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Cavovarus Correction in Charcot-Marie-Tooth Disease
PROCEDURE 34
Cavovarus Correction in Charcot-Marie-Tooth Disease Glenn B. Pfeffer
PITFALLS
• Charcot-Marie-Tooth (CMT) disease includes a wide spectrum of hereditary motor and sensory neuropathies. These diseases are often progressive, which can compromise the long-term results of a surgical reconstruction. • The feet of older adolescents and adults usually require simultaneous osteotomies, tendon transfers, and soft-tissue balancing. Young adolescents and children may benefit from soft-tissue procedures alone, especially in the early stages of the disease.
INDICATIONS CONTROVERSIES
• Early surgical intervention may prevent the progression of deformity and minimize impairment. There are no established guidelines, however, that address the appropriate age for surgery. Each case should be dealt with on an individual basis. • In children <14 years of age, it is often preferable to take an incremental approach to surgery, rather than correcting all deformities at once. This chapter examines the surgical options most appropriate for the older adolescents and adults with CMT disease. • Patients with mild to moderate involvement can often be treated successfully with nonoperative care. Cushioned shoes for shock absorption, soft inserts for metatarsalgia, hightopped shoes and lace-up ankle braces for ankle instability, and bracing for foot drop can help avoid surgery. Physical therapy for range of motion, strength, and proprioception can also be helpful. • The overarching goals of surgery are preservation of joint motion, creation of a plantigrade foot, and balance of muscle forces.
INDICATIONS • Chronic pain or deformity that interferes with activities of daily living • Failure of conservative measures, including bracing, shoe modification, and physical therapy • A relatively flexible deformity without arthritic changes in the involved joints
EXAMINATION/IMAGING Physical Examination • CMT disease can also affect the hips (dysplasia), spine (scoliosis), and upper extremities (Fig. 34.1). Weakness of the first dorsal interosseous muscle in the hand is one of the earliest signs of upper extremity involvement. • A complete orthopedic examination of the lower extremities is required. There is often atrophy of the anterior and lateral compartments of the leg. • Examine the foot from all sides while the patient is standing (Fig. 34.2). • Closely examine the lateral foot to evaluate the apex of the sagittal deformity (Fig. 34.3). • Document the calluses on the plantar aspect of the foot (Fig. 34.4). • Determine if claw toes are passively correctable (Fig. 34.5). • A Coleman block test (Paulos et al., 1980) can be helpful in sorting out forefootdriven heel varus. • When the patient stands with a block beneath the lateral border of the foot, the medial column is unsupported and the first metatarsal head drops off the side of the block (Fig. 34.6A). • If the subtalar joint is flexible and there is no fixed varus deformity of the heel, the hindfoot will no longer be in varus when viewed from behind (see Fig. 34.6B).
FIG. 34.1
272
PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
A
FIG. 34.3
B FIG. 34.2 FIG. 34.4
A
B FIG. 34.5
273
274
PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
A
B FIG. 34.6
• Document motor strength, including knee flexion and extension. Measure sensibility. • Typically, the peroneus longus, long toe extensors, and posterior compartment muscles will maintain strength long after the foot intrinsics, peroneus brevis, and tibialis anterior become weak. • Evaluate the imbalance between muscle agonists and antagonists (i.e., peroneus longus and tibialis anterior; posterior tibial and peroneus brevis; toe intrinsic flexors and extrinsic extensors). • Overpull of the posterior tibial tendon should be carefully evaluated and often has to be corrected at the time of surgery. • Observe the patient’s gait. A foot drop is often effectively treated with an ankle foot orthosis. The addition of an anterior tibial shelf often provides better balance to the patient. Surgery may still be required if a nonplantigrade foot deformity precludes effective bracing. • A dynamic electromyogram may be particularly helpful when evaluating potential tendon transfers preoperatively. • Multiple incisions are frequently required, which can create problems with skin healing. In patients with previous surgery, make sure that both the dorsalis pedis and posterior tibial pulses are present. If not palpable, a Doppler evaluation is indicated. • Spasticity, asymmetric reflexes, or marked hyperreflexia is not typical of CMT disease. If these symptoms are noted, magnetic resonance imaging of the spine should be obtained. • A neurologic consultation with electromyography/nerve conduction study and genetic testing (Athena Diagnostics, Worcester, MA, USA) is often appropriate. What is often considered idiopathic cavovarus is probably a form of CMT disease. • Document ankle laxity. Although patients often complain of instability during gait, objective ankle laxity is not often present. Extreme varus laxity can masquerade as normal subtalar motion. • Is the foot flexible? During the non–weight-bearing examination, the subtalar, transverse tarsal, and tarsal–metatarsal joints should be reasonably flexible. A fixed deformity will most commonly require a triple arthrodesis, which is not appropriate in a foot that has some preservation of motion in the hindfoot. • Evaluate gastrocnemius and soleus tightness. Typically, both the gastrocnemius and the soleus will have to be surgically lengthened at the level of the Achilles tendon.
PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
275
FIG. 34.8
A
B FIG. 34.7
FIG. 34.9
TREATMENT OPTIONS
Imaging • Standing anteroposterior (Fig. 34.7A) and lateral (see Fig. 34.7B) radiographs of the foot and ankle should be carefully examined to evaluate arthritic changes and determine the need for corrective osteotomies. Standing anteroposterior and lateral images of the foot should be repeated using a Coleman block, which presents a more accurate view of the foot and its true deformity. • The calcaneal pitch angle (normal <30°) and the talus–first metatarsal angle (Meary line; normal = 0°) are particularly useful in preoperative planning. If the calcaneal pitch corrects with the Coleman block in place, a corrective osteotomy of the heel may not be needed. • On the lateral standing radiograph, determine if the apex of the cavus is at the metatarsal–cuneiform joint or the midfoot. The deformity should be surgically corrected through its apex. • A three-dimensional computed tomography reconstruction can be helpful in the assessment of complex deformities and revision surgery (Fig. 34.8).
