Cam deformities of the femoral head contribute to femoroacetabular impingement (FAI) and correlates strongly with development of osteoarthritis. Surgery on patients with FAI is performed with increasing frequency; it is unknown whether this prevents osteoarthritis in later life. As cam deformity is triggered during late puberty by impact loading of the hip, it is important to elucidate the aetiology of cam deformity.