FR2776918A1 - Hip prosthesis cotyloid cup implant - Google Patents

Abstract

The cup (1) has its inner surface (2) shaped to receive the spherical head of a femoral implant, and an outer wall (3) of varying thickness. The wall has a thickened section (4) covering some two-thirds of its periphery, the thickness of which varies progressively according to the anatomical sector it faces. The additional thickness of the thickened wall section is between 1 and 5 mm.

Description

The subject of the present invention is an acetabular prosthesis implant

  total hip. In a known manner, in order to carry out a prosthetic reconstruction of the hip joint, an implant in the form of a cup receiving, with the possibility of pivoting, the spherical head is placed at the level of the acetabular cavity of the iliac bone. 'another

implant fixed in the femur.

  For several decades, these cups were cemented; a significant failure rate prompted orthopedic surgeons to find cementless solutions. In this specific case, the problem of the implant placed without cement essentially concerns its behavior after implantation; this must be sufficient to allow the bone to grow back and anchor around the prosthesis within a few months of implantation. Various solutions have been proposed to achieve this objective such as the impaction of an oversized hemisphere but this creates constraints on the bottom of the acetabulum which is thin and fragile instead of the edges which are thick and more resistant. To move the constraints towards the periphery, hemispherical models, slightly oversized and flattened in the polar region, have been proposed. In doing so, the stresses are indeed transferred to the equatorial region, but the possibility of leaving a vacuum between the background of the acetabulum and the implant is detrimental to regrowth.

and bone anchoring.

  Another solution, aimed at ensuring contact over the entire surface of the cup while promoting the clamping in the equatorial zone, consists, as in US Pat. No. 4,707,127, of finishing the hemisphere with a cylinder or of creating a bulge peripheral annular as in patent EP 0381351 which describes a double radius cup. However, the sudden variation in geometry, created by the double

  radius, makes impaction difficult with risk of bone micro-fractures.

  Cups with a progressive peripheral annular bulge limit this risk; they exert, however, non-selective tightening over the entire perimeter of the acetabulum; the acetabulum is not anatomically homogeneous, the cup to be fixed therein should not be either. The present invention proposes to remedy these drawbacks and, to do this, relates to a cup which achieves a selective and progressive tightening with respect to the naturally most deformable zones of the acetabulum by a sectoral increase in its

external profile.

  According to the invention, the cup placed in force in the acetabular cavity previously fitted using a hemispherical bur has: an internal wall making it possible to articulate a patella type with the

  spherical head of an implant fixed in the femur.

  an external wall comprising a discontinuous excess thickness limited substantially to two thirds of the periphery of the cup, said excess thickness varying progressively as a function of the anatomical sector opposite which the cup is positioned according to four zones described with reference to the drawings

  attached which illustrate embodiments by way of nonlimiting examples.

  Figure I is a perspective view showing the variation of the extra thickness of the external wall as a function of the anatomical sector of the acetabulum opposite which the cup is ideally positioned; the maximum allowance being located towards the bottom of the cup

  at the horseshoe opening, as shown in Figure 2.

  Figure 3 is a top view showing the location of the extra thickness zones

(Zh, Z2, Z2 ', Z3).

  Figure 4 is a representation in the plane, passing through the base of the cup, of the angular positions of the zones (Z1, Z2, Z2, Z3) and remarkable sections (AA ', BB', CC ', DD') according to which are described the variations in geometry of the external wall. Figures 5 to 8 show the schematic sections (AA ', BB', CC ', DD') of the

  wall in planes perpendicular to the base of the cup.

  According to one embodiment of the invention, the cup (1) which is fixed by press-

  fit in the acetabular cavity of the iliac bone is made of a biocompatible metal preferably titanium or chromium-cobalt and has an internal wall (2) which allows articulation with an implant fixed in the femur and an external wall (3) the extra thickness (4) which gradually varies according to the anatomical sector in

  gaze of which the cup is positioned according to the zones (Z1, Z2, Z2, Z.).

