Cadaveric Simulation of Flatfoot and Surgical Corrective Techniques: The Evans Osteotomy vs the Z-Osteotomy

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Background: Progressive collapsing flatfoot deformity (PCFD) describes the pathologic form of a flatfoot (pes planus). Pes planus is often treated with lateral column–lengthening (LCL) procedures such as the Evans LCL. The Z-osteotomy has been explored as an alternative to the Evans LCL. We aim to compare bone position using radiographs and dynamic movement using a robotic gait simulator (RGS). Methods: Flatfoot was produced in cadaveric specimens by attenuating medial arch supporting ligaments and cyclically loading through the tibia. Clinical diagnostic measures from radiographs were used to assess foot shape. Each flatfoot underwent testing on the RGS with ground reaction forces scaled to 25% of the donor’s body weight and the stance phase simulated 6 times slower than physiologic gait (4.09 seconds). After flatfoot data collection, one foot in each pair received either the Evans LCL or Z-osteotomy. Postoperative radiographs were taken, and the feet were again tested on the RGS. Kinematic and kinetic data were collected and compared for both flatfoot and postsurgical trials. Results: All radiographic parameters were significantly ( P < .05) different after the flattening procedure, indicating arch collapse, forefoot abduction, and hindfoot eversion. The calcaneal pitch angle decreased, although not to the level seen in physiologic flatfoot. Changes toward arch restoration were seen in the radiographic parameters after surgeries, but there were no radiographic differences between surgery type for the number of specimens we tested (7 pairs). Peak pressure under the lateral forefoot significantly ( P < .05) increased after both surgeries but did not differ between procedures. Kinematic data only showed a few differences between the Evans and the Z-osteotomy. Conclusion: Radiographic evidence demonstrated that our model produced a mild flatfoot from neutrally aligned cadaveric specimens, and postsurgical feet showed significant improvement ( P < .05). Few differences between the surgical techniques were seen in the kinematic and kinetic data. Clinical Relevance: This cadaveric simulation study found that the Evans and Z-osteotomies are similar in their ability to biomechanically address mild flatfoot.

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