The acetabular wall index for assessing anteroposterior femoral head coverage in symptomatic patients.
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.


OBJECTIVE
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.


METHODS
We 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.


METHODS
Level III, diagnostic study. See Instructions for Authors for a complete description of levels of evidence.
Department of Orthopaedic Surgery, University of Bern, Inselspital, Freiburgstrasse, 3010 Bern, Switzerland. klaus.siebenrock@insel.ch
Klaus A
KA
Siebenrock
Lea
L
Kistler
Joseph M
JM
Schwab
Lorenz
L
Büchler
Moritz
M
Tannast
D000077:Acetabulum / Q000000981:diagnostic imaging*; D000293:Adolescent; D000328:Adult; D000368:Aged; D003198:Computer Simulation; D005260:Female; D005270:Femur Head / Q000000981:diagnostic imaging*; D006621:Hip Joint / Q000000981:diagnostic imaging*; D006801:Humans; D007592:Joint Diseases / Q000000981:diagnostic imaging*; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D011237:Predictive Value of Tests; D011379:Prognosis; D011859:Radiography; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012720:Severity of Illness Index; D055815:Young Adult