MEASUREMENT OF THE SURFACE MICROGEOMETRY OF ARTICULAR-CARTILAGE

Difficulties of quantitative measurement of the roughness of articular cartilage are discussed, with particular reference to replication and scanning electron microscopy. An investigation of the fidelity of replication of the surface texture of optical flats and standard engineering components suggests that neither flatness nor roughness is always well reproduced by acrylic materials. Previous techniques of preparation for scanning electron microscopy are found to produce dimensional changes of up to 19% in human femoral heads. The feasibility of direct measurement of cartilage surface with a stylus instrument is established by indentation experiments which indicate an effective elastic modulus of 370 MPa for cartilage under transient load. Statistical analyses of stylus measurements on a femoral head yield roughnesses of up to 7 μm, slopes of up to 2° and peak radii of up to 0.9 mm. Height distributions are Gaussian and power spectra obey a square law like many other natural and man-made surfaces. Opposing surfaces of a knee joint are mapped by the stylus instrument, and computer-constructed isometric views and contour maps of simulated contact are presented. © 1979.