Abstract
Research Type:
Level 3 - Retrospective cohort study, Case-control study, Meta-analysis of Level 3 studies
Introduction/Purpose:
Hindfoot malalignment is associated with altered subchondral bone mineral density (BMD) distribution and ankle osteoarthritis (AOA). Increased subchondral density may indicate regions of heightened stress, potentially correlating with cartilage degeneration and joint space narrowing. 3D Distance Mapping from weight-bearing CT (WBCT) enables quantification of joint space changes, while density mapping identifies load-bearing regions. This study aimed to investigate the spatial correlation between subchondral density clusters and joint space narrowing in ankles with varus or valgus hindfeet. We hypothesized that areas of higher subchondral density would align with regions of smaller joint space width, reflecting mechanical overload.
Methods:
This retrospective cohort study compared 13 varus (mean Foot Ankle Offset (FAO)=-9.65(±4.38), and 13 valgus hindfeet (mean FAO=11.05(±3.62)) comparable for side (p=0.99), age (p=0.65), BMI (p=0.31), and sex (p=0.99). WBCT datasets were analyzed using Minerva research platform (Vent Creativity, NY, USA) to generate subchondral density maps for tibia, talus and 3D joint space distance maps. The densest 30% Hounsfield Units (HU), consistent with cortical and subchondral bone were considered for analysis. Density and contact point clusters were identified via Gaussian Mixture Models and mapped to a normalized reference frame with the sagittal plane aligned with the second metatarsal. The primary outcome measure was the spatial alignment of high-density areas with joint space narrowing, assessed via correlation analyses. Repeated-measures ANOVA were used to compare tibia/talus density centroids and contact points. Statistical significance was set at α = 0.05.
Results:
Subchondral density clusters were significantly displaced medially in varus (2.94 mm ± 1.11) and laterally in valgus hindfeet (0.40 mm ± 2.1) (p < 0.001). Joint space narrowing followed the same pattern (respectively 0.70 mm ± 1.3 valgus and 0.45 mm ± 0.78 varus shifts), aligning with high-density areas (p < 0.02). Talus density and joint contact location demonstrated a moderately positive correlation in both X (ρ=0.66, p< 0.001) and Y (ρ=0.65, p< 0.001) axes. No significant correlation was found for tibial density and joint contact (p=0.789). Varus hindfeet had significantly more medialized talar density (p < 0.001), while valgus hindfeet had lateralized talar density (p < 0.001).
Conclusion:
This study demonstrates a direct spatial correlation between subchondral density and joint space narrowing, with higher-density regions aligning with reduced joint space, indicating increased stress and a potential risk for asymmetric ankle osteoarthritis. Talar density and joint contact were strongly correlated, whereas tibial density was not, likely due to the tibia’s less consistent positioning under load. These findings suggest that WBCT-based density mapping could serve as a predictive marker for malalignment-induced osteoarthritis. Future research should assess longitudinal progression and determine whether these imaging biomarkers can inform early intervention strategies to prevent AOA development.
