Error in acetabular socket alignment due to the thick anterior pelvic soft tissues.

The aim of this study was to assess how much the digitizing error attributable to the thick soft tissues in the anterior pelvic area can affect the targeted acetabular socket alignment. The acetabular socket orientation angle was measured by using a synthetic pelvic model and an OrthoPilot total hip arthroplasty (Aesculap AG & Co KG, Tuttlingen, Germany) navigation system. The anterior pelvic plane was defined using 3 bony landmarks: the ipsilateral and contralateral anterior superior iliac spines (ASIS) and the center of the 2 pubic tubercles. The digitization error of 1 cm at the ipsilateral ASIS, contralateral ASIS, and the center of the two pubic tubercles resulted in 1.8 degrees , 4.4 degrees , and -6.8 degrees in anteversion, and 1.4 degrees , 0.2 degrees , and -0.2 degrees in abduction, respectively. The current navigation system based on the anterior pelvic plane may produce considerable error in guiding the acetabular socket anteversion for patients with thick soft tissue in the anterior pelvic area.