Summary

Kinematically aligned total knee replacement corrects fixed flexion deformity with less bony resection and soft tissue release compared to mechanical alignment.

Abstract

Background

Kinematic aligned (KA) total knee arthroplasty (TKA) has emerged as an alternative approach to the intraoperative alignment targets of mechanically aligned (MA) TKA. Whilst the clinical outcomes of the two philosophies have been investigated, further investigation is required to quantify how they differ in their approach to correcting the deformities encountered in osteoarthritic knees such as fixed flexion deformities (FFD) and coronal malalignment. The aim of this paper was to compare the efficacy and efficiency of MA and KA philosophies in TKA on the intra-operative correction of FFD and coronal malalignment and quantify how each philosophy achieves a well-balanced knee that can reach full extension.

Methods

A retrospective review of prospective data collected from 210 consecutive TKA’s performed by a single surgeon between March 2015 and May 2017 was undertaken. MA and KA cases were compared in terms of pre-operative patient deformity and characteristics, intraoperative steps taken to correct FFD (including bony resections, soft tissue releases and components used) and postoperative alignment achieved.

Results

120 MA and 90 KA TKA’s were analysed. There was no significant difference in terms of patient age, gender and preoperative coronal and sagittal deformity between the two cohorts. KA TKA’s were able to achieve the same degree of sagittal correction as MA TKA’s with significantly less bony resection (8.1 vs. 9.1mm), less soft tissue releases (3.3 vs. 72.5% of cases) and no difference in final limb alignment (1.1 vs. 0.4 degrees varus). Laxity on varus-valgus stress testing at 0, 30 and 90 degrees was significantly different pre and postoperatively in the MA TKA group, but not at 0 and 90 degrees in the KA TKA group.

Conclusion

This study shows that using a kinematic alignment philosophy in total knee arthroplasty results in the achievement of extension range-of-motion and soft tissue balance goals with less bone resection, less soft tissue release, and no difference in final overall limb alignment. This leads to increased intraoperative efficiency, minimization of trauma due to less bony resection and soft tissue release and potentially improved patient outcomes. Further study is required to correlate these results with patient reported outcomes and determine their clinical significance.