The Anatomy of Cavus Foot Deformity - NUCRE

The Anatomy of Cavus Foot Deformity
Arash Aminian, MD a, *, Bruce J. Sangeorzan, MD b,c,d
a St. Jude Medical Heritage, 100 E. Valencia Mesa Drive,
Suite 105, Fullerton, CA 92835, USA
b VA Center of Excellence for Limb Loss Prevention and Prosthetic Engineering,
VAPSHCS, 1660 S Columbian Way, Seattle, WA 98195, USA
c University of Washington, 1959 NE Pacific, Seattle, WA 98195, USA
d Department of Orthopaedics and Sports Medicine, Harborview Medical Center,
325 Ninth Avenue, Box 359799, Seattle, WA 98104, USA
The term ‘‘cavus foot’’ is used to describe a spectrum of foot shapes that
have in common a high arch. The arch may be high because of a high pitch
angle of the hindfoot, excessive plantar flexion of the forefoot, or excessive
bend in the midfoot. It may be driven by a narrow talo-calcaneal angle and
the midfoot may have a torsional component in complex cases. The components
of cavus are increased pitch and varus of the hindfoot, plantar flexion
of the midfoot, and varus and adduction of the forefoot. The cavus shape is
associated with changes in the mechanics of the foot. It is less flexible and
balanced than a neutral foot. Although one fifth to one quarter of the population
has a cavus foot [1], there is little anatomic description in the literature.
This manuscript describes the anatomy and function of cavus foot.
Normal foot mechanics
Foot Ankle Clin N Am
13 (2008) 191–198
The gait cycle is divided into two phases: stance phase and swing phase. It
begins when one foot contacts the ground and ends when that foot contacts
the ground again. Stance phase accounts for approximately 60%, and swing
phase for approximately 40% of the gait cycle. Stance phase of gait is divided
into four periods: heel contact, midstance, terminal stance, and preswing.
Swing phase is divided into three periods: initial swing, midswing,
and terminal swing.
During the normal gait cycle the arch of a normal foot changes shape. At
heel strike, there is medial rotation of the forefoot and inversion of the heel.
* Corresponding author.
E-mail address: aminian75@hotmail.com (A. Aminian).
1083-7515/08/$ - see front matter Ó 2008 Elsevier Inc. All rights reserved.
doi:10.1016/j.fcl.2008.01.004 foot.theclinics.com

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.

THE ANATOMY OF CAVUS FOOT DEFORMITY
Fig. 2. The front view of a three-dimensional model of a cavus foot, left, shows the rotation of
the foot, the varus of the forefoot, and the narrow talo-calcaneal angle. The lateral view on the
right shows the navicular perched on the superior surface of the cuboid. This prevents flexion of
the midfoot. The foot is in varus and the fifth ray is overloaded.
When the talo-calcaneal angle is narrowed, the navicular moves to a position
superior to the cuboid instead of medial to it. This makes it difficult
for the Choparts joint to function. During the gait cycle, the foot remains
locked in hindfoot inversion and forefoot varus throughout the stance
phase, causing less stress dissipation. This can result in metatarsalgia, stress
fracture of the fifth metatarsal, plantar fasciitis, medial longitudinal arch
pain, and ilio-tibial band syndrome [2] and instability.
This locking and unlocking of the Choparts joint is a critical element in
the cavus foot. The talus is the connector of the foot and the ankle. In
Fig. 3. This is a view from the front (ventral) into the Choparts joint from three patients. A
volume has been generated from the talus (in green) and calcaneus (in blue) of (from left to
right) a flexible flat foot, a neutrally aligned foot, and a cavus foot. The tarsal and metatarsal
bones have been removed. The red line indicates an approximate axis of the combined axes of
the talo-navicular and calcaneo-cuboid joints. Note that the cavus foot (right) has an axis that
blocks chopart joint motion.
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194 AMINIAN & SANGEORZAN
Fig. 4. Forefoot-driven hindfoot varus mechanics. (A) Plantarflexed first ray leading to an inversion
thrust of the hindfoot. (B) Normal forefoot with hindfoot in neutral position.
a neutral or flat foot, the foot rotates around the talus. The cuboid follows
the calcaneus. In a neuromuscular cavus foot, the calcaneus is rotated internally
beneath the talus resulting in a narrow anterior-posterior talocalcaneal
angle. Since the cuboid follows the calcaneus, the cuboid is plantar
Fig. 5. Pressure data from the right foot of three individuals with different types of cavus foot.
Light blue areas are low pressure; red areas are the highest pressure. The foot on the far left is
a subtle cavus foot with forefoot-driven cavus. The first ray is hyper-plantarflexed resulting in
high pressure under the first metatarsal head with little under the fourth and fifth. The middle
foot shows a foot with a lot of hindfoot rotation and pitch and midfoot rotation resulting in
increased pressure under the heel and the lateral border of the foot. The foot on the right is
so severe that only the lateral border bears significant weight.

