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.

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 (r2 ≤ 0.39) and weakly correlated with plantar pressure changes under the hindfoot, the first metatarsal, and the hallux (r2 ≤ 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.

Category: Hindfoot Introduction/Purpose: While there are established associated conditions, the intrinsic cause of symptomatic adult flatfoot is not known. There are published data suggesting that the relationship of the hindfoot bones in acquired flatfoot are subluxated. And there is some support in 2 D for the concept that the bones are shaped differently in flatfoot but the complexity of bone shape and human variation makes comparisons difficult. The purpose of this study was to utilize principal component analysis (PCA) to determine whether morphology of the hind- and midfoot bones differs in neutral and plano-valgus feet. Methods: Forty subjects (23 male and 17 Female, average age 52.6 +/- 8.9) with no history of injury or surgery underwent bilateral foot WB CT scan for another study. The talus, calcaneus, navicular and cuboid were segmented into bone models from these previously acquired CT images. Morphometric Shape analysis software (Geomorph) was used to assess shape variations among foot types using Principal component analysis (PCA). PCA is a statistical modelling technique used to study variation in the shape of structures that are difficult to compare and bring out strong patterns in a dataset objectively. Forty feet had been classified into 4 foot groups prior to this study; neutral, cavus, asymptomatic flatfoot and symptomatic flatfoot. This study included the painful flatfeet and neutral feet. Each bone was compared between the feet that were flat and those that were neutral. Comparisons were made between men and women as well. Results: There were no differences between groups in age or sex. There were 38 principle components identified. The first two PC accounted for 38% of the calcaneal variation and 33% of the talar variation. Subtle differences between men and women were found only at the talus and navicular. The cuboid did not exhibit any differences between foot types. The navicular in symptomatic planus had a more posteriorly positioned tuberosity (tuber wrapped around the medial side of the talus) and were wider than neutral feet. The calcaneus showed planus feet to have calcanei that have decreased height and increased length compared to neutrally aligned feet. The cross -sectional area of the calcaneus was reduced compared to neutral feet. The talar shape was not different in the PC. Conclusion: A flat foot is present in over 20% of the population and most often not symptomatic. The root cause of symptomatic adult plano valgus foot is not known and is likely multi factorial. The study demonstrates that there is intrinsic difference in the shape of the calcaneus and navicular bones in flat foot. it is possible that the catalyst for collapse is bony rather than soft tissue.