CONTRIBUTION OF COMPUTER-ASSISTED SURGERY IN TOTAL KNEE ARTHROPLASTY: 50 CASES

Abstract

Purpose: One of the biomechanical objectives of total knee arthroplasty (TKA) is to achieve a mechanical femorotibial axis of 180°. Frontal angulation greater or equal to 7° is a factor of poor implant survival. The development of computer-assisted navigation systems has led to the discovery of new concepts: dynamic goniometry, quantitative evaluation of ligament balance. The purpose of this study was to evaluate the influence of the rotational position of the femoral implant and its variation during flexion.

Material and methods: We reviewed the files of 50 patients who underwent surgery between October 2001 and December 2002 for computer-assisted implantation (Orthopilot(r)). We studied femorotibial axis at 0°, 30°, 60° and 90° before the bone cuts, after the tibial cuts and at the end of the procedure after definitive fixing of the implants.

Results: The population, mean age 70 years, was evenly distributed: 17 valgum and 32 varum. The mean femorotibial axis at the end of the operation with the definitive implants in place was 0° in extension with balanced ligaments (±2°) and more often increased varus at 30°, 60° and 90° flexion.

Discussion: External rotation of the femoral piece was not systematic. Certain normally aligned knees in extension after the tibial cut presented significant varus in flexion, probably due to external rotation of the femoral epiphysis. On the contrary, knees with internal rotation of the femoral epiphysis, irrespective of the cause, showed a trend to valgus during flexion. Using external rotation of the femoral implant systematically for both knee morphotypes cannot be done without deteriorating the ligament balance in certain patients.

Conclusion: The advent of navigation systems for TKA has led to the discovery of new concepts such as dynamic goniometry. This has enabled study of femorotibial alignment in flexion, the working position of the knee during walking. This study showed that systematic external rotation of the femoral implant for TKA is not appropriate for all patients.