Prevalence of femoroacetabular impingement in asymptomatic contralateral hips in patients with unilateral idiopathic osteoarthritis

Radiographic findings of femoroace tabular impingement in the contralateral asymptomatic hip of patients who had undergone total hip arthroplasty because of primary osteoarthritis (n = 44) were compared with controls (n = 40). The centre-edge angle and caput-collum-diaphyseal angle were measured and the presence of crossover sign and a prominent ischial spine noted on anteroposterior radiographs of the pelvis. The α-angle and offset ratio were measured on cross-table lateral radiographs of the hip. The centre-edge angle and offset ratio were significantly lower and the α-angle significantly higher in the study group compared with controls. While the number of cases with an abnormal centre-edge angle was similar in both groups, the numbers with an α-angle > 50° and the number with an offset ratio ≤ 15 were significantly higher in the study group. It was concluded that morphological anomalies associated with femoroacetabular impingement are seen more frequently in the asymptomatic contralateral hip of patients who have undergone hip replacement for primary osteoarthritis than in controls.