Coronal plane alignment changes do not affect in vivo kinematics for robotically performed total knee arthroplasty.

Abstract

Total knee arthroplasty (TKA) is effective for alleviating pain and restoring function in knee osteoarthritis patients, yet 10% report dissatisfaction due to persistent pain and functional limitations. Conventionally, mechanically aligned (MA) TKA often fail to replicate native kinematics. Kinematic alignment (KA) aims to replicate pre-arthritic alignment for better function. The coronal plane alignment of the knee (CPAK) system classifies knees into nine groups. Changes in CPAK may alter load distribution, ligament tension and joint congruence. Conflicting studies exist on the impact of CPAK changes on outcomes. No prior study has used fluoroscopy to examine weight-bearing kinematics stratified by CPAK changes post-TKA. This retrospective analysis used data from a registry of primary robotic-assisted TKAs (2019-2023) using NAVIO/CORI (Smith & Nephew) systems, with Journey II BCS implants. Exclusions: prior ipsilateral surgery, complicating conditions or missing radiographs. Procedures used MA or KA per surgeon preference, with standardized protocols. Demographics, operative data, pre/post-operative Knee Society Scores (KSS/KSFS) at 12 months were collected. CPAK was calculated from radiographs. Patients performed weight-bearing deep knee bends under fluoroscopy; kinematics were extracted via 3D-to-2D registration, assessing flexion, condylar positions and axial rotation. Cohorts: CPAK change (<i>n</i> = 33) versus no change (<i>n</i> = 9). Student's <i>t</i> test compared outcomes (<i>p</i> < 0.05). No differences in maximum flexion (Change: 105 ± 11.9° vs. No Change: 101 ± 11.4°, <i>p</i> = 0.42), lateral condyle rollback (-13.1 ± 5.6 mm vs. 10.1 ± 5.2 mm, <i>p</i> = 0.15), medial condyle rollback (-5.9 ± 3.1 mm vs. -4.7 ± 2.7 mm, <i>p</i> = 0.29) or axial rotation (8.9 ± 5.9° vs. 6.5 ± 4.1°, <i>p</i> = 0.27). KSFS improvements (+28 ± 21.1 vs. +17 ± 19.2, <i>p</i> = 0.16) and KSS (+38 ± 19.2 vs. +38 ± 25.9, <i>p</i> = 0.95) were similar. Post-operative CPAK 3 was the most frequent (45.2%). CPAK changes after robotic-assisted TKA do not affect in vivo kinematics or short-term outcomes, supporting alignment flexibility with precise techniques. Level IV.