosphere was air with a relative humidity of 100%. The temperature during testing was 37 C. The speed of testing was 1 mm/min. The value of the tensile modulus is the average value of 5 test specimens.

Example 1

[0068] The shape of a healthy meniscus was determined by performing MRI scans. A computer model of the shape of a human meniscus was made based on the collected data. An aluminum mold was prepared based on the computer model of an average human meniscus. From the computer model the dimensions for the fixation parts were determined. Together with the necessary through holes the surface area of the cross section of the fixation parts was determined. According to literature, 60 N is known as a normal load that can act upon a human meniscus horn. This load, the surface area of the fixation part and a safety factor of 40% generated stress levels of 5.5 MPa. This stress level was chosen to test the fatigue properties of the second material of the fixation parts.

[0069] Bionate 75D and Bionate 65D of DSM Biomedical were injection molded in a mold of 80804 mm. From this test piece strips were cut with dimensions 6.615.44 mm. In the end of these strips a hole was drilled identical in size of the through hole of the meniscus design. The resulting surface area of the test strips was chosen to be equal to the surface area of the actual meniscus fixation parts. One end of the test specimen was held in the grip of a dynamic tensile testing machine. The other end was connected through a pin in hole to the other grip of the tensile machine. Testing was performed according to ISO-527-1. Prior to the start of the test the samples were conditioned in a buffered physiological salt solution with pH 7.4 of 37 C. until the samples reached a constant weight. This conditioning took about 3 weeks. During the test the whole specimen was kept immersed in the buffered physiological salt solution with pH 7.4 of 37 C. A sinusoidal tensile load between 0.2 and 11 MPa stress was applied on the 2 mm round pin (1.8-100 N) for 5 million cycles.

[0070] Another test was to determine the loads until break of the horn fixation design according to ISO 527-1.

[0071] Result: The test specimen could endure 5 million load cycles and showed permanent deformation of less than 1.5 mm. It was concluded that the material could easily withstand the ambient stress levels in the horn fixation area.

Example 2

[0072] In the meniscus prosthesis good adhesion of the components is important. At the interface of the two materials a weak spot in the design could be formed. However it is essential that the two parts adhere strongly to each other to ensure long term performance of the meniscus prosthesis of which this interface is dynamic mechanically loaded.

[0073] The reference sample was an injection molded 1 mm thick test specimen according to ISO 527-2 made from Bionate II 80A. All other samples were also 1 mm in thickness but contained an adhesion interface that was created by placing half of a test specimen according to ISO 527-2 made from Bionate II 80A in the mold prior to injection molding of the other using Bionate II 80A under varying process conditions. These process conditions are given in Table A. In FIG. 3 the top photo is half of the tensile bar according to ISO 527-1 and the bottom photo is a tensile bar with a visible interface.

[0074] Standard molding conditions for the first halves of the tensile bars were: [0075] Melt Temperature 210 C., Mold temp 50 C., injection time 0.4 sec, overmolding after 5 min in environment, no preheating, melt residence time 4.4 min, holding pressure 50 MPa.

[0076] The standard molding conditions for the reference sample were: [0077] Melt Temperature 210 C., Mold temp 50 C., injection time 0.4 sec, no preheating, melt residence time 4.4 min, holding pressure 50 MPa.

[0078] Testing was performed according to ISO-527-1. Testing was performed after annealing (24 h at 80 C. under nitrogen) and conditioning in a buffered physiological salt solution with pH 7.4 of 37 C. in a heated chamber kept under 70% relative humidity (RH) conditions until the samples reached a constant weight. 3-5 samples were prepared and tested for each molding condition. All samples broke at the adhesion interface.

[0079] The test results are given in Table A.

TABLE-US-00001 TABLE A Tensile strength Elongation at Molding parameters (MPa) average sd break (%) sd 1 Standard without adhesion 17.4 0.7 297 9 interface 2 Standard with adhesion 18.5 0.8 304 10 interface 3 10 C. lower melt temperature 14.9 0.7 264 11 4 20 C. lower melt temperature 8.2 1.2 96 21 5 Holding pressure 40 MPa 22.2 2.0 350 17 6 Holding pressure 60 MPa 18.9 4.0 309 45 7 Long Melt Residence time 19.1 2.0 346 21 (4.4 .fwdarw.12.2 min) 8 Long Injection time 19.2 1.4 310 13 (0.4 .fwdarw.1.2 sec) 9 Long storage (5 min .fwdarw.72 hrs) 18.3 1.6 332 20 first half (23 C. dry, N2) 10 lower mold temperature 14.9 1.6 268 23 (50.fwdarw.30 C.) 11 preheating first half 13.9 4.0 267 60 (23 .fwdarw.110 C. for 30 min) Sd = standard deviation

Observations

[0080] Maintaining of the normal processing conditions led to a surprisingly strong adhesion at the interface. No loss of strength and elongation properties is observed. [0081] The values for tensile strength and elongation at break of samples 1 and 2 do not show a large difference. It can thus be concluded that under standard molding conditions the presence of an adhesion interface does not make a lot of difference for tensile strength and elongation at break of a sample. [0082] When the temperature during molding is lowered with 10 resp. 20 C. (see samples 2, 3 and 4) the tensile strength and the elongation at break of a sample become worse. It can be concluded that variations in the melt temperature during molding have a strong influence on the properties of the samples. [0083] When the mold temperature is lowered from 50 to 30 C. (compare samples 2 and 10) and the mold is preheated at a temperature of 110 C. (compare samples 2 and 11) this has a clear negative influence on the tensile strength and the elongation at break of the samples. [0084] Variations in the holding pressure (sample 5 and sample 6), melt residence time (sample 7), storing samples for 72 hrs (sample 9) and longer injection time (sample 8) have a small influence on the on the tensile strength and the elongation at break of the samples when compared with sample 2.