Accurate and highly reproducible measurements of the rate of progression of osteoarthritis is crucial to assessing structural change, and requires adherence to exacting standards of positioning, which include specifications for flexion and rotation of the joint, and angulation of the x-ray beam. The progression of osteoarthritis traditionally has been measured using radiographic joint space width (JSW). Over the past two decades, numerous knee radiographic protocols have been developed with various levels of complexity and performance as they relate to detecting JSW loss (ie, joint space narrowing). Semiautomated software has been developed to improve the accuracy of JSW measurement over manual methods. JSW measurements include minimum JSW, mean JSW or joint space area and JSW at fixed locations.