A closed-loop cadaveric foot and ankle loading model.

Investigations of human foot and ankle biomechanics rely chiefly on cadaver experiments. The application of proper force magnitudes to the cadaver foot and ankle is essential to obtain valid biomechanical data. Data for external ground reaction forces are readily available from human motion analysis. However, determining appropriate forces for extrinsic foot and ankle muscles is more problematic. A common approach is the estimation of forces from muscle physiological cross-sectional areas and electromyographic data. We have developed a novel approach for loading the Achilles and posterior tibialis tendons that does not prescribe predetermined muscle forces. For our loading model, these muscle forces are determined experimentally using independent plantarflexion and inversion angle feedback control. The independent (input) parameters -- calcaneus plantarflexion, calcaneus inversion, ground reaction forces, and peroneus forces -- are specified. The dependent (output) parameters -- Achilles force, posterior tibialis force, joint motion, and spring ligament strain -- are functions of the independent parameters and the kinematics of the foot and ankle. We have investigated the performance of our model for a single, clinically relevant event during the gait cycle. The instantaneous external forces and foot orientation determined from human subjects in a motion analysis laboratory were simulated in vitro using closed-loop feedback control. Compared to muscle force estimates based on physiological cross-sectional area data and EMG activity at 40% of the gait cycle, the posterior tibialis force and Achilles force required when using position feedback control were greater.

Posterior calcaneal osteotomy with wedge: cadaver testing of a new procedure for insufficiency of the posterior tibial tendon.

Insufficiency of the posterior tibial tendon is challenging to treat. When the deformity is flexible, treatment options have included tendon transfer, often combined with a medial slide calcaneal osteotomy and/or a lengthening of the lateral column. Posterior calcaneal osteotomy has been shown to give correction, although not full correction. Lengthening of the lateral column also has been shown to give correction and has been used in the more severe flexible deformities, but it involves either fusion of the calcaneocuboid joint or risk of arthritis at this joint. An osteotomy combining the calcaneal medial slide with a lengthening of the lateral column at the same osteotomy site has been tested in the laboratory. This combined osteotomy provides a lengthening of the lateral column, but it is positioned away from the calcaneocuboid joint. In this study, the osteotomy was compared with a medial slide calcaneal osteotomy and an Evans lengthening of the lateral column, using a cadaver flatfoot model. Radiographic measurements were made to evaluate correction of the planovalgus deformity after each of these procedures. There was statistically significant improved correction with the new osteotomy compared with that in a standard medial slide, and correction was comparable to that in the lengthening of the lateral column. This combined osteotomy may be a reasonable alternative when more correction is desired than can be obtained from a medial slide alone and when the surgeon wishes to avoid an osteotomy near the calcaneocuboid joint.

Achilles tendon insertion: an in vitro anatomic study.

Seventeen adult fresh-frozen below-knee amputation cadaver specimens were studied. Calcific Achilles tendinitis was present in three specimens. After exposing the Achilles tendon insertion on the calcaneus, the insertion was outlined with waterproof paint. The specimens were photographed on a special plexiglass apparatus to highlight important findings. For the purpose of showing the length of insertion on lateral radiographs, lead beads were placed on the most superior and most inferior aspects of the insertion. All specimens showed that the tendon terminated at the medial and lateral bone borders of the calcaneus without significant extension around the medial or lateral wall. All specimens revealed a greater distance of insertion on the medial calcaneus than on the lateral side. In the specimens that had calcific Achilles tendinitis, the posterior bone surface of the spurs was devoid of tendinous insertion, instead, the insertion occurred between the spur and the posterior wall of the calcaneus. All spurs were located laterally at the most inferior border of the tendon insertion.

Lateral column lengthening with calcaneocuboid fusion: range of motion in the triple joint complex.

Lengthening the lateral column of the foot has been shown to correct flatfoot deformity. In adults, however, lengthening leads to calcaneocuboid arthritis. Lateral column lengthening with calcaneocuboid fusion, which lengthens the lateral column of the foot and prevents calcaneocuboid arthritis, was investigated in a cadaver model to determine the remaining range of motion in the talonavicular and subtalar joints. Inversion/eversion motion was produced by tendon pulls and the range of motion was measured in three dimensions using a magnetic space tracker. After lateral column lengthening with calcaneocuboid fusion, 48% of talonavicular and 70% of subtalar joint range of motion were preserved. Analysis of the inversion and eversion ranges of motion suggests that the lengthening fusion limits eversion more than inversion. These findings demonstrate the need for clinical investigation of this procedure, which could preserve motion in the talonavicular and subtalar joints, correct deformity, and obviate calcaneocuboid arthritis.