 - Comorbid conditions including: known other causes of arthritis infectious arthritis, rheumatoid arthritis, connective tissue disease, gout, pseudogout, or psoriatic arthritis, bony or soft tissue malignancy or skin lesions or peripheral neuropathy involving the lower extremities, cardiopulmonary disease which limits walking more than knee pain, knee instability defined as report of knee buckling or locking within the past month of the study knee, major neurologic deficit that affects gait, psychiatric illness that limits informed consent 