The purpose of this study was to analyze the accuracy of the mechanical axis and implant positions postoperatively and to evaluate the radiology results of computer assisted navigation surgery for bone cutting and ligament balancing in revision TKA.

13 consecutive revision TKAs were performed by a single surgeon with use of computer assisted surgery (CAS) from July 2004 to August 2005. At the revision, the mean age was 64.7 years. The mean interval from the index arthroplasty was 9.8 years. The cause of the revision included 11 cases of polyethylene wear and 2 cases of loosening. Two observers measured the mechanical axis, position of the implants, and level of joint lines.

By observer I, the mechanical axis improved from varus 11.9° to valgus 1.5°, and the mean α, β, γ and δ angles were 95.3, 90.8, 3.9 and 87.6° respectively. From observer II, the mechanical axis improved from varus 11.6° to valgus 1.6°, and mean α, β, γ and δ angles were 95.5, 90.5, 4.1 and 87.9° respectively. The measured angles from observers I and II showed a good correlation.

Accurate bone cutting and verification in each step are possible using real time information provided by the CAS. The mechanical axis, component positions, joint line could be checked and adjusted with feedback of navigation system. Information about flexion and extension gap and ligament balancing could be verified during revision surgery.