Surgical Reconstruction of Progressive Collapsing Foot Deformity Restores Kinematics during Simulated Level Walking

CATEGORY: Basic Sciences/Biologics; Hindfoot INTRODUCTION/PURPOSE: Progressive collapsing foot deformity (PCFD) is a complex 3-dimensional pathology with a wide variety of surgical treatments. Regardless of technique, operative management of PCFD aims to restore normal foot architecture with attention to avoid the consequences of under- or over-correction. However, current methods of evaluating PCFD correction rely on static measurements, which do not assess dynamic function of the foot. Recent advances in robotic technology allow for the dynamic assessment of surgical correction of PCFD. This study sought to assess the effects of 2 osteotomies for PCFD, the medializing calcaneal osteotomy (MCO) and lateral column lengthening (LCL), on kinematics and plantar pressure during simulated gait. We hypothesized that the combination of LCL and MCO would restore joint kinematics and plantar pressure values to normal levels. METHODS: Twelve cadaveric mid-tibia specimens (mean age 73 years, 8 female) were loaded on a 6-degree of freedom robotic gait simulator. Ground reaction forces and muscle forces were optimized utilizing an established iterative process. An 8-camera motion capture system was utilized to calculate joint kinematics using reflective markers attached by k-wires into bone. Plantar pressures were recorded using a pedography mat attached to the force platform. Testing was performed first in the native intact state, and again after creation of the flatfoot model. After flatfoot testing, surgical reconstruction and testing were performed in stages with MCO, and LCL with sequential 6mm and 8mm grafts. Bias-corrected bootstrapped 95% confidence intervals were calculated from the repeated measures difference between normal, flatfoot, post-MCO, post-MCO and post-reconstructive conditions. Center of plantar pressure excursion index (CPEI) was calculated and compared between conditions using a repeated measures ANOVA with Tukey post hoc analysis. RESULTS: Overall, surgical correction restored kinematics to normal levels (Figure). MCO alone resulted in statistically significant improvement in subtalar eversion in the first 20% of stance, and post-MCO subtalar kinematics were statistically similar to normal. LCL (either 6mm and 8mm) alone did not significantly correct talonavicular abduction after PCFD. However, in conjunction with MCO, LCL was able to significantly correct talonavicular kinematics throughout the majority of stance phase, with kinematics statistically similar to normal levels. Each surgical step (LCL 6mm, LCL 8mm, MCO) resulted in sequential lateralization of the center of plantar pressure. At the culmination of surgical reconstruction (MCO + LCL), plantar pressure was significantly corrected compared to PCFD (P<0.0001). After surgical reconstruction, CPEI was slightly increased (lateralized) in comparison to normal, but was not significantly different from the normal state. CONCLUSION: The findings from this study support our hypothesis that surgical reconstruction of PCFD via MCO and LCL restores normal level walking kinematics. While the isolated effect of MCO and LCL resulted in significant changes in subtalar and talonavicular kinematics, the synergistic effect of combining MCO and LCL were most effective in restoring normal kinematics. However, lateralization of plantar pressure after combining MCO and LCL compared to the normal condition indicates the potential for overload of the lateral column, as described previously. Therefore, surgeons should be cautious in increasing osteotomy size at the lateral column to avoid overload.