Calcaneal lengthening: investigation of deformity correction in a cadaver flatfoot model.

Background: Evans showed that lengthening the lateral column by inserting structural bone graft into the anterior calcaneus could correct abduction and valgus deformity in flatfoot. To better understand the mechanism of correction and the three-dimensional effect of this procedure a cadaver study was done.

Methods: Three cadaver flatfoot models were used. Computed tomographic (CT) scans were made of each specimen before and after lengthening. Data from these scans were used to determine the center of volume of the talus, navicular, cuboid, and calcaneus. The angular and translational motions for each bone were determined.

Results: On average, relative to the talus, the navicular moved 18.6 degrees of rotation in adduction, 2.6 degrees of rotation in pronation, and 3.4 degrees in plantarflexion. The average translation was 5.6 mm medial, 0.4 mm posterior, and 1.8 mm plantar. The cuboid moved an average of 24.2 degrees of rotation in adduction and lengthening, 13.9 degrees in pronation, and 1.9 degrees in plantarflexion. The average translation was 9.4 mm medial, 2.6 mm distal, and 1.5 mm plantar. The calcaneus moved an average of 4.4 degrees of rotation in adduction, 0.1 degrees of rotation in eversion, and 1.3 degrees of plantarflexion. The average translation was 3 mm medial and 0.7 mm posterior with no plantar translation.

Conclusions: The mechanism of Evans calcaneal lengthening involves adduction and plantarflexion of the midfoot relative to the hindfoot. The cuboid and navicular appear to move as a unit. The shape of the talar head, axis of the subtalar joint, degree of initial deformity, competence of plantar soft tissues, such as the long plantar ligament, and adequate length of the Achilles tendon are important. Knowing what qualitative three-dimensional changes take place allows a better understanding of the mechanics of the procedure and its possible applications.