30 Cavovarus Reconstruction Abstract The deformity of cavovarus foot is typically a result of muscular imbalance with an underlying neurologic disorder. The most common cause of symptomatic cavovarus deformity is hereditary motor sensory neuropathies including Charcot–Marie–Tooth disease. Other causes include trauma, tumor, stroke, poliomyelitis, and idiopathic problems. Classical pathologic changes such as forefoot pronation, high arch, hindfoot varus, and Achilles contracture may lead to abnormal load distribution resulting in ankle instability, peroneal tendonitis, lateral column overload or stress fracture, and finally degenerative arthritis. Surgical treatment is indicated in symptomatic and/or progressive cavovarus deformity. Many procedures are available for foot and ankle surgeons to employ in the surgical correction of the equinovarus foot. In this chapter, we will discuss the tricks of the trade of cavovarus deformity correction. Keywords: cavovarus deformity, surgery, Charcot–Marie–Tooth disease, calcaneal osteotomy, first metatarsal osteotomy, tendon transfer, Achilles lengthening, arthrodesis • Cavovarus deformity occurs as a result of muscle imbalance around the foot and ankle. As it is the most discussed, the Charcot–Marie–Tooth (CMT) disease is a good example for understanding the pathology of cavovarus deformity. • The tibialis anterior and peroneus brevis muscles are usually affected first, which is followed by dysfunction of the intrinsic muscles. Their muscular antagonists, the peroneus longus and tibialis posterior muscles, are relatively stronger, leading to plantar flexion of the first ray and medialization of the navicular, which results in pronation and adduction of forefoot. • As the deformity progresses, forefoot-driven hindfoot varus may develop. The deformity of cavovarus foot is often flexible in the early phase, which may gradually become rigid over time. Peroneal tendonitis and lateral instability can be present due to overloading. • Contracture of plantar fascia and Achilles tendon is often found. • A great toe cock-up deformity can develop with compensation of the relatively normal extensor hallucis longus (EHL) to dorsiflex the ankle. • With the intrinsic muscles weakened, the stronger pull of the extrinsic extensor digitorum longus (EDL) and flexor digitorum longus (FDL) tendons can lead to claw toe formation. Painful arthritic change can be presented in late stage cases. • The patient should be examined standing and walking with bare feet. • The peek-a-boo sign (Fig. 30.1), a common finding, is present when the examiner can see the medial aspect of the heel when viewed from the front. • Forefoot pronation along with adduction, cock-up great toe, clawed lesser toes, elevated longitudinal arch, hindfoot varus, and calf atrophy can be seen. • Foot drop and balance problems can be observed during walking as the anterior tibial muscle continues to weaken. • With the patient seated, range of motion and tenderness are accessed for the ankle, hindfoot, midfoot, and forefoot to evaluate for possible arthritis and rigid deformities. • It is essential to perform a complete neurologic examination to evaluate muscle strength and sensory deficits, and to differentiate an upper motor neuron versus a lower motor neuron–based pathology. Fig. 30.1 The peek-a-boo sign, a common finding, is present when the examiner can see the medial aspect of the heel from the front. • The Coleman block test can be used to evaluate whether the hindfoot deformity is flexible or fixed. • If the heel reduces into valgus by weight bearing on a block supporting only the lateral column of the foot (Fig. 30.2), the cavovarus deformity is defined as forefoot driven or flexible and can be corrected by addressing the forefoot deformity alone. Fig. 30.2 Coleman block test showed fixed hindfoot varus. • If not, then the deformity is rigid and a bony correction of the hindfoot varus may be necessary. • If ankle equinus is observed only with extension of the knee, a gastrocnemius contracture is diagnosed, and it should be treated by a gastrocnemius recession. • If contracture is found throughout the complete range of motion of the knee, then a formal Achilles tendon lengthening is indicated. • Weight-bearing anteroposterior (AP) and lateral X-rays are necessary cavovarus deformity evaluation. • An increased calcaneal pitch, Meary’s angel, and Hibbs’ angles can be found on the lateral view. A posterior fibula and a flat-topped talus may also be found. • A Saltzman view is essential to evaluate the degree of hindfoot varus and the angle of the subtalar joint. • The talar tilt can be assessed on the AP view. • Computed tomography and magnetic resonance imaging (MRI) can be helpful to find joint degenerative changes and possible tarsal coalitions. • Laterally posted custom orthotic inserts, with posting extended out to the midfoot. • Accommodative shoe wear. • Custom ankle foot orthosis (Arizona brace, Richie brace, and molded ankle–foot orthosis [MAFO] brace). • Physical therapy. • The contraindications