The Anatomy of Cavus Foot Deformity - NUCRE

192 AMINIAN & SANGEORZAN
In midstance, the subtalar joint assumes a valgus position, unlocking the midtarsal
joints. This allows partial stress distribution. At the end of the stance
phase, there is metatarsophalangeal dorsiflexion and locking of the midtarsal
joints. The elevated arch becomes a rigid lever. The posterior leg muscles
permit push-off and provide energy for forward propulsion.
Cavus foot mechanics
Pes cavus was first described in the American literature in 1885 by Shaffer
[1]. Clinically it is an abnormal elevation of the medial arch in weight bearing.
Biomechanically, ‘‘cavus’’ is defined as a varus hindfoot, high calcaneal
pitch, high-pitched midfoot (defined by the navicular height), and plantarflexed
and adducted forefoot (Fig. 1 A–C).
Fig. 1. Three-dimensional model of the cavovarus foot. This model was created from the CT
scan of a severe cavus. (A) Viewed from above, the near complete overlap of the talus and calcaneus
is seen; the navicular is forced medially. (B) Viewed from front to back, the twisting of
the midfoot is apparent with inversion of the forefoot relative to the hindfoot. In this model
there is dramatic plantarflexion of the first ray. (C) Viewed from the medial side, the hyperplantarflexion
of the first ray is more apparent as well as the position of the navicular on the superior
and medial surface of the talus.