• Many surgical options are used to address the wide array of deformity and motor imbalance that occurs. This chapter presents one of the most common operative approaches, which includes Achilles lengthening, triplane calcaneal osteotomy, Steindler release of the plantar fascia, peroneus longus-to-peroneus brevis transfer, closing wedge metatarsal or midfoot (Cole) osteotomy, correction of claw toes, interphalangeal fusion of the great toe, and extensor tendon transfers to the metatarsal necks. While often performed at the same time, forefoot reconstruction can be performed during a separate operative procedure. • With the hindfoot held in neutral, evaluate forefoot cavus (valgus) caused by flexion of the medial metatarsals from overpull of the peroneus longus (Fig. 34.9). Commonly, only the first metatarsal is involved, although the second and third may be as well. Involvement of the fourth and fifth metatarsals that requires operative correction is rare. If a plantar-flexed metatarsal is not corrected, the surgical outcome will be poor.
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PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
SURGICAL ANATOMY • Varus heel (Fig. 34.10A) • Valgus forefoot (see Fig. 34.10B) • High calcaneal pitch angle (Fig. 34.11A) • Meary line (see Fig. 34.11B)
A
B FIG. 34.10
A
B FIG. 34.11
PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
POSITIONING • Place the patient in a partial lateral decubitus position to gain easy exposure to the lateral side of the foot. A deflated beanbag is placed behind the ipsilateral hip to help support the patient in this position. The beanbag can easily be removed during the surgery, allowing the patient to drop down into a supine position. • Use a thigh tourniquet. • A femoral-sciatic or popliteal block will help with postoperative pain control (Fig. 34.12). CMT disease is not a contraindication to a regional block.
PORTALS/EXPOSURES • If indicated, perform a triple-cut lengthening of the Achilles tendon using a #11 blade, leaving the lateral insertion intact (Fig. 34.13). It is usually not sufficient to perform a Strayer procedure to lengthen the gastrocnemius alone. • Begin the incision with a #15 blade just proximal to the tip of the fibula. • Extend it distally over the calcaneal tuberosity, along the posterior border of the peroneal sheath. The incision should have a straight component over the portion of the calcaneus that will be osteotomized. • Extend the incision distally over the peroneals, ending at the insertion of the peroneus brevis (Fig. 34.14). If a midfoot osteotomy is required, the incision can be extended distally over the lateral axis of the cuboid bone. • Identify and protect the sural nerve (Fig. 34.15).
POSITIONING PEARLS
• The patient should be very well padded because of potential susceptibility to pressure palsies. PORTALS/EXPOSURES PEARLS
• Once the patient is under anesthesia, perform a fluoroscopic examination of the ankle for laxity. The surgical approach can be modified depending on the results of this examination. • If ankle laxity has to be corrected, two incisions are preferable: one for the ligament reconstruction and tendon transfer, and the other for the calcaneal osteotomy. With one incision, too large a flap has to be dissected to expose both the calcaneal tuberosity and the anterior ankle. It is unusual, however, to find pathologic ankle laxity in these patients, and one incision can almost always be used to expose the heel and the peroneal tendons.
FIG. 34.12 FIG. 34.13
FIG. 34.14
277
FIG. 34.15
PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
278
STEP 1 PEARLS
• The calcaneal osteotomy is performed as anteriorly as possible in the tuberosity, to allow for maximal correction of the heel deformity. The osteotomy is usually located at the posterior border of the peroneal sheath. • A centimeter of bone is the most that can usually be removed from the calcaneus without shortening the heel unduly. Superior displacement of the tuberosity adds some length to the calcaneus because of the obliquity of the cut. • When the calcaneus is displaced superiorly, the Achilles tendon is effectively lengthened, and an additional triple-cut lengthening may not be required. • If there is 4+ strength of the posterior tibial tendon, but little peroneus brevis function or peroneus longus function, an excellent surgical option is a closing wedge fusion of the subtalar joint (to correct hindfoot varus), and transfer of the posterior tibial tendon through the interosseous membrane onto the dorsum of the foot (lateral cuneiform or cuboid). A simultaneous osteotomy of the heel may still be required.
STEP 1 PITFALLS
• A simple lateral displacement or Dwyer osteotomy of the tuberosity is rarely sufficient. The posterior tuberosity should be displaced superiorly, laterally, and rotated out of varus. A closing wedge of up to 1 cm may also be required.
PROCEDURE Step 1 • Expose the lateral wall of the calcaneus. Under fluoroscopic guidance, determine the appropriate position of the osteotomy. This is usually just posterior to the peroneal sheath. • Under cool water lavage, use a microsagittal saw to cut perpendicular to the axis of the tuberosity (Fig. 34.16A). Superiorly, it should exit 1 cm posterior to the subtalar joint. • The osteotomy should be angled obliquely (see Fig. 34.16B–C), from superior–proximal to inferior–distal, to allow rotation of the heel out of varus (as opposed to a medial displacement osteotomy used in the correction of pes planus, which is oriented closer to the axis of the tibia). Avoid the subtalar joint superiorly. • If a simple closing wedge is all that is needed (which is not usually the case), leave the medial cortex intact; compress the osteotomy, and place three 16 × 25-mm staples (Fig. 34.17). Excellent rigid fixation will be obtained without the need for compression screws. • Many patients require correction of both heel varus and a high calcaneal pitch angle (hindfoot cavus) by a triplane osteotomy. In such a case, continue the cut through the medial cortex, being very careful not to damage the neurovascular bundle. • Carefully make the distal cut of the osteotomy first, as there are several structures at risk anteriorly (peroneal tendons, neurovascular bundle, and subtalar joint). The second cut is made posterior and parallel to the first, removing the appropriate amount of bone (usually 7–10 mm). • Gently widen the osteotomy with a lamina spreader to facilitate displacement of the tuberosity (Fig. 34.18). The medial nerves will not be stretched by this maneuver. • Displace the osteotomy approximately 1 cm superiorly and 1 cm laterally, to centralize the weight-bearing axis of the heel. • Close the osteotomy laterally and hold it with one or two fluoroscopically placed 6.5–7.3-mm cannulated screws (Fig. 34.19A). One screw may be sufficient if good bone purchase is obtained (see Fig. 34.19B). • Use a reciprocating power rasp to smooth down the lateral wall of the calcaneus (Fig. 34.20).
