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Charcot-Marie-Tooth Disease and the Cavovarus Foot
Foot Ankle Clin N Am 13 (2008) 259–274
Charcot-Marie-Tooth Disease and the Cavovarus Foot Timothy C. Beals, MD*, Florian Nickisch, MD University of Utah School of Medicine, University Orthopaedic Center, 590 Wakara Way, Salt Lake City, UT 84108, USA
The purpose of this article is to focus on the cavovarus foot shape, with particular emphasis on those patients who have Charcot-Marie-Tooth disease (CMT). The features of the cavovarus foot deformity have received more attention in the last few years. This understanding has led to a greater appreciation of how the underlying condition drives deformity progression and treatment of the problems associated with cavovarus foot deformity. For example, the unilateral cavovarus foot due to an asymmetric spinal cord or peripheral nerve compression phenomenon is unlikely to progress significantly in terms of the deformity once the underlying problem is identified and treated. In contrast, CMT is typically a progressive condition, so the treating physician must factor in the likelihood of deformity progression into the treatment plan. Additionally, because CMT characteristically manifests in the growing child, the resultant shape of bones and the planes of motion of joints are recognized to be atypical in many cases, which affects the predictability of the application of standardized treatment ‘‘recipes’’ for particular patterns of foot deformity. For example, the plantar-flexed first ray that is the sine quo non of the cavus portion of the deformity in a cavus-shaped and flexible foot will respond to either a laterally posted forefoot orthosis or dorsiflexion osteotomy of the first ray. However, in the patient who has CMT, the predictability of that correction is compromised. It is the nuances of CMT that are emphasized here. Pertinent history and genetics In 1884, Friedrich Schultze initially described what is now known as CMT. The early descriptions of the phenotypic syndrome by Jean-Martin * Corresponding author. E-mail address: [email protected] (T.C. Beals). 1083-7515/08/$ - see front matter Ó 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.fcl.2008.02.004 foot.theclinics.com
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Charcot and Pierre Marie in France in 1886 and Howard Henry Tooth in London the same year established an understanding of the condition as being based on abnormal peripheral nervous system function [1,2]. These investigators recognized that the condition manifested itself through a neuropathic, rather than a myopathic, process. Through the years, it was learned that the condition was based on genetic mutations. The past 2 decades have seen a dramatic increase in the number of defined genetic abnormalities that lead to what is still referred to as CMT. However, as an understanding of the heterogeneity of the condition has progressed, the dogma of diagnosis and treatment has become challenged. At this time, it is important that the treating physician recognize the different types of CMT from a genetic standpoint because the risk of progression and deformity may not be the same for different mutations. For the practicing orthopedic surgeon, it is important to recognize CMT as a condition with a more or less typical phenotypic manifestation of a complex genetic disorder, with variable underlying causative genetic abnormalities resulting in greatly variable clinical severity. The most common segmentation of CMT patients is into so-called ‘‘type 1’’ and ‘‘type 2’’ patients. Classically, type 1 is a condition in which the myelin surrounding the nerve is abnormal, whereas the axonal function is abnormal in patients who have type 2 disease. Electrophysiologic nerve testing demonstrates that the speed of impulse transfer is slowed in type 1 because of the nerve sheath dysfunction. In type 2, the rate of impulse transfer is normal but the magnitude of the impulse is decreased, as manifested by the loss of sensory- and motor nerve–evoked response amplitudes. Roughly two thirds of patients who have CMT have type 1 and one third have type 2 [3,4]. About 37 in 100,000 people are affected. The term ‘‘type 3’’ has been applied to Dejerine-Sottas disease, which is a form of hereditary peripheral neuropathy that is severe in its clinical manifestations but results in a similar phenotype. The understanding of the genetic abnormalities underpinning the different types of CMT is well beyond our ability to apply that knowledge in the clinical setting. The most common genetic abnormality that has been identified as causative of CMT is a gene defect on chromosome 17, known as CMT 1A. CMT 1B is caused by a gene defect identified on chromosome 1. Genetic testing is currently commercially available for CMT 1A. The most common abnormality identified on chromosome 17 is a duplication of a part of the PMP22 gene, but other variants have been identified. Both the gene defects on chromosome 17 and 1 are inherited in an autosomal dominant pattern. An X-linked form of type 1 CMT disease with a known gene defect also exists [5]. Autosomal recessive forms of CMT have also been identified. The genetic underpinning of CMT type 2 is less well understood but it is important to recognize it as a distinct condition, particularly as it relates to foot deformities and treatment. Like type 1, it is inherited in an autosomal dominant pattern. Defects in chromosomes 1 and 3 have been associated
