Reliable evaluation of joint space width and subchondral sclerosis of osteoarthritic joints is difficult. The present study describes a new digital method to analyse standard radiographs of the ankle.
Standardized radiographs were taken of the ankle of 12 patients with severe osteoarthritis (OA) under full weight-bearing conditions, before treatment and 1 year after initiation of treatment. Treatment consisted of 3 months distraction of the tibio-talar joint, for which clinical benefit has been shown previously. The width of the joint space was measured on digitized images of the radiographs by means of the newly developed semi-automatic digital technique called AIDA (Ankle Images Digital Analysis) and by means of the most widely used conventional analogue measurements. In addition, AIDA was used to assess subchondral sclerosis by measuring the intensity of the radiograph at fixed positions at the bone-cartilage interface.
AIDA appeared to be a reliable method for measuring small changes in joint space width and subchondral sclerosis because the intra- and interobserver variation was small. Mean JSW for two observers was 1.96 and 2.00 mm, with mean differences between two observations of 0.05 and -0.01, respectively. Mean subchondral sclerosis in the tibia was 1.52 and 1.61 with mean differences between two observations of, respectively, 0.00 and 0.03. In addition to conventional measurements, AIDA could demonstrate a decrease in subchondral sclerosis as a result of joint distraction of 71% and 69% after 1 year for talus and tibia, respectively.
The use of AIDA is preferable to the conventional analogue method for evaluating the severity of ankle OA, because the method provides quantitative data not only for the joint space width but also for subchondral sclerosis.