Overview

Correction of the cavus foot can be daunting. With adherence to some basic principles, however, the deformity can be well corrected and the foot dynamically balanced, with maintenance of as much motion as possible. The presurgical evaluation should ascertain the following:

• 1.
  

  Where is the apex of the deformity?

  
  
• 2.
  

  Is this a midfoot or a forefoot cavus?

  
  
• 3.
  

  Is the forefoot in equinus?

  
  
• 4.
  

  Is this a global equinus, or does it involve only the first or perhaps the middle metatarsal?

  
  
• 5.
  

  How mobile is the first metatarsal?

  
  
• 6.
  

  Is the foot rigid, or is the deformity passively correctable?

  
  
• 7.
  

  What tendons (muscles) are available for transfer?

  
  
• 8.
  

  What is the extent of muscle imbalance between the peroneus longus and the anterior tibial muscles, and the posterior tibial and the peroneus brevis muscles?

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) This patient was an adolescent. The heel corrected into neutral with the test, suggesting more of a forefoot-driven varus deformity.

These are two cases that demonstrate the need to evaluate carefully the clinical as well as the radiographic outcome of cavus foot correction. A similar midfoot procedure was performed in both cases. Although both patients were symptomatically improved, both had complaints of persistent pressure under the fifth metatarsal. The pre- and postoperative images are demonstrated. Note that in both cases, the height of the base of the fifth metatarsal to the floor has been improved but remains low relative to the medial cuneiform. This is an important radiographic finding indicating fifth metatarsal overload (A–D).

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.

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 of that joint for correction. A varus deformity associated with ankle arthritis and global foot cavus deformity is ideally treated with a tibiotalocalcaneal (TTC) or a pantalar arthrodesis ( Fig. 11.3 ). In the literature from the 1980s, the triple arthrodesis was not associated with a good and predictable outcome for the cavus foot. We disagree with this finding, since a triple arthrodesis is a good procedure, provided that the foot is correctly balanced with additional osteotomy and tendon transfers as needed. The triple arthrodesis gained a poor reputation for correction of the cavus foot, particularly that associated with Charcot-Marie-Tooth (CMT). 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 posterior tibial tendon (PTT) 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. One must be aware of the apex of the deformity since this will determine the type of procedure, in particular when an arthrodesis is selected. Frequently there is more than one apex, and if so, one either has to be able to derotate the foot around the hindfoot arthrodesis or perform a second arthrodesis, which in this case was at the first tarsometatarsal (TMT) joint ( Fig. 11.4 ). In many cases, the hindfoot has little to no motion, and if the deformity has an apex at the Chopart’s joint, a triple arthrodesis is the most effective method to correct deformity with little functional loss. Given the rigidity of the deformity, wedge resection may be required to gain sufficient correction (Video 11.2 ).

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.

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. Note that the apex of the deformity is clearly at the subtalar joint but then also at the midfoot, indicating a double apex (A and B). 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 (C).

In general, for the flexible foot, we perform a combination of a calcaneal osteotomy, a first metatarsal osteotomy, and a plantar fascia release and correction of equinus (gastrocnemius vs. Achilles lengthening). We then add whatever else is necessary to complete the correction, which may include an ankle ligament reconstruction, or a midfoot arthrodesis/osteotomy ( Fig. 11.5 ). 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.

Bilateral flexible deformity associated with ankle instability in a 31-year-old patient with Charcot-Marie-Tooth disease (A). 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 (B and C).

It is rare that a triple arthrodesis needs to be performed for a flexible cavus foot. The triple arthrodesis, although not contraindicated in the presence of a rigid deformity, can be associated with long-term complications, particularly ankle arthritis, and the mobility of the hindfoot must be preserved if possible.

When one approaches the rigid cavus deformity, it is possible to perform an anatomic correction of the foot initially with a triple arthrodesis, but 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 therefore made through the interosseous membrane to the dorsal of the foot. If the anterior tibial muscle is strong and the predominant deformity is adductovarus, then the peroneus longus is transferred into the peroneus brevis tendon. One can consider a posterior transfer of the PTT to the peroneus brevis, but we have not had much success with this procedure.

Plantar Fascia Release

The plantar fascia release is an integral part of correction of the cavus foot deformity and is therefore usually the first procedure that we 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 we used to make an incision directly under the arch of the foot medial to the fascia, we 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.

The easiest procedure 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 ( Fig. 11.6 ). 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.

The plantar fascia release is performed with a short transverse incision at the junction of the dorsal and plantar skin (A). A retractor is used to sweep the fatty tissue toward the plantar surface, exposing the fascia (B). The fascia is cut with scissors and a segment of the fascia is excised to prevent recurrent scarring (C).

The branch of the lateral plantar nerve is usually not visible and does not need to be looked for. Copious fatty tissue under the incision needs to be reflected with a large soft tissue retractor until the fascia is visualized. We then split the fascia directly off the calcaneus using scissors from a medial to lateral direction. The scissors are advanced without a cutting motion until both the medial and lateral bands are completely released.