1–1.5 cm laterally based closing wedge 1 cm
A
B
C FIG. 34.16
PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
FIG. 34.18 FIG. 34.17
A
B FIG. 34.19
FIG. 34.20
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280
PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
Step 2
STEP 2 PITFALLS
• Stay close to the calcaneus during the dissection to avoid inadvertent injury to the lateral plantar nerve. • To avoid injury to the medial neurovascular structures as the saw advances make sure the blade is not tilted and remains perpendicular to the lateral wall of the calcaneus.
• If a peroneal tendon transfer is planned, extend the incision over the peroneals, as noted earlier (Fig. 34.21). Use the skin marker to note the resting length of both tendons, which will help place the longus at the appropriate resting length. Protect the sural nerve that crosses obliquely. • Divide the peroneus longus as it passes beneath the cuboid. Use a Pulvertaft weave to transfer the longus into the distal most aspect of the brevis. Three weaves of the tendon create a very strong transfer. Use 3-0 Ethibond sutures to secure the transfer (Fig. 34.22). The fibrous tunnel of the distal peroneal sheath may have to be removed, and the trochlear process smoothed down, to facilitate unobstructed motion of the transfer. • If a midfoot osteotomy is not required, the wound is irrigated and closed in layers, using an absorbable subcutaneous suture and alternating horizontal mattress and simple 3-0 nylon sutures in the skin. • At this point evaluate the posterior tibial tendon. It is often a cause of deformity. If the posterior tibial tendon has four-fifths strength, it is preferable not to simply release. Why waste a functioning muscle in a patient with CMT? The tendon can be lengthened through a separate incision proximal to the ankle joint, or transferred to assist with ankle dorsiflexion or hindfoot eversion.
STEP 3 PEARLS
Step 3
• If the first metatarsal is not adequately corrected, a simultaneous closing wedge osteotomy of the medial cuneiform can be added. • Occasionally, an osteotomy of the second metatarsal will be required (approximately 10% of cases). If two osteotomies are anticipated, base the initial incision more laterally, between the metatarsals. If more than two basilar osteotomies are needed, a better correction will be obtained with a midfoot osteotomy (see later). A midfoot osteotomy will also facilitate the correction of an adduction deformity.
• Remove the beanbag and place the patient into a supine position with the foot slightly externally rotated. • Make a 3-cm oblique incision over the medial heel where the plantar fascia attaches. This incision will avoid the medial calcaneal nerve branch, which is easily injured with a longitudinal incision. • Divide the superficial abductor fascia and strip the abductor muscle and its deep fascia from their attachments on the medial calcaneus (Fig. 34.23). Avoid injury to the first branch of the lateral plantar nerve, which runs deep to the abductor. • Locate the medial edge of the plantar fascia and divide the fascia with small tenotomy scissors, pushing from medial to lateral. Use a small key elevator to strip the calcaneal attachments of the plantar intrinsic muscles. • Irrigate and close the skin with simple nylon sutures.
FIG. 34.21
FIG. 34.22
PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
Step 4
STEP 4 PEARLS
• Most frequently, the forefoot cavus (valgus) can be corrected with a closing wedge osteotomy at the base of the first metatarsal. • Make a 4-cm incision over the base of the first metatarsal (Fig. 34.24). Identify the extensor hallucis longus and retract it laterally. • Identify the first metatarsal–cuneiform joint and, with a microsagittal saw, make a cut in the metatarsal 1.5 cm distal and parallel to the joint (Fig. 34.25). Irrigate with cool water lavage when using the power saw. During the cut, place slight plantar pressure on the distal metatarsal, which will start to hinge open the osteotomy prior to completion of the cut. It is essential to leave the plantar cortex intact. • Make a second oblique cut several millimeters distal to the first cut (see Fig. 34.25B). Initially, only a small amount of bone (3–5 mm) should be removed. It is difficult to close the osteotomy if more than 7–8 mm is removed. • Place a 4.0 partially threaded screw into the proximal fragment (see Fig. 34.25B). Do not seat it completely. • Use a 0.062-inch Kirschner wire (K-wire) or comparable drill to make a transverse hole 1 cm distal to the osteotomy, just dorsal to the longitudinal axis of the metatarsal (see Fig. 34.25B). Pass a 20-gauge wire through the hole from medial to lateral. Use a small hemostat to grab the wire in the first metatarsal space. Place the wire in a figure-of-8 configuration around the screw head. Using a partially threaded screw allows the wire to seat securely beneath the screw head. • Carefully close the osteotomy, tighten the wire, and advance the screw (Fig. 34.26). Do not overtighten the screw, which can cause the wire to break. Carefully examine the transverse alignment of the metatarsal heads. Repeat a similar osteotomy on additional metatarsals, as needed.
FIG. 34.23
• Small plates can also be used to secure the Cole midfoot osteotomy, although they tend to be bulkier and are more likely to require removal in the future.
FIG. 34.24
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282
PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
FIG. 34.26
A
B FIG. 34.25
STEP 5 CONTROVERSIES
• Some surgeons are concerned about the rate of nonunion from this osteotomy. The broad cancellous surfaces, however, have little trouble healing. A nonunion is very rare if good bone apposition is obtained at the time of surgery. • Others are concerned about potential arthritis of the adjacent joints because of inadvertent injury during the osteotomy cuts. Careful placement of the K-wires under fluoroscopic guidance completely avoids this potential complication. The decrease of motion that results from fusion of the navicular–cuneiform joints is insignificant.
