An Alternative Radiographic Measure for Cam-Type Fai in Patients with Idiopathic Hip Pain

Abstract

Femoroacetabular impingement (FAI) has been accepted as a potential cause of idiopathic hip pain and osteoarthritis. Few cases of FAI have been reported in the Chinese population. We reviewed radiographic features of patients with idiopathic hip pain to characterize FAI in the Chinese population, any alternative radiographic measures, and potential symptom association. All anteroposterior pelvic radiographs of outpatients (n = 1,128) between December 2007 and August 2008 were reviewed. The radiographic measurements, including anteroposterior alpha angle (AP-α), radial height/radius ratio (R1), and 1/2 radial height/radius ratio (R2) as well as crossover signs, were recorded on both hip joints of all patients. The differences in AP-α, R1, and R2 were compared between cam-type hips (including mixed FAI) and non-cam-type hips (including non-FAI). From the group of patients, 269 were eligible for further evaluation, including those exhibiting FAI at the site of complaint (n = 38) or without symptoms (n = 7). FAI was significantly associated with hip pain (p = 0.009). For painful hips, the frequency of FAI was higher in males than in females (p = 0.038). AP-a was significantly higher in cam-type hips than in non-cam-type hips for either gender (p < 0.001, p < 0.001). R1 was comparable between the 2 subgroups for either gender (p > 0.05, p > 0.05), whereas R2 differed significantly (p < 0.001, p < 0.001). The occurrence of FAI was underestimated in Chinese patients showing negative radiographic findings with idiopathic hip pain. In addition, R2 was used to differentiate cam-type FAI from non-cam-type FAI.