In Vivo Biomechanical Interactions between Bones, Patellar Tendon, and Cartilage Surfaces at the Knee during Cycling

Stationary cycling is essential in rehabilitation programs for various patient groups, such as knee osteoarthritis and cruciate ligament injuries and reconstruction. The study aimed to measure in vivo the 3D rigid-body and articular surface kinematics of the knee and the patellar tendon orientations during stationary cycling and isolated flexion-extension exercise in healthy young adults using a model-based tracking approach with dual-plane fluoroscopy.

Ten healthy left knees were imaged by computed tomography and magnetic resonance imaging to reconstruct subject-specific volumetric 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.

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 with the recovery phase, the power phase showed significantly greater external rotations, adductions, and posterior translations for flexions greater than 45° ( P < 0.05) with significantly more posterior medial and lateral contact positions for flexion angles less than 45° ( P < 0.05) and more vertical patellar tendon orientations for flexion angles lesser than 60° ( P < 0.05).

The contact locations and loads on the posterior half of the tibial articular surface during the first half of the power phase indicate that stationary cycling as a daily and rehabilitative exercise is safe for people with anterior medial knee osteoarthritis.