Meeting Abstract
The human foot has evolved to facilitate obligate bipedal locomotion. There are many theories but little data on the in vivo function of the bones in the foot and how they contribute to efficient bipedal locomotion. For example, the talus serves as the mechanical link between the hindfoot, midfoot, and proximal segments but its in vivo function during locomotion has never been non-invasively measured. The purpose of this study was to use a unique dataset of in vivo foot bone surfaces in motion to understand how the talus inverts during loading, and then everts during propulsion. The talus is uniquely passive because its motion is dictated by ligament and cartilage contact forces. Three or more tantalum beads were inserted into the talus, calcaneus, tibia, fibula, cuboid, navicular and the first metatarsal. A CT scan was acquired to generate bone surface files and digitize the beads. The beads were then tracked using biplanar videoradiography (250 Hz) during hopping and jogging. Ligaments were modeled using anatomical texts and bony landmarks. We found that the cervical ligament (CL) resists eversion while the anterior tibiotalar part of the deltoid ligament (DLAT) resists inversion. We further examined whether these two ligaments act to balance each other by computing moment arms and ligament elongation. The CL and DLAT had opposite moment arms. The moment vectors were oriented nearly opposite to each other (175+/-2 degrees). Opposing movements elongated these ligaments as well. Coupling this information with rotation axes may enable comparative studies that can infer subtalar and midtarsal function from ligament insertion locations. This information can be further explored to determine how these ligaments may have controlled the talus in early humans leading to a greater understanding of the evolution of bipedal gait in humans.
