Stability of the arch of the foot.

We defined the relative contributions of six ligaments in stabilizing the arch of the foot: plantar aponeurosis, long-short plantar ligaments, plantar calcaneonavicular ligament (spring ligament), medial talocalcaneal ligament, talocalcaneal interosseous ligament, and tibionavicular portion of the deltoid ligament. Nineteen fresh-frozen human foot specimens were used. A load of 445 N was applied axially to simulate standing-at-ease posture. Three-dimensional positions of tarsal bones before and after ligament sectioning were determined with the use of a magnetic tracking device. The motions were presented in the form of screw axis displacements, quantitating rotation, and axis of rotation orientation. After sectioning one structure, the arch did not collapse on any specimen and there was no obvious change by visual inspection. There were, however, measurable changes in tarsal bone position. Metatarsal-to-talus total rotation difference was greatest with spring ligament and deltoid ligament sectioning, with an average of 2.1 degrees +/- 1.7 degrees and 2.0 degrees +/- 0.2 degree difference, respectively. Calcaneus-to-talus rotation difference was greatest with talocalcaneal interosseous ligament sectioning, with an average of 1.7 degrees +/- 1.5 degrees. The spring ligament, deltoid ligament, and talocalcaneal interosseous ligament were most important for arch stability.