Effects of Degree of Surgical Correction for Flatfoot Deformity in Patient-Specific Computational Models.

A cohort of adult acquired flatfoot deformity rigid-body models was developed to investigate the effects of isolated tendon transfer with successive levels of medializing calcaneal osteotomy (MCO). Following IRB approval, six diagnosed flatfoot sufferers were subjected to magnetic resonance imaging (MRI) and their scans used to derive patient-specific models. Single-leg stance was modeled, constrained solely through physiologic joint contact, passive soft-tissue tension, extrinsic muscle force, body weight, and without assumptions of idealized mechanical joints. Surgical effect was quantified using simulated mediolateral (ML) and anteroposterior (AP) X-rays, pedobarography, soft-tissue strains, and joint contact force. Radiographic changes varied across states with the largest average improvements for the tendon transfer (TT) + 10 mm MCO state evidenced through ML and AP talo-1st metatarsal angles. Interestingly, 12 of 14 measures showed increased deformity following TT-only, though all increases disappeared with inclusion of MCO. Plantar force distributions showed medial forefoot offloading concomitant with increases laterally such that the most corrected state had 9.0% greater lateral load. Predicted alterations in spring, deltoid, and plantar fascia soft-tissue strain agreed with prior cadaveric and computational works suggesting decreased strain medially with successive surgical repair. Finally, joint contact force demonstrated consistent medial offloading concomitant with variable increases laterally. Rigid-body modeling thus offers novel advantages for the investigation of foot/ankle biomechanics not easily measured in vivo.

A population of patient-specific adult acquired flatfoot deformity models before and after surgery.

Following IRB approval, a cohort of 3-D rigid-body computational models was created from submillimeter MRIs of clinically diagnosed Adult Acquired Flatfoot Deformity patients and employed to investigate postoperative foot/ankle function and surgical effect during single-leg stance. Models were constrained through physiologic joint contact, passive soft-tissue tension, active muscle force, full body weight, and without idealized joints. Models were validated against patient-matched controls using clinically utilized radiographic angle and distance measures and plantar force distributions in the medial forefoot, lateral forefoot, and hindfoot. Each model further predicted changes in strain for the spring ligament, deltoid ligament, and plantar fascia, as well as joint contact loads for three midfoot joints, the talonavicular, navicular-1st cuneiform, and calcaneocuboid. Radiographic agreement ranged across measures, with average absolute deviations of <5° and <4 mm indicating generally good agreement. Postoperative plantar force loading in patients and models was reduced for the medial forefoot and hindfoot concomitant with increases in the lateral forefoot. Model predicted reductions in medial soft-tissue strain and increases in lateral joint contact load were consistent with in vitro observations and elucidate the biomechanical mechanisms of repair. Thus, validated rigid-body models offer promise for the investigation of foot/ankle kinematics and biomechanical behaviors that are difficult to measure in vivo.