This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Osteoarthritis (OA), a progressive destruction of articular cartilage, ultimately leads to joint space narrowing, progressive erosion of bone and ligament laxity. Knee OA is often associated with disabling pain and accounts for a large portion of functional disability in older Americans. The medial compartment of the knee is most frequently involved and is associated with medial joint space narrowing, genu varum and laxity of the medial joint structures. Genu varum itself leads to an excessive adduction moment at the knee that may exacerbate the progression of the OA. Progression of knee OA also involved an intricate interaction between muscle weakness, sensory loss and knee instability, all of which are negatively effected by the bony malalignment. Realignment procedures performed to correct the varus deformity in active individuals provide a model for assessment of the effect of skeletal alignment on thosevariables purported to contribute to the progression of knww OA, muscle weakness, proprioception, knee joint laxity, and function. The overall goal of this study is to determine whether anatomic realignment of the tibiofemoral joint in patients with moderate genu varus deformity allows for changes in muscle strength, knee joint laxity, knee joint instability and proprioception that is compatible with halting the progression of knee OA. Aim 1: demonstrate the effect of anatomic realignment of the tibiofemoral joint in restoring quadriceps activation, quadriceps strength and mediolateral joint stability in persons with painful, medial compartment OA. Aim 2: demonstrate the effect of anatomic realignment of the tibiofemoral joint on normalization of muscle activation and movement patterns (timing, level of activation and degree of co-contraction) during walking in persons with painful, medial compartment OA. Aim 3: demonstrate the effect of anatomic realignment of the tibiofemoral joint on normalization of the neuromuscular response to a medial perturbation at the knee in persons with painful, medial compartment OA. Aim 4: Predict functional outcome from linear combinations of quadriceps function, knee motion, moments, and neuromuscular responses in people with painful, medial compartment OA and genu varum before and after anatomic realignment of the tibiofemoral joint. An alternative surgery, the opening wedge osteotomy involves the creation of an opening on the medial side of the tibia which can be distracted slowly over time. The purpose of this study is to characterize the differences in movement and muscle activity before and after an opening wedge osteotomy with callus distraction to correct genu varum.