The invention shows a patella prosthesis, which consists of an artificial slide member (2) made from polyethylene with sliding surface (3), with the slide member (2) being mounted on the rear of the patella (1) by means of an attachment. The sliding surface (3) consists of the sector of a polyethylene sphere, which comprises a metal grid (4) of an attachment member (9). The attachment member consists of a metal sandwich construction having a central support sheet and metal grids (4, 6) spot welded on both sides, with bevelled sheet metal flanges (7) for the primary attachment of the support sheet (5) protruding through recesses (8) in the metal grid (6) on the side of the patella.

The invention relates to a patella prosthesis which consists of an 
artificial slide member having a sliding surface which is mounted from the 
rear of the patella by means of an attachment. 
U.S. Patent specification No. 4,479,271 shows a patella prosthesis in which 
the primary attachment is performed by pegs, which consist of a metal core 
which is surrounded by a porous fibrous shell, which in turn is placed 
with dimensional accuracy on the outside and on the inside of a 
non-metallic peg made of polyethylene. The recesses for the pegs have to 
be incorporated in the patella and should lie with their axes at right 
angles to the plane for the actual mounting surface so as to enable its 
abutment and subsequent fusion. The spacing and position of the location 
holes in the patella also have to be very precise. 
The invention finds a solution to this problem. The object of the invention 
is to attach a patella prosthesis in the patella with only very simple 
preparatory work being required. This object is achieved according to the 
invention in that the sliding surface consists of the sector of a 
polyethylene sphere, which comprises a metal grid of an attachment member, 
and in that the attachment member consists of a metal sandwich 
construction having a central support sheet and metal grids spot welded on 
both sides, with bevelled sheet metal flanges for the primary attachment 
of the support sheet protruding through recesses in the metal grid on the 
side of the patella. 
The advantages of the invention are regarded as being that only one plane 
supporting surface has to be created on the patella as a preparation, that 
the prosthesis has high inherent strength and dimensional stability and 
that the delimitation surface for the fusing osseous tissue is made of 
metal. The design of the prosthesis also produces advantages from the 
point of view of manufacturing engineering by an attachment part being 
created using purely sheet metal working methods and the slide member 
being attached thereto in a simple joining operation. 
For the primary attachment of the prosthesis it is sufficient to 
manufacture a flat surface element on the rear of the patella. This may be 
done by a flat rasp, for example, with the exact relative position of the 
flat surface element having secondary importance, as the sliding surface 
of the prosthesis is formed from the sector of a sphere. The prosthesis is 
placed in the correct place by the surgeon and pressed into the patella 
for the primary attachment. Knife-like sheet metal flanges form a 
self-locking primary attachment in the osseous tissue without damaging it. 
The loss of osseous tissue is slight. 
The invention is described below by means of an exemplified embodiment. 
FIG. 1 shows the longitudinal section through a patella having a prosthesis 
as specified by the invention, and 
FIG. 2 shows the view of the lower side of the prosthesis close to the 
patella shown in FIG. 1.

In the figures is shown a patella prosthesis which consists of an 
artificial slide member 2 made of polyethylene with sliding surface 3, 
with the slide member 2 being mounted on the rear of the patella 1 by 
means of an attachment. The sliding surface 3 consists of the sector of a 
polyethylene sphere, which comprises a metal grid 4 of an attachment 
member 9. The attachment member consists of a metal sandwich construction 
having a central support sheet and metal grids 4, 6 spot welded on both 
sides, with bevelled sheet metal flanges 7 for the primary attachment of 
the support sheet protruding through recesses 8 in the metal grid 6 on the 
side near the patella. 
FIG. 1 shows the sandwich construction of the attachment member 9, which 
consists of a central titanium sheet 5 having a wall thickness of 0.5 mm 
and grids 4, 6 made of titanium spot welded on both sides. The attachment 
member 9 is cut to size as a disc with a diameter of 27 mm. The slide 
member 2 consists of a disc having the same diameter and ends with a 
spherical sliding surface 3 having a radius of 30 mm and a central point 
in the axis 12 of the discs. The metal grid 4 on the side of the slide 
member 2 penetrates it and is surrounded by polyethylene right up to the 
support sheet 5. 
In FIG. 2 the metal grid 6 on the side of the patella has four rectangular 
recesses 8 in the orientation of the grid, through which a bevelled sheet 
metal flange 4 mm wide by 6 mm protrudes from the support sheet 5. The 
sheet metal flanges 7 have been cut free from the support sheet 5 with a 
blanking die (not shown) along the protruding contour and have been bent 
by an angle 11 of 90.degree. from the plane of the support sheet 5. 
The attachment is made on the inside of the patella on a per se plane 
attachment surface 10, which was produced with a flat rasp (not shown) at 
right angles to the chord. The prosthesis is placed in a position on the 
patella 1 which is corrected by the length of the protruding sheet metal 
flange and pressed into its final position. The knife-like sheet metal 
flanges 7 become embedded in the osseous tissue and by self-locking in the 
displaced osseous tissue form a primary attachment for the whole 
prosthesis. The osseous tissue can fuse without obstruction right to the 
support sheet 5 through the metal grid 6 on the side of the patella. The 
support plate 5 is so rigid per se that forces on the contact points of 
the sliding surface 3 are evenly transmitted to the osseous tissue fused 
in the metal grid 6.