1 . The arterial pattern and the histological features in the femoral head and neck were studied at necropsy in twenty-five specimens with intracapsular fractures. An improved visual-arteriographic method employing barium sulphate dyed with Prussian blue was used. Twenty-three of the fractures were from a few days to twenty-four weeks old and two were seven and ten years old. Nineteen had been nailed or nail-plated.2. The results were divided into four groups according to the state of the femoral head. In the first group, four heads were histologically viable and had a normal vascular pattern; in the second group, four showed partial avascular necrosis with part of the head retaining a normal blood supply; in the third group, ten had avascular necrosis in all or most of the head and showed little or no revasculanisation; and in the fourth group, seven showed extensive revascularisation of grossly necrotic heads. Total or subtotal capital necrosis had occurred in 64 per cent and total or partial necrosis in 84 per cent of the specimens. The results indicated that interruption of the retinacular vessels was the cause of gross necrosis; and that in most cases an intact blood supply through the ligamentum teres cannot keep more than a part of the head alive when the other vessels are cut off. Occasionally the ligamentum teres is torn by the nail, or though intact, its blood supply is interrupted. This accounts for completion of avascular necrosis in most cases with total capital necrosis. Viability of the subfoveal area from an intact supply through the ligamentum teres was the main source of revascularisation after capital necrosis. Other sources—from across a uniting fracture line, from growth of soft tissue round the head and neck and from other small viable foci in the head and neck—were much less important and the degree of revascularisation was generally limited. Revascularisation was accompanied by fibrocellular invasion of the marrow, differentiation of cells and the formation of oil cysts whereby the necrotic fat is removed; but bony reconstitution was limited.3. Six fractures were uniting and another had united by bone making an overall union frequency of 50 per cent considering only the nailed fractures older than two weeks. Four of them (57 per cent) showed total or subtotal capital necrosis. In fractures older than two weeks the frequency of union among the eleven nailed fractures with avascular necrosis was 36 per cent, and it was 100 per cent among the three nailed ones with viable or substantially viable heads. Necrosis of the neck side of the fracture was unrelated to non-union because it soon becomes invaded by fibrovascular tissue and new bone.4. Fibrosis was the basis of union when the head was dead but examination of older fractures at necropsy is needed to assess the long-term results of revascularisation and union. The clinical desirability or otherwise of capital revascularisation after necrosis also needs to be studied.
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