Effect of surgical corrections on flexible and fixed severe flatfoot deformity studied through a dynamic model of the foot and ankle

Luigi Piarulli

doi:10.17918/00010881

Foot arch stability is primarily maintained by a combination of passive structures, such as ligaments, and active structures, consisting of muscles. These soft tissues work together to keep the foot in proper alignment, ensuring that the arch supports the body weight, during functional activities. When these supportive structures are damaged or injured, the arch begins to collapse, leading to a condition known as Acquired Adult Flatfoot Deformity. This collapse can vary in severity, with some cases presented as a flexible deformity, where the arch deformity occurs only when the foot is loaded, and a fixed deformity, where the arch collapse is permanent. The severity of deformity determines the appropriate treatment approach. For flexible deformities, tendon transfer surgeries are typically used to restore the function of the affected muscles. Fixed deformities generally require fusion surgeries to correct the bones alignment and prevent further collapse of the arch. The purpose of this study is to explore the contributions of key passive structures to arch stability and to assess and compare the effectiveness of different surgical treatments aimed at restoring the arch and maintaining its long-term stability. Previously developed and validated patient-specific models were used. To assess the role of key passive structures, long plantar ligament and plantar fascia, nine models obtained by nine normal feet were used. For the study of the treatment of flexible flatfoot, six models obtained from six feet were used. To simulate flexible flatfoot in these six models, the stiffness of key ligaments was reduced, and tendon transfer procedure was simulated. For the study of the treatment of fixed flatfoot, five models from the feet of five patients were used. These patients underwent pre-surgical and post-surgical CT scans. Dynamic computational models were created for four groups: pre-operative, single fusion, triple fusion, and triple fusion with additional maneuver. Once the effect of the surgeries on foot architecture was assessed, the response of the foot to bodyweight was evaluated. The parameters used to evaluate all these simulations for all the goals included morphological angles between the bones, forces in the long plantar ligament and plantar fascia, contact positions between the talus and tibia, and talonavicular coverage. The results show that both long plantar ligament and plantar fascia are crucial for maintaining arch height, with complete collapse occurring only when both ligaments are absent. In flexible flatfoot deformity, tendon transfer successfully restored the medial longitudinal arch height, compensating for both muscular and ligamentous dysfunction. However, the surgery did not address forefoot abduction or hindfoot alignment. In fixed flatfoot deformity, the results suggest that single fusion sufficiently corrects the foot architecture, without running the risk of overcorrection. Other techniques, while leading to a more normal foot morphology, overcorrecting the foot by reducing talonavicular coverage and increasing foot rigidity. These findings highlight the importance of personalized surgical approaches tailored to the patient's specific deformity, improving treatment outcomes while minimizing risks.

Effect of surgical corrections on flexible and fixed severe flatfoot deformity studied through a dynamic model of the foot and ankle

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Effect of surgical corrections on flexible and fixed severe flatfoot deformity studied through a dynamic model of the foot and ankle

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