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Background We observed cases of extensive osteolysis of the femoral head following acetabular fractures even though the original fracture did not involve the femoral head or neck. This observation has been called massive osteolysis of the femoral head (MOFH). Purpose To evaluate the clinical and imaging features of MOFH to gain a better understanding of its patho-etiology. Material and Methods We retrospectively collected cases of acetabular fractures seen over a period of 10 years and evaluated the clinical features and imaging characteristics. The findings were compared with the features of other complications such as osteonecrosis, rapidly progressive osteoarthritis, or post-traumatic osteolysis. Results Fifteen patients (M:F ratio 9:6; mean age, 61.6 years) out of 244 had MOFH (prevalence: 6.1%). Motor vehicle collision and falls were the most common mechanisms of injury. The time interval for developing MOFH was in the range of 1-18 months after the initial injury. Patterns of femoral head osteolysis varied from eccentric (12 cases) to transcervical (3 cases). Four cases of eccentric osteolysis developed high-degree of osteolysis. MOFH was observed near the surgical hardware in 6/15 cases. One biopsy specimen did not reveal typical features of osteoarthritis or avascular necrosis. Conclusion MOFH appears to be a distinct entity from avascular necrosis or rapidly progressive osteoarthritis. It is suggested that MOFH is a variant of post-traumatic osteolysis that is evident in a subset of patients.

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