Biomechanics of the first ray. Part I. The effects of peroneus longus function: a three-dimensional kinematic study on a cadaver model.

The closed kinetic chain effects of peroneus longus (PL) activity on the medial column of the foot were investigated in seven fresh-frozen cadaver specimens using a three-dimensional radiowave tracking system. Specimens, consisting of the distal half of the leg and the intact ankle and foot, were mounted on a nonmetallic loading frame which allowed positioning of the foot to simulate midstance position of gait. The tibia and fibula were axially loaded to 400 N. Receiving transducers were attached to the first metatarsal, medial cuneiform, navicular, and talus. Tarsal movements were measured as specimens were axially loaded and midstance motor function was simulated using pneumatic actuators. Tensile loads of 0-150% of predicted maximum force were incrementally applied to the PL tendon. Three-dimensional data sets recording osseous positions and orientations were collected and analyzed. Significant frontal plane rotation of the medial column in the direction of eversion occurred when PL strength was increased (p = .0001). Increasing PL loads produced significant but less pronounced angular changes in the sagittal and transverse planes of the medial column. The patterns of motion suggest that PL creates an eversion "locking" effect on the first ray of the foot, stabilizing the medial column.