MULTIPARAMETER CT ASSESSMENT OF NON-CAS TOTAL KNEE REPLACEMENTS

Introduction and Aims: A total knee replacement (TKR) needs to be well aligned for it to function well and avoid premature failure. Computer Assistance system has been designed to improve that alignment. The rationale for these systems rests on the assumptions that we currently have an alignment problem. To date, there have been no comprehensive survey of alignment outcomes and therefore no evidence of the size of the problem. Method: The Perth CT protocol was used to measure the alignment of 164 primary TKRs, male/female = 76/88, mean age 69.4 years, performed by seven surgeons. One hundred and twenty-four patients were approached in the immediate post-operative phase and 40 within three years of surgery. Six alignment parameters were measured. The Perth Alignment Index was used as a measure of the quality of outcome. A parameter was judged perfect if it was within two degrees of the target alignment. Results: In the coronal plane femoral alignment was ‘perfect’ in 74% (value range −3 to +6 degrees) and tibial alignment in 84% (value range −5 to +7 degrees). In the sagittal plane femoral flexion/extension was perfect in 75% (range −3 to +9 degrees), while tibial slope was perfect in 44% (value range −6 to +16 degrees). Femoral component rotation was perfect in 66% (range −8 to +9 degrees) and femorotibial matching was 45% (−14 to +13degrees). The mean PAI was 5.11:1.98, with only 14 patients (9%) having a perfect score. Conclusion: The alignment of conventional jig-assisted TKR is far from perfect and efforts to improve the results seem to be justified.