Step 5 • If the apex of the sagittal foot deformity is in the midfoot, the best correction is with a Cole osteotomy through the navicular–cuneiform joints medially and the cuboid laterally. • This truncated closing wedge osteotomy provides excellent multiplanar correction of the deformity. It also places the incisions on either side of the foot, away from the multiple dorsal incisions that may be needed to correct claw toes. • This osteotomy should be used if more than two metatarsals require an osteotomy, or an adduction of the midfoot needs correction. • The lateral incision should be extended over the longitudinal axis of the cuboid. Medially, an incision is made over the navicular–cuneiform joint, in the plane between the tibialis posterior and tibialis anterior tendons. Protect both of these tendons, particularly the tibialis anterior, which is vulnerable during the saw cuts. • Under fluoroscopic guidance, place two 0.062-inch K-wires approximately 1.5 cm apart, from medial to lateral (Fig. 34.27A). • The pin placement is oblique, as the cuboid is inferior to the medial navicular–cuneiform joint. • The more distal pin passes through the medial cuneiform and exits through the distal cuboid; the more proximal pin passes medially across the navicular and exits through the proximal cuboid (see Fig. 34.27B–C). • Avoid penetration of the fourth and fifth metatarsal–cuboid joints. • Using blunt dissection and a small key elevator, completely dissect the soft-tissue envelope around the bone of the midfoot. Protect the neurovascular structures dorsally and plantarly with small Hohmann retractors. • Cut along the inside of each pin, removing a trapezoidal wedge of bone that includes the navicular–cuneiform joints (Fig. 34.28). Irrigate with cool saline lavage. • Make every effort to create flat cuts, without redirecting the saw blade. Imagine that the apex of the wedge is at the plantar fascia, which enables a trapezoidal piece of bone to be resected.
PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
A
B
C FIG. 34.27
FIG. 34.28
• Adduction of the midfoot can be corrected with appropriately placed bone cuts. • Remove the K-wires. • The forefoot can now be dorsiflexed and rotated into the correct position. Make sure that the transverse metatarsal arch is well aligned and that the forefoot valgus is corrected. • Place the two K-wires temporarily across the osteotomy and place three 16 × 20 mm 3M power staples across the osteotomy sites both medially and laterally. Excellent fixation can be obtained in this manner (Fig. 34.29). • Deflate the tourniquet. Obtain hemostasis and close the wounds in two layers, with alternating 3-0 nylon horizontal mattress and simple sutures in the skin.
FIG. 34.29
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284
PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
Sutures
Periosteum of distal metatarsal Extensor tendon
FIG. 34.31
FIG. 34.30
STEP 6 PEARLS
• A bulk transfer of the long toe extensors into the lateral cuneiform or cuboid may provide more effective ankle dorsiflexion than individual transfers into the metatarsal necks.
Step 6 • Claw toes should be corrected using standard techniques that involve resection of the distal aspect of the proximal phalanx (see Procedure 14). The extensor digitorum longus tendon of each toe is transferred to the distal metatarsal using a deep periosteal stitch (Fig. 34.30). A small drill hole in the bone can be used but is time consuming and probably unnecessary, given that the foot will be immobilized for at least 6 weeks in neutral position. • If clawing of the great toe is present, the interphalangeal joint should be fused through a transverse incision. The extensor hallucis longus is transferred into the distal metatarsal through a transverse drill hole. • Correction of the forefoot deformity, by either metatarsal or midfoot osteotomy, can create extrinsic flexor tightness, especially in the lesser toes. Even after the clawing is corrected, hyperflexion of the toe may persist. A closed or open tenotomy of the flexor digitorum longus to the toe will correct this problem (Fig. 34.31).
POSTOPERATIVE CARE AND EXPECTED OUTCOMES • A bulky dressing and a three-sided splint are applied in the operating room after all of the osteotomies are checked for a final time by fluoroscan. • The patient returns to the office 10–12 days after surgery for the placement of a short-leg non–weight-bearing cast. Sutures are removed at this point, if the wounds are completely healed. Anteroposterior (Fig. 34.32A) and lateral (see Fig. 34.32B) radiographs are taken in the cast. • Six weeks after surgery, the cast is removed and radiographs are taken. An additional short-leg, nonremovable cast is applied. The patient can start weight bearing as tolerated. This second cast is removed at 10 weeks postoperatively. Physical therapy should be started at this point, along with appropriate footwear. • An excellent and enduring correction of the deformity can be expected (Fig. 34.33; the right foot has had surgery). See also Video 34.1, Cavovarus Correction in Charcot-Marie-Tooth Disease.
PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
A
B FIG. 34.32
A
B FIG. 34.33
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286
PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
EVIDENCE Cole WH. The treatment of claw-foot. J Bone Joint Surg Am 1940;22:895–905. Original description of the Cole osteotomy for midfoot cavus (Level V evidence). Guyton GP. Current concepts review: orthopaedic aspects of Charcot-Marie-Tooth disease. Foot Ankle Int 2006;27:1003–10. An excellent review of the topic and the literature. Mann RA, Missirian J. Pathophysiology of Charcot-Marie-Tooth disease. Clin Orthop Relat Res 1988;(234):221–8. This paper examines CMT deformity and the contribution of muscle imbalance (Level V evidence). Nagel MK, Chan G, Guille JT. Prevalence of Charcot-Marie Tooth disease in patients who have bilateral cavovarus feet. J Pediatr Orthop 2006;26:438–43. Seventy-eight percent of children with “idiopathic” cavovarus feet were diagnosed with CMT disease by neurophysiologic and genetic testing (Level IV evidence). Paulos L, Colemann SS, Samuelson KM. Pes cavovarus: review of surgical approach using selective soft-tissue procedures. J Bone Joint Surg Am 1980;62:942–53. Review of 39 feet in children with cavovarus deformity. The use of the Coleman block test to distinguish forefoot-driven heel varus is described (Level IV evidence). Pfeffer GP, Michalski MP, Basak T, Giaconi J. The Use of 3D Prints to Compare the Efficacy of Three Different Calcaneal Osteotomies for the Correction of Heel Varus. In American Academy of Orthopaedic Surgeons Annual Meeting 2017.
