Number of Segments Within Musculoskeletal Foot Models Influences Ankle Kinematics and Strains of Ligaments and Muscles.

Multi-segment foot models (MFMs) are becoming a common tool in musculoskeletal research on the ankle-foot complex. The purpose of this study was to compare ankle joint kinematics as well as ligament and muscle strains that result from MFM with a different number of segments during vertical hopping. Ten participants were recruited and performed double-limb vertical hops. Marker positions and ground reaction forces were collected. Two-segment (2MFM), three-segment (3MFM), and five-segment MFM (5MFM) were used to calculate ankle kinematics and the strains of the anterior talofibular and calcaneofibular ligaments and of the soleus and gastrocnemius muscles. Ranges of motion and peak strains were analyzed with Kruskal-Wallis and post hoc tests, whereas the time-series of the ankle kinematics and ligament and muscle strains were analyzed with statistical parametric mapping. There were significant main effects for MFM in the talocrural joint range of motion and peak strains of ligaments and muscles. In addition, there were significant main effects for MFM in time-series data of the talocrural joint angle as well as for ligament and muscle strains. In all cases, the post hoc analyses showed that the 2MFM consistently overestimated the range of motion and tissue strains compared to the 3MFM and 5MFM, while 3MFM and 5MFM did not differ from each other in the most variables. This study showed that the number of segments in MFM significantly affects the biomechanical estimates of joint kinematics and tissue strains during hopping. Clinical significance: MFM that combine all foot structures beyond the talus into one segment likely overestimate ankle joint biomechanics. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2231-2240, 2019.