Increased femoral anteversion and alpha angle are associated with lower delayed gadolinium enhanced MRI of cartilage score in femoroacetabular impingement

Abstract

Purpose: Femoroacetabular impingement (FAI) syndrome is a disorder of the hip associated with heightened risk for future hip osteoarthritis (OA). Radiologically, FAI has been quantified using the alpha angle (αA), a measure of femoral head-neck junction asphericity, however this parameter has low specificity for the prediction of symptoms and subsequent OA change. It has been postulated that additional anatomical parameters interact with the αA to determine a hip's propensity to impinge. Decreased femoral anteversion, acetabular anteversion, and femoral neck-shaft angle (FNSA) have each been proposed to increase the likelihood and severity of impingement, by reducing the amount of flexion, adduction and internal rotation possible before the hip impinges anteriorly. This study sought to determine whether any of these morphological parameters are associated with delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) score. dGEMRIC uses T1 relaxation time to quantify glycosaminoglycan concentration and hence detect early OA change in cartilage. We hypothesized that decreased femoral anteversion, acetabular anteversion, and FNSA would be associated with poorer cartilage health (lower dGEMRIC score).

Methods: Thirty-five participants were diagnosed with FAI syndrome (25 cam, 2 pincer, 8 mixed) by an orthopaedic surgeon, and received radiographs and hip MRI with dGEMRIC on one of two 3T scanners (Siemens Prisma & Skyra). The αA was measured in four reconstructed radial planes, at 30-degree intervals from the superior to anterior locations; LCEA and FNSA were measured on AP pelvis X-rays; femoral version was measured using axial hip and knee MRI sequences (Fig. 1); and acetabular version was measured at 1cm inferior to the acetabular sourcil using axial hip MRI sequences. The dGEMRIC scanning protocol used inversion recovery sequences acquired in the sagittal plane. dGEMRIC scores were calculated for a 1cm region of interest encompassing acetabular and femoral head cartilage adjacent to the chondrolabral junction at the antero-superior acetabular rim (Fig. 2). Patient factors were recorded, including age, gender, body mass index, and modified UCLA activity level score. Statistical analyses included Pearson’s linear regressions, student’s T-tests and one-way analysis of variance (ANOVA). Results: The 35 participants (31.8 ± 10.7 years, 40% female) had a mean dGEMRIC score of 601 ± 113ms. Parameters associated with dGEMRIC score included femoral version (r = −0.419, P = 0.015) and the αA in the superior radial plane (r = −0.380, P = 0.026). Multiple linear regression analysis showed femoral version and αA in the superior plane to be predictors of dGEMRIC score (Table 1). No other variables were associated with dGEMRIC score. ANOVA detected a significant difference (P = 0.015) between participants with ‘decreased femoral anteversion’ (<5 degrees, n = 7), ‘normal femoral anteversion’ (5–25 degrees, n = 23) and ‘prominent femoral anteversion’ (>25 degrees, n = 5). Pairwise comparison between groups revealed the mean dGEMRIC score for participants with decreased anteversion (708 ± 54) to be higher than for those with normal anteversion (571 ± 114) (P = 0.005) and prominent anteversion (574 ± 100) (P = 0.013). There was no significant difference between those with normal anteversion and prominent anteversion (P = 0.960). There were no other significant differences between groups.