APPROPRIATENESS OF PLANE PRESSURE-SENSITIVE FILM CALIBRATION FOR CONTACT STRESS MEASUREMENTS IN ARTICULAR JOINTS

Objective. To examine how accurately calibration stains from pressure- sensitive film sam pi es com pressed between perfectly flat surfaces r epresent contact pressures measured with the film inserted between cur ved joint surfaces. Design. Experimental study. Background. Contact pr essure distributions and areas in joints are often quantified using pr essure-sensitive film inserted between the articular surfaces, Absolut e pressure values are recovered from the film through a calibration pr ocedure, Since the calibration is typically performed in a different e nvironment from the experimental measurements, a systematic error in t he pressure magnitudes may be introduced. Methods. Calibration stains were produced with ail Instron machine using a flat and a slightly cur ved indenter. Calibration curves were fitted to the raw data of both i ndenters using a model representing the functional characteristics of the pressure-sensitive film. Results. No systematic differences betwee n the calibration curves from the fiat and the curved indenter were ob served. Conclusions. It appears that calibration with the film in a fl at configuration is adequate for contact pressure measurements between moderately curved articular surfaces.