Three-Dimensional Osseous Alignment and Morphology Patterns of Ankle and Hindfoot Osteoarthritis

Background: Patients with advanced ankle and hindfoot osteoarthritis (OA) experience substantial functional limitations and reduced quality of life. Conventional 2-dimensional imaging provides limited insight into 3-dimensional (3D) shape and alignment of the foot and ankle, making it unclear whether isolated subtalar OA (STOA), isolated tibiotalar OA (TTOA), and combined disease (TTSTOA) represent distinct morphologic entities related to foot type. Methods: A retrospective cohort of 196 weightbearing computed tomography (WBCT) scans was analyzed, including 130 OA patients (STOA, TTOA, TTSTOA) and 66 non-osteoarthritic controls classified as planus, rectus (neutral), or cavus. A 14-bone statistical shape model (SSM) characterized 3D morphology and alignment. Principal components analysis (PCA), Hotelling’s T 2 tests, computationally derived radiographic measurements, and joint space analysis quantified alignment patterns and joint space narrowing. Results: PCA mode 1 reflected a cavus-to-planus alignment spectrum, whereas mode 3 captured joint space narrowing. TTOA was most similar to cavus alignment with increased varus hindfoot and higher sagittal arch measures. STOA was most similar to rectus foot type. TTSTOA spanned the widest range, encompassing varus and valgus presentations, and was among the lower observed joint space distances across both joints. The planus group differed from all OA groups across all analyses. Conclusion: Hindfoot and ankle OA presentations were characterized by joint-specific degenerative changes occurring within a broader alignment environment, reflecting altered load distribution and compensatory adaptations. This relationship between local joint degeneration and global alignment underscores the importance of evaluating the foot and ankle as an integrated system, particularly when assessing disease extent, severity, and patterns of multijoint involvement. Level of Evidence: Level III, retrospective cross-sectional study.