How To Assess And Treat The Cavus Foot
The cavus foot is probably the most difficult foot type to manage. Most of these feet are rigid and therefore are very unforgiving when the foot plants on the ground. Flexible flat feet, for example, are good accommodators of the ground and most of these feet are relatively asymptomatic or require orthotics to help limit pronation.
The cavus foot typically overloads the lateral column, setting up pain syndromes on the lateral aspect of the foot and ankle. Patients with cavus feet will experience problems with ankle instability, peroneal tendinitis/tendinosis, lateral tibial stress syndrome, iliotibial band syndrome, etc. The common denominator is lateral overloading of the foot.
The lateral overload results from a combination of calcaneal varus and a plantarflexed first ray (forefoot valgus). Oftentimes, there is concomitant metatarsus adductus as well.
Treatment of the cavus foot usually begins with orthotics. I explain to my patients that the purpose of orthotics in their case is not to hold the arch up as in a flatfoot but rather to allow the entire foot to bear weight. This eliminates high pressures on the heel, the lateral border of the foot and on the ball of the foot. If the patient is having significant dorsolateral foot fatigue and pain, I may build up a cork valgus wedge on the polypropylene shell (with an intrinsic heel grind) to allow for mild pronation of the foot. This is contradictory to most orthotic prescriptions, which are designed to be anti-pronating devices.
From a surgical perspective, it is important to think globally. If I have a patient who has lateral ankle instability with torn lateral ankle ligaments, it may be a disservice to fix the lateral ankle ligaments when there is a significant cavus deformity. Otherwise, it just is a matter of time before the ligaments tear again due to biomechanical influences. The same scenario is true for peroneal tendon pathologies.
When evaluating the cavus foot, simply divide the foot up into the hindfoot and forefoot. If there are significant hammertoes of the lesser toes, then one should perform hammertoe repair (arthrodesis of the proximal interphalangeal joints). Typically, the surgeon does not fuse the fifth toe but you can make a case for fusion in the neurologic cavus foot.
One should then proceed to address the first metatarsal for plantarflexion. Determine whether the deformity is rigid. If so, then a dorsiflexory base wedge osteotomy is in order. If it is flexible, then a Jones tenosuspension is preferred. Remember, if the hallux is hammered, you will need to do a fusion of the interphalangeal joint (always perform this with a Jones tenosuspension).
Assess the hindfoot for calcaneal varus. A calcaneal axial X-ray is helpful in determining the shape of the heel. A Coleman block test determines whether the calcaneus has a structural or functional varus deformity. Perform this test by placing the foot on a textbook with the first metatarsal (which is usually plantarflexed) hanging off the edge of the book. If the heel remains in a varus attitude without the influence of the first metatarsal, then you know the heel has a structural deformity of varus that you can address with a Dwyer type osteotomy. If the heel returns to vertical, then the inversion of the heel is secondary to the biomechanical effects of a plantarflexed first ray.
When doing a Dwyer osteotomy, I will usually address the heel in three planes. First, I will remove a wedge as described by Dwyer, which addresses frontal plane deformity. Then I will slide the heel laterally to gain transverse plane correction. Finally, I will shift the heel superiorly to help lower the arch in the sagittal plane. I call this a modified Dwyer osteotomy.
The final decision to make is whether a midfoot osteotomy needs to occur. If the apex of the deformity is in the region of the midfoot, then a Cole osteotomy is preferred. If the apex of the deformity in the hindfoot, then one can do a triple arthrodesis, especially if there is any degenerative joint disease.
My personal experience is that the Cole osteotomy is a much more powerful procedure to lower the arch than a triple arthrodesis. Therefore, I reserve the triple arthrodesis for feet that have gross instability of the hindfoot or arthritis. Another advantage of the Cole osteotomy is that the healing time is much quicker than for a triple arthrodesis due to the nature of the osteotomy in cancellous bone and no joints to fuse.
The cavus foot is bar none the most difficult foot type to manage. The bottom line is whatever you do as far a treatment goes should allow the foot to plant on the ground evenly.