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with this condition [6]. More information is being accumulated that documents that the progression of type 2 disease is not as relentless as has been assumed in the past. A prospective study of patients over a 5-year period who had the axonal (type 2) form of CMT did not demonstrate an increase in the number of patients who had a cavus foot shape, and only slow progression of the disease was observed [7]. More than 30 different gene defects have been identified as being related to different forms of what clinicians refer to as ‘‘Charcot-Marie-Tooth disease.’’ Clinical examination of patients who have Charcot-Marie-Tooth disease When evaluating a patient who has a cavovarus foot deformity, it is important to determine the underlying cause of the condition [8]. When a patient presents with a known diagnosis of CMT, the physician has a tendency to confirm the classic clinical findings because they are emphasized throughout medical education as being so characteristic of the disease. Classically, the clinical findings of CMT include weakness of the intrinsic muscles of the hands and feet, and peroneal muscle atrophy and weakness. However, one of the keys to proper evaluation of such patients is to appreciate the individuality of the patients who have this condition. In recent years, the examination of patients has been reassessed in light of the improved understanding of the genetic variability of the disease. Although many articles have been written that parrot the historical descriptions of the classic findings, senior clinicians often remark on the variability in presentation and outcomes of treatment. A recent MRI study of a small sample of patients who had CMT type 1A demonstrated consistent abnormalities of the intrinsic muscles of the foot and a notable variability in the MRI findings of fatty infiltration of leg muscles. The investigators felt their results help explain the development of the cavus deformity but, more importantly, demonstrated abnormalities in what otherwise appeared to be clinically normal muscles and variability among patients [9]. Documentation of the strength of all the muscle groups of the lower extremities is important because it allows an assessment of the progression of the disease over time and helps the surgeon best understand the options for surgical reconstruction, if the symptoms warrant intervention. Burns and colleagues [10] studied the reliability of a hand-held dynamometry unit in the evaluation of CMT patients and compared the patients to normal controls. They concluded that such testing provided a reliable and objective measure of muscle strength, which further allowed them to understand the degree of muscle imbalance. The clinical findings of CMT can be appreciated in young patients. Given the autosomal dominant pattern of inheritance and the ability to test genetically for CMT 1A, it is possible to evaluate children at risk from an early age. Berciano and colleagues [11] serially evaluated a group of 12 children known to have this condition and found that each of the children demonstrated a lack of lower limb reflexes
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and a subtle weakness most often demonstrated by a difficulty with heel walking. Physical examination of the patient who has CMT includes observation of standing posture and assessment of the ability to walk on the heels and toes. Such efforts allow the clinician to appreciate the degree of difficulty with balance and to assess for other associated deformities of the spine or hips (Fig. 1). An assessment of the range of motion of the ankle is important, with particular attention to determining if the ankle rolls normally or whether it functions more as a hinge. This assessment is particularly important in patients who have undergone prior surgical treatment. The ankle must be assessed for evidence of ligamentous instability, which is a common presenting symptom of patients presenting with CMT. In all patients who have ankle instability, it is wise to assess for the presence of a contributory cavus or cavovarus deformity and, if present, to consider the diagnosis of an underling neuromotor dysfunction. Although no practical way to quantify rotatory ankle instability exists at present, the examiner should be cognizant that patients who have CMT have rotatory asymmetries of the ankle region and may manifest a degree of rotatory instability. The shape of the foot must be characterized, noting the presence or absence of clawing of the toes and the presence or absence of a varus hindfoot. The so-called ‘‘peek-a-boo’’ heel sign is readily observed when viewing the patient from the front. Normally, the heel is hidden behind the foot, but its medial side is readily observed when the patient has a cavus foot shape [12]. The degree of flexibility of the forefoot and hindfoot must be assessed and a determination made of the presence or absence of an equinus
Fig. 1. (A) Bilateral anteroposterior weight-bearing radiographs of a 65-year-old woman with CMT 1A who had limited surgical treatment. Deformity was severe and walking capacity was limited with the use of a walker. (B) Same patient 6 years later after ankle fusion, calcaneal osteotomy, and forefoot dorsiflexion osteotomy. Deformity was moderate but the patient was fully ambulatory without assistive devices.
