Exploring the biomechanical mechanisms of neuromuscular joint facilitation intervention in patients with knee osteoarthritis: a finite element analysis.

INTRODUCTION: Knee osteoarthritis (KOA) causes joint pain and gait disorders in older adults. Exercise is an effective non-pharmaceutical therapy. Neuromuscular joint facilitation (NJF) improves knee joint function by combining neuromuscular facilitation with intra-articular joint motion; however, its biomechanical mechanism remains unclear. Finite element analysis, the mechanisms by which two NJF movement patterns-knee extension with lateral tibial rotation and knee flexion with medial tibial rotation-affect the stress distribution on the meniscus and major ligaments in patients with KOA.

METHODS: Six KOA patients were recruited. Inertial motion capture and handheld dynamometer measured tibial rotation angles and force conditions: active knee extension/flexion (AKE/AKF) pattern, distally single-resisted knee extension and flexion (DKE/DKF) pattern, and NJF technique (double-resisted movement). A knee finite-element model was built from one subject's CT/MRI. Loaded parameters were used to analyze the stress distribution characteristics of the medial collateral ligament (MCL), lateral collateral ligament (LCL), anterior/posterior cruciate ligament (ACL/PCL), and medial/lateral menisci at flexion angles of 0°, 30°, 60°, and 90°.

RESULTS: Knee rotation ICCs from inertial motion capture were all >0.75 (P < 0.05). In the knee flexion-medial tibial rotation pattern, at all flexion angles, meniscal stress was highest during AKF and lowest during NJF; conversely, ligament stress was lowest during AKF and highest during NJF. In the extension-lateral tibial rotation mode, meniscal stress was highest during AKE and lowest during NJF, whereas ligament stress changes were angle-dependent. The NJF technique can produce a traction effect along the long tibial axis by coordinating proximal and distal tibial resistances. This applies a force of approximately 30° to the long axis of the tibia, thereby reducing the load within the joint capsule.

DISCUSSION: The NJF technique can redistribute load between the meniscus and ligaments in this subject-specific finite element model, reducing peak meniscal load while moderately increasing ligament mechanical stimulation. These computational findings suggest a distinctive biomechanical profile of NJF compared with traditional resistance training in this subject-specific model. This provides a preliminary theoretical basis for future research, but the clinical relevance of these biomechanical observations requires confirmation through prospective clinical trials.