Digital radiographic assessment of tibiofemoral joint space width: a variance component analysis

This study aimed to evaluate sources of variability when the metatarsal-phalangeal (MTP) semiflexed radiographic technique is used to measure the tibiofemoral joint space width in the medial and lateral compartments of the knee. Three independent digital MTP radiographs were obtained from both knees of 9 participants. The joint space widths of both compartments of each knee were measured 3 times by 2 independent examiners. Intraclass correlation coefficients were high between repeated radiographs, between examiners, and within examiners (range, 0.91-0.98). These 3 error components accounted for 9% and 14% of the total variance for the medial and lateral compartments, respectively. The estimated SDs across radiographs for the medial and lateral compartments were 0.093 mm and 0.155 mm. The digital radiographic technique based on the MTP view is a simple and reliable technique for measuring the joint space width that can be readily used to track longitudinal changes in cartilage thickness after knee joint surgery.