CHAPTER 15 Cavus Foot Correction

OVERVIEW

Correction of the cavus foot can be daunting. With adherence to some basic principles, however, the deformity usually can be well corrected and the foot dynamically balanced, with maintenance of as much motion as possible. The presurgical evaluation should ascertain the following: Where is the apex of the deformity? Is this a midfoot or a forefoot cavus? Is the forefoot in equinus? If so, is this a global equinus, or does it involve only the first or perhaps the middle metatarsal? How mobile is the first metatarsal? Is the foot rigid, or is the deformity passively correctable? Surgeons rely on the Coleman block test to determine flexibility of the hindfoot and forefoot (Figure 15-1). This test is certainly acceptable, but I also recommend manipulating the heel to see the effects of the hindfoot on the forefoot. If the heel can be reduced into heel valgus, then perhaps less correction will need to be done in the hindfoot and more in the forefoot. Finally, the most important component of the evaluation is to identify additional deforming forces on the foot. Invariably, the peroneus longus muscle is stronger than the anterior tibial muscle, and the posterior tibial muscle is stronger than the peroneus brevis muscle, with a variable degree of contracture of the gastrocnemius and soleus muscles present.

Figure 15-1 The Coleman block test is performed by placing a block under the lateral foot and allowing the first metatarsal to come to the ground. A and B, In these photographs, the foot is quite rigid, and no correction of the heel varus took place. C, The patient was an adolescent. The heel corrected into neutral with the test, suggesting more of a forefoot-driven varus deformity.

DECISION MAKING

What are the indications for arthrodesis? At times a specific indication is obvious—for example, the presence of severe ankle arthritis will necessitate an arthrodesis for correction. A varus deformity associated with ankle arthritis and global foot cavus deformity is not ideally treated with a joint replacement (Figure 15-2). A triple arthrodesis is a good procedure, provided that the foot is correctly balanced with additional osteotomy and tendon transfer. The triple arthrodesis gained a poor reputation for correction of the cavus foot, particularly that associated with Charcot-Marie-Tooth disease, correctly named hereditary sensorimotor neuropathy. These arthrodesis procedures were performed in isolation, and as might be expected, the deformity recurred. The posterior tibial tendon inserts distal to the talonavicular joint, and unless the tendon is transferred, the medial foot deformity will gradually recur, with onset of adductovarus. Therefore, if a triple arthrodesis is thought to be the procedure of choice, it should be performed with appropriate transfer of the posterior tibial tendon, as well as additional tendon transfers as required (Figure 15-3).

Figure 15-2 Note the severe ankle arthritis associated with the hindfoot varus and the chronic nonunion of a fifth metatarsal stress fracture. An ankle arthrodesis with a calcaneus osteotomy with resection of the base of the fifth metatarsal was selected as the treatment approach.

Figure 15-3 A and B, A very rigid cavus deformity in a 33-year-old patient with Charcot-Marie-Tooth disease. The hindfoot and forefoot were very rigid, and pain was present along the lateral foot. C, Correction was accomplished with a triple arthrodesis, a dorsiflexion arthrodesis of the first tarsometatarsal joint, arthrodesis procedures of the hallux and lesser toe interphalangeal joints, and transfer of the posterior tibial tendon to the dorsum of the foot.

Generally, I perform a combination of a calcaneal osteotomy, a first metatarsal osteotomy, and a plantar fascia release. I then add whatever else is necessary to complete the correction, which may include a resection of the base of the fifth metatarsal, an ankle ligament reconstruction, or a midfoot osteotomy (Figure 15-4). The calcaneus osteotomy is a very utilitarian procedure to correct a cavus foot and, depending on the magnitude of the deformity, is always required in one form or another (Figure 15-5).

Figure 15-4 A, Bilateral flexible cavovarus deformity associated with ankle instability in a 31-year-old patient with Charcot-Marie-Tooth disease. B-E, Initial correction in the right foot was accomplished using a “standard reconstruction,” including a triplanar calcaneus osteotomy, a first metatarsal osteotomy, a plantar fascia release, a peroneus longus-to-brevis transfer, and a transfer of the posterior tibial tendon to the dorsum of the foot, and a modified Chrisman-Snook procedure.

Figure 15-5 A, The residual effect of mild idiopathic bilateral cavus deformity in a 53-year-old woman. B and C, The deformity was corrected with a peroneus longus-to-brevis transfer, a plantar fascia release, and a calcaneus osteotomy.

It is rare that a triple arthrodesis needs to be performed. In fact, this arthrodesis, although not contraindicated, is associated with numerous long-term complications, particularly ankle arthritis. The mobility of the hindfoot must be preserved if possible.

Although it is possible to perform an anatomic correction of the foot initially with a triple arthrodesis, these procedures are insufficient in the long term if muscular imbalance remains. Integral to the success of any of these procedures is a corrected foot posture, a plantigrade hindfoot relative to the forefoot, and muscle balance. Even with perfectly executed surgery, if the posterior tibial muscle is overactive relative to the evertors of the hindfoot, the foot will ultimately “fail,” with further adductovarus deformity. The posterior tibial muscle must therefore be transferred in many of these procedures. Frequently, a cavus deformity is associated with slight weakness of the anterior tibial muscle, and the posterior tibial tendon can be transferred as part of this corrective procedure. Usually, the transfer is to the dorsal aspect of the foot through the interosseous membrane. Occasionally, however, if the anterior tibial muscle is strong and the predominant deformity is adductovarus, then a split posterior tibial transfer can be performed, with the lateral limb being transferred into the peroneus brevis tendon. Not much of the split tendon is needed for the transfer; enough is transferred so that it can pass behind the tibia and fibula and hook into the peroneus brevis tendon with an effective suture tenodesis.

PLANTAR FASCIA RELEASE

The plantar fascia release is an integral part of correction of the cavus foot deformity and therefore usually is the first procedure that I perform as part of the correction. Correcting the position of the calcaneus is difficult without first releasing the plantar fascia. From a technical standpoint, although I used to make an incision directly under the arch of the foot medial to the fascia, I found this counterproductive. Although this incision was easy to perform, it always left a large hypertrophic nodular scar, almost like fibromatosis, that was difficult to soften, even with aggressive rehabilitation. Subsequently, I attempted the entire plantar fascia release from the lateral incision inferior to the calcaneal osteotomy. This approach worked fairly well, but releasing the medial bundle through this access is difficult. If there is severe cavus deformity, the medial band over the abductor fascia cannot be released. The incision does, however, provide reasonable access for the fascia release. This modification of the original Steindler procedure is performed by extending the incision for the calcaneal osteotomy slightly more distally and cutting across the fascia transversely with Metzenbaum scissors.

The easiest procedure for me is a complete fascia release through a medial longitudinal incision adjacent to the heel, which is made slightly more distally at the junction of the dorsal and plantar skin (Figure 15-6). Unfortunately, some patients may be left with a small patch of numbness on the medial aspect of the heel pad from this incision, and the potential for this outcome must be explained to patients preoperatively. The incision is made over a 2-cm length. With the incision kept longitudinally in the axis of the foot, no problems occur with wound healing during the lengthening and flattening of the medial column; problems would occur, however, if a vertical incision were made along the axis of the tarsal canal.