AU7423298A

AU7423298A - Plastic implant with metal netting

Info

Publication number: AU7423298A
Application number: AU74232/98A
Authority: AU
Inventors: Peter Bamert; Hans-Walter Staudte; Peter Studer
Original assignee: Mathys Medizinaltechnik AG
Current assignee: Synthes Bettlach GmbH
Priority date: 1998-06-03
Filing date: 1998-06-03
Publication date: 1999-12-20
Also published as: EP1082074B8; JP2002516711A; DE59813320D1; EP1082074B1; WO1999062438A1; EP1082074A1; ATE314027T1

Abstract

The inventive implant consists of a plastic core (1) whose surface is covered by metal netting (2). Said metal netting is woven into a braided fabric with warp wires (3) and weft wires (4) using linen binding. The implant produces optimal osseo-integration results with a minimum effect on its rigidity.

Description

1631/US PLASTIC IMPLANT WITH METAL NETTING. The invention relates to an implant defined in the preamble of claim 1. The European patent document 212,087 B discloses an artificial hip-bone socket constituted by a semi-spherical plastic shell receiving on its outside a multi-ply metal netting that shall come to rest against the hip bone. This configuration allows bone growth into the open net meshes. This known hip-bone socket incurs the following drawbacks: (a) free surface zones of the plastic shell outside that are not covered by the netting hamper bone growth, (b) the netting being made of several plies, the surface zones are somewhat less accessible and the rigidity of the hip-bone socket is considerably and disadvantageously altered, (c) in case of repairs, the bone integration may severely damage the hip-bone socket. The objective of the invention is palliation. The goal of the invention is to create an implant which, while its rigidity is minimally affected, shall exhibit optimal bone-integrating behavior. The invention solves this problem by means of a surgical implant defined by the features of claim 1. The invention attains the advantage that the full implant surface -- which now is protected by a tight metal netting -- allows optimal bone growth instead of the conventional bone anchorage into the metal netting. Because the metal netting is braided, the bone can optimally grow onto the implant. The expression "braid" herein denotes a "linen" weave wherein however the warps are far apart and the fillings tightly together. Also, the warps are thicker than the fillings. The 2 1631/US "linen weave" also is known as "smooth weave". A warp each time is woven over a filling and vice versa. In the "braids" of the invention, the metal warps are such a distance apart from each other that the metal filling can just be bent around the warp without tearing. To attain optimal bone growth, titanium or titanium alloy wires were found advantageous. In principle other metal. alloys also may be appropriate provided they exhibit osteo-conductive properties similar to those of titanium. The metal netting's elasticity does not significantly affect the rigidity of the implant's plastic core. Because of the comparatively large thickness of the metal netting of the invention, being typically 1.1 to 2.2 mm, preferably 1.5 to 2.0 mm, a single-play netting may be used and provided there be a typical depth of impression of 20 % to 80 %, preferably 30 % to 60 %, of the metal netting into the surface of the plastic (for instance polyethylene), an adequately safe distance to the bone shall be attained. The braid's warp wires are farther apart from each other than the filling wires are. Typically the spacing between the warp wires is 1.0 to 3.0 mm, preferably 1.3 to 1.8 mm; the spacing between the filling wires typically is less than 0.4 mm, preferably less 0.2 mm. The braid's warp-wire diameter is larger than the diameter of the filling wires. Typically the warp wire diameter is between 0.6 and 1.2 mm, preferably between 0.8 and 1.0 mm; the spacing between the filling wires is between 0.3 and 0.6 mm, preferably between 0.45 and 0.55 mm. As a result an advantageous macro-structure of the implant of the invention is attained. The bone integration may be improved further by roughening the metal netting's wire surface, for instance by pickling. The surface roughness of the warp wires and filling wires typically is between 5 and 100 p, preferably between 10 and 70 p. This microstructure enhances bone growth onto the implant.

