A patient with HIV is on therapy with protease inhibitors. He presents with limitation of abduction and internal rotation of the hip. The most probable diagnosis is:

Limitation of abduction and internal rotation of hip is often seen in avascular necrosis of femoral head or Legg-Calve-Pehes disease. Hyperiglyceridemia is a well known risk factor of avascular necrosis of femoral head (AVN). It has been suggested that treatment with protease inhibitors increase triglyceride levels, thereby increasing risk of avascular necrosis of femoral head. Ref: Current Diagnosis and Treatment of Pain (CDTP), 2006, Page 305; Antiretrol Therapy By Clercq, 2001, Page 167; Apley's System of Ohopaedics and Fractures By Louis Solomon, 9th Edition, Chapter 19, The Hip, Pages 511-15