Abstract: An endoprosthetic device for replacing the patellar articular surface is provided in multi-part constructional form and comprises: a first part adapted for securement in the posterior region of the patella, and a second part separately connected with said first part and having an exposed surface shaped to simulate the patellar articular surface. This device can be used for replacement of the patellar articular surface in isolation, and can be subsequently modified, when appropriate, by replacement of the second part for accommodation with a fuller replacement of articular surfaces in the knee joint. Conveniently, the afore-mentioned parts have aligned bores and are interconnected by a replaceable snap-fit third part.