Altered Range of Motion and Plantar Pressure in Anterior and Posterior Malaligned Total Ankle Arthroplasty: A Cadaveric Gait Study.

BACKGROUND: Malaligned ankle arthroplasty components have been associated with increased postoperative pain and reduced ankle range of motion. With this study, we aimed to quantify how anterior and posterior malalignment of the talar component affects foot bone kinematics and plantar pressures in a dynamic, cadaveric gait simulation. METHODS: Ten cadaveric foot specimens received a modified ankle prosthesis. Proper alignment was defined as the prosthesis being neutral to a plantigrade foot, where varus/valgus and internal/external rotation were determined using the tibial alignment guide from the prosthesis manufacturer. Axially loaded lateral radiographs were made to measure the tibiotalar ratio (TTR) preoperatively and postoperatively. Specimens were prepared for gait simulation and mounted into the robotic gait simulator. Foot bone kinematics and plantar pressures were measured for each alignment condition. RESULTS: Posterior malalignment of the talar component decreased mean sagittal-plane range of motion (p ≤ 0.0005) in the tibiotalar joint (by up to 3.9°) and in the first metatarsophalangeal joint (by up to 7.7°) and increased sagittal-plane range of motion (p ≤ 0.0005) in the calcaneocuboid joint (by up to 2.0°). Posterior malalignment increased mean transverse-plane range of motion (p ≤ 0.0005 and p = 0.012) in the tibiotalar joint (by up to 2.3°) and in the calcaneocuboid joint (by 2.3°). Posterior malalignment decreased mean peak plantar pressures (p = 0.001 and p = 0.013) under the hallux and the first metatarsal (by up to 82.1 and 110.1 kPa, respectively) and increased (p = 0.012 and p = 0.0006) peak plantar pressures under the third metatarsal and the hindfoot (by 23.0 and 47.8 kPa, respectively). Anterior malalignment decreased (p = 0.0006) mean hindfoot peak plantar pressure (by 127.7 kPa). Anterior and posterior malalignments shifted center of pressure laterally during early and late stance. The TTR weakly to moderately correlated with range-of-motion changes in the tibiotalar, calcaneocuboid, and first metatarsophalangeal joints (r ≤ 0.39) and weakly correlated with plantar pressure changes under the hindfoot, the first metatarsal, and the hallux (r ≤ 0.15). CONCLUSIONS: Anterior and posterior malalignments of the talar component altered foot bone kinematics and plantar pressures. Mild malalignments produced fewer significant differences than moderate and extreme malalignments. A greater number of significant differences were found for posterior malalignments than for anterior. The TTR weakly to moderately correlated with changes in range of motion and plantar pressures. CLINICAL RELEVANCE: The observed changes in range of motion and plantar pressures may explain why malaligned ankle arthroplasties are associated with unfavorable clinical outcomes and poor prosthesis longevity. Posterior malalignments may produce worse clinical outcomes than anterior malalignments.

Hind- and midfoot bone morphology varies with foot type and sex.

Foot type has been associated with pain, injury, and altered gait mechanics. Morphological variations in foot bones due to foot type variation may impact surgical and therapeutic treatments. The purpose of this study was to utilize principal component analysis (PCA) to determine how morphology of the hind- and midfoot bones differs among foot types and sex. The calcaneus, talus, navicular, and cuboid were segmented using previously obtained computed tomography (CT) scans and converted to surface models. The CTs were sorted into four foot types-cavus, neutrally aligned, asymptomatic planus, and symptomatic planus. Morphometric shape analysis software (Geomorph) was used to perform a PCA to determine which components varied between foot types and between sexes. The calcaneus showed planus feet of both types to have calcanei that have decreased height and increased length compared to neutrally aligned feet. The talus demonstrated increased posterior mass for cavus feet compared to neutrally aligned feet. For the navicular, symptomatic planus had a more posteriorly positioned tuberosity and were wider than asymptomatic planus feet. The cuboid did not exhibit any differences between foot types. Sex differences, found only at the talus and navicular, were subtle. PCA is an objective technique that helped elucidate differences in bone morphology between foot types and sex without needing to determine the features of interest before comparing groups. Understanding these variations can help inform diagnosis of foot pathologies and surgical protocols as well as improve computer models of the foot. Published 2018. This article is a U.S. Government work and is in the public domain in the USA. J Orthop Res 9999:1-16, 2019.