Early Tibiotalar Joint Changes Following Subtalar Arthrodesis for Progressive Collapsing Foot Deformity: A 3D Distance Mapping Short Scientific Report.

Background: Subtalar joint (SJ) fusion may be required to treat subtalar osteoarthritis in progressive collapsing foot deformity (PCFD). Our goal was to understand how anterolateral arthroscopic subtalar arthrodesis (ALAPSTA) may alter joint congruency at the tibiotalar level.

Methods: We retrospectively assessed pre- and postoperative weightbearing computed tomography images of patients diagnosed with PCFD 2A (arthritic SJ) and/or 2D (peritalar subluxation) which underwent isolated ALAPSTA. Foot alignment was evaluated using the Foot and Ankle Offset. Distance mapping at the tibiotalar joint (in 9 quadrants) allowed to assess changes in joint interaction between pre- and postoperative images.

Results: Thirty-three PCFDs were selected. Foot alignment significantly improved after ALAPSTA. We found a significant increase in mean distances occurring in the posterior-medial, posterior-middle, and posterior-lateral zones (from 5.5 to 6.3 mm [adjusted  = .036], from 4.6 to 5.7 mm [adjusted  = .009], and from 4.5 to 5.4 mm [adjusted  = .04], respectively) along with a significant decrease in the anterior-medial, anterior-middle, and anterior-lateral zones (from 9.1 to 8.3 mm [adjusted  = .04], from 8.9 to 7.3 mm [adjusted  = .007], and from 8.9 to 7.1 mm [adjusted  < .008], respectively).

Conclusion: In patients diagnosed with PCFD 2A and/or 2D who had undergone ALAPSTA, we observed a significant early imaging-based change in the spatial relationship of the tibiotalar joint in quiet standing, demonstrating dorsiflexion of the talus over the calcaneus, consistent with a "re-saddling" effect. These findings are exploratory and require further clinical correlation.