Cadaveric Simulation of Flatfoot and Surgical Corrective Techniques: The Evans versus the Z-osteotomy
Roush, Grant Corwin
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The main clinical purpose of this study is to compare two different surgical procedures, the Evans calcaneal osteotomy and the Z-osteotomy, both of which are used to correct Stage II (flexible) cases of flatfoot deformity. This work is a follow-up to a pilot study completed previously by the VA Center of Excellence for Limb Loss Prevention and Prosthetic Engineering (VA RR&D). In that study, the feet (both flat and corrected) were statically placed at mid-stance of the gait cycle and data were collected. Kinematic and kinetic comparisons were made to see how each surgery performed in restoring the foot to normal shape and function. This research looks to build on that study by using a fully dynamic <italic>in vitro</italic> simulation of the stance phase of gait. A process of ligament attenuation coupled with axial loading of the foot has been developed by our group to induce a flexible flatfoot on neutrally aligned cadaveric specimens. Previous research has shown the ligaments most involved in supporting the medial arch were the superomedial and inferomedial calcaneonavicular (spring), talocalcaneal interosseous, plantar naviculocuneiform, plantar first metatarsocuneiform, and anterior superficial deltoid ligaments. To induce weakening in our study, these ligaments were either sectioned or attenuated with multiple longitudinal incisions parallel to the fiber orientation, after which the foot was cyclically loaded from 10 N to body weight at 2 Hz until visual evidence of flatfoot was seen. In addition, X-rays were taken and clinical measurements were performed to assess foot shape initially, after the flattening procedure, and post-surgery. The repeatability of making these measures was also investigated. Gait simulation was performed with the robotic gait simulator (RGS) at the VA RR&D. The RGS was developed to allow for <italic>in vitro</italic> simulation of the stance phase of gait using cadaveric specimens. It has been shown to accurately simulate both the kinematics and kinetics of the foot during the stance phase of gait. Having a physiologically correct model will allow for the most accurate representation of <italic>in vivo</italic> gait currently possible, while also allowing the utilization of invasive measurement techniques (such as insertion of bone pins) or multiple surgical procedures that would otherwise be impossible on living human subjects. Results from this work have shown that our flatfoot model has the ability to create a mild Stage II flatfoot deformity in previously neutrally aligned cadaveric specimens. Additionally, evidence proved our process for collecting and measuring clinically relevant radiographic measures was highly repeatable. Both static radiographic evidence and dynamic simulation showed significant differences after lateral column lengthening, most notably an increase in lateral peak plantar pressures post-surgery, but there were few differences when comparing the two surgical procedures.
- Mechanical engineering