  As shown in Figure 3 - in the zone (Zl), the external wall (3) of the cup (1) is inscribed in a hemisphere of radius (RI); the surface of said zone (Z1) constitutes the reference level with respect to which the excess thicknesses of the zones (Z2, Z2. and Z3) are defined; - the zones (Z2 and Z2,) constitute transition zones in which the additional thickness of the external wall (FIG. 6) increases in a progressive progressive manner from 0 at the level of the limits (ZI-Z2) and (Z1-Z2 ) up to a minimum minimum value (xm) at the zone limit (Z2-Z3 and Z2.-Z3); - the zone (Z3) has a constant maximum thickness (4) (xm), such

as illustrated in Figures 7 and 8.

  The angular amplitude of the zones (Zi, Z2, Z2, and Z3) is specified, by way of nonlimiting example, in FIG. 4, by the definition of the angles (and, IB, 13 ′, y) and is understood respectively between 0 and 40 (o), 0 and 160 ({3 and {3 '), 0 and 90 (y) and o said angles

  are linked by the relation cOe + 13 + [3 '+ y = 360.

  The profile of the external wall (3) in the section of FIG. 5 has a constant radius

  (RI) in the angular sector (oc), as shown in Figure 4.

  In the angular sectors (13, {3 'and y), the profile of the external wall (3) shown successively in Figures 6 and 7 is defined by the succession of two tangent radii between them characterized in that, in the angular sectors (13 and 3 '), the radii (R1) and (R2) are linked by the relation R2 = RI + xo (x) is the value of the extra thickness (4) which varies minimally between 0 and the maximum value ( xm) between 1 and mm in the angular sector (y), the two radii (Rl) and (R3) are linked by the

  relation R3 = RI + xm o (xm) is constant.

  Thus, the extra thickness (4) of the external wall (3) only exists in the zones (Z2,

  Z2 'and Z3) located in the peripheral annular region of the cup (Fig. 3, 6, 7 and 8).

  Over a height at least equal to (X), the external wall (3) of the cup (1) is

  constituted by a portion of sphere (5) of radius (RI).

  In Figure 8, a section in the plane of symmetry of the cup allows to appreciate the

  difference in geometry of the sections in the angular sectors (oe) and (Y ').

  Figure 6 shows the geometry of the sections in the previous perpendicular plane

on the cited plan.

  It goes without saying that the invention is susceptible of various variant embodiments, in particular as regards the variety of complementary fixing means and

  means of articulation with the spherical head of the implant fixed in the femur.

Claims (2)

CLAIMS I - Cotyloid implant of total hip prosthesis in the form of a cup (1) receiving on its internal wall (2) the spherical head of an implant fixed in the femur, characterized in that the external wall (3) of the cup ( 1) has a discontinuous excess thickness (4) limited substantially to 2/3 of the periphery of said cup; the additional thickness (4) varying progressively as a function of the anatomical sector opposite which the cup (1) is positioned according to the zones (Zi, Z2, Z2, Z3) and o - in (Z1), the external wall (3) of the cup (1) is part of a hemisphere of radius (RI) - in (Z2 and Z2 '), the excess thickness (4) of the external wall (3) increases continuously progressively from 0 to a maximum minimetric value (xm ) - in (Z3), said extra thickness (4) of the wall is constant and equal to (xm) 2 - Cotyloid implant according to claim 1, characterized in that the angular sectors (ca, ó, 13 ', y), which define the zones (Z1, Z2, Z2, Z3) at the periphery of the cup, are linked by the relation a + 13 + 13 '+ y = 360, the respective angular amplitude being between 0 and 40 O (cc) , 0 and 160 (13 and 13 '), 0 and 90 (y).   3 - acetabular implant according to claim 1, characterized in that the maximum value (xm) of the extra thickness (4) limited in annular zones (Z2. Z2 and Z.) is between 1 and 5 mm.   4 - acetabular implant according to claim 1, characterized in that, over a height at least equal to (X), the outer wall (3) of the cup (1) is constituted by a   portion of sphere (5) of radius (R1).