Novel measurement technique for knee joint laxities using polymeric capacitive strain gauges

Non-invasive evaluation of knee joint laxities is crucial in the diagnostics of post-traumatic knee injuries such as ACL ruptures. Current clinical standard and daily routine for orthopaedic surgeons are for instance the Lachman-Test or the Anterior Drawer-Test in the evaluation of knee joint displacement. Those tests, while quickly and easily performed, are dependent on the experience of the examining surgeon and subject to his personnel assessment. Individual and inter-individual patient discrepancies are difficult to be taken into account and may lead to a false negative diagnosis without any pathology. A novel measurement technique based on highly flexible capacitive strain gauges is presented in this work to allow a highly accurate, reliable and quantifiable method for pre-operative diagnosis and post-operative evaluation of patients with knee joint laxities. The measurement system is non-invasive and independent from the examiners personnel experience as the distance of the displacement is measured in length. Those measured values become comparable and implications regarding the severity of a displacement and the outcome of an operative reconstruction may be derived. In further studies this may enable an evaluation of surgical techniques to the knee joint and lead to a new standard procedure in the diagnosis of injuries at the knee joint.