Kinematic Interactions Between Bones, Patellar Tendon, And Cartilage Surfaces During Cycling By Three-dimensional Fluoroscopic Imaging

Stationary cycling has been an essential component in rehabilitation programs for various patient groups such as those with knee ligament injuries and reconstruction. Knowledge of the biomechanical interactions at the knee during cycling will be helpful in using stationary cycling as a rehabilitation modality and developing strategies for preventing overuse injuries. PURPOSE: The current study aimed to measure the in vivo 3D skeletal rigid-body and articular surface kinematics and the patellar tendon angles of the knee during isolated flexion/extension and stationary cycling in healthy young adults using dual-plane fluoroscopy with a DRR-based 2D/3D registration method and subject-specific bone-cartilage models. METHODS: Ten healthy left knees were imaged by CT and MRI to reconstruct subject-specific bone-cartilage models. The 3D rigid-body and articular surface kinematics and patellar tendon angles during stationary cycling and isolated knee flexion-extension exercise were measured in vivo using a dual-plane fluoroscopy with a voxel-based registration method, compared between tasks and between power and recovery phases. RESULTS: Significant differences in the rigid-body and surface kinematics and patellar tendon orientations were found between the power and recovery phases and between the power phase and isolated knee extension. Compared to the recovery phase, the power phase showed significantly greater external rotations, adductions, and posterior translations for flexions greater than 45o with significantly more posterior medial and lateral contact positions for flexion angles less than 45o and more vertical patellar tendon orientations for flexion angles lesser than 60o. CONCLUSIONS: The contact locations on the posterior half of the tibial during the first half of power phase indicate that stationary cycling is safe for anterior medial knee OA as exercises. During the same period when the quadriceps were firing to produce extensor moments, the patellar tendon was directed posteriorly and thus pulled the tibia posteriorly, suggesting a mechanism protecting the reconstructed ACL from being overstretched during muscle strengthening. The current findings will aid future basic research and the effective use of stationary cycling as a rehabilitation modality.