Factors affecting successful restrictive kinematic alignment with robotic total knee arthroplasty

Abstract

<p>Restricted kinematic alignment (rKA) with target mechanical axes between -3° to +6° have been proposed to reduce the impact of outlier knee anatomy on the mechanics and wear of implants. However, there is no consensus for the targets. Methods: All robotic-arm-assisted primary total knee arthroplasty (TKA) for knee osteoarthritis at an academic institution between January 2019 and December 2021 were included. Exclusion criteria included a preoperative valgus alignment. Coronal alignment and osteophyte sizes were measured on preoperative weight-bearing long-films. Intraoperative screencaptures before and after osteophyte removal were collected. Results: A total of 244 consecutive TKAs (194 patients) were included, mean age was 65.3 ± 5.6. Female-to-male ratio was 1.7:1. The mean preoperative alignment was 11.9°±5.1° varus and the mean alignment after osteophyte removal was 5.1° ± 3.4° varus, with a mean deformity correction of 6.8° ± 3.7°. rKA was achieved in 36.9% TKAs at a target of ≤3° varus and up to 72.1% at ≤6° varus. Preoperative varus deformity was lower in TKAs that achieved rKA across all target alignment (p<0.05) and was positively correlated with degree of deformity correction after osteophyte removal (p<0.01). The mean medial tibial osteophyte size was 6.1% ± 2.9% and was statistically smaller in all groups that achieved rKA across all target alignments (p<0.05). It is positively correlated with preoperative varus alignment (p<0.01) and degree of deformity correction (p<0.01). Conclusion: Preoperative varus deformity and medial tibial osteophyte size are important factors when adopting a rKA protocol. For moderate to severe varus deformities, additional medial soft tissue release or reduction osteotomy should be considered.<br></p>