Keys To Correcting Cavus Foot Deformities

Emphasizing thorough preoperative diagnosis and planning, these authors review principles to classifying cavus foot deformities and offer step-by-step surgical pearls for achieving acute and gradual correction.

Cavus deformity correction is a complex undertaking that requires a complete understanding of the planes of deformity and resulting compensations. Procedure choice hinges upon the degree of flexibility of the cavus foot deformity. Preoperative radiographic and clinical examinations are critical for understanding both the degree of soft tissue involvement as well as the level and extent of bony deformities present. The findings from these examinations will help surgeons ensure sound preoperative planning for cavus deformity correction via osseous and soft tissue procedures.  

These procedures aim to equalize muscular imbalances between the posterior and anterior/lateral compartments that produce deformities such as equinus and dropfoot. Equinus is present with or without spasticity of the superficial or deep muscles of the posterior compartment. Ankle equinus is typically not a significant deformity in the cavus patient. A dropfoot deformity may result from weakness of the anterior and lateral compartment musculature, or from a neurological insult.

Other inherent imbalances in cavus deformity result in inversion and plantarflexion of the foot and ankle. These occur due to the increased pull of both the peroneus longus and the tibialis posterior, which plantarflex the first ray and invert/plantarflex the foot respectively. A forefoot valgus deformity compensates for a rearfoot varus deformity. However, if the rearfoot varus deformity is flexible, then the rearfoot will reduce to neutral and the forefoot will not need to compensate. Conversely, if the forefoot valgus (plantarflexed first metatarsal osteotomy) is fixed, this imparts a retrograde varus deformity influence to the rearfoot. Additionally, digital contractures occur due to the increased mechanical advantage of the long extensors over the intrinsic musculature.

A Guide To Deformity Classification
The first step in preoperative planning is through classification of the deformity. Multiple classification schemes exist and are organized according to the deformity’s apex, etiology and reducibility. One would determine the most suitable corrective surgical procedure based on this classification.

Etiology of cavus deformity is one major classification criteria and we can divide this into congenital, developmental and posttraumatic roots. Patients with congenital cavus typically have a more severe underlying orthopedic condition including tibial or fibular hemimelia, clubfoot or polydactyly. Developmental cavus is progressive in nature and accompanies neuromuscular disorders such as Charcot-Marie-Tooth disease.¹ Aside from a high-arched foot, typical deformities associated with Charcot-Marie-Tooth include digital contractures and a varus heel. Posttraumatic deformities may result from malunion following fracture or dislocation.

Classification according to the location of the apex of deformity includes three types of cavus: anterior cavus, posterior cavus and combined cavus. Anterior cavus is based in the forefoot, posterior cavus is based in the rearfoot and combined cavus has components of both.² Classification of the reducibility or flexibility of the rearfoot or forefoot deformity is important for preoperative diagnosis. Physical examination, non-weightbearing and weightbearing evaluation are critical to determine the flexibility of the cavus deformity. Additionally, weightbearing radiographic images are very helpful to determine the maximum deformity and non-weightbearing stress fluoroscopy can determine the amount of deformity reducibility.

Current Concepts With Acute And Gradual Correction
Treatment of cavus deformity consists of both soft tissue and bony procedures. If the deformity is entirely inherent to the soft tissues, treatment should entail soft tissue releases, transfer/lengthening/shortening of tendons or distraction of the cavus contracture.^3,4 One must evaluate cavus deformities of bony origin to determine where the center of rotation angulation (CORA) or apex of the deformity lies. In cases of anterior cavus in which equinus is present at the midfoot or forefoot, treatment should entail a midfoot osteotomy. When it comes to posterior cavus, which is usually notable for increased calcaneal pitch and varus heel, one can perform a calcaneal osteotomy.

In the correction of cavus deformity, whether it is of soft tissue or bony origin, the two approaches are acute or gradual. The surgeon can perform acute correction through wedge or chevron-type osteotomies (the Japas osteotomy and the V-osteotomy through the midfoot are examples) whereas gradual correction would involve the use of external fixation to obtain correction over time via distraction osteogenesis or soft tissue distraction.²

Significant progress has occurred with external fixation techniques and materials in recent years, particularly with regard to their use in deformity correction. The use of external fixation in cavus deformity correction has multiple advantages over acute correction in certain patients.

