Objective: To compare the cup and stem position in matched pairs of cadaveric hips performing a minimally invaisve total hip arthroplasty (MIS-THA) either by using manual guidance tools or by the STRYKER Hip-track Navigation System.

Background: Minimally invasive techniques are currently introduced to THA. Our workgroup has developed a direct anterior single incission approach. Special instruments have been designed for retraction and implantation. Instruments are navigable with the STRYKER hiptracksystem. Perfect positioning of the acetabular and femoral component are among the most important factors in THA. Malpositioning may result in significant clinical problems such as dislocation, impingement, limited range of motion or extensive wear.

Design/Methods: In twelve fixated human cadavers hemispherical pressfit cups (TRIDENT, Stryker, Alledale, NJ) and straight femoral components (ACCOLADE, Stryker, Allendale, NJ) were implanted. All implantation were done throught the minimally invasive direct anterior approach. On one side the surgery was performed with spezial MIS instruments. On the oposite side the navigation system was used for placement of the implants. The aim was to achieve an alignment for the cups with 45° of inclination and 15° of anteversion in reference to the frontal pelvic plane. For the stem the goal was to position the stem in 0° of varus/valgus relative to the proximal shaft axes. This plane and the resulting cup positions were measured on CT-scans with a 3D imaging software (Stryker-Leibinger, Freiburg, Germany).

Results: The Innsbruck MIS approach to the hip could be performed in all cases. For both groups cup and stem position where within the range of variation reported in the literature. Yet, variance of the deviation from the goal was higher in the conventional group for both inclination and anteversion with the medians for the navigated group for inclination, anteversion and stem position being closer to the goal then in the conventional group.

Conclusion: The described minimally invasive approach to the hip is feasible and renders results compareable to those reported for conventionally operated THA. By the use of the navigation system tested it is possible to increase placement precission