Dynamic in-vivo force transfer in the lapine knee loaded by quadriceps muscle contraction

The rabbit knee is a frequently used model for experimental osteoarthritis (OA). Despite the acknowledged importance of joint loading in the onset and progression of OA, the load transfer in the three compartments of the intact rabbit knee remains unknown. Therefore, this study was aimed at determining load transfer in the three compartments for isometric, concentric, and eccentric knee extensor contractions.

Maximal and sub-maximal isometric, concentric, and eccentric knee extensor contractions were produced by electrical stimulation of the femoral nerve in 13 rabbits. Knee extensor forces were measured using a custom-built servomotor. Contact areas and pressure distributions were measured in the patello-femoral, and the medial and lateral tibio-femoral joints using Fuji Presensor film.

Contact areas and peak pressures increased with increasing quadriceps forces for all compartments. Maximal knee extensor forces, joint moments, and contact pressures reached values of 504 N, 5.5 Nm and 60 MPa, respectively. Force transfer in the patello-femoral joint was about twice that observed in the individual tibio-femoral joints. During isometric contractions, force transfer was higher in the medial compared to the lateral tibio-femoral joint, while this trend was reversed for dynamic contractions.

The results of this study suggest that the increasing muscular forces are transferred through an increased contact area, thereby limiting the increase in average contact pressure. These results may be used as reference data for contact pressures in the intact rabbit knee and may form the foundation for studies using the lapine knee as an experimental model of osteoarthritis.