The kinematics characteristics of the human knee joint can be represented by its centrodes. This paper provides a method, called the photograph method, to construct the centrodes by using commercial digital camera to take the sequential pictures. In order to eliminate the undesired movements, a testing chair and a brace are specially designed. Two types of curve fitting methods are introduced to smooth the measured data. The differential method is applied to construct the centrodes of knee joints from the measured data. This paper provides a safe way to measure the centrodes of human knee joints.

Osteoarthritis (OA) is a degenerative condition of articular cartilage that affects more than 25 million people in the US. Joint injuries, like anterior cruciate ligament (ACL) tears, can lead to OA due to a change in articular cartilage loading. Gait analysis combined with knee joint finite element modeling (FEM) has been used to predict the articular cartilage loading. To predict the change of articular cartilage loading during gait due to various ACL injuries, a tibiofemoral FEM was developed from magnetic resonance images (MRIs) of a 33 year male, with no prior history of knee injuries. The FEM was validated for maximum contact pressure and anterior tibial translation using cadaver knee studies. The FEM was used to model gait of knees with an intact ACL, anteromedial (AM) bundle injury, posterolateral (PL) bundle injury, complete ACL injury, AM deficiency, PL deficiency, complete ACL rupture, as well as a bone-patellar tendon-bone (BPTB) graft. Generally, the predicted maximum contact pressure and contact area increased for all the ACL injuries when compared to intact ACLs. While an increase in maximum contact pressure and contact area is an indication of an increased risk of the development of OA, the percent of increase was typically small suggesting that walking is a safe activity for individuals with ACL injuries.