Osteogenesis is inherently the more predictable technique as it employs incremental correction over time, which exerts gradual stretch on soft tissue structures. Distraction osteogenesis allows for naturally regenerating bone formation, thereby eliminating the need for bone grafting and the potential complications associated with healing and donor site morbidity.

One typically applies the fixator in a minimally invasive fashion, reducing scarring risk and maximizing healing potential. Additionally, patients may bear weight as tolerated immediately following the procedure, decreasing the risk and complications associated with disuse osteoporosis. Patients may also shower or bathe as desired postoperatively. External fixation also enables joints to remain mobile since it allows for range of motion exercises.⁵

In a staged fashion, one can address combined deformities in which elements of both soft tissue and bony deformities are present. Generally, address the bony deformity first and follow with additional soft tissue manipulation if warranted.

Pertinent Insights On Obtaining Correction
There are specific surgical procedures that surgeons frequently employ to correct the soft tissue and bony elements of cavus deformity. Soft tissue procedures to address contracture vary from simple plantar fascia release to joint capsule releases. The Steindler stripping procedure involves releasing the proximal plantar fascia from the calcaneus. The more extensive Tachdjian plantar fasciotomy removes the entire plantar fascia and releases both the long and short plantar ligaments. Surgeons may also employ partial or full tendon transfers to correct soft tissue imbalance. For example, a posterior tibial tendon transfer may help decrease the cavus deformity and simultaneously maintain correction.^6,7

Surgeons can utilize external fixation in the correction of soft tissue cavus contracture via gradual distraction realignment. The most efficient Ilizarov construct includes a tibial ring fixated by wires and half-pins, a half-ring fixated to the hindfoot by wires through the calcaneus and talus, and another half-ring attached to the forefoot with two wires. One can use medial and lateral plantar distraction rods to push the forefoot distal, thereby decreasing the cavus at the rate of 0.5 mm per day. Apply an anterior threaded rod in order to pull up on the anterior half-ring, flattening the arch at a rate of 1 mm per day.^2,4,6 More recently, surgeons have used computer assisted gradual correction external fixation devices, such as the Taylor Spatial Frame (Smith and Nephew) and the TL-Hex (Orthofix).

Choose bony procedures based on the CORA/apex of the cavus deformity and correct the deformity either acutely or gradually. Treat posterior cavus with acute closing wedge or dome-type osteotomies of the calcaneus. Surgeons frequently perform the Dwyer calcaneal osteotomy to correct a varus heel through a laterally based wedge resection.

One technique for the Dwyer calcaneal osteotomy to ensure accurate realignment of the hindfoot relative to the tibia involves strategic placement of guide wires. Using fluoroscopic guidance in a calcaneal axial position, insert one 1.8 mm wire through the lateral heel incision into the calcaneus perpendicular to the long axis of the tibia. Use a second 1.8 mm wire posterior to the first wire and position it perpendicular to the lateral wall of the calcaneus. The wires converge and form a wedge with the apex at the medial calcaneal cortex. One subsequently performs two bone cuts along each wire. Following removal of the bone wedge and realignment of the calcaneus into a vertical position, the surgeon can achieve fixation with two 7-0 cannulated screws in a parallel fashion, perpendicular to the osteotomy.^7,8

Alternatively, one can perform gradual plantar opening wedge correction with external fixation to correct posterior cavus. The gradual correction typically occurs in a larger deformity or in the case of significant soft tissue compromise. Prior to placing the fixator, execute an osteotomy through the posterior calcaneus.^2,4  

Surgeons can treat anterior cavus acutely with a closing wedge or a Japas osteotomy through the cuneiforms. One may apply an external fixator to perform a gradual opening wedge midfoot osteotomy. The surgeon can execute this procedure across either the navicular and cuboid, the cuboid and cuneiforms, or the neck of the talus and anterior calcaneus (though one should avoid this location if there is adequate motion about the subtalar joint).^4,7 Use a Gigli saw to perform the osteotomy in a percutaneous fashion by placing wires on either side of the osteotomy (stirrup wires).

How To Maintain Correction
Maintaining correction after fixating the deformity can be challenging, particularly in cases of progressive or neuromuscular cavus. It is prudent for these patients to have a custom ankle foot orthosis (AFO) to support the pedal alignment, which is most essential in the first six to 12 months of the postoperative period. This is particularly crucial when one has performed soft tissue distraction or a tendon transfer procedure.² An AFO utilizing a midfoot strap will help flatten the medial longitudinal arch.

