Traumatic Osteonecrosis of the Femoral Head Following Intracapsular Fracture: Incidence and Earliest Radiological Features

A sub-capital fracture of the femoral neck is common particularly in the elderly female with non-union occurring in 25% and osteonecrosis in up to 24% of united fractures. Assessment of the viability of the femoral head in the early stages is unreliable and initial diagnosis of osteonecrosis depends on recognition of radiological features. Many reports imply that structural failure of the joint surface is the initial abnormality. 121 patients with a sub-capital fracture have been followed up for at least a year and as long as three and a half years. The incidence of osteonecrosis was 8% in Grade I fractures; 4% in Grade II and 21% and 30% in the more severe Grade III and Grade IV fractures. Of the 24 patients with osteonecrosis, increased radiological density developed in 13 at a time interval of 3 months to 36 months after the fracture with a mean time of 10 months and seven subsequently developed structural failure. Eleven patients developed structural failure as an initial feature at a time interval of 5 months to 24 months with a mean of 13 months. From this it is clear that either an absolute increase in radiographic density or structural failure are the earliest radiological features. Good quality radiographs, clearly demonstrating trabecular detail, are essential for the recognition of osteonecrosis.