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contracture. As one considers the position of the hindfoot, it is worth noting that in patients who have known CMT 1A, a review of weight-bearing lateral foot radiographs demonstrated that the hindfoot was actually in dorsiflexion and that the apparent foot equinus observed was caused by the plantar flexion of the first ray [13]. Perhaps Coleman and Chestnut [14] presented the single most important contribution to the development of a salient methodology for the assessment of the cavovarus foot in 1977. In their classic manuscript, they described an elegant and simple method to assess the degree of flexibility of the hindfoot in a patient who has a cavus deformity. The ‘‘Coleman block test’’ requires a patient to stand on a block of wood with the heel and the lateral forefoot supported by the block, which allows the plantar-flexed first ray to drop. This test allows the examiner, positioned behind the patient, to determine if the hindfoot varus deformity is corrected by this maneuver. Simply put, if dropping the first ray over the edge of the block allows the hindfoot to correct to a valgus position, the hindfoot is flexible. If correction of the varus is not observed, the hindfoot is rigid (Fig. 2). This single determination drives the decision making for treatment, whether it is for the manufacture of an orthosis or for surgical treatment. The phenotypic expression of CMT is known to be variable even among families with similar genotypes, but the physical examination helps define the subtle differences of this condition. Carefully identifying the static and dynamic characteristics described earlier and assessing the reflexes of the lower extremities should allow the identification of patients who have this condition and lead the clinician to a logical conclusion about the options for management. The phenotypic expression of this genetic disorder is
Fig. 2. Patient who has cavovarus foot shape with apparent hindfoot varus. (A) Standing appearance of a patient who has bilateral cavovarus feet. Note hindfoot varus. (B) Same patient standing on a Coleman block supporting the lateral forefoot and heel, allowing the first metatarsal to drop to the floor, enabling the hindfoot to correct passively into a valgus position.
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variable and this should be expected, given the other phenotypic variability seen in siblings (Fig. 3). Pathogenesis of deformity Several insightful manuscripts make an effort to describe the pathogenesis of the deformities characteristic of this group of diseases. Tynan and colleagues [15] reviewed 41 leg MRI scans in patients who had neuromuscular disorders and cavus feet. They concluded that in most of the patients who had forefoot cavus, the peroneal compartment was enlarged relative to normal controls, with biopsies confirming the absence of pseudohypertrophy of the peroneus longus. The peroneus longus muscle is thought to be selectively spared in the development of the cavovarus deformity, with wasting of the peroneus brevis being evident early in the disease. Mann and Missirian [16] made this clinical observation in 1988. Characteristically, muscle involvement in CMT progresses from distal to proximal. However, the described patterns of muscle function have limitations. Relative sparing of the extensor hallucis longus can be observed, which is felt to be contributory to the development of the clawed hallux. Because the innervation of this muscle is more distal to the characteristically weak anterior tibialis, it is not clear why it would be spared. It is the ‘‘push me, pull you’’ relationship of weak dorsiflexion power of the anterior tibialis and the strongly plantar-flexing peroneus longus acting on the
Fig. 3. Siblings with CMT demonstrating significant differences in many phenotypic features.