Cavovarus Correction in Charcot-Marie-Tooth Disease Glenn B. Pfeffer
PITFALLS
• Charcot-Marie-Tooth (CMT) disease includes a wide spectrum of hereditary motor and sensory neuropathies. These diseases are often progressive, which can compromise the long-term results of a surgical reconstruction. • The feet of older adolescents and adults usually require simultaneous osteotomies, tendon transfers, and soft-tissue balancing. Young adolescents and children may benefit from soft-tissue procedures alone, especially in the early stages of the disease.
INDICATIONS CONTROVERSIES
• Early surgical intervention may prevent the progression of deformity and minimize impairment. There are no established guidelines, however, that address the appropriate age for surgery. Each case should be dealt with on an individual basis. • In children <14 years of age, it is often preferable to take an incremental approach to surgery, rather than correcting all deformities at once. This chapter examines the surgical options most appropriate for the older adolescents and adults with CMT disease. • Patients with mild to moderate involvement can often be treated successfully with nonoperative care. Cushioned shoes for shock absorption, soft inserts for metatarsalgia, hightopped shoes and lace-up ankle braces for ankle instability, and bracing for foot drop can help avoid surgery. Physical therapy for range of motion, strength, and proprioception can also be helpful. • The overarching goals of surgery are preservation of joint motion, creation of a plantigrade foot, and balance of muscle forces.
INDICATIONS • Chronic pain or deformity that interferes with activities of daily living • Failure of conservative measures, including bracing, shoe modification, and physical therapy • A relatively flexible deformity without arthritic changes in the involved joints
EXAMINATION/IMAGING Physical Examination • CMT disease can also affect the hips (dysplasia), spine (scoliosis), and upper extremities (Fig. 34.1). Weakness of the first dorsal interosseous muscle in the hand is one of the earliest signs of upper extremity involvement. • A complete orthopedic examination of the lower extremities is required. There is often atrophy of the anterior and lateral compartments of the leg. • Examine the foot from all sides while the patient is standing (Fig. 34.2). • Closely examine the lateral foot to evaluate the apex of the sagittal deformity (Fig. 34.3). • Document the calluses on the plantar aspect of the foot (Fig. 34.4). • Determine if claw toes are passively correctable (Fig. 34.5). • A Coleman block test (Paulos et al., 1980) can be helpful in sorting out forefootdriven heel varus. • When the patient stands with a block beneath the lateral border of the foot, the medial column is unsupported and the first metatarsal head drops off the side of the block (Fig. 34.6A). • If the subtalar joint is flexible and there is no fixed varus deformity of the heel, the hindfoot will no longer be in varus when viewed from behind (see Fig. 34.6B).
FIG. 34.1
272
PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
A
FIG. 34.3
B FIG. 34.2 FIG. 34.4
A
B FIG. 34.5
273
274
PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
A
B FIG. 34.6
• Document motor strength, including knee flexion and extension. Measure sensibility. • Typically, the peroneus longus, long toe extensors, and posterior compartment muscles will maintain strength long after the foot intrinsics, peroneus brevis, and tibialis anterior become weak. • Evaluate the imbalance between muscle agonists and antagonists (i.e., peroneus longus and tibialis anterior; posterior tibial and peroneus brevis; toe intrinsic flexors and extrinsic extensors). • Overpull of the posterior tibial tendon should be carefully evaluated and often has to be corrected at the time of surgery. • Observe the patient’s gait. A foot drop is often effectively treated with an ankle foot orthosis. The addition of an anterior tibial shelf often provides better balance to the patient. Surgery may still be required if a nonplantigrade foot deformity precludes effective bracing. • A dynamic electromyogram may be particularly helpful when evaluating potential tendon transfers preoperatively. • Multiple incisions are frequently required, which can create problems with skin healing. In patients with previous surgery, make sure that both the dorsalis pedis and posterior tibial pulses are present. If not palpable, a Doppler evaluation is indicated. • Spasticity, asymmetric reflexes, or marked hyperreflexia is not typical of CMT disease. If these symptoms are noted, magnetic resonance imaging of the spine should be obtained. • A neurologic consultation with electromyography/nerve conduction study and genetic testing (Athena Diagnostics, Worcester, MA, USA) is often appropriate. What is often considered idiopathic cavovarus is probably a form of CMT disease. • Document ankle laxity. Although patients often complain of instability during gait, objective ankle laxity is not often present. Extreme varus laxity can masquerade as normal subtalar motion. • Is the foot flexible? During the non–weight-bearing examination, the subtalar, transverse tarsal, and tarsal–metatarsal joints should be reasonably flexible. A fixed deformity will most commonly require a triple arthrodesis, which is not appropriate in a foot that has some preservation of motion in the hindfoot. • Evaluate gastrocnemius and soleus tightness. Typically, both the gastrocnemius and the soleus will have to be surgically lengthened at the level of the Achilles tendon.
PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
275
FIG. 34.8
A
B FIG. 34.7
FIG. 34.9
TREATMENT OPTIONS
Imaging • Standing anteroposterior (Fig. 34.7A) and lateral (see Fig. 34.7B) radiographs of the foot and ankle should be carefully examined to evaluate arthritic changes and determine the need for corrective osteotomies. Standing anteroposterior and lateral images of the foot should be repeated using a Coleman block, which presents a more accurate view of the foot and its true deformity. • The calcaneal pitch angle (normal <30°) and the talus–first metatarsal angle (Meary line; normal = 0°) are particularly useful in preoperative planning. If the calcaneal pitch corrects with the Coleman block in place, a corrective osteotomy of the heel may not be needed. • On the lateral standing radiograph, determine if the apex of the cavus is at the metatarsal–cuneiform joint or the midfoot. The deformity should be surgically corrected through its apex. • A three-dimensional computed tomography reconstruction can be helpful in the assessment of complex deformities and revision surgery (Fig. 34.8).
