82. INTRAOPERATIVE CONTROL OF LOWER LIMB LENGTH DURING TOTAL HIP ARTHROPLASTY: COMPARISON BETWEEN NAVIGATION AND CONVENTIONAL IMPLANTATION

Abstract

Purpose of the study: Leg length discrepancy (LLD) can be a common reason for patient dissatisfaction after implantation of a total hip arthroplasty (THA). The failure rate is non negligible for conventional implantation techniques. Navigation systems might be able to improve precision.

Material and method: We used an imageless navigation system (Orthopilot™, Aesculap, FRG) for routine first-intention THA. LLD was determined on the AP view of the pelvis in the upright position to determine the desired correction. Captors were screwed onto the homolateral iliac crest and femur. The system analysed their respective positions at the beginning of the procedure thus defining the reference length. During implantation, the size and the height of the femoral implant and the length of the prosthetic neck were programmed virtually by the navigation system in order to obtain the desired correction which was then reproduced on the definitive implants. At the end of the operation, the final length of the limb was measured the same way as initially. The result of the correction was measured on the AP view of the pelvis in the upright position under the same conditions as initially. We compared 30 navigated THA with 30 THA implanted with the conventional technique. We analysed the residual length discrepancy and the percentage of the cases where the desired correction was achieved. Student’s t test and the chi-square test were used for the statistical analysis taking p< 0.05 as significant.

Results: Residual length discrepancy was 5 mm for the navigated THA and 9 mm for the conventional THA. The mean difference between the desired correction and the final correction was 2 mm for the navigated THA and 6 mm for the conventional THA. The desired length was obtained in 26 hips with navigated THA and in 17 with conventional THA. Residual LLD > 10mm was observed in 2 navigated THA and 9 conventional THA. All differences were significant.

Discussion: The navigation system used in this study enabled improved quality correction of lower limb length after implantation of a THA. Patient satisfaction should be globally improved.