In-vitro measurement of static pressure distribution in synovial joints--Part II: Retropatellar surface.

This second part of a two-part paper is concerned with the measurement of static pressure distribution on the retropatellar surface. The study has been performed in a loading apparatus designed to simulate individually the lines of action and the magnitudes of the tensions in the components of the quadriceps femoris muscle group. Results have been obtained using 24 specimens in the knee flexion range 0 to 130 deg and employing a net quadriceps tension of 734 N. Particular emphasis has been placed on the evaluation of the sensitivity of the results to variations in the characteristics of the simulated quadriceps tension. The pressure distribution results have been interpreted in terms of variation of the normal force and the average contact stress on the retropatellar surface as a function of flexion angle. It has been shown that the "pulley" model of the patella consistently overestimates the actual patellofemoral joint reaction force throughout the range of flexion. Clinical implications of the results, in terms of etiology of degeneration of patellar cartilage, have been discussed.