Loosening of the femoral component of the ICLH double cup hip prosthesis. A biomechanical investigation with reference to clinical results.

The cancellous bone in the proximity of the rim of the ICLH femoral cup may not only be subjected to an axial stress that is about three times the value physiologically encountered, but the cup also tends to move transversally away from the medial bone margin in this area. Hence, fracture of the trabecular structure in this area can occur, accompanied by cleavage formation. Across the gap which thus forms between cement and bone, the mating surfaces that are now no longer joined, probably move relative to each other with every subsequent walking cycle. This relative motion leads to bone resorption and the development of a thick intermediate layer of fibrous connective tissue that spreads until eventually the whole cup becomes loosened. In the meantime the bone further proximal probably undergoes atrophy due to mechanical inactivity. This presentation includes a biomechanical analysis which might explain the discouraging observations made in a series of forty-three implantations carried out between 1976 and 1979 in our clinic.