Removal of the superficial zone of bovine articular cartilage does not increase its frictional coefficient

SummaryObjectiveTo investigate the role of the superficial zone in regulating the frictional response of articular cartilage. This zone contains the superficial protein (SZP), a proteoglycan synthesized exclusively by superficial zone chondrocytes and implicated in reducing the friction coefficient of cartilage.DesignUnconfined compression creep tests with sliding of cartilage against glass in saline were carried out on fresh bovine cylindrical plugs (∅6mm, n=35) obtained from 16 bovine shoulder joints (ages 1–3 months). In the first two experiments, friction tests were carried out before and after removal of the superficial zone (∼100μm), in a control and treatment group, using two different applied load magnitudes (4.4N and 22.2N). In the third experiment, friction tests were conducted on intact surfaces and the corresponding microtomed deep zone of the same specimen.ResultsIn all tests the friction coefficient exhibited a transient response, increasing from a minimum value (μmin) to a near-equilibrium final value (μeq). No statistical change (P>0.5) was found in μmin before and after removal of the superficial zone in both experiments 1 and 2. However, μeq was observed to decrease significantly (P