Summary
Although ML balance and laxity were similar between piKA and pGB, piKA better restored native joint line and CPAK type.
Abstract
Introduction
Inverse Kinematic Alignment (iKA) and Gap Balancing (GB) aim to achieve a balanced TKA via component alignment. However, iKA aims to recreate the native joint line versus resecting the tibia perpendicular to the mechanical axis. This study aims to compare how two alignment methods impact 1) gap balance and laxity throughout flexion and 2) the coronal plane alignment of the knee (CPAK).
Methods
Two surgeons performed 75 robotic assisted iKA TKA’s using a cruciate retaining implant. An anatomic tibial resection restored the native joint line. A digital joint tensioner measured laxity throughout flexion prior to femoral resection. Femoral component position was adjusted using predictive planning to optimize balance. After femoral resection, final joint laxity was collected. Planned GB (pGB) was simulated for all cases posthoc using a neutral tibial resection and adjusting femoral position to optimize balance. Differences in mediolateral (ML) balance, laxity, medial proximal tibial angle (MPTA), lateral distal femoral angle (LDFA), and CPAK were compared between planned iKA (piKA) and pGB. ML balance and laxity were also compared between piKA and final (fiKA). Native CPAK was calculated from intraoperative landmarking data using a wear correction factor based on preop alignment.
Results
piKA and pGB had similar ML balance and laxity, with mean differences <0.4mm. piKA more closely replicated the native MPTA (Native=86.9±2.8°, piKA=87.8±1.8°, pGB=90±0°), and the native LDFA (Native=87.5±2.7°, piKA=88.9±3°, pGB=90.8±3.5°). piKA planned for a more native CPAK distribution, with the most common types being II (22.7%), I (20%), III (18.7%), IV (18.7%) and V (18.7%). Most pGB knees were type V (28.4%), VII (37.8%), and III (16.2%). fiKA and piKA had similar ML balance and laxity, however fiKA was more variable in midflexion and flexion (p<0.01).
Conclusions
Although ML balance and laxity were similar between piKA and pGB, piKA better restored native joint line and CPAK type. The bulk of pGB knees were moved into types V, VII, and III due to the neutral tibial cut. Future work should investigate how postoperative CPAK alignment affects long patient outcomes