Avascular necrosis of the hip

Abstract

### What you need to know A 36 year old woman presents to her GP with a history of left groin pain radiating to the knee. The pain is severe, worse on walking, and associated with a limp. The patient revisits the GP a year later with persistent pain despite analgesia. Plain radiographs of the hip and knee show slight narrowing of the hip joint space with no other features and she is referred to a secondary care orthopaedic clinic. A magnetic resonance imaging (MRI) scan of the hip shows classic features of avascular necrosis of the femoral head (AVNFH) with collapse. Osteonecrosis of the femoral head (AVNFH) causes loss of integrity of subchondral bone structure due to abnormal microcirculation. The underlying pathogenesis is unclear1; risk factors are likely to affect microcirculation in some way but this has not been confirmed by research. The common end point is abnormal microcirculation and necrosis. Subchondral bone subsequently collapses, which leads to progressive secondary arthritis. Mean age of presentation in the UK is 58.3 years, with a prevalence of two per 100 000 patients.2 On average, AVNFH occurs earlier in life than typical osteoarthritis. It is more common in men and the highest prevalence is in men aged 25 to 44 and women aged 55 to 75.3 In the UK it is the third most common indication for total hip replacement in people under 50.4 The following factors are associated with an increased risk of …