Abstract: A passively extensible long bone component in an endoprosthetic bone joint device for a child includes two parts, of which one (10,20) has a bearing portion (22) to serve the articulatory function at one end of the bone, a seat portion (11) to engage the bone one end proximally of the growth plate therein and a stem (21) to pass longitudinally into the bone, and of which the other part (30) is a generally tubular socket adapted to receive the stem in sliding engagement and for securement with the bone distally of the growth plate. The bearing part can be cushioned against shock, at least partially separable, and extend as a further socket between the first socket and the stem. The component can allow rotation of the bearing and stem about the bone long axis or inhibit such rotation.

Abstract: An endoprosthetic knee joint device has femoral and tibial components respectively adapted for connection to the femur and tibia, and respective bearing surfaces for mutual articulatory engagement to simulate natural joint movements. It is now proposed that the femoral component has two transversely spaced sockets as bearing surfaces, and that the tibial component has two upstanding ball parts for respective articulation in the sockets. The ball parts can be separable, by the provision of stems engageable in apertures in the base part. Preferably, the sockets are enlarged relative to the balls to allow mutual rotation about the axis of the leg. Also, the sockets and balls can be of different material from their respective base parts, the latter suitably being of metal.