The Synovial Fingerprint of Ankle Fractures: A Central Role for WNT Pathway Activation in Posttraumatic Ankle Osteoarthritis.

BACKGROUND

Osteoarthritis (OA) of the ankle is a disabling and understudied disease, most commonly emerging posttraumatically after ankle fractures (PTOA). Despite its prevalence, the molecular mechanisms linking joint trauma to ankle OA are not well defined, limiting opportunities for early intervention. This study characterized synovial transcriptional changes to identify early molecular drivers of disease onset in fracture-induced ankle PTOA.

METHODS

Synovium was collected under an institutional review board-approved protocol from patients undergoing ankle fracture fixation, and ankle arthroplasty for end-stage PTOA after a prior ankle fracture, or nontraumatic OA (NTOA). Synovium from patients with no or minimal OA served as controls. Bulk RNA sequencing was performed, followed by differential gene expression analysis and Gene Ontology (GO) enrichment. Machine learning clustering (k-means and hierarchical) and classification (logistic regression) models were employed to distinguish transcriptomic signatures of synovial subtypes.

RESULTS

RNA-seq and unsupervised clustering revealed distinct synovial transcriptional profiles separating NTOA and PTOA, with a uniquely shared signature between Fracture and PTOA synovium. WNT signaling was enriched across all groups compared to controls, with particularly broad activation in PTOA. WNT7B showed the strongest upregulation in Fracture and PTOA, with a smaller increase in NTOA. Logistic regression classified synovial subtypes based on gene expression profiles with high accuracy.

CONCLUSION

These findings support the hypothesis that ankle OA following fracture represents a molecularly distinct subtype. Although WNT pathway activation has been known in OA, its broader activation in PTOA suggests that joint trauma initiates a pathologic synovial cascade, with WNT pathway activation playing a central role. The clear timing of most ankle fractures offers a unique opportunity for early therapeutic intervention. Focused research on the synovial molecular link between ankle fractures and PTOA could underpin the development of targeted, disease-modifying strategies in the immediate postinjury period.