[FAI - concept and etiology]

Femoroacetabular impingement (FAI), a recently proposed mechanical concept regarding the development of osteoarthritis (OA) of the hip, is gaining increased acceptance. Both osseous deformity and use of the hip may result in hip damage. Osseous deformities are seen on the acetabular (pincer) or the femoral (cam) side of the hip, leading to characteristic alterations of the acetabular rim. Cam FAI is found in 20-30-year-old athletic men, revealing deep cartilage avulsions from the acetabular rim while the labrum is frequently intact. In pincer FAI, found in 30-40-year-old women, the labrum is frequently significantly destroyed with only minor damage to the acetabular rim. Professional or athletic impact activities can trigger even mild FAI deformities to become symptomatic. For some FAI deformities, the etiologies are known, but for most of them the exact causes are unknown. An improved understanding of the etiology of FAI and its role in the development of hip OA might lead to a reduction in the prevalence of so-called primary OA of the hip.