Radiographic Evaluation of Pincer-type FAI

Abstract

Objectives:Radiographic analysis is utilized by surgeons to evaluate for the presence of both cam- and pincer-type femoroacetabular impingement (FAI). Coxa profunda, in which the acetabular fossa crosses or touches the ilioischial line medially, as well as the acetabular crossover sign, in which the anterior acetabular wall is more lateral than the posterior wall, are two of the methods historically employed in making a diagnosis of pincer-type FAI. It has also been proposed that lateral center edge (LCE) angles > 40 degrees are indicative of acetabular overcoverage.Methods:Between March 2005 and September 2006, 677 consecutive patients presented to the clinic for surgical treatment of hip pain due to FAI and associated chondrolabral dysfunction. All patients underwent radiographic imaging consisting of an AP pelvis as part of a standard clinical evaluation. From these radiographs, the presence of coxa profunda, the crossover sign, and the lateral center edge angle were prospectively recorded for each patient. Patients were included in the study if they had a properly performed AP radiograph of the pelvis. Exclusion criteria included a history of avascular necrosis, previous hip fracture, systemic inflammatory disease affecting the hip, or any prior hip surgery. The incidence of coxa profunda and the acetabular crossover sign was determined. We hypothesized that coxa profunda and the crossover sign are not associated with increased lateral center edge angles.Results:There were 207 patients that met the inclusion criteria and were included in the study. The average age of the patients was 42 (range, 18 to 77). The prevalence of coxa profunda and the acetabular crossover sign was 127/207 (61.3%) and 79/207 (38.1%), respectively. The average LCE angle was 34 degrees (range, 20 to 52). There was no significant difference between LCE angles and gender (p = 0.809) and the presence of an acetabular crossover sign and gender were not associated (p = 0.468). Coxa profunda was more commonly associated with female gender (p = 0.0001). Coxa profunda was not associated with the presence of a crossover sign (p = 0.890), nor was it associated with a LCE angle greater than 40 degrees (p = 0.732). Twenty-eight hips had LCE over 40(13%). There was no significant difference in the LCE angle in patients with a positive crossover sign(34.3 vs 34.0;p = 0.657) or coxa profunda (34.6 vs 33.3;p = 0.119).Conclusion:Coxa profunda and the presence of a crossover sign are not associated with significant lateral acetabular overcoverage (LCE angles > 40 degrees). The presence of an elevated LCE angle does not always indicate acetabular overcoverage.