Introduction Malpositioning of cup and stem in total hip replacement can result in significant clinical problems such as dislocation, impingement, limited range of motion and increased polyethylene wear. The use of mechanical alignment guides for correct cup positioning has been shown to result in large variations of cup inclination and version.

Methods Bilateral total hip replacements were performed in twelve human cadavers. While in each cadaver the operation on one side was performed with the aid of a non image based hip navigation system, the cup positioning at the contralateral hip was controlled by use of a conventional mechanical alignment guide. Post-operative cup position relative to the pelvic reference plane was assessed in both groups by the use of a 3D digitizing arm.

Results By aiming for 45° inclination and 20° anteversion for cup position the median inclination was assessed as 45.5° for the navigated group and 41.8° for the control group. Median anteversion in the navigated group was calculated as 21.9° and 24.6° for the control group. The 90 percentile showed a much wider range for the control group (36.1° to 51.8° inclination, 15° to 33.5° anteversion) than for the navigated group (43.9° to 48.2° inclination, 18.3 ° to 25.4° anteversion).

Conclusions The cadaver study demonstrates that computer assisted cup positioning using a non-image based hip navigation system allowed a more precise placement of the acetabular component in the surgeon’s desired orientation with less variance than in the control group.

In relation to the conduct of this study, one or more the authors have received, or are likely to receive direct material benefits.