Influence of loading duration on the start-up friction in synovial joints: measurements using a robotic system

Objective. To determine how much and why static load influences friction in synovial joints. Design. Start-up coefficient of friction in canine stifles was measured after different duration of static load. Background. Previous investigators have shown that friction of cartilage on cartilage contact configurations sharply increases with stationary load duration. This phenomenon has not been confirmed in the entire synovial joint. Methods.: A system to measure joint friction was designed using a robotic arm. Ten canine stifles from six animals were used. Start-up friction of the femoral condyle on the tibial plateau and femoral condyle on glass plate contact configurations was measured. The glass plate was chosen as a rigid surface where ploughing effect cannot occur. Results. The mean value of the start-up frictional coefficient from femoral condyle on tibial plateau was 0.012 (SD 0.005) at 0 s stationary loading, and sharply increased with the stationary loading duration to 0.313 (SD 0.095) at 1800 s. Those from femoral condyles on glass plate were 0.005 (SD 0.003) at 0 s and 0.457 (SD 0.128) at 1800 s. Conclusions. Friction in synovial joints sharply increases with duration under static load. The ploughing effect on this increase is slight in friction in canine stifles.