[Diagnosis of avascular necrosis of the femoral head].

Mechanical factors have now been excluded as the main cause of non-union in fractures of the femoral neck : the development of efficient methods of internal fixation has removed this source of non-union and the chief remaining cause is disturbance of the circulation of blood to the capital fragment. The incidence of avascular necrosis of the femoral head appears to depend upon normal variations in the vascular pattern and also upon the severity of the vascular injury (Kolodny 1925, Wolcott 1943, Tucker 1949). It is possible that delayed vascular occlusion may play a part ; but the vascular damage is usually sustained at the time of the original injury, although it may perhaps be increased by inadequacy of immobilisation, violence of manipulation and by the effects of some forms of internal fixation. It is a striking fact that there may be a mass of avascular bone in the body without any means of distinguishing it clinically or radiographically from living bone. This is true particularly during the first few months after fracture of the femoral neck with vascular occlusion ; there is no reliable clinical evidence as to the viability of the femoral head. Eyre-Brook and Pridie (1941), in reporting a series of such fractures, noted that avascular necrosis of the capital fragment did not develop when the fracture-shaft angle was greater than 37 degrees ; but apart from this observation there is little evidence on which the diagnosis can be based and each fracture is an enigma. The surgeon must wait for several months, or even for several years, before the fate of the head can be predicted with certainty.