• Many surgical options are used to address the wide array of deformity and motor imbalance that occurs. This chapter presents one of the most common operative approaches, which includes Achilles lengthening, triplane calcaneal osteotomy, Steindler release of the plantar fascia, peroneus longus-to-peroneus brevis transfer, closing wedge metatarsal or midfoot (Cole) osteotomy, correction of claw toes, interphalangeal fusion of the great toe, and extensor tendon transfers to the metatarsal necks. While often performed at the same time, forefoot reconstruction can be performed during a separate operative procedure. • With the hindfoot held in neutral, evaluate forefoot cavus (valgus) caused by flexion of the medial metatarsals from overpull of the peroneus longus (Fig. 34.9). Commonly, only the first metatarsal is involved, although the second and third may be as well. Involvement of the fourth and fifth metatarsals that requires operative correction is rare. If a plantar-flexed metatarsal is not corrected, the surgical outcome will be poor.
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PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
SURGICAL ANATOMY • Varus heel (Fig. 34.10A) • Valgus forefoot (see Fig. 34.10B) • High calcaneal pitch angle (Fig. 34.11A) • Meary line (see Fig. 34.11B)
A
B FIG. 34.10
A
B FIG. 34.11
PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
POSITIONING • Place the patient in a partial lateral decubitus position to gain easy exposure to the lateral side of the foot. A deflated beanbag is placed behind the ipsilateral hip to help support the patient in this position. The beanbag can easily be removed during the surgery, allowing the patient to drop down into a supine position. • Use a thigh tourniquet. • A femoral-sciatic or popliteal block will help with postoperative pain control (Fig. 34.12). CMT disease is not a contraindication to a regional block.
PORTALS/EXPOSURES • If indicated, perform a triple-cut lengthening of the Achilles tendon using a #11 blade, leaving the lateral insertion intact (Fig. 34.13). It is usually not sufficient to perform a Strayer procedure to lengthen the gastrocnemius alone. • Begin the incision with a #15 blade just proximal to the tip of the fibula. • Extend it distally over the calcaneal tuberosity, along the posterior border of the peroneal sheath. The incision should have a straight component over the portion of the calcaneus that will be osteotomized. • Extend the incision distally over the peroneals, ending at the insertion of the peroneus brevis (Fig. 34.14). If a midfoot osteotomy is required, the incision can be extended distally over the lateral axis of the cuboid bone. • Identify and protect the sural nerve (Fig. 34.15).
POSITIONING PEARLS
• The patient should be very well padded because of potential susceptibility to pressure palsies. PORTALS/EXPOSURES PEARLS
• Once the patient is under anesthesia, perform a fluoroscopic examination of the ankle for laxity. The surgical approach can be modified depending on the results of this examination. • If ankle laxity has to be corrected, two incisions are preferable: one for the ligament reconstruction and tendon transfer, and the other for the calcaneal osteotomy. With one incision, too large a flap has to be dissected to expose both the calcaneal tuberosity and the anterior ankle. It is unusual, however, to find pathologic ankle laxity in these patients, and one incision can almost always be used to expose the heel and the peroneal tendons.
FIG. 34.12 FIG. 34.13
FIG. 34.14
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FIG. 34.15
PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
278
STEP 1 PEARLS
• The calcaneal osteotomy is performed as anteriorly as possible in the tuberosity, to allow for maximal correction of the heel deformity. The osteotomy is usually located at the posterior border of the peroneal sheath. • A centimeter of bone is the most that can usually be removed from the calcaneus without shortening the heel unduly. Superior displacement of the tuberosity adds some length to the calcaneus because of the obliquity of the cut. • When the calcaneus is displaced superiorly, the Achilles tendon is effectively lengthened, and an additional triple-cut lengthening may not be required. • If there is 4+ strength of the posterior tibial tendon, but little peroneus brevis function or peroneus longus function, an excellent surgical option is a closing wedge fusion of the subtalar joint (to correct hindfoot varus), and transfer of the posterior tibial tendon through the interosseous membrane onto the dorsum of the foot (lateral cuneiform or cuboid). A simultaneous osteotomy of the heel may still be required.
STEP 1 PITFALLS
• A simple lateral displacement or Dwyer osteotomy of the tuberosity is rarely sufficient. The posterior tuberosity should be displaced superiorly, laterally, and rotated out of varus. A closing wedge of up to 1 cm may also be required.
PROCEDURE Step 1 • Expose the lateral wall of the calcaneus. Under fluoroscopic guidance, determine the appropriate position of the osteotomy. This is usually just posterior to the peroneal sheath. • Under cool water lavage, use a microsagittal saw to cut perpendicular to the axis of the tuberosity (Fig. 34.16A). Superiorly, it should exit 1 cm posterior to the subtalar joint. • The osteotomy should be angled obliquely (see Fig. 34.16B–C), from superior–proximal to inferior–distal, to allow rotation of the heel out of varus (as opposed to a medial displacement osteotomy used in the correction of pes planus, which is oriented closer to the axis of the tibia). Avoid the subtalar joint superiorly. • If a simple closing wedge is all that is needed (which is not usually the case), leave the medial cortex intact; compress the osteotomy, and place three 16 × 25-mm staples (Fig. 34.17). Excellent rigid fixation will be obtained without the need for compression screws. • Many patients require correction of both heel varus and a high calcaneal pitch angle (hindfoot cavus) by a triplane osteotomy. In such a case, continue the cut through the medial cortex, being very careful not to damage the neurovascular bundle. • Carefully make the distal cut of the osteotomy first, as there are several structures at risk anteriorly (peroneal tendons, neurovascular bundle, and subtalar joint). The second cut is made posterior and parallel to the first, removing the appropriate amount of bone (usually 7–10 mm). • Gently widen the osteotomy with a lamina spreader to facilitate displacement of the tuberosity (Fig. 34.18). The medial nerves will not be stretched by this maneuver. • Displace the osteotomy approximately 1 cm superiorly and 1 cm laterally, to centralize the weight-bearing axis of the heel. • Close the osteotomy laterally and hold it with one or two fluoroscopically placed 6.5–7.3-mm cannulated screws (Fig. 34.19A). One screw may be sufficient if good bone purchase is obtained (see Fig. 34.19B). • Use a reciprocating power rasp to smooth down the lateral wall of the calcaneus (Fig. 34.20).