to the navicular, not beside it. This locks the midfoot and overloads the
lateral side of the foot (Fig. 2).
Another way to look at Chopart function is to view the foot from the
front with the forefoot removed (Fig. 3). If an axis drawn through the
two joints is parallel to the ground, there will be relatively free flexion.
The more the axis approaches a vertical orientation, the less flexion will
be possible (see Fig. 3).
Pathologic mechanics
THE ANATOMY OF CAVUS FOOT DEFORMITY
Cavus foot deformity rarely presents in the young child (younger than
3 years) but may develop as the child grows. The etiology can be attributed
to the brain, spinal cord, peripheral nerves, or to structural problems of the
foot. When motor imbalance begins before maturation of the skeleton, there
can be substantial change in healthy bone morphology. When cavus is
acquired after skeletal maturity, there may be little or no change in the morphology.
Two thirds of adults with symptomatic cavus foot have an underlying
neurologic condition, most commonly Charcot-Marie-Tooth (CMT)
disease [3,4].
Mechanically, cavus deformity can be a result of a plantarflexed first ray.
Studies suggest that patients with CMT have early degeneration of the
Fig. 6. Plantar footprint of a cavus midfoot. This is a black-and-white image of a cavus foot
viewed from below through plexiglass. The part of the foot in contact with the glass is represented
by red. The midfoot is rotated into varus so that the first and second metatarsals are
not in contact with the ground during standing.
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196 AMINIAN & SANGEORZAN
Fig. 7. Talo-first metatarsal relationship. (A) Cavus foot. (B) Normal foot. (C) Flat foot.
Fig. 8. Lateral radiograph of a cavus foot deformity. (A) Preoperatively, showing a ‘‘flat-topped’’
talus and a posteriorly displaced fibula. (B) Postoperatively (lateralizing calcaneal osteotomy
and first tarso-metaratsal dorsiflexion osteotomy), showing restoration of the malleolar
relationship and the dome of the talus.

intrinsic muscles of the foot. With the lumbrical muscles not acting to stabilize
the metatarsophalangeal joints (MTP), the unopposed extensor digitorum
longus hyperextends the unstable lesser toes at the MTP joint while the
flexor digitorum longus and brevis flex the phalanges. The plantarflexed
metatarsal heads and plantar fascia shortening amplify forefoot equinus.
Eccentric hallucal muscle activity and the mobile lever arm of the first ray
lead to first metatarsal plantarflexion. Over time, the flexible plantarflexed
first ray becomes fixed leading to secondary hindfoot varus. The Achilles
tendon becomes a secondary invertor and becomes contracted. With heel inversion,
the lateral foot supinates and the peroneal longus depresses the first
ray to permit the foot to assume a tripod position and a plantigrade foot.
When untreated, the increasing muscle imbalance converts a flexible foot deformity
to a fixed deformity (Fig. 4).
Other causes of cavus deformity include chronic ankle stability with
a varus tilt of the mortise and midfoot deformity owing to muscle imbalances.
Midfoot cavus can be a result of anterior tibialis or posterior tibialis
spasticity. The shape of the foot varies with the cause and duration of the
motor imbalance that created the deformity (Figs. 5 and 6).
Radiographic signs
Radiographic hallmarks of a cavus deformity include the following:
Increased calcaneal pitch (measured between a line along the undersurface
of the calcaneus and the floor; normal is 30 ).
Increased angle of Meary (measured by the long axis of the talus and
first metatarsal) (Fig. 7).
Increased navicular height.
Increased Hibbs angle (measured by a line through the axis of the calcaneus
and the first metatarsal; in normal feet the Hibbs angle is !45 and
in cavus feet it is near 90 ).
A posterior fibula with a ‘‘flat-topped’’ talus. These appearances are artifactual
because with a cavus deformity, a standard lateral view is in fact
an oblique view (Fig. 8) [5–11].
Summary
THE ANATOMY OF CAVUS FOOT DEFORMITY
The most common type of cavus foot is cavovarus with elevated arch,
plantarflexed first ray, and a hindfoot varus. Initially the deformity is flexible,
but over time the deformity develops into a fixed bony deformity with
arthrosis. The goals of surgery are to create a plantigrade, mobile, pain-free,
and more stable foot. This is accomplished through osteotomies, muscle
transfers, and fusions. Understanding the anatomy is key to understanding
treatment.
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