include severe cardiovascular diseases, poor vascularization of the lower extremity, heavy smokers, local infection, and noncompliant patients. • For children younger than 8 years, arthrodesis should be avoided because it may result in growth arrest of more than 25% compared to the contralateral foot. Soft-tissue balancing procedures are often effective for mild to moderate cases with flexible deformity. Combining bony correction procedures may help with those having rigid deformities. Joint sparing correction is always the first choice until arthritic changes develop, which indicates necessary arthrodesis. The goal of surgical correction is to reconstruct a plantigrade foot without pain. • Recreating balance between muscular agonist/antagonist groups. • Realignment of the bony structures of the foot through osteotomies. • Joint preservation through tendon transfers and osteotomies to try to avoid arthrodesis procedures whenever possible. • Rebalance the muscle groups of the foot. • Recreate a balanced bony tripod of the foot to create a plantargrade foot for ambulation. The contracted plantar fascia plays an important role in keeping the high arch and the hindfoot varus; hence, plantar fascia release is usually indicated for cavovarus deformity reconstruction. The plantar fascia should be released completely from the origin on the calcaneus. This procedure allows further forefoot cavus correction and lowering the longitudinal arch. The patient is placed in the supine position with the lower limb externally rotated for better visualization of the foot. A thigh-level tourniquet is applied. Either an oblique incision or a longitudinal one may work to expose the insertion of the plantar fascia as well as the fascia of the abductor hallucis. A transection is then performed at the origin of the plantar fascia, taking care to protect the neurovascular bundle. In addition, the fascia of the abductor hallucis muscle is released (Fig 30.3). Tensioning the windlass mechanism with dorsiflexion of the metatarsal phalangeal joints may facilitate the release of the plantar fascia. With some cases of severe cavus deformity, releasing the fascia of the abductor hallucis may be necessary. The surgeon must be cautious to protect the lateral plantar nerve that passes through the medial side of the heel. Achilles contracture can often be found in cavovarus feet. Lengthening the Achilles may help reduce the stress of the forefoot and improve gait pattern by regaining normal dorsiflexion of the ankle. The modified Strayer procedure is performed for Achilles contracture with a positive Silfverskiöld’s test (gastrocnemius contracture only). Otherwise, the Hoke procedure is utilized. The patient is placed in the supine position with the lower limb externally rotated. A bump under the contralateral hip can help visualize the posteromedial part of the leg. A thigh-level tourniquet is applied. Flex the knee with the hip flexed and externally rotated. A longitudinal 3-cm posteromedial incision is made over the junction of the gastrocnemius–soleus complex, either posteromedially or directly posterior. After incising the fascia in line with the skin incision, the gastrocnemius tendon can be identified. The fascia is identified. This is carefully incised transversely, taking care to avoid injury to the sural nerve. The foot is then maximally dorsiflexed elongating the gastrocnemius. Using a speculum, either vaginal or nasal, or malleable retractors can be helpful for visualization in a modified Strayer procedure. This is a three-step hemicut within the distal Achilles tendon. An assistant holds the elevated limb while dorsiflexing the ankle. The first incision is placed about 2 cm proximal to the insertion into the heel. A no. 15 or 11 blade is used to pierce through the skin at the middle of the width of the tendon. The blade is inserted parallel with the tendon fibers. Once through, the scalpel is turned 90 degrees medially and the medial half of the tendon fibers are severed. The next incision is made about 3 cm proximal to the first. The tendon is again stabbed centrally; this time the lateral half of the tendon is severed. A third and the final incision is placed another 3 cm proximal to the second stab with the medial half of the tendon being transected. Dorsiflex the ankle joint with the knee extended and Achilles lengthening of up to 1.5 cm can be achieved.
30.1 Indications and Pathology
30.1.1 Clinical Evaluation
Coleman Block Test
Silfverskiöld’s Test
30.1.2 Radiographic Evaluation
30.1.3 Nonoperative Options
30.1.4 Contraindications
30.2 Goals of Surgical Procedure
30.3 Advantages of Surgical Procedure
30.4 Key Principles
30.5 Operative Technique
30.5.1 Surgical Procedure: Plantar Fascia Release
Preoperative Preparation
Operative Technique
Tips and Pearls
Hazards and Pitfalls
30.5.2 Surgical Technique: Achilles Tendon Lengthening
Preoperative Preparation
Operative Technique
The Modified Strayer Procedure
The Hoke Procedure
Musculoskeletal Key
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