Acetabular orientation with different pelvic registration landmarks

This study determined the relationship of various pelvic landmarks to the pelvic plane in the lateral position. Five whole-body cadavers were used in this study. All navigation data were collected using the OrthoPilot navigation system (B. Braun Aesculap, Tuttlingen, Germany) to register all landmarks. The pelvic plane was registered with the body in the supine position for comparison. The ipsilateral posterosuperior iliac spine (PSIS) and contralateral PSIS were registered for comparison of the line made by the 2 anterosuperior iliac spines (ASIS) in the supine position. Registration points along the acetabular rim at the 12-, 3-, and 9-o'clock positions were recorded, and the transverse acetabular ligament (TAL) was registered using the ends and middle of the ligament for the 3 registration points. Inclination as determined by the TAL was 49.7 degrees +/-25.8 degrees , whereas the acetabular rim resulted in an inclination of 36.3 degrees +/-7.2 degrees . When the interspinal posterior line was calculated, the difference in inclination compared with the pelvic plane was 1.8 degrees +/-1.7 degrees . Anteversion using the acetabular rim resulted in a difference of 8.1 degrees +/-4.9 degrees and using the TAL resulted in a difference of 13.4 degrees +/-7.9 degrees . The difference in anteversion using the pelvic plane and the posterior interspinal line was 1.2 degrees +/-1.3 degrees . This study determined that the alternative landmarks of the acetabular rim and the TAL were not as accurate as using the posterior interspinal line as determined by registering the PSIS.