3 1631/US In a further preferred embodiment, the plastic core is fitted with at least two continuous holes to receive bone screws (to assure good primary stability) and also blind holes to seat a handling implement. Moreover the plastic core of the surgical implant may be reinforced, for instance by non metallic fibers or metal reinforcements. The implant of the invention is widely applicable. Herebelow, however, it shall be described solely in relation to an endo-joint prosthesis, in particular an artificial hip-bone socket preferably comprising two stubs radially projecting from the plastic core's outside surface and primarily preventing rotation. Fig. 1 is a schematic sideview of an artificial hip-bone socket of the invention, Fig. 2 is a schematic view of the hip-bone socket of Fig. 1 rotated by 900, Fig. 3 is a topview of a metal netting of the hip-bone socket of the invention, Fig. 4 is a longitudinal section of a warp wire of the netting of Fig. 3 perpendicular to the plane of the netting, and Fig. 5 is a front view of the cross-section of the metal netting of Fig. 3 perpendicular to the plane of the netting. The artificial hip-bone socket shown in Figs. 1 and 2 substantially consists of plastic core 1 in the form of a spherical shell and illustratively made of ultrahigh molecular-weight polyethylene, a metal netting 2 made of pure titanium being deposited on the outside surface of said core, where said surface shall rest against the hip bone. As shown in detail in Figs. 3 - 6, the warp wires 3 and the filling wires 4 of the metal netting 2 are woven into a braid in the form of a linen weave. The plastic hip-socket further comprises four continuous holes 5 which shall receive bone screws and two stubs 7 radially projecting from the outside surface of the plastic core 1. The holes 5 enable screwing, that is additionally anchoring, the hip-bone socket onto the hip bone and the stubs 7 secure against rotation.

4 1631/US Blind holes 9 also are present on the periphery of the artificial hip-bone socket to seat a handling implement with which to handle the hip-bone socket and to position it. The inside surface of the artificial hip-bone socket receiving the femur head is neither reinforced nor coated per se in order not to degrade the tribology. Accordingly the metal netting 2 is deposited only on those surfaces of the plastic core 1 where the bone shall grow onto them. As shown in Figs. 3 - 5, the metal netting 2 comprises a braid. The warp wires 3 of the metal netting 2 are mutually spaced apart by 1.3 to 1.8 mm whereas the filling wires 4 are tightly adjacent so that practically no space exists between them. The diameter of the warp wires 3 is 0.8 to 1.0 mm and larger than the diameter of the filling wires 4, which 0.45 to 0.55 mm. The surface roughness of the warp wires 3 and filling wires 4 is 10 to 70 p and is implemented by pickling the metal netting 2. As shown in Fig. 5, the metal netting 2 of a thickness between 1.5 and 2.0 mm is imbedded in a first manufacturing stage by 30 to 60 % of its thickness into the plastic core 1 and as a result a solid mechanical junction is implemented between the plastic core 1 and the metal netting 2.

Claims

1. An implant consisting of a plastic core (1) covered at its surface by a metal netting (2), characterized in that the metal netting is woven from warp wires (3) and filling wires (4), as a linen weave, into a braid.

2. Implant as claimed in claim 1, characterized in that the warp wires (3) are mutually spaced apart more than the filling wires (4).

3. Implant as claimed in one of claims 1 through 3, characterized in that the clear spacing between the warp wires (3) is 1.0 to 3.0 mm, preferably 1.3 to 1.8 mm.

4. Implant as claimed in one of claims I through 3, characterized in that the clear spacing between the filling wires (4) is less than 0.4 mm and preferably less than 0.2 mm.

5. Implant as claimed in one of claims 1 through 4, characterized in that the diameter of the warp wires (3) is larger than that of the filling wires (4).

6. Implant as claimed in one of claims 1 through 5, characterized in that the diameter of the warp wires (3) is between 0.6 and 1.2 mm, preferably between 0.8 and 1.0 mm.

7. Implant as claimed in one of claims 1 through 6, characterized in that the diameter of the filling wires (4) is between 0.3 and 0.6 mm, preferably between 0.45 and 0.55 mm. 6 1631/US

8. Implant as claimed in one of claims 1 through 7, characterized in that the surface roughness of the warp wires (3) and of the filling (wires (4) is between 5 and 100 p, preferably between 10 and 70 p.

9. Implant as claimed in one of claims 1 through 8, characterized in that the thickness of the metal netting is between 1.1 and 2.2 mm, preferably between 1.5 and 2.0 mm.

10. Implant as claimed in one of claims 1 through 9, characterized in that the metal netting (2) is imbedded by 20 to 80 %, preferably 30 to 60 % of its thickness into the plastic (1).

11. Implant as claimed in one of claims 1 through 10, characterized in that the metal netting (2) is made of titanium or of a titanium alloy.

12. Implant as claimed in one of claims 1 through 11, characterized in that the plastic core (1) comprises at least two continuous holes (5) to receive bone screws.

13. Implant as claimed in one of claims 1 through 12, characterized in that the plastic core (1) is fitted with blind holes (9) to seat a handling implement.

14. Implant as claimed in one of claims 1 through 16, characterized in that it is an endo-joint prosthesis, in particular an artificial hip-bone socket, which preferably comprises two stubs (7) projecting radially from the outside surface of the plastic core (1).