Contact mechanics of normal tarsometatarsal joints

Background: The current treatment of tarsometatarsal joint injuries is associated with suboptimal long-term results. The objective of the present study was to measure the contact mechanics of the tarsometatarsal joints in normal adult cadaveric feet in order to develop a foundation for more effective treatment. Methods: Six fresh cadaveric lower legs and feet were subjected to four different axial compressive loads (0.5, 1.0, 1.5, and 2.0 times body weight) at each of five different positions. For each position, load, and tarsometatarsal joint, the contact pressures and areas were measured with use of pressure-sensitive film. Contact forces were calculated from the ratio of pressure to area. Contact pressure, area, and force were analyzed as a function of load, the specific tarsometatarsal joint, and foot position. Results: The forces across these joints ranged from 2 to 541 N, but pressures ranged only from 0.5 to 5.7 MPa. In general, changes in load and foot position, in both the sagittal and the frontal plane, were associated with changes (p < 0.05) in tarsometatarsal joint contact areas and forces. In contrast, the contact pressures across these joints varied minimally with changes in load and foot position. Conclusions: These data suggest that the tarsometatarsal joints are designed to regulate pressure in each joint by means of two mechanisms: (1) at small loads, an intrajoint mechanism regulates tarsometatarsal joint pressure by increasing contact area within the joint in response to increasing force, and (2) at larger loads, an interjoint mechanism engages to regulate tarsometatarsal joint pressure by redirecting force to other tarsometatarsal joints. Clinical Relevance: The data provide both absolute (normal contact forces, areas, and pressures) and relative (intrajoint and interjoint regulating mechanisms) performance (functional) criteria for the development of new treatments for diseased or traumatized tarsometatarsal joints.