Objective Analysis of Regional Tibiotalar Joint Changes in Ankle Osteoarthritis Assessed by Semi- Automated 3D Distance Mapping

Abstract

Category: Ankle Arthritis; Ankle Introduction/Purpose: Ankle osteoarthritis is a degenerative joint disease characterized by the narrowing of the tibiotalar joint space and in late stages, eventual tibiotalar contact and subchondral bone loss. Traditional methods of assessing changes in the joint space (such as assessment on 2D radiographs) are subjective and do not fully consider the three-dimensional nature of articular surfaces. Weight-bearing CT (WBCT) provides a unique perspective by placing the joints of the lower extremity in a loaded, functional position, and may help to better quantify changes in joint space. Determining the presence and progression of ankle arthritis is difficult. It is our hope that novel 3D distance mapping technologies using images acquired from WBCT may assist with the detection and characterization of progression of ankle osteoarthritis. Methods: In this IRB-approved, retrospective case-control study, we analyzed WBCT data of 9 ankle osteoarthritis patients and 20 healthy controls. Patients included in this study had no identifiable talar tilt. Segmentations were created using an automated segmentation software package (DISIOR Bonelogic 2.0) Principal component analysis was used to divide the talar dome into nine subregions. The articular facet of the medial malleolus was also analyzed. We used 3D distance mapping to objectively measure joint space width across the tibiotalar joint and assessed changes in distance in each of the nine subregions of the talar dome articular surface. Overall mean distances for each subregion analyzed were calculated. Comparisons between the control and ankle arthritis cases were performed with independent t-tests, assuming unequal variances. P-values < 0.05 were considered significant. Results: Changes in the mean distances are reported in the attached figure. The medial side of the talar experienced significant decreases in mean joint space width. The middle medial subregion experienced the largest decrease in mean joint space width with a reduction of 35% when compared to controls (p = 0.017). Increases in joint space width were observed on the lateral aspect of the talar dome, However, these increases were not found to be significant. Conclusion: The purpose of this study is twofold: to quantify changes in joint space using 3D distance mapping technique and to evaluate the utility of a commercial automated segmentation software package. In this cohort, there was a significant decrease on the medial side of the talar dome – this change can be attributed to cartilage degeneration. To our knowledge, this is the first study to analyze changes in ankle osteoarthritis using a fully automated segmentation method. Automated segmentation and 3D distance mapping provide a useful tool for the quantification of osteoarthritis-associated joint space changes.