Pelvic morphology differs in rotation and obliquity between developmental dysplasia of the hip and retroversion.
BACKGROUND
Developmental dysplasia of the hip (DDH) and acetabular retroversion represent distinct acetabular pathomorphologies. Both are associated with alterations in pelvic morphology. In cases where direct radiographic assessment of the acetabulum is difficult or impossible or in mixed cases of DDH and retroversion, additional indirect pelvimetric parameters would help identify the major underlying structural abnormality.


OBJECTIVE
We asked: How does DDH and retroversion differ with respect to rotation and coronal obliquity as measured by the pelvic width index, anterior inferior iliac spine (AIIS) sign, ilioischial angle, and obturator index? And what is the predictive value of each variable in detecting acetabular retroversion?


METHODS
We reviewed AP pelvis radiographs for 51 dysplastic and 51 retroverted hips. Dysplasia was diagnosed based on a lateral center-edge angle of less than 20° and an acetabular index of greater than 14°. Retroversion was diagnosed based on a lateral center-edge angle of greater than 25° and concomitant presence of the crossover/ischial spine/posterior wall signs. We calculated sensitivity, specificity, and area under the receiver operating characteristic (ROC) curve for each variable used to diagnose acetabular retroversion.


RESULTS
We found a lower pelvic width index, higher prevalence of the AIIS sign, higher ilioischial angle, and lower obturator index in acetabular retroversion. The entire innominate bone is internally rotated in DDH and externally rotated in retroversion. The areas under the ROC curve were 0.969 (pelvic width index), 0.776 (AIIS sign), 0.971 (ilioischial angle), and 0.925 (obturator index).


CONCLUSIONS
Pelvic morphology is associated with acetabular pathomorphology. Our measurements, except the AIIS sign, are indirect indicators of acetabular retroversion. The data suggest they can be used when the acetabular rim is not clearly visible and retroversion is not obvious.


METHODS
Level III, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.
Department of Orthopaedic Surgery, Murtenstrasse, Inselspital, University of Bern, 3010 Bern, Switzerland. moritz.tannast@insel.ch
Moritz
M
Tannast
Peter
P
Pfannebecker
Joseph M
JM
Schwab
Christoph E
CE
Albers
Klaus A
KA
Siebenrock
Lorenz
L
Büchler
D000077:Acetabulum / Q000002:abnormalities / Q000000981:diagnostic imaging; D000293:Adolescent; D000328:Adult; D001696:Biomechanical Phenomena; D060751:Bone Retroversion / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000503:physiopathology; D005260:Female; D006618:Hip Dislocation, Congenital / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000503:physiopathology; D006621:Hip Joint / Q000002:abnormalities / Q000000981:diagnostic imaging; D006801:Humans; D008297:Male; D008875:Middle Aged; D010384:Pelvic Bones / Q000002:abnormalities* / Q000000981:diagnostic imaging / Q000503:physiopathology; D011237:Predictive Value of Tests; D012372:ROC Curve; D011859:Radiography; D016059:Range of Motion, Articular; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D055815:Young Adult