1–1.5 cm laterally based closing wedge 1 cm
A
B
C FIG. 34.16
PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
FIG. 34.18 FIG. 34.17
A
B FIG. 34.19
FIG. 34.20
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PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
Step 2
STEP 2 PITFALLS
• Stay close to the calcaneus during the dissection to avoid inadvertent injury to the lateral plantar nerve. • To avoid injury to the medial neurovascular structures as the saw advances make sure the blade is not tilted and remains perpendicular to the lateral wall of the calcaneus.
• If a peroneal tendon transfer is planned, extend the incision over the peroneals, as noted earlier (Fig. 34.21). Use the skin marker to note the resting length of both tendons, which will help place the longus at the appropriate resting length. Protect the sural nerve that crosses obliquely. • Divide the peroneus longus as it passes beneath the cuboid. Use a Pulvertaft weave to transfer the longus into the distal most aspect of the brevis. Three weaves of the tendon create a very strong transfer. Use 3-0 Ethibond sutures to secure the transfer (Fig. 34.22). The fibrous tunnel of the distal peroneal sheath may have to be removed, and the trochlear process smoothed down, to facilitate unobstructed motion of the transfer. • If a midfoot osteotomy is not required, the wound is irrigated and closed in layers, using an absorbable subcutaneous suture and alternating horizontal mattress and simple 3-0 nylon sutures in the skin. • At this point evaluate the posterior tibial tendon. It is often a cause of deformity. If the posterior tibial tendon has four-fifths strength, it is preferable not to simply release. Why waste a functioning muscle in a patient with CMT? The tendon can be lengthened through a separate incision proximal to the ankle joint, or transferred to assist with ankle dorsiflexion or hindfoot eversion.
STEP 3 PEARLS
Step 3
• If the first metatarsal is not adequately corrected, a simultaneous closing wedge osteotomy of the medial cuneiform can be added. • Occasionally, an osteotomy of the second metatarsal will be required (approximately 10% of cases). If two osteotomies are anticipated, base the initial incision more laterally, between the metatarsals. If more than two basilar osteotomies are needed, a better correction will be obtained with a midfoot osteotomy (see later). A midfoot osteotomy will also facilitate the correction of an adduction deformity.
• Remove the beanbag and place the patient into a supine position with the foot slightly externally rotated. • Make a 3-cm oblique incision over the medial heel where the plantar fascia attaches. This incision will avoid the medial calcaneal nerve branch, which is easily injured with a longitudinal incision. • Divide the superficial abductor fascia and strip the abductor muscle and its deep fascia from their attachments on the medial calcaneus (Fig. 34.23). Avoid injury to the first branch of the lateral plantar nerve, which runs deep to the abductor. • Locate the medial edge of the plantar fascia and divide the fascia with small tenotomy scissors, pushing from medial to lateral. Use a small key elevator to strip the calcaneal attachments of the plantar intrinsic muscles. • Irrigate and close the skin with simple nylon sutures.
FIG. 34.21
FIG. 34.22
PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
Step 4
STEP 4 PEARLS
• Most frequently, the forefoot cavus (valgus) can be corrected with a closing wedge osteotomy at the base of the first metatarsal. • Make a 4-cm incision over the base of the first metatarsal (Fig. 34.24). Identify the extensor hallucis longus and retract it laterally. • Identify the first metatarsal–cuneiform joint and, with a microsagittal saw, make a cut in the metatarsal 1.5 cm distal and parallel to the joint (Fig. 34.25). Irrigate with cool water lavage when using the power saw. During the cut, place slight plantar pressure on the distal metatarsal, which will start to hinge open the osteotomy prior to completion of the cut. It is essential to leave the plantar cortex intact. • Make a second oblique cut several millimeters distal to the first cut (see Fig. 34.25B). Initially, only a small amount of bone (3–5 mm) should be removed. It is difficult to close the osteotomy if more than 7–8 mm is removed. • Place a 4.0 partially threaded screw into the proximal fragment (see Fig. 34.25B). Do not seat it completely. • Use a 0.062-inch Kirschner wire (K-wire) or comparable drill to make a transverse hole 1 cm distal to the osteotomy, just dorsal to the longitudinal axis of the metatarsal (see Fig. 34.25B). Pass a 20-gauge wire through the hole from medial to lateral. Use a small hemostat to grab the wire in the first metatarsal space. Place the wire in a figure-of-8 configuration around the screw head. Using a partially threaded screw allows the wire to seat securely beneath the screw head. • Carefully close the osteotomy, tighten the wire, and advance the screw (Fig. 34.26). Do not overtighten the screw, which can cause the wire to break. Carefully examine the transverse alignment of the metatarsal heads. Repeat a similar osteotomy on additional metatarsals, as needed.
FIG. 34.23
• Small plates can also be used to secure the Cole midfoot osteotomy, although they tend to be bulkier and are more likely to require removal in the future.
FIG. 34.24
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PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
FIG. 34.26
A
B FIG. 34.25
STEP 5 CONTROVERSIES
• Some surgeons are concerned about the rate of nonunion from this osteotomy. The broad cancellous surfaces, however, have little trouble healing. A nonunion is very rare if good bone apposition is obtained at the time of surgery. • Others are concerned about potential arthritis of the adjacent joints because of inadvertent injury during the osteotomy cuts. Careful placement of the K-wires under fluoroscopic guidance completely avoids this potential complication. The decrease of motion that results from fusion of the navicular–cuneiform joints is insignificant.
