A Rigid Body Spring Model to Investigate the Lateral Shift - Restraining Force Behavior of the Patella

Patellar lateral stability was studied using a 2D transverse plane model with deformable articular surfaces. Quadriceps muscles and patellar tendon were considered as strings with predefined forces and lateral and medial retinaculum as tensile springs. Deformation behavior of articular cartilage was modeled by a set of compression springs perpendicular to articular surfaces, based on rigid body spring model method (RBSM). Patellar lateral stability was investigated using restraining force method (the external force required to cause up to 10 mm lateral displacement on patella). The results were in good agreement with experimental reports for normal joint, vastus lateralis and vastus medialis relieved. Small changes in the femoral trochlear groove geometry provided significant variation in patellar stability. Simulation of different surgical treatments showed that the tibial tubercle medialization is the most effective procedure for patellar subluxation and dislocation disorders.