JOA - 2026-08-27 - Journal Article
Lateral Femoral Joint-Line Distalization Increases Lateral Collateral Ligament Strain During Total Knee Arthroplasty.
Kitchen JM, Richards JA, Powers J, Quesada P, Mont MA, Malkani AL
Topics
Key Takeaway
Lateral femoral joint-line distalization of ≥4 mm increases LCL strain to 6.0%, approaching microstructural injury thresholds and suggesting a critical biomechanical threshold between 2 and 4 mm.
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Summary
This cadaveric study quantified isolated LCL strain response to progressive lateral femoral joint-line distalization during rKA TKA using robotic assistance and reflective marker motion capture at 0°, 30°, 60°, and 90° of flexion. Baseline post-rKA median peak LCL strain was 1.6%; 2-, 4-, and 6-mm distalization increased strain to 1.9%, 6.0%, and 8.1%, respectively, with statistically significant differences at ≥4 mm. A stepwise response identified a potential biomechanical threshold between 2 and 4 mm distalization, beyond which strain enters ranges associated with ligament microstructural injury in animal models.
Key Limitation
Injury thresholds are extrapolated from animal ligament in vitro studies rather than validated human LCL failure data, making the clinical significance of the 6.0% and 8.1% strain values uncertain.
Original Abstract
BACKGROUND
Optimal coronal alignment strategy during total knee arthroplasty (TKA) remains controversial. Joint-line alteration has been associated with abnormal knee kinematics, ligament imbalance, and patient dissatisfaction; however, the isolated biomechanical consequences of lateral femoral joint-line distalization on lateral collateral ligament (LCL) strain remain poorly understood.
METHODS
There were six non-arthritic cadaver knees that underwent robotic-assisted TKA using restricted kinematic alignment (rKA) to approximate native joint-line orientation. A motion capture technique utilizing reflective markers applied to the LCL quantified strain across knee flexion angles (0, 30, 60, and 90°). Progressive distalization of the lateral femoral condyle was simulated using 2-mm shims placed between the implant and the lateral distal femur. The median peak LCL strain across flexion arcs and ligament regions was recorded and compared using paired statistical testing.
RESULTS
Native LCL strain demonstrated physiologic relaxation with increasing knee flexion. Following rKA TKA, the baseline median peak LCL strain measured 1.6%. Progressive lateral femoral joint-line distalization resulted in increases in strain to 1.9, 6.0, and 8.1% with 2-, 4-, and 6-mm distalization, respectively. Statistically significant increases in strain were observed between zero and four mm, zero and six mm, and four and six mm distalization (P < 0.05). A stepwise strain response was observed, demonstrating a potential biomechanical threshold between two and four mm distalization.
CONCLUSIONS
Lateral distal femoral joint-line distalization independently increases LCL strain following TKA. Distalization exceeding approximately four mm results in strain magnitudes associated with a microstructural injury threshold based on in vitro studies of animal ligaments. These findings suggest that joint-line alteration may contribute to lateral soft-tissue imbalance and postoperative dissatisfaction.