Step 5 • If the apex of the sagittal foot deformity is in the midfoot, the best correction is with a Cole osteotomy through the navicular–cuneiform joints medially and the cuboid laterally. • This truncated closing wedge osteotomy provides excellent multiplanar correction of the deformity. It also places the incisions on either side of the foot, away from the multiple dorsal incisions that may be needed to correct claw toes. • This osteotomy should be used if more than two metatarsals require an osteotomy, or an adduction of the midfoot needs correction. • The lateral incision should be extended over the longitudinal axis of the cuboid. Medially, an incision is made over the navicular–cuneiform joint, in the plane between the tibialis posterior and tibialis anterior tendons. Protect both of these tendons, particularly the tibialis anterior, which is vulnerable during the saw cuts. • Under fluoroscopic guidance, place two 0.062-inch K-wires approximately 1.5 cm apart, from medial to lateral (Fig. 34.27A). • The pin placement is oblique, as the cuboid is inferior to the medial navicular–cuneiform joint. • The more distal pin passes through the medial cuneiform and exits through the distal cuboid; the more proximal pin passes medially across the navicular and exits through the proximal cuboid (see Fig. 34.27B–C). • Avoid penetration of the fourth and fifth metatarsal–cuboid joints. • Using blunt dissection and a small key elevator, completely dissect the soft-tissue envelope around the bone of the midfoot. Protect the neurovascular structures dorsally and plantarly with small Hohmann retractors. • Cut along the inside of each pin, removing a trapezoidal wedge of bone that includes the navicular–cuneiform joints (Fig. 34.28). Irrigate with cool saline lavage. • Make every effort to create flat cuts, without redirecting the saw blade. Imagine that the apex of the wedge is at the plantar fascia, which enables a trapezoidal piece of bone to be resected.
PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
A
B
C FIG. 34.27
FIG. 34.28
• Adduction of the midfoot can be corrected with appropriately placed bone cuts. • Remove the K-wires. • The forefoot can now be dorsiflexed and rotated into the correct position. Make sure that the transverse metatarsal arch is well aligned and that the forefoot valgus is corrected. • Place the two K-wires temporarily across the osteotomy and place three 16 × 20 mm 3M power staples across the osteotomy sites both medially and laterally. Excellent fixation can be obtained in this manner (Fig. 34.29). • Deflate the tourniquet. Obtain hemostasis and close the wounds in two layers, with alternating 3-0 nylon horizontal mattress and simple sutures in the skin.
FIG. 34.29
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PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
Sutures
Periosteum of distal metatarsal Extensor tendon
FIG. 34.31
FIG. 34.30
STEP 6 PEARLS
• A bulk transfer of the long toe extensors into the lateral cuneiform or cuboid may provide more effective ankle dorsiflexion than individual transfers into the metatarsal necks.
Step 6 • Claw toes should be corrected using standard techniques that involve resection of the distal aspect of the proximal phalanx (see Procedure 14). The extensor digitorum longus tendon of each toe is transferred to the distal metatarsal using a deep periosteal stitch (Fig. 34.30). A small drill hole in the bone can be used but is time consuming and probably unnecessary, given that the foot will be immobilized for at least 6 weeks in neutral position. • If clawing of the great toe is present, the interphalangeal joint should be fused through a transverse incision. The extensor hallucis longus is transferred into the distal metatarsal through a transverse drill hole. • Correction of the forefoot deformity, by either metatarsal or midfoot osteotomy, can create extrinsic flexor tightness, especially in the lesser toes. Even after the clawing is corrected, hyperflexion of the toe may persist. A closed or open tenotomy of the flexor digitorum longus to the toe will correct this problem (Fig. 34.31).
POSTOPERATIVE CARE AND EXPECTED OUTCOMES • A bulky dressing and a three-sided splint are applied in the operating room after all of the osteotomies are checked for a final time by fluoroscan. • The patient returns to the office 10–12 days after surgery for the placement of a short-leg non–weight-bearing cast. Sutures are removed at this point, if the wounds are completely healed. Anteroposterior (Fig. 34.32A) and lateral (see Fig. 34.32B) radiographs are taken in the cast. • Six weeks after surgery, the cast is removed and radiographs are taken. An additional short-leg, nonremovable cast is applied. The patient can start weight bearing as tolerated. This second cast is removed at 10 weeks postoperatively. Physical therapy should be started at this point, along with appropriate footwear. • An excellent and enduring correction of the deformity can be expected (Fig. 34.33; the right foot has had surgery). See also Video 34.1, Cavovarus Correction in Charcot-Marie-Tooth Disease.
PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
A
B FIG. 34.32
A
B FIG. 34.33
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PROCEDURE 34 Cavovarus Correction in Charcot-Marie-Tooth Disease
EVIDENCE Cole WH. The treatment of claw-foot. J Bone Joint Surg Am 1940;22:895–905. Original description of the Cole osteotomy for midfoot cavus (Level V evidence). Guyton GP. Current concepts review: orthopaedic aspects of Charcot-Marie-Tooth disease. Foot Ankle Int 2006;27:1003–10. An excellent review of the topic and the literature. Mann RA, Missirian J. Pathophysiology of Charcot-Marie-Tooth disease. Clin Orthop Relat Res 1988;(234):221–8. This paper examines CMT deformity and the contribution of muscle imbalance (Level V evidence). Nagel MK, Chan G, Guille JT. Prevalence of Charcot-Marie Tooth disease in patients who have bilateral cavovarus feet. J Pediatr Orthop 2006;26:438–43. Seventy-eight percent of children with “idiopathic” cavovarus feet were diagnosed with CMT disease by neurophysiologic and genetic testing (Level IV evidence). Paulos L, Colemann SS, Samuelson KM. Pes cavovarus: review of surgical approach using selective soft-tissue procedures. J Bone Joint Surg Am 1980;62:942–53. Review of 39 feet in children with cavovarus deformity. The use of the Coleman block test to distinguish forefoot-driven heel varus is described (Level IV evidence). Pfeffer GP, Michalski MP, Basak T, Giaconi J. The Use of 3D Prints to Compare the Efficacy of Three Different Calcaneal Osteotomies for the Correction of Heel Varus. In American Academy of Orthopaedic Surgeons Annual Meeting 2017.