Contact stress gradient detection limits of Pressensor film

Fuji Pressensor film has been widely used for measurement of contact stresses in articular joints. In relatively smooth contact fields, measurement errors are reported to be in the range of approximately 10-15 percent. However, when local incongruities exist, strong contact stress gradients are present. This study investigates the film's capability to accurately transduce such gradients. Standardized stress distributions were produced by compressing the film between a rigid cylinder and an elastic layer supported by a rigid substrate. Seven different cylinder radii were used to obtain a range of gradient magnitudes. The resulting stains were digitized, and the contact stress gradients assessed by image analysis. Experimentally detected gradients were compared with those predicted analytically. The film's capability to reliably transduce contact stress gradients was shown to be sufficient for usage in the study of typical local articular incongruities.