Doubles ostéotomies assistées par ordinateur dans les grands genu varum: Résultats préliminaires à propos de 16 cas

Abstract

Purpose of the study The aim of this work was to assess radiographic outcome after double femoral and tibial osteotomy for severe genu varum. Among 197 computer-assisted osteotomies performed in our department between August 2001 and February 2006, 16 (8.1%) were double level osteotomies. Material and methods Five women and nine men, mean age 51.19±11.15 years (range 20-63 years) underwent surgery (both sides for two men). The right side was involved in nine cases, the left in seven. Inclusion criteria were genu varum > 10° and/or a mechanical femur angle ≥90° in a context of a varus tibial mechanical axis. Exclusion criteria were a femoral mechanical angle at 90° and a tibial mechanical angle > 88°. Using the modified Ahlbäck classification, the knees were: grade 2 (n=1), grade 3 (n=9), grade 4 (n=4) and grade 5 (n=1). One patient did not present osteoarthritic degradation but a particularly unaesthetic deformity. The radiological femorotibial mechanical angle (HKA) measured preoperatively was on average 168.44°±2.42° (range 164°-173°). The average preoperative femoral mechanical angle was 87.38°±2.45° (range 81°-90°) and the mechanical tibial angle was 84.5°±2.19° (range 80°-88°). The main preoperative objective was to obtain a mechanical femorotibial angle of 182°±2° without an oblique joint space giving a tibial mechanical angle of 90±2°). All operations were computer-assisted using the Orthopilot TM navigation system. After acquisition of the mechanical axis, the closed wedge lateral distal femoral osteotomy was performed first to achieve the desired femoral correction. The open wedge proximal medial tibial osteotomy was then performed to obtain the planned femorotibial mechanical axis. A control goniometry in the weight bearing position was obtained three months postoperatively. Results There were no complications. The mean preoperative computer-measured HKA was 168.63°±2.22° (range 164°-173°), i.e. an angle corresponding perfectly with the preoperative goniometry. After the osteotomies, the mean computer-measured mechanical angle was 183°±0.94° (range 181°-184°). Three months after the operation, the weight-bearing goniometry gave a mean HKA angle at 181.25°±1.84° (range 177°-184°). The mean femoral mechanical angle was 93.13°±2.25° (range 89°-97°) and the mean tibial mechanical angle was 90.31°±1.20° (range 88°-92°). The preoperative objective was achieved in 14 of the 16 patients (87.5%). The two failures were undercorrections (177° and 179°). Joint spaces were not oblique on the x-rays. Discussion Tibial osteotomy is an excellent method for the treatment of osteoarthritic genu varum. However, in patients with very severe deformity, femoral varus is also involved so that the overcorrection necessary to achieve a good result (3-6° valgus) could often produce an oblique joint space corresponding to excessive tibial valgus. Since osteotomy is generally considered as a palliative measure before later implantation of a total prosthesis, an oblique joint surface would compromise the success of the subsequent surgery. Double-level osteotomy is a way to avoid this problem, keeping in mind that the risk of over or under correction is not negligible for this difficult operation. We used our experience with computer-assisted navigation for total knee arthroplasty and for tibial osteotomy to prepare this technique for double-level osteotomy. Conclusion Computer-assisted double-level osteotomy is a reliable, accurate and reproducible method for the treatment of severe genu varum. The two failures observed in this series were within a tolerable range (177° and 179°). The use of a navigation procedure simplifies a technique which in general requires skillful application to achieve the preoperative objective. The development of this technique is important in order to avoid an oblique joint space which can compromise the success of subsequent prosthesis implantation.