What it is
In a cavus foot the arch is abnormally high and the heel tips inward, which is why the full description is usually cavovarus. The result is a foot that carries too much load on its outer border and too little across the middle.
Why it matters
- Recurrent ankle sprains, because the heel sits in an inverted position and the ankle is starting from a position of instability.
- Pain under the ball of the foot, particularly under the first and fifth metatarsal heads.
- Clawing of the toes, from imbalance between the long and short muscles.
- Stress fractures of the fifth metatarsal.
- Peroneal tendon problems on the outside of the ankle.
- Early arthritis of the ankle from the persistent varus load.
Finding the cause
The most important question is whether the foot is idiopathic or neurological. A cavovarus foot that is progressing, or that is worse on one side, warrants a neurological examination and often nerve conduction studies and genetic testing. Charcot-Marie-Tooth disease is the commonest identifiable cause. Other causes include previous compartment syndrome, spinal cord abnormalities and residual clubfoot.
The Coleman block test is used at the bedside to establish whether the heel position is flexible and driven by the forefoot, which directly determines whether the heel bone needs to be cut.
Treatment
Non-operative treatment is aimed at offloading and stability: a lateral wedge, a cushioned orthosis, a boot with a higher upper for people who sprain repeatedly, and peroneal strengthening.
Surgery is planned around the specific deformity and typically combines:
- Plantar fascia release, where the arch is tethered
- First metatarsal dorsiflexion osteotomy, which lifts the plantarflexed first ray that is driving the heel into varus
- Calcaneal osteotomy, to shift the heel back out of varus where it is rigid
- Tendon transfer, most often the peroneus longus to peroneus brevis, to rebalance the foot
- Toe correction for fixed clawing
- Ankle ligament reconstruction, where instability has developed
Correcting the shape without rebalancing the tendons is the common reason these feet deform again.