Friction and Wear Changes in Synovial Joints

Synovial joints have complex and poorly understood friction and wear properties. The relative importance of synovial fluid and cartilage in terms of lubrication is still unclear. The friction and wear characteristics of cartilage surface was investigated by sliding the orthopaedic cartilage of an adult rat femur against a stainless steel prate. Tests were performed dry and with irrigation by synovial fluid or saline solution. Friction and wear of the cartilage were initially low but increased in severity as a superficial lubricating layer was progressively removed by wear. Irrigation of the cartilage by synovial fluid reduced friction to very low levels, but saline solution had no lubricating effect. Microscopic examination of worn cartilage surface showed that low friction coincided with limited damage to the cartilage surface. It has been concluded that the outer surface of orthopaedic cartilage is covered by a substance capable of providing lubrication for limited periods when synovial fluid is unable to prevent contact between opposing cartilage surfaces.