A novel approach for determining three-dimensional acetabular orientation: results from two hundred subjects.
BACKGROUND
The inherently complex three-dimensional morphology of both the pelvis and acetabulum create difficulties in accurately determining acetabular orientation. Our objectives were to develop a reliable and accurate methodology for determining three-dimensional acetabular orientation and to utilize it to describe relevant characteristics of a large population of subjects without apparent hip pathology.


METHODS
High-resolution computed tomography studies of 200 patients previously receiving pelvic scans for indications not related to orthopaedic conditions were selected from our institution's database. Three-dimensional models of each osseous pelvis were generated to extract specific anatomical data sets. A novel computational method was developed to determine standard measures of three-dimensional acetabular orientation within an automatically identified anterior pelvic plane reference frame. Automatically selected points on the osseous ridge of the acetabulum were used to generate a best-fit plane for describing acetabular orientation.


RESULTS
Our method showed excellent interobserver and intraobserver agreement (an intraclass correlation coefficient [ICC] of >0.999) and achieved high levels of accuracy. A significant difference between males and females in both anteversion (average, 3.5°; 95% confidence interval [CI], 1.9° to 5.1° across all angular definitions; p < 0.0001) and inclination (1.4°; 95% CI, 0.6° to 2.3° for anatomic angular definition; p < 0.002) was observed. Intrapatient asymmetry in anatomic measures showed bilateral differences in anteversion (maximum, 12.1°) and in inclination (maximum, 10.9°).


CONCLUSIONS
Significant differences in acetabular orientation between the sexes can be detected only with accurate measurements that account for the entire acetabulum. While a wide range of interpatient acetabular orientations was observed, the majority of subjects had acetabula that were relatively symmetrical in both inclination and anteversion.


CONCLUSIONS
A highly accurate and reproducible method for determining the orientation of the acetabulum's aperture will benefit both surgeons and patients, by further refining the distinctions between normal and abnormal hip characteristics. Enhanced understanding of the acetabulum could be useful in the diagnostic, planning, and execution stages for surgical procedures of the hip or in advancing the design of new implant systems.
3071 Montfort Loop, Richmond, VA 23294. E-mail address: sehiggin@vt.edu.
Sean W
SW
Higgins
Virginia Commonwealth University, P.O. Box 843067, Richmond, VA 23284-3067. E-mail address: spratleyem@vcu.edu. E-mail address for J.S. Wayne: jwayne@vcu.edu.
E Meade
EM
Spratley
615 North 23rd Street, Richmond, VA 23223. E-mail address: boera@vcu.edu.
Richard A
RA
Boe
VCU Medical Center, Main Hospital, 1101 East Marshall Street, Room 3-444, Richmond, VA 23298. E-mail address: cwhayes@vcu.edu.
Curtis W
CW
Hayes
VCU Medical Center, West Hospital, 1200 East Broad Street, 9th Floor, East Wing, P.O. Box 980153, Richmond, VA 23298-0153. E-mail address: wjiranek@gmail.com.
William A
WA
Jiranek
Virginia Commonwealth University, P.O. Box 843067, Richmond, VA 23284-3067. E-mail address: spratleyem@vcu.edu. E-mail address for J.S. Wayne: jwayne@vcu.edu.
Jennifer S
JS
Wayne
D000077:Acetabulum / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D008297:Male; D008953:Models, Anatomic; D015588:Observer Variation; D010388:Pelvis / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed