Protocols for precise radio-anatomical positioning of the tibiofemoral and patellofemoral compartments of the knee.

Quantitative assessment of radiographic features, in particular joint space width, are important in the diagnosis and treatment of knee osteoarthritis (OA). Protocols defining radiographic procedures are essential to maintain quality control and hence reliable and reproducible measurement of these features. Criteria governing variability in radiographic procedures are discussed and include defining the precise radio-anatomical position of the joint, standard criteria for X-ray beam alignment, allowance for inherent radiographic magnification and precise definition of anatomical boundaries. Protocols incorporating these criteria are described for standard radiography of the anteroposterior view of the tibiofemoral compartment in the standing semi-flexed position, and for the standing lateral and axial views of the patellofemoral joint. In these views, the radio-anatomical position of the joint is based upon the principal that there is only one plane in which the central ray of the X-ray beam will pass between the margins of the joint space so that both margins and space are optimally defined, in a position consistent with the functional loading of that joint.