Correlation of Arthrodesis Stability with Degree of Joint Fusion on MDCT

OBJECTIVE. The purpose of our study was to correlate clinically determined joint stability with the degree of bone fusion in the ankle or subtalar joint on MDCT examinations after arthrodesis. MATERIALS AND METHODS. We performed a retrospective review of 42 consecutive MDCT examinations from 29 patients. All patients had previously undergone arthrodesis of their ankle or subtalar joints and had persistent or recurrent hindfoot or ankle pain. Two musculoskeletal radiologists examined in consensus sagittal 2-mm-thick reformatted slices, measuring on each image the length of the joint surface and the length of the fused portion of the joint space. The sum of the lengths of the fused segments on all slices was then divided by the sum of the lengths of the joint surfaces to calculate the fusion ratio. For the standard of reference, the medical records were reviewed and operative reports, diagnostic injections, and physical examinations were used to classify the joints as stable or unstable. RESULTS. Twelve clinically unstable joints had fusion ratios of 0-32.8%, whereas 30 clinically stable joints had fusion ratios of 33.2-100%. Using receiver operating characteristic analysis, we selected the cutoff level that maximized Youden's index (the sum of sensitivity and specificity). Using a 33% fusion ratio as the lower limit cutoff for joint stability, the sensitivity was 100%; specificity, 100%; and accuracy, 100%. CONCLUSION. After arthrodesis of the ankle or subtalar joint, MDCT scans can be used to determine whether that joint is likely to be stable if > 33% of the joint has visible bone fusion on sagittal MDCT images.