What is femoroacetabular impingement?

Femoroacetabular impingement (FAI) has gained much attention over the past decade. It has been associated with hip and groin pain, decreased hip function and can ultimately lead to osteoarthritis.1 A recent consensus meeting defined FAI as “a clinical entity in which a pathological mechanical process causes hip pain when morphological abnormalities of the acetabulum and/or femur, combined with vigorous hip motion (especially at the extremes), lead to repetitive collisions that damage the soft-tissue structures within the joint itself.”2 However, there is a lack of clarity regarding the definition of morphological abnormalities. The presence of a cam or pincer deformity is a prerequisite for defining cam-type and pincer-type of FAI. Although an obvious cam deformity is not difficult to recognise, there may be subtle differences between normal and abnormal bony morphology. This is illustrated by a study showing poor correlation between the subjective assessment of the head–neck junction and objective measures.3 Poor reliability of radiologists and orthopaedic surgeons in quantifying morphological abnormalities has also been demonstrated.4 Objective methods to quantify a cam deformity are, therefore, preferable. Several …