Validation of neck axis distance as a radiographic measure for acetabular anteversion

Abstract

Excessive acetabular anteversion is an important treatment consideration in hip preservation surgery. There is currently no reliable quantitative method for determining acetabular anteversion utilizing radiographs alone. The three main purposes of this study were to: (i) define and validate the neck axis distance (NAD) as a new visual and reproducible semi-quantitative radiographic parameter used to measure acetabular anteversion; (ii) determine the degree of correlation between NAD and computed tomography (CT)-measured acetabular anteversion; (iii) establish a sensitive and specific threshold value for NAD to identify excessive acetabular anteversion. This retrospective cohort study included all patients presenting to a single institution over a 14-month period who had undergone a dedicated musculoskeletal CT pelvis along with a standardized anteroposterior (AP) pelvis radiograph. Trained observers measured the NAD on the AP pelvis radiograph and equatorial acetabular anteversion on CT for all hips. Mixed model analysis was used to find prediction equations, and ROC analysis was used to evaluate the diagnostic accuracy of NAD. NAD is a valid semi-quantitative predictor of acetabular anteversion and strongly correlates with CT-measured equatorial acetabular anteversion (P < 0.0001). A NAD measurement of greater than 14 mm predicts excessive acetabular anteversion with 76% sensitivity and 78% specificity. NAD is an accurate radiographic predictor of acetabular anteversion, which may be readily used as an effective screening tool during the evaluation of patients with hip pain.

Over one third of patients with symptomatic femoroacetabular impingement display femoral or acetabular version abnormalities

“…Thresholds for determining increased femoral version range from > 15 o to > 25 ° and decreased femoral version ranging from < 10 ° to < 0 ° [10, 12, 14, 26, 30, 59]. Similarly, authors have proposed various ranges for normal acetabular version including 10–25 ° and 13–20 o [30, 42]. Therefore, for the purpose of this review, the normal range for femoral and central acetabular version of 10–25 ° originally proposed by Tönnis was used [59].…”

Editorial Commentary: Treating Hip Impingement Without a Computed Tomography Scan? You Might as Well Operate With a Blindfold

“…These variables, however, fail to capture what happens in the axial plane, and additional measurements are needed to provide a more complete description, including the posterior wall sign, crossover sign, anterior wall index, posterior wall index, neck axis distance, and transverse axis distance. 3,4 These axial-plane acetabular indices aim to approximate acetabular version, further informing surgical decision making. It is important to note that no such radiograph-based analog exists for assessing femoral version, whichduntil recentlydhas largely been excluded from the decision-making algorithm for the evaluation and treatment of hip impingement.…”