Cavovarus

Definition

Describes a deformity which consists of 2 components:

a) Cavus of the foot with a plantar flexed 1st metatarsal and

b) A varus heel in most cases accompanied by a muscular imbalance with tibialis posterior and peroneus longus overpull and a weakness of the tibialis anterius and peroneus brevis muscle.

The deformity can be flexible, semirigid or rigid.

Causes

In most cases  the deformity is caused by a neuromuscular disorder, typically in cases of HSMN- disease (Charcot- Marie- Tooth) with a weak peroneus brevis and a peroneus longus overpull what leads to a pathological plantarflexion of the 1st ray and a reduced pronation/eversion of the foot.

Secondary the deformity is caused by an overpull of the tibialis posterior with  increased adduction and inversion forces what then leads to the varus of the heel and adduction of the forefoot.

Symptoms

Change of the gait pattern, increasing with the duration of the underlying disease. As earlier the onset and as longer the duration of the symptoms the deformity will be more rigid.

The disease and deformity ends up with more rigidity in males and more weakness in females.

If the deformity is getting increasingly rigid we find usually also increasing callus formation under the base of the 5th metatarsal and under the head of the 1st metatarsal.

Over the time there is increasing limitation of walking ability- in many cases walking is only possible with the help of orthopedic shoe wear.

The diagnose is made clinically, with x-ray and ca be confirmed with electrophysiological tests.

If there is suspicion for HSMN- disease a gene- testing can clearify the diagnosis.

Non-Surgical Treatment

Following the general rule the primary treatment should be non-surgical. In cavovarus deformities remain only few conservative treatment options:

1. Insoles and the use of orthopedic shoes as well the use of a peroneus orthosis to support the weak peroneus brevis muscle.
2. A general rule is to perform early weightbearing and to continue the use of the weak muscles to prevent a fast increasing weakness.

Surgical Treatment

Surgical treatment has to be divided in soft tissue procedures and bony procedures.

1. Soft tissue procedures:
   1. In flexible deformities the main interventions are for soft tissue correction: The reduction of the plantar fascia as well as tendon transfers for restoring lost function, e.g. transfer of the tibialis posterior tendon to the dorsum of the foot for the lost    function of elevators.
   2. If the medial gastrognemius is short it also should be released but it has to be avoided to plantarflex a calcaneus if it is already severely plantar flexed.
   3. If the posterior tibial tendon is transferred the FDL is an appropriate muscle to restore a bit of the tib. post. function. The FHL can be used to restore the function of the peroneus brevis. The peroneus longus should be lengthened in cases of plantar flexed first ray.
2. bony procedures:
   1. In rigid deformities we prefer the calcaneal sliding osteotomy, often with an additional resection of a wedge out of the osteotomy. The resection arthrodesis of the TMT I with resecting a dorsal open wedge  can prevent plantar ulceration because of   to much pressure to the MT I- Head.
   2. Only in very severe rigid cases the correction osteotomy of the calcaneus can be combined with an intertarsal wedge resection and correction arthrodesis.
   3. In severe cavus deformities even a resection of the navicular bone in combination with the dorsal wedge resection in the intertarsal line is necessary.
   4. If the whole hindfoot is rigid and already with severe arthrosis a triple arthrodesis, evt. in combination with a dorsal elevation of the tarsus ( lambrinudi technique) might be the right joice.

If the varus of the foot and hindfoot is caused by a supramalleolar varusposition the correction should take place at the level of deformity.

Postoperative therapy

In the initial stage a cast has to be worn for a minimum time of 2 weeks.

If bony and soft tissue procedures were combined the disabling time frame goes up to 10 weeks. About 2- 4 weeks after operation the weightbearing starts with physiotherapy and about 20 – 30 kg/KG for the 3 rd week after operation. After the weightbearing is changing from week to week- full weightbearing should be reached after week 8- 10 after operation.

In the beginning the patient should wear a walker or a brace to stabilize the ankle until week 8- 10 after the operation.