Clinical and Cadaveric Evidence for Inlay Technique Fixation in Ruptured MCL Inferior Attachment Treatment Running title: Inlay Technique Fixation for MCL Inferior Attachment Ruptures

Background Although well-documented for ligament graft fixation, the inlay technique remains largely unexplored for distal MCL avulsions, presenting a significant opportunity. A comprehensive evaluation of this approach utilizing an interference screw is now demanded, focusing on its biomechanical properties, kinematic influence, and ultimate clinical efficacy. Methods The MCL dynamic trajectories were recorded during full range of motion in three cadaveric specimens, and the mechanical strength were compared between inlay and onlay techniques using isokinetic tensile tests. Twenty-six patients with ruptured MCL inferior attachments underwent inlay technique fixation surgery 2 cm proximal to the distal insertion. Lateral stress tests, knee joint Lysholm scores, and MRIs used to evaluate knee stability and function. Results MCL dynamic trajectories showed no displacement within 3 cm of the ligament's distal end during full range of motion. Inlay technique exhibited significantly higher mechanical strength and shorter displacement compared to onlay technique. Twenty-six patients underwent this surgical technique, with negative lateral stress and drawer tests post-operation. Knee joint Lysholm scores significantly increased from 30 (17,48) pre-operation to 65 (30,90) at 3 months, 81 (60,95) at 6 months, and 90 (83,95) at 12 months post-operation (P < 0.05). MRI results showed satisfactory tendon-bone healing and ligament tension. Conclusions Inlay technique offers superior mechanical strength, earlier stability and tendon-bone healing for treating the inferior attachment of the MCL. An upward shift of the MCL insertion point within 3 cm does not impair knee joint motion trajectory. Level of evidence Level Ⅳ.