FEMOROACETABULAR IMPINGEMENT CAUSING HIP OSTEOARTHRITIS: A NEW RADIOGRAPHIC SIGN FOR SCREENING INDIVIDUALS AT RISK

Abstract

Background: Femoroacetabular Impingement is now considered a prearthritic hip mechanism. It frequently occurs in patients with subtle anatomic abnormalities of the acetabulum, “acetabular retroversion”, which is often difficult to detect on standart xrays. Early diagnosis is of utmost importance as surgical intervention in early stages can most likely halt progression of disease. The objective of this study was to assess wether an easily visible anatomic landmark on an anteroposterior (AP) pelvic xray can be used to screen patients with acetabular retroversion.

Methods: The AP pelvic xrays of 1010 patients who were seen at the autors’ institution for a painful hip were reviewed over a 16 year period. Those xrays that did not meet standardized criteria were excluded leaving 149 AP radiographs (298 hips) for analysis. The ‘crossover sign’ (COS), indicative of acetabular retroversion, was recorded for each hip. An easily visible landmark, the prominence of ischial spine (PRIS) into the true pelvis was also recorded and measured. Interobserver and intraobserver variability was assessed.

Results: The presence of the PRIS as diagnostic of acetabular retroversion showed a sensitivity of 91% (95%CI 0.85 to 0.95), a specifity of 98% (95% CI 0.94 to 1.00), a positive predictive value of 98% (95%CI 0.94 to 1.00), a negativ predictive value of 92% (95% CI 0.87 to 0.96). There was good and very good intraobserver and interobserver reliability for measurements of the COS and PRIS, respectively.

Conclusion: There was excellent sensitivity and positive predictive value of the PRIS as a radiographic marker of acetabular retroversion. The rims of the anterior and posterior walls are sometimes not clearly visible, and even if they are, their translation into a reliable interpretation of acetabular retroversion is difficult. The PRIS sign appears as a good visible prominence on the AP radiographs which can’t be easily confused.