Abstract
1. A study of late segmental collapse in twelve femoral heads shows that it may not develop until two and a half years after the fracture.
2. Until the articular surfaces had collapsed the patients usually had no symptoms. The fractures were united and there was no obvious radiographic evidence of ischaemic necrosis.
3. There was histological evidence that the whole of the femoral heads had been necrotic at one time. The term late segmental collapse is more appropriate than late segmental necrosis.
4. The blood vessels of the ligamentum teres played little or no part in revascularisation which, when it occurred, was almost entirely across the fracture line.
5. In only one femoral head was revascularisation approaching completion and apparently continuing. In the other eleven much of the head remained necrotic and the process appeared to have halted.
6. An increase in radiological density was caused by new bone laid down on unresorbed necrotic trabeculae and was most prominent behind the line of revascularisation when the process had halted.
7. Trabecular collapse was evident within dead bone. In ten of the femoral heads it occurred in the subchondral region and in four just beyond the junction of reossified and dead bone.
8. Osteoarthritic changes occurred in the cartilage covering revascularised bone at the periphery of the head, especially when collapse was severe.
