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 0.112 (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. RELEVANCE: The lubrication mechanism is worth investigating to understand the pathology of joint diseases. Determining friction behaviour is necessary for the investigation of the lubrication mechanism.