Abstract
Purpose
Implant positioning is one of the critical factors influencing the postoperative outcome in total hip arthroplasty (THA). Conventional (manual) intraoperative stem adjustment may result in variability and inaccuracy of stem antetorsion (AT). Since March 2013, we have measured stem antetorsion with CT free Navigation system (OrthoPilot Navigation System THA Pro Ver4.2, B/Braun Aesculap Germany: Navi). We have developed a simple instrument, the Gravity-guide (G-guide), for intraoperative assessment and adjustment of stem AT. We evaluated the accuracy and effectiveness of G-guide and navigation software as referenced to postoperative CT evaluation with 3D template system (Zed hip, LEXI, Japan).
Method
Between March 2013 and December 2014, 50 patients underwent primary THA were evaluated. Surgeries were performed with routine techniques with a modified Hardinge approach with the patient at a lateral decubitus position in all cases. The G-guide consists of two parts: one attached to the lower leg and the other attached to the handle of the rasp. During surgery, AT value was determined with navigation at the time of final rasping of the femur. Additionally, the G-guide was utilised at the time of final rasp insertion. In intraoperative AT assessment using this instrument, a correction was required considering the discrepancy between the perpendicular to the posterior condylar axis and the longitudinal axis of the lower leg. The angle of discrepancy between posterior condylar line and femoral trans-epicondyler axis needs to be taken into consideration. Therefore, correction by the angle between the trans-epicondylar and posterior condylar lines (correction angle) was required for each patient when the intraoperative AT as measured by the G-guide. Therefore, the correction angle should be added to the AT value obtained from the G-guide for comparison with postoperative value measured with Zed Hip.
Result
The discrepancy between the intraoperative G-guide with correction angle and postoperative Zed Hip measurements was 4.7° ± 3.9°. The discrepancy between Navi AT and postoperative Zed HIP measurements was 5.9° ± 4.1°. A discrepancy was 10° or more were 7 cases in Navi and 4 cases in G-guide.
Conclusion
Navi and G-guide measured intraoperative stem antetorsion was comparable utility.
