BACKGROUND:
Personalized alignment in total knee replacement (TKR) is an increasingly popular surgical approach. It is important to evaluate the accuracy of the tibial cut when using manual instrumented alignment. This is particularly pertinent for a bone balanced or inverse kinematic alignment approach to TKR, in which the tibial cut is made at a predetermined angle based on the medial proximal tibial angle (MPTA) on pre-operative long leg x-rays. In bone balancing approaches, all subsequent femoral cuts are based on the tibial cut angle.
METHOD:
A prospective study was conducted to evaluate the accuracy of manual extra articular alignment of the tibial cut in 854 TKRs selected from a database. Two surgeons (A and B) performed TKRs using the same bone balancing surgical technique. An extra-articular tibial cutting jig was initially positioned at a neutral MPTA of 90 degrees. Each surgeon then adjusted the jig to achieve the planned degree of varus or valgus, as determined from pre-operative long leg x-rays. During surgery, the surgeon recorded the angle at which the tibial cut was made (intra-operative tibial cut angle). After surgery, patients underwent post-operative long leg x-rays to measure the MPTA. The intra-operative tibial cut angle recorded by the surgeon was then compared to the post-operative MPTA. The difference between the intra-operative tibial cut angle and the post-operative MPTA measurements was analyzed using Bland-Altman analysis, both overall and within the varus and valgus subgroups.
RESULTS:
For Surgeon A, the mean bias was -0.30° (standard deviation of the differences [SD]1.20°) for all cases (n=134). By subgroup analysis, the mean bias was -0.30° (1.00°) in varus cases (n=50) and -0.30° (1.30°) in valgus cases (n=84). For Surgeon B, the overall mean bias was -0.27° (1.55°) (n=720). By subgroup analysis, the mean bias was -0.42° (1.55°) in varus cases (n=451) and -0.00° (1.53°) in valgus cases (n=269).
Comparison of overall mean bias between Surgeons A and B using the Mann–Whitney U test showed no significant difference (p = 0.531).
CONCLUSION:
Manual extra-articular alignment is a reliable technique for personalized tibial cuts in TKR, producing comparable results across different operators.
