Peritalar Kinematics Restored with Combined Subtalar Fusion and Medial Ligament Reconstruction in a Simulated Advance Progressive Collapsing Flatfoot Deformity Model
Authors: Tecle Nahom , Oh Irvin , Gira Emma , Awad Hani A. 
Published: January 2022

Category: Midfoot/Forefoot; Other Introduction/Purpose: Progressive collapsing flatfoot deformity (PCFD) leads to a disruption of the medial peritalar ligaments with progressive loss of the medial arch and further valgus alignment of the subtalar and tibiotalar joints. This ultimately leads to peritalar instability with subtalar and tibiotalar osteoarthritis. Conventional joint sparing reconstruction methods alone may not correct the valgus heel alignment. Some have suggested subtalar fusion (SF) with or without combined medializing calcaneal osteotomy (MCO) as an option. Although SF provides a more effective correction of hindfoot alignment, a resultant increase in valgus moment arm with a larger strain on the medial ankle ligament has been reported. The study aim is to investigate the efficacy of a combined MCO with SF and medial tibionavicular ligament (TNL) reconstruction on restoring peritalar stability. Methods: Ten fresh-frozen cadaveric foot specimens were employed to create a severe PCFD model. Reflective markers were placed on the tibia, talus, navicular, calcaneus, and first metatarsal. A multiple-camera motion capture system (OptiTrack, Prime13) was utilized to document peritalar joint kinematics. Severe AAFD model was created by sectioning the medial capsuloligamentous complex followed by cyclic axial loading. Sequential surgical procedures were performed, including MCO, SF, MCO + SF, and MCO + SF + medial tibionavicular ligament (TNL) reconstruction. Subtalar joint coronal angle, tibiotalar coronal angle, forefoot abduction axial angle, and talo-first metatarsus (Meary's) lateral angle were calculated for each sequential procedure and compared to the severe flatfoot model. The kinematic changes were calculated between groups utilizing a custom MatLab code and statistical significance was determined using a one-way ANOVA and a Tukey's multiple comparison test. Results: The subtalar joint valgus angle of the severe PCFD model (mean 8.1°) was significantly reduced by the MCO+SF+TNL reconstruction (mean 3.2°, p = 0.019). The tibiotalar joint valgus angle of the severe flatfoot model (mean 4.4°) was significantly reduced by the MCO (mean 1.0°, p = 0.04), but increased after combined MCO with SF (mean 2.5°, p = 0.01). The increased valgus tibiotalar angle of the MCO+SF was reduced by adding TNL reconstruction (mean 0.75°, p = 0.027). Forefoot abduction angle was found to be significantly reduced in all reconstruction methods compared to the severe flatfoot model. Meary's angle was also significantly improved after the MCO+SF and MCO+SF+TNL reconstruction (P= 0.015 and 0.006, respectively). Conclusion: Although addition of SF to MCO improved forefoot abduction and Meary's angles of advanced PCFD model, it resulted in increased tibiotalar valgus angle. The subsequent increase in medial ligament strain may be reduced by adding TNL reconstruction which can support medial stability while improve kinematics in all planes. Addition of TNL may be considered when performing SF for correction of PCFD, especially when a residual valgus heel alignment remains.