The Acetabular Wall Index for Assessing Anteroposterior Femoral Head Coverage in Symptomatic Patients

Abstract

Background Understanding acetabular pathomorphology is necessary to correctly treat patients with hip complaints. Existing radiographic parameters classify acetabular coverage as deficient, normal, or excessive but fail to quantify contributions of anterior and posterior wall coverage. A simple, reproducible, and valid measurement of anterior and posterior wall coverage in patients with hip pain would be a clinically useful tool. Questions/Purposes We (1) introduce the anterior wall index (AWI) and posterior wall index (PWI), (2) report the intra-and interobserver reliability of these measurements, and (3) validate these measurements against an established computer model. MethodsWe retrospectively reviewed 87 hips (63 patients) with symptomatic hip disease. A validated computer model was used to determine total anterior and posterior acetabular coverage (TAC and TPC) on an AP pelvis radiograph. Two independent observers measured the AWI and PWI on each film, and the intraclass correlation coefficient (ICC) was calculated. Pearson correlation was used to determine the strength of linear dependence between our measurements and the computer model. Results Intra-and interobserver ICCs were 0.94 and 0.99 for the AWI and 0.81 and 0.97 for the PWI. For validation against the computer model, Pearson r values were 0.837 (AWI versus TAC) and 0.895 (PWI versus TPC). Mean AWI and PWI were 0.28 and 0.81 for dysplastic hips, 0.41 and 0.91 for normal hips, 0.61 and 1.15 for hips with a deep acetabulum. Conclusions Our data suggest these measures will be helpful in evaluating anterior and posterior coverage before and after surgery but need to be evaluated in asymptomatic individuals without hip abnormalities to establish normal ranges. Level of Evidence Level III, diagnostic study. See Instructions for Authors for a complete description of levels of evidence.

Periacetabular osteotomy: a review of swiss experience

“…The following radiographic parameters are measured: Tönnis grade osteoarthritis [35], lateral center edge angle (LCE) of Wiberg [36], the Acetabular Index [37][38][39], crossover sign, posterior wall sign [40], and ischial spine sign [41]. To assess the anterior and posterior femoral head coverage the acetabular wall index is calculated [42]. As a sign of subluxation of the head the Shenton line [43] is measured.…”

Acetabular Wall Indices Help to Distinguish Acetabular Coverage in Asymptomatic Adults With Varying Morphologies

“…In this costconscious era, the ability to use plain film radiographs to assess acetabular morphology is warranted. It may be challenging to properly diagnose those hip pathomorphologies associated with anterior and posterior coverage with plain film radiography [10,14,15]. To better evaluate anterior and posterior coverage, Siebenrock et al [15] developed measurements on plain films that take into consideration femoral head size and relative anterior and posterior walls to better quantify wall coverage relative to the femoral head diameter.…”

“…Additionally, the relative coverage contributed by each wall (anterior wall index [AWI] and posterior wall index [PWI]) can then be used to assess overall acetabular coverage as well as acetabular morphology and orientation. However, Siebenrock et al [15] only examined a small number of symptomatic patients with apparent pathomorphologies who had undergone either periacetabular osteotomy or surgical hip dislocation with or without rim trimming. More recently, Tannast et al [16] provided reference values for acetabular coverage using well-established measurements.…”

CORR Insights®: Acetabular Wall Indices Help to Distinguish Acetabular Coverage in Asymptomatic Adults with Varying Morphologies

“…The authors evaluated anterior and posterior femoral head coverage in ''normal'' hips using the anterior wall index (AWI) and posterior wall index (PWI) [10].…”

“…Siebenrock and colleagues [10] introduced the concept of AWI and PWI as a measurement on plain films to quantify the contribution of anterior and posterior wall coverage in acetabular pathomorphology of symptomatic patients. Numerous radiographic angles, indices, and ratios-including the lateral center-edge angle, ACM angle, sharp angle, acetabular and extrusion indices, cranio-caudal acetabular coverage, AP acetabular coverage, and crossover and posterior wall sign-also describe the acetabular anatomic morphology projected on the AP pelvic radiograph [11].…”