Pathogenesis of ischemic necrosis of the femoral head.

The findings of elevated BMP in the preradiologic stages of INFH and the histologic findings of extensive bone marrow ischemia and necrosis preceding trabecular death support the pathogenetic concept that INFH represents a compartment syndrome similar to the anterior tibial compartment syndrome following tibial fracture and increased intracranial pressure following closed head injury. The documentation by multiple authors that decompression instituted in the preradiologic stage leads to a high percentage of success both in relief of symptoms and lack of radiographic progression further supports this hypothesis. The compartment syndrome can be viewed as the final common path down which multiple etiologic entities proceed to a clinical syndrome that has a remarkably uniform clinical and radiographic expression. Acceptance of this pathogenetic concept leads to an aggressive approach to early diagnosis and treatment. Even in these circumstances, the majority of patients with INFH will seek help for the first side only after collapse has begun, at which time a decompression offers only a temporary relief of symptoms but does not appear to significantly alter the course of the disease over the long term. However, since the majority of patients with nontraumatic INFH will develop the disease on the second side and since only a small percentage have bilaterally collapsed femoral heads, an opportunity frequently exists to salvage the second side.