Anterior femoro-acetabular impingement. Radiological signs in young patients diagnosed with hip osteoarthritis

Purpose. To determine the incidence of the characteristic radiological signs of anterior femoro-acetabular impingement (AFAI) in young patients diagnosed with idiopathic hip osteoarthritis. Materials and methods. Retrospective review of the clinical records of patients under 50 years of age diagnosed with idiopathic hip osteoarthritis between 1995 and 2000. The functional assessment of the hip was made by means of the Merle D’Aubigne scale. The radiological study that revealed the presence of the figure-of-8 sign and the head/neck bump sign. The hip joint was evaluated by means of Tönnis’ scale. Results. Fifty-one (43%) of the 121 patients under 50 were diagnosed with idiopathic hip osteoarthritis. We reviewed 45 hips. The mean age in this group was 44.5 years (range: 30-50). The mean value obtained on the Merle d’Aubinge scale was 16 (range: 12-17). In 10 hips (22 %) the figure-of8 sign was observed, in 26 (58%) the head/neck bump sign was observed. Both signs were observed in 6 cases (13%). Thirty hips (66%) presented with at least one of these radiological signs. In 18 hips (60%) lytic images were seen in the proximal femur. Seventy percent of patients that had at least one of the characteristic signs of FAI were grade I on the Tonnis classification; the remaining 30% were grade II. Conclusions. In our series, 66 % of patients diagnosed with idiopathic hip osteoarthritis presented, at the time when the diagnosis was made, radiological signs characteristic of AFAI. Also, AFAI could be construed as the cause for the primary hip osteoarthritis in some of the patients.