This study involved a biomechanical examination of the first and second tar-sometatarsal (TMT) joints. In the in vitro testing protocol, physiologic joint moments were applied to the first and second TMT joints of 10 cadaver specimens, which had been dissected to yield only the midfoot components comprising the tarsals, metatarsals, and associated ligaments. The isolated joints were placed in a 37 °C water bath and were independently cycled into and out of dorsiflexion, while angular displacement and resultant joint moments were collected. The specimens were sequentially cycled between zero and peak moment levels of 2.5, 5.0, 7.5, and 10 Nm, after which mean moment-angle curves were plotted for each TMT joint at each loading condition. Least-squares curve-fitting procedures, employing a root mean square error threshold of 0.005 Nm, were used to describe the average overall moment vs. angle relationship of each joint. Curves for the first and second TMT joints exhibited similar behavior. The joints displayed reasonably constant stiffness at low angles of dorsiflexion, followed by rapidly increasing stiffness at higher angles of dorsiflexion. These data provide new insight into the behavior of the TMT joints under load and are valuable for use in numerical models of the foot, as well as in the understanding and treatment of certain foot pathologies.
Center for Locomotion Studies, 29 Rec Bldg
Dept. of Kinesiology, The Pennsylvania State University, University Park, PA 16802
Dept. of Orthopaedics and Rehabilitation, The Pennsylvania State University, Hershey, PA 17033.