The term “pes cavus” or “cavus foot” is used to describe a wide spectrum of foot shapes that have an abnormal elevation of the medial longitudinal arch [4]. High arch of the foot is frequently associated with hindfoot varus, forefoot adduction and plantar flexion, and ankle equinus.

The etiology is most frequently attributed to the neuromuscular disorders involving brain, spinal cord, or the peripheral nerves. Two thirds of adults with symptomatic cavus foot have an underlying neurological condition [5]. Among them, Charcot-Marie-Tooth (CMT) disease, a hereditary sensory motor neuropathy, is most frequently reported. The probability of a patient who has bilateral cavovarus feet being diagnosed with CMT is 78% [6].

The progressive muscle involvement from distal to proximal, most frequently affects the intrinsic muscles, the tibialis anterior, and the peroneus brevis. Extensor hallucis longus is relatively spared. Relative weakness in one of the two opposing muscles causes muscle imbalance and structural deformity. Structural deformation is more substantial when the motor imbalance begins before maturation of the skeleton [4, 7].

Muscle imbalance can occur between the extrinsic and intrinsic muscles, between the posterior tibial and the peroneus brevis muscles, and between the anterior tibial and the peroneus longus muscles. Weak anterior tibial relative to the peroneus longus results in plantar flexion of the first metatarsal. The flexion power of the peroneus longus becomes much stronger as the foot is positioned in equinus [2, 8]. Recruitment of extensor hallucis longus produces cock up deformity of the great toe, which further depresses the metatarsal head. With weak intrinsic muscles, the unopposed extensor digitorum longus hyperextends the unstable lessor toes at the metatarsophalangeal joint while the flexor digitorum longus and brevis flex the phalanges. The resultant claw toe deformity and plantarflexed metatarsal heads amplify forefoot equinus [4, 7].

The plantar flexed forefoot forces the hindfoot into varus. Hindfoot varus is initially flexible, but can gradually become rigid over time. With the rigid hindfoot varus, the Achilles tendon becomes a secondary invertor and becomes contracted [4, 7].

A mild variation of the cavovarus deformity without an identifiable underlying neurological deficit has been increasingly reported in recent literature [2, 9, 10]. This foot shape has been referred to as the subtle, nonneurologic, or idiopathic cavus. Although the exact etiology for this entity has been subject to debate, both intrinsic and extrinsic muscle imbalances may play a role [11, 12]. Chronic ankle instability with a varus-tilted mortise can also result in a cavovarus foot.

Cavus foot, even subtle deformity, can cause various problems through out the foot and ankle (Table 1). Metatarsalgia due to forefoot overload is related to the combined effect of cavus foot and tight heel cord. When examining a patient with metatarsalgia, cavus foot should be in the list of differential diagnoses along with Morton’s neuroma and long metatarsals. Overload on the 1^st metatarsal head can lead to sesamoiditis or sesamoid fractures. Overload on the lateral border can result in stress fracture of the 5^th metatarsal. Stress fracture of the 5^th metatarsal is difficult to treat without addressing the underlying cavus deformity.

Reduced shock absorption due to rigid hindfoot and tight heel cord can lead to plantar fasciitis or Achilles tendinitis. Haglund deformity can become symptomatic more easily if the heel is in varus because the posterior superior calcaneal tuberosity will become more prominent. Rigid joints can progress to joint destruction and develop arthritis over time.

Chronic lateral ankle instability and recurrent sprain is inevitable in a patient with cavus foot. Prolonged lateral overload and recurrent sprain can lead to peroneal tendon problems. Any attempt to repair the lateral ligamentous problems will not be successful if the bony structure is remained in varus. If left untreated, prolonged cavus foot will eventually lead to varus ankle osteoarthritis.

An elevated medial longitudinal arch in a weight bearing foot is indicative of a cavus foot (Fig. 1A). Along with the high arch, prominent dorsolateral foot and the extensor digitorum brevis, claw toes, depression of 1^st metatarsal (Fig. 1B), callosity under first or fifth metatarsal heads, thickening or callosities over the lateral border of the foot may be present in a cavus foot.

Fig. (1). A 19 year-old male patient presented with recurrent ankle sprains on the right side. Elevated medial longitudinal arch is indicative of a cavus foot (A)M. Depressed 1st metatarsal head can accompany plantar callus (B). Observation of the medial border of the heel from the front, a positive peek-a-boo heel sign, is suggestive of heel varus (C).

While severe cavus foot can be easily determined, a subtle cavus deformity requires careful inspection of the foot with high threshold of suspicion. A “peek-a-boo heel sign [13]” is gaining popularity as a sign of heel varus determined by mere observation from the front. With the patient standing with the feet at shoulder width apart and the medial borders of the hallux of both feet in parallel alignment, any appearance of the medial border of the heel is considered a sign of heel varus (Fig. 1C). This sign is not present when there is valgus or neutral hindfoot position. Heel varus is then confirmed from the rear (Fig. 2A) to rule out any possible false positive peek-a-boo sign due to a very large heel pad or severe metatarsus adductus with externally rotated lower extremities.

Fig. (2). The same patient as in Fig. (1), seen from behind. Varus alignment of the right heel (A) is corrected by Coleman block test (B).

