THE REPRODUCTION OF THE NATIVE LAXITY PHENOTYPE GUARANTEES A MORE NATURAL KNEE KINEMATICS COMPARED TO THE RESTORATION OF THE STATIC MORPHOTYPE: A GAIT ANALYSIS EVALUATION FOLLOWING TOTAL KNEE ARTHROPLASTY

Introduction Alternative alignments in total knee arthroplasty (TKA) are gaining popularity over mechanical alignment because they aim to replicate patients’ natural alignment and restore the original joint line position and obliquity as measured on preoperative weight-bearing X-rays. Supporters of these alternative methods also argue that their approach more accurately replicates natural knee motion. This study presents gait analysis data from patients who underwent TKA, comparing objective outcomes after restoring their preoperative bony morphotype with those after achieving ideal native ligament laxity. Materials and Methods This gait analysis study included 41 patients who underwent TKA. Inclusion criteria were a minimum 9-month follow-up after successful primary medial-pivot or medially congruent TKA for isolated degenerative knee disease. Patients were randomly assigned to three surgical groups, matched by age, sex, and BMI: A) Unrestricted Kinematic Alignment (uKA) (#12); B) Robot-assisted (#12) restricted-KA (rKA: ±3° from the neutral hip-knee-ankle axis) with a slight asymmetry in the intercompartmental gap (maximum 2 mm lateral opening); C) Augmented reality-assisted (#17) TKA (AR) with the medial collateral ligament (MCL) exhibiting nearly isometric intraoperative behavior throughout the range of motion. In groups B and C, intraoperative soft-tissue balancing was recorded at 30° of knee flexion using the included classification (Figure 1) based on ideal native ligament laxity. Gait analysis was performed on instrumented treadmills equipped with 3D cameras, and both spatiotemporal and kinematic parameters were recorded. Results Sagittal knee kinematic data: During the early-stance phase of gait, the uKA group exhibited less consistent weight acceptance and a less efficient transition from the first knee-flexion peak to the mid-stance extension plateau than the rKA and AR groups. Analysis of the flexion peak during gait showed a statistically significant difference between the uKA group (38º±6.0º) and the rKA (45º±10.0º) and AR (49.0º± 9.34º) groups. Spatiotemporal and gait quality data: No statistically significant differences were found among the three groups in walking speed and step length, though the rKA and AR groups showed a trend toward better performance. Conclusion This study presents objective data indicating that newer alignment techniques, which aim to restore patients’ static phenotype and native joint line obliquity as determined on preoperative long, weight-bearing films, do not reproduce near-normal native knee kinematics; better performance was achieved by targeting a slight intercompartmental asymmetry.