Anterior femoroacetabular impingement: an update

Abstract

Anterior femoroacetabular impingement can cause early hip osteoarthritis. The typical patient is an adult younger than 50 years of age, often with a history of sporting activities. The main symptom is intermittent pain triggered by static flexion (low seats) or dynamic flexion (during sporting or occupational activities that require repeated hip flexion). The characteristic physical finding is pain triggered by placing the hip in internal rotation and 70 to 110° of flexion. In additional to anteroposterior and false-profile radiographs, lateral Dunn or Ducroquet views should be obtained on both sides to visualize the anterior part of the head-neck junction. Instead of being concave, the head-neck junction is either flat or convex, causing a cam effect that damages the labrum and anterosuperior cartilage. Non-sphericity of the femoral head with an anterior ovoid bulge induces a similar cam effect. In pincer impingement, which is less common, over-coverage by the anterosuperior acetabular rim pinches the labrum between the rim and the femoral head-neck junction when the hip is flexed. Pincer impingement is related to acetabular retroversion or protrusion. Arthrography coupled with computed tomography or magnetic resonance imaging visualizes the morphological abnormalities (e.g., ovoid shape of the femoral head or retroversion of the acetabulum) and detects secondary lesions such as labral tears or separation or damage to the anterosuperior cartilage. Arthroscopy allows removal of the damaged labrum and correction of the morphological abnormalities via femoroplasty to restore the normal concave shape of the neck and/or acetabuloplasty to eliminate over-coverage. Short- or mid-term results are satisfactory in 75 to 80% of patients. However, the presence of degenerative lesions in about two-thirds of patients at the time of arthroplastic surgery limits the probability of achieving good long-term results.