Once the heel varus is confirmed, the flexibility of the hindfoot varus should be checked using the Coleman block test [14]. A block is placed under the lateral side of the foot, allowing the first metatarsal bone to drop. If the hindfoot is flexible and the hindfoot varus is completely driven by the pronated forefoot, the heel varus will be corrected into slight valgus (Fig. 2B). If the heel varus persists, further evaluation is required to investigate accompanying tarsal coalition, subtalar arthrosis, previous fracture, or muscular spasm.

A thorough neurological examination should be performed, paying special attention to the peroneus longus and brevis, as well as tibialis posterior and anterior muscles.

The following radiographic features can help in considering the diagnosis of a cavus foot [4, 9, 15, 16] (Fig. 3):

Fig. (3). Radiographic findings of a patient with severe cavovarus foot. A standing lateral view (A) shows a plantar flexed 1st ray, elevated navicular height, depressed 5th metatarsal base, and claw toe deformities. Exact Meary angle can not be measured due to severe tilting of the talus. The posterior facet of the subtalar joint as well as the Chopart joints are clearly viewed in this lateral radiograph due to rotation of the hindfoot. The distal fibular is enlarged and posteriorly located. Secondary osteoarthritis of the ankle joint is noted. A heel-alignment view (B) confirms the degree of heel varus. From the dorsoplantar foot X-ray, the metatarsals are adducted and the 1st metatarsal appears short due to plantar flexion.

Increased calcaneal pitch (angle between a line along the undersurface of the calcaneus and the floor; normal is <30°).

Increased Meary angle (due to the plantar flexed first metatarsal, the angle between a line drawn along the axis of the first metatarsal and that of the talus is increased. Normal is 0 ± 5°)

Increased Hibbs angle (angle between a line through the axis of the calcaneus and the first metatarsal; normal is <45°; cavus is near 90°).

Increased navicular height

Posterior position of fibula (the fibula appears more posterior to the tibia than normal due to the varus hindfoot position and external rotation of the lower limb.).

Subtalar view (Due to the inversion of the hindfoot, the posterior facet of the subtalar joint is clearly visible in a lateral foot radiograph).

In order to correctly measure some of the angles mentioned above, true dorsoplantar and lateral weight-bearing foot radiographs are required. However, when the deformity is severe, the talus and calcaneus tilt into varus, making it impossible to draw a correct axis of the bone. Therefore, the reference values mentioned above are to be used as guidelines rather than definitive diagnostic criteria.

Patients with milder symptoms associated with a cavus deformity can benefit from conservative treatment consisting of gastrocnemius muscle stretching exercise and specialized foot orthotics. The aim of applying an orthotic is to realign the hindfoot correctly to offload the lateral border of the foot. Therefore, an ideal orthotic for a subtle cavus foot should support the lateral hindfoot and midfoot with a wedge [17]. Medial arch support should be minimized since it can further tilt the foot in supination [9].

When considering an operative treatment for a cavus foot, the goal is to obtain a stable plantigrade foot with preservation of joints if possible. In order to do that, one should recognize the muscle imbalance and understand the structural alterations in the foot. The foot will not be balanced with any uncorrected structural deformity and the deformity will recur if the foot is not balanced. So, for any cavus foot, one has to correct the muscle imbalance and correct any structural deformity.

Since every deformity is unique, there is no such thing as a standard protocol that can be applied universally. Instead, there is a list of many procedures and surgical options that we can choose from to optimally reconstruct each cavus foot (Table 2).

6.5. Muscle Balancing

If the deformity is originated from or related to any kind of muscle imbalance, a tendon transfer is always necessary. Without well-balanced muscle power, the deformity will recur and the correction will eventually fail.

Fig. (4). A Z osteotomy allows lateral translation of the posterior fragment. Removing small wedges from the anterior and posterior facets of the osteotomy can be added depending on the severity of the deformity. Care should be exerted not to injure the sural nerve.

Peroneus longus transfer to brevis is the most commonly performed tendon transfer. Since peroneus longus plantar flexes the 1^st metatarsal, removing this deforming force is essential in preventing the recurrence. It is also beneficial because the transferred peroneus longus tendon augments the peroneus brevis, which is frequently weakened or problematic. If the peroneus brevis is severely torn or degenerated, the pathologic portion should be repaired or excised before the transfer.

Posterior tibial tendon produces an unopposed pull in the presence of the peroneus brevis dysfunction. As a result, foot inversion and progressive contracture of the medial soft tissues will develop. Therefore, the goal of the posterior tibial tendon transfer is to weaken the deforming power and to strengthen the deficient function of the foot. The transferred posterior tibial tendon is inserted to one of the cuneiforms, where it functions as an ankle dorsiflexor.

In less severe deformities, the anterior tibial tendon can be transferred laterally to the middle cuneiform. Lateralizing the anterior tibial tendon reduces the supination vector while maintaining the dorsiflexion power. If strength of the anterior tibial muscle is maintained, an isolated transfer is performed. If the tendon is weak, augmentation with simultaneous transfer of the extensor digitorum longus can be considered [19].

Besides tendon transfers, repairing or augmenting the lateral ankle ligaments is frequently performed since lateral ankle instability is almost always accompanied in a cavus foot. Ligament repair with extensor retinaculum augmentation is the procedure of choice. Peroneus transfer to brevis also augments the lateral stability.