Purpose: The purpose of this work was to assess the mechanical axis of 28 computer-assisted osteotomies (group A) with 28 manual osteotomies (group B) selected at random from 140 osteotomies performed between January 1997 and December 2000.

Material and methods: The populations were comparable for age, gender, side, degree of osteoarthritis (modified Ahlback stages) and varus malalignment (group A: 173±3.80° (160°–178°), group B 172.8±3.18° (164°–178°) using a pangonometer to measure the HKA angle). For 52 knees, open-wedge tibial osteotomy was performed and fixed with a tricalcium phosphate wedge (Biosorb(r)) and an AO T-plate. For four knees (two in group A and two in group B), a double tibial (open wedge) and femoral (closed wedge) osteotomy was used due to genu varum measuring greater than 15°. Preoperative planning for the classical method used a plumb line from the centre of the femoral head identified fluoroscopically. The Orthopilot(r) computer-assisted method also relied on preoperative planning but intraoperative control was based on computer acquisitions of the centre of the hip, the knee and the ankle. The objective of the intervention was to obtain a mechanical axis between 182° and 186°. All knees were evaluated with pangonometry at three months to check axis correction.

Results: In group A, the mean postoperative HKA was 183±0.99° (181°–185°). In group B it was 184±2.28° (181°–189°). The objective was attained in 96% of knees in group A and in 71% in group B, giving a statistical difference between the absolute data (p=0.0248) and between the standard deviations (p=0.0015).

Conclusion: Computer-assisted osteotomy to correct for genu varum using the Orthopilot(r) method is feasible and remarkably reproducible. In our hands Orthopilot(r) enabled attaining the surgical objective set preoperatively. The kinetics of the acquisition of the centre of the hip, the knee, and the ankle associated with palpation of remarkable extra-articular points is an excellent method avoiding the need for intra-articular palpation which might complicate the surgical procedure.