Where is the primate transverse tarsal joint? Chopart vs. Lisfranc

The concept of the transverse tarsal joint is typically associated with accommodative twists of the foot, and with a midfoot flexion known as the midtarsal break. The specific joints associated for these motions are often assumed, but are rarely validated. The two most common candidates are “Chopart’s Joint,” which separates the cuboid and navicular from the calcaneus and talus, and “Lisfranc’s Joint,” formed by a combination of all the tarsometatarsal joints. Both of these joints were initially identified as sites for surgical amputations and were not based on any presumed function. This study investigates the utility of these composite joints as sites of foot motion for humans and for some non‐human primates. Data were drawn from 3D kinematic evaluations of the cadaveric feet of 12 humans, 11 chimpanzees, and 11 baboons. Data were collected in response to an anterior‐posterior and medial‐lateral driving motion of the leg over the foot. Data were derived from rigid cluster tracking of individual foot bones during an anterior‐posterior motion of the leg, typically associated with dorsiflexion‐plantarflexion, and a medial‐lateral leg motion, associated with inversion‐eversion and/or supination‐pronation. Data were analyzed using the Functional Alignment procedure to derive the orientation of axes of rotation for the involved joints. Results show that the axis orientation of Chopart’s Joint is not a good compromise between the very different motions of the talonavicular and calcaneocuboid joints in any primate. This observation applies to results drawn from both anterior‐posterior and medial‐lateral driving motions. The rotational axis of Lisfranc’s Joint in the different primates is also quite divergent from the individual tarsometatarsal joint axes when responding to the anterior‐posterior driving action, but the axis is more parallel to those of the tarsometatarsal joints during the medial‐lateral driving action. However, it should be noted that the joint axes of the individual tarsometatarsal joints are almost identical, while the Lisfranc’s Joint axis stands apart. These results show that the individual joint actions are more complicated than their composite forms expressed as Chopart’s or Lisfranc’s joints. The concept of single “transverse tarsal” joint may not be functionally justified, within the human animal or as a basis for comparison of humans and non‐human primates. Researchers should reassess how well these traditional joint concepts apply to their specific questions of foot biomechanics. The author conveys his respect and gratitude to the persons whose remains are associated with this project.