The principles of a noninvasive measurement of the shock absorbing capacity of the knee are presented. Accelerometry, which has been proven to be a useful tool for noninvasive measurements in biomechanical investigation, was employed for quantitative evaluation of the knee's shock absorbing capacity by registration of bone vibrations resulting from the gait. Results of the experiments show that both patients with painful knee and patients after meniscectomy suffer from insufficient shock absorbing capacity of the knee. It was found that the shock absorbing capacity of a normal knee is about 20% higher than that of a pathological one. The results indicate that while meniscectomy may reduce pain, instability, swelling, etc. in an injured knee, it cannot improve its reduced shock absorbing capacity, which eventually will lead to development of degenerative osteoarthritis. It seems that the pain syndrome is a biological reaction to severe repetitive overloading of the knee. Noninvasive in vivo determination of the knee's shock absorbing properties may be useful as an additional clinical technique to reveal a knee's pathology. It may lead to early discovery of knee insufficiency, so that preventive steps can be taken to delay or reverse the process of degeneration.

This paper presents a "fast and simple" (FAS) detection algorithm based on the digital image correlation for measurement of the surface deformation of planar objects. The proposed algorithm uses only fine search at the pixel level resolution and surface fitting for sub-pixel level. Two different specimens are investigated to explore the feasibility of this proposed algorithm. The displacements calculated by the FAS algorithm are compared with the ones obtained from Newton-Raphson method (N-R) and Enhanced Sequential Similarity Detection Algorithm (ESSDA). The results show that the experimental data are in good agreement with the theoretical solution. The proposed algorithm is found to be much faster than Newton-Raphson method with inferior, yet reasonable, accuracy for displacement and strain evaluation in the cases of uniaxial tension and disk under diametrical compression tests.