Targeting ligament boundaries rather than alignment boundaries in augmented-reality-assisted total knee arthroplasty ensures comparable gait patterns between operated and contralateral limbs.

purposeModern personalised total knee arthroplasty (TKA) techniques aim to mimic natural knee kinematics by focusing on soft-tissue dynamics rather than static alignment. However, a consistent definition of the optimal ligamentous balance has not yet been established. This study had three aims: to assess intraoperative collateral ligament tension and the overall balance between the medial and lateral compartments; to evaluate postoperative gait analysis parameters and compare them with the healthy contralateral knee; and to determine whether the achieved intercompartmental balance affects the final coronal alignment of the knee.

methodsA prospective single-cohort study was conducted to evaluate 102 primary AR-assisted TKAs performed for end-stage unilateral knee osteoarthritis between September 2021 and June 2024. A total of 17 patients out of 102 were ultimately included following the application of the study's inclusion and exclusion criteria. Intraoperative data were collected on MCL and LCL elongation patterns during passive ROM both before and after trial component placement. Additionally, the study examined differences in intercompartmental ligament balancing. Postoperative coronal alignment was radiographically evaluated using the hip-knee-ankle (HKA) angle. Functional outcomes were measured using 3D markerless gait analysis at least 9 months after surgery. A repeated-measures analysis of variance (ANOVA) and a Pearson correlation were employed to examine trends in ligament asymmetry and their relationship with alignment.

resultsThe medial collateral ligament (MCL) exhibited nearly isometric behaviour throughout the range of motion (0.3 ± 1.11 at 0°, -2.4 ± 2.71 at 20°, -2.3 ± 3.96 at 40°, -2.3 ± 4.16 at 60°, -1.5 ± 4.03 at 80°, -0.7 ± 4.52 at 100°, -0.2 ± 4.97 at 120° preoperatively; 2.2 ± 2.98 at 0°, 2.1 ± 3.40 at 20°, 1.4 ± 4.02 at 40°, 1.2 ± 4.41 at 60°, 0.8 ± 4.48 at 80°, 1.5 ± 4.42 at 100°, 1.6 ± 5.09 at 120° postoperatively). Conversely, the LCL showed progressive detensioning (0.0 ± 2.03 at 0°, -3.1 ± 2.07 at 20°, -3.9 ± 2.72 at 40°, -4.9 ± 3.34 at 60°, -6.6 ± 3.63 at 80°, -8.5 ± 4.13 at 100°, -9.6 ± 4.40 at 120° preoperatively; -2.1 ± 5.16 at 0°, -3.1 ± 4.03 at 20°, -4.7 ± 3.80 at 40°, -5.8 ± 3.19 at 60°, -7.0 ± 3.86 at 80°, -6.6 ± 4.55 at 100°, -7.0 ± 5.08 at 120° postoperatively), leading to asymmetric ligament balancing with the opening of the lateral compartment. This trapezoidal soft-tissue configuration persisted postoperatively. No significant differences were observed in gait parameters between the operated and contralateral limbs, all p-values being > 0.05. A notable negative correlation was seen between postoperative HKA and ligament asymmetry at early flexion angles (0°, 20°, 40°; r = -0.63, r = -0.67, r = -0.48, respectively), indicating that soft-tissue balancing affects coronal alignment.

conclusionsFocusing on dynamic soft-tissue boundaries rather than static alignment targets may preserve knee kinematics after TKA. Augmented reality-assisted balancing techniques provide real-time, personalised ligament management, which aligns with the patient's native kinematics and could be an encouraging direction in modern knee arthroplasty. More research is needed to confirm these findings across larger groups and different technologies. LEVEL OF EVIDENCE: Level III.