Cartilage deformation of the feline patellofemoral joint obtained from laser scanning

We know that normal articular cartilage deforms under load, but the magnitude of this deformation in-vivo is uncertain. The purpose of this study was to develop a method to precisely quantify articular cartilage surface deformation in the feline patellofemoral joint using a laser scanner. The accuracy and precision (2SD) of the scanner on a flat, inert surface were 3.8 μm and 19.5 μm, respectively. The joint surfaces were mapped before and after a static stress-relaxation load of physiological magnitude was applied to the joint. In addition, the bone surfaces were scanned. The unloaded and loaded cartilage surfaces, and the bone surface were aligned, modelled with the Thin-Plate Splines, and subtracted from each other to obtain cartilage deformation and cartilage thickness. Results from the femoral groove showed a compression of 103 μm ± 75 μm (2SD), and an elevation of the cartilage surface surrounding the contact area. Cartilage thickness was difficult to interpret because of a suspected cartilage translucency. Results for the patella were not reliable because of surface alignment difficulties. The laser scanning technique allowed for quantification of articular cartilage surface deformations with an estimated accuracy of 30 μm. The approach developed here may prove useful when attempting to correlate cartilage surface deformations to micro-structural deformations, and possible biological responses.