For severe deformity, in which cavo-adductovarus is present, the fascia of the abductor hallucis tendon must also be completely released. For some of these severe deformities, the intrinsic muscles must be stripped off the calcaneus completely, in addition to the fascia release. The stripping can be done using scissors or a broad periosteal elevator from within the same medial incision. This release must be very carefully planned, because multiple incisions cannot be used for the posterior tibial tendon transfer, the abductor fascia release, and the plantar fascia release ( Fig. 11.7 ).

The radiographs of a very severe recurrent deformity after a failed triple arthrodesis (A and B). In addition to the revision of the triple arthrodesis, treatment included a transfer of the posterior tibial tendon, a plantar fascia release, and a stripping of the abductor fascia, performed from a single extensile medial incision was performed (C–E).

Calcaneus Osteotomy

The incision for the calcaneal osteotomy varies according to the type of procedure performed. If an osteotomy alone is performed, then a shorter incision is made directly inferior to the peroneal tendons. Invariably however, the calcaneal osteotomy often needs to be performed with additional lateral procedures, including repair of the peroneal tendon, reconstruction of lateral ankle instability, or a peroneus longus to brevis tendon transfer. For these cases, the incision is simply extended posteriorly along the axis of the peroneal tendons behind the fibula.

The incision is deepened through subcutaneous tissue in the plane between the peroneal tendon and the sural nerve. The nerve can be retracted either superiorly or inferiorly, depending on its position. The periosteum needs to be elevated over a broad area, because a wedge is going to be removed. We insert a retractor to separate the soft tissues and then place two small, curved retractors on either side of the calcaneus to expose the entire lateral tuberosity. A saw, not an osteotome, should be used to make the cut; a wide, fan-shaped saw blade should be selected. The cut is first initiated perpendicular to the axis of the calcaneus at a 45-degree angle to the tuberosity. Two Kirschner wires (K-wires) may be used to mark out the osteotomy and verified with an axial radiograph to ensure that an appropriate cut is made with the apex at the medial cortex ( Fig. 11.8 ). We use a gentle pressing action with the saw blade so that we can feel the medial cortex as it is perforated. Once the first cut has been made, the second cut is made at an angle to this of approximately 20 degrees, but the appropriate angle depends on the size of the wedge. It is far easier to start out with a smaller wedge and then remove more bone if the correction is not sufficient ( Fig. 11.9 ). Once the wedge or bone has been removed, we then pull the heel into valgus. The osteotomy rarely closes down perfectly at this time, so additional perforation of the calcaneus is typically necessary to permit it to close down smoothly. This perforation to permit smooth reapposition of the cut surfaces can be accomplished by reinserting the saw blade while the osteotomy is partially closed (using a carpentry term, “kerfing”). The cuts are then completed with multiple minor perforations. Depending on the deformity, the calcaneus is moved in two or three planes. The valgus closing wedge osteotomy constitutes the first plane. The tuberosity is then always shifted lateral to its axis under the subtalar joint, which improves the weight-bearing axis of the hindfoot. Movement in a third plane consists of a cephalad shift, which is added according to the pitch angle of the calcaneus. We try to flatten out the talocalcaneal angle, and the calcaneus–first metatarsal angle, in particular, flattens as the calcaneal tuberosity is moved cephalad. We use two guide pins to hold the calcaneus in the corrected position. The first guide pin is inserted centrally into the body of the posterior tuberosity, which is then manipulated into the corrected position. While the guide pin is being held and the heel is forced into the desired position, a second guide pin is introduced for screw fixation. It is best to insert the screw from slightly posterior lateral to slightly anterior and medial to gain maximal compression. Tamping the overhanging inferior ledge of bone is unnecessary.

Intraoperative axial view of Kirschner-wire placement to assist in ensuring an appropriate angle and amount of resection for a lateral closing wedge calcaneal osteotomy.

Calcaneus osteotomy procedure. (A) The incision is placed directly above the peroneal tendons and above the level of the sural nerve. (B) The periosteum is reflected and retractors are inserted on either side of the tuberosity. (C and D) The wedge is removed using a wide saw applied with a punching action; the width of the wedge is usually approximately 5 mm but will be determined by the defect. (E and F) The heel is translated laterally by approximately 5 mm, and then two guide pins are inserted, one directly through the osteotomy and the other to manipulate the heel into valgus (E), followed by cannulated screw insertion (F).

One has to be careful with the magnitude of the wedge and the lateral shift of the osteotomy in severe deformity cases, since this will place traction on the tibial nerve and cause an acute tarsal tunnel syndrome. This condition has been well demonstrated cadaverically and is more pronounced with shifts of 1 cm, and we have seen this complication occur particularly in patients with CMT who already have compromise of the tibial nerve function. In severe deformities, we therefore will routinely add a tarsal tunnel release to the osteotomy. It is difficult to know in which cases this release is necessary, but as stated, we use it in particular when marked heel varus is corrected with the calcaneus osteotomy. The same development of tibial nerve loss can occur when performing a triple arthrodesis for severe deformity, and in these cases we will add the prophylactic tarsal tunnel release. To minimize the risk of this complication, we are more aggressive with the size of the closing wedge osteotomy to gain correction and limit the amount of shift to 5 mm.