In cases in which relapse has occurred, tendon transfers alone or in combination with isolated fusions may be required to maintain correction on a long-term basis. The tibialis posterior and extensor hallucis longus tendons lend themselves to tendon transfer particularly well. In patients with Charcot-Marie-Tooth disease, transferring the tibialis posterior tendon to the dorsum of the foot through the interosseous membrane neutralizes the tendon’s excessive force brought about by weakness of the anterior compartment muscles. One can detach the extensor hallucis longus tendon from its insertion on the distal phalanx of the hallux and attach the tendon to the neck of the first metatarsal in order to increase supination and dorsiflexion of the forefoot.^2,7 Arthrodesis of the subtalar, talonavicular or the calcaneocuboid joints in combination with tendon transfers or alone may also prevent relapse.

When one has performed gradual correction via distraction osteogenesis in cavus deformity correction, there are potential complications associated with external fixation of which the surgeon must be cognizant. Some of these include pin tract infections and neurovascular injury, both of which are treatable if one recognizes these complications early. Most pin site problems are attributed to movement of the skin relative to the pin and typically develop from the outside and progress into the pin site. Maintaining adequate wire tension and pin stability will minimize pin site infections. Gauze, Ilizarov sponges with antiseptic and plain sponges act as barriers between the air and the skin. Wrapping the pins with gauze from the skin to the fixator prevents the skin from pistoning up and down the half-pin, which decreases pin site inflammation. In addition, preoperative patient education on correct pin care and external fixation adjustments are extremely important to limit pin site issues.⁹

Neurovascular injury related to distraction osteogenesis may be associated with the technique, rate of lengthening and tension of the surrounding soft tissue on the vessels. Knowledge of the cross-sectional anatomy and muscle layers and compartments of the foot is imperative, and prevents intraoperative neurovascular injury. Insert drill guides before drilling for half-pins for accuracy and prevention of mechanical damage to the soft tissues.

Elicitation of paresthesias in the distribution of a nerve postoperatively may require decreasing the rate of gradual correction, removal of the pin or urgent nerve decompression. Vascular injury is rare and typically self-limiting due to the tamponade that ensues following damage to blood vessels.⁹

Dr. Lamm is the Head of Foot and Ankle Surgery and the Director of the Foot and Ankle Deformity Correction Fellowship at the Paley Institute at Palm Beach Children’s Hospital and St. Mary’s Medical Center in West Palm Beach, Fla.

Dr. Knight is a Clinical Fellow with the Foot and Ankle Deformity Correction Fellowship at the International Center for Limb Lengthening at the Rubin Institute for Advanced Orthopedics within the Sinai Hospital of Baltimore.

Dr. Pugh is a Clinical Fellow with the Foot and Ankle Deformity Correction Fellowship at the International Center for Limb Lengthening at the Rubin Institute for Advanced Orthopedics within the Sinai Hospital of Baltimore.

References

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2.     Kirienko A, Villa A, Calhoun JH. Ilizarov Technique for Complex Foot and Ankle Deformities. Marcel Dekker, New York, 2004.
3.     Paley D. Ankle and foot considerations. In: Principles of Deformity Correction. Second Edition. Springer-Verlag, Berlin, 2003, pp. 571-645.
4.     Paley D. Principles of foot deformity correction: Ilizarov technique. In: Gould S (ed.). Operative Foot Surgery. WB Saunders, Philadelphia, 1994, pp. 476-514.
5.     Lamm BM, Gottlieb HD, Paley D. A two-stage percutaneous approach to charcot diabetic foot reconstruction. J Foot Ankle Surg. 2010; 49(6)517-22.
6.     Tachdjian MO. Clinical Pediatric Orthopedics: The Art of Diagnosis and Principles of Management. Appleton & Lange, Stanford, CT, 1997.
7.     Paley D, Lamm BM. Correction of the cavus foot using external fixation. Foot Ankle Clin N Am. 2004;9(3):611- 624.
8.     Lamm BM, Gesheff MG, Salton HL, et al. Preoperative planning and intraoperative technique for accurate realignment of the Dwyer calcaneal osteotomy. J Foot Ankle Surg. 2013; 51(1):743-748.
9.     Lamm BM, Gourdine-Shaw MC. Problems, obstacles, and complications of metatarsal lengthening for the treatment of brachymetatarsia. Clin Podiatr Med Surg. 2010; 27(4):561-582.