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medial midfoot that is felt to be the primary driver of the cavus deformity once the intrinsic musculature is dysfunctional. Despite the original descriptions of early functional loss of the peroneal and anterior compartments of the leg, it is the tibial nerve–innervated intrinsic musculature that fails first in this family of disorders. Despite the thorough description of the patterns of weakness in specific muscle groups, no mention is typically made of a side-to-side difference in strength. The authors routinely note an asymmetry of the severity of involvement of the lower extremities in terms of strength and deformity. The characteristic deformities of the cavovarus foot in CMT are accepted to be the result of motor imbalance. Ankle dysfunction, most commonly manifested by a foot drop, is due to the relative loss of strength of the tibialis anterior relative to the superficial posterior compartment muscles. Despite the relative weakness of the tibialis anterior, it can continue to be a powerful deforming force because of its static resistance to eversion in a patient who has a varus hindfoot. The hindfoot varus is presumed to be developing passively, secondary to the forefoot cavus from the described first ray plantar flexion (forefoot-driven hindfoot varus) and the imbalance between the strong posterior tibialis and the weak peroneus brevis that serves as its antagonist in balancing the foot (Fig. 4). The forefoot deformities appear to develop after loss of the function of the intrinsic muscles and, once again, an imbalance of the extrinsic muscles. Lesser toe clawing develops after the intrinsic function of plantar flexion of the metatarsophalangeal joints and interphalangeal extension is lost. The development of the clawed hallux may be caused by the spared extensor hallucis longus muscle, which is often described as serving as an ankle extensor in the absence of the other anterior compartment muscles [17–19]. Nonsurgical treatment Little literature describes the outcome of nonsurgically treated patients who have CMT. Specifically, no large natural history studies of this
Fig. 4. (A) Left and (B) right weight-bearing lateral radiographs of a child with CMT demonstrating high arches, clawing of toes, and plantar-flexed first metatarsal. Note the asymmetry in the two sides.
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population exist. Despite that, most patients are indeed treated nonsurgically with shoe modifications, orthoses, braces, and physical therapy. A review article that attempted to evaluate the efficacy of surgical and nonsurgical care for patients who had drop foot from neuromuscular causes identified only one study that demonstrated a positive effect on the ability to walk, and that was an exercise program for people with CMT [20]. An anecdotal report of improvement in a patient who had CMT with orthopedic shoes has been published but no significant studies on orthosis use in this population [21]. One randomized trial assessing nighttime ankle bracing in patients who had CMT 1A has been published and it demonstrated no benefit [22]. Because of the cavovarus foot shape, the development of ankle instability is common in patients who have CMT. For many patients, ankle instability is often their initial presenting clinical concern. Because of the cavovarus foot shape, excess stress is placed on the lateral hindfoot structures, particularly given the progressive weakness of the peroneus brevis. The relative overpull of the more medially inserting tendons leads to a progressive tendency toward inversion, and then the progressive static deformities of a cavus foot shape accentuate that tendency, with patients developing lateral instability. Classic therapy with peroneal strengthening and proprioceptive retraining are likely less effective in this patient population that has sensory and motor deficits, particularly with regard to eversion strength, but it can be attempted. Some patients, especially adolescents with milder deformities who are still flexible, as determined by a Coleman block test, can be treated initially with foot orthoses, which elevate the lateral forefoot, allowing the first ray to drop effectively into a hole and keep the subtalar joint in a more neutral position.
Surgical options Several different operations have been described in isolation and in combination in the treatment of patients who have cavovarus foot deformities secondary to CMT. The broad categories of ‘‘bony’’ and ‘‘soft tissue’’ procedures have been described, with a progressive realization that the combination of both is typically necessary for optimal outcome [23,24]. It appears that soft tissue procedures alone do not offer significant lasting benefit. Bony procedures include the use of fusion of the ankle, hindfoot, midfoot, or the great toe interphalangeal joint, and all are performed in concert with deformity correction. Joint-sparing osteotomies, most commonly of the calcaneus and metatarsals or medial midfoot, have the same goals. The recent drift to joint-sparing procedures is driven by an appreciation that a significant degree of deformity correction can be achieved through osteotomy and an acknowledged concern about ‘‘adjacent joint arthritis’’ that has been observed primarily in patients undergoing triple arthrodesis. Given the young age of
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so many of the patients treated for deformities associated with CMT, this consideration is logical. Soft tissue operations that have been described in the treatment of patients who have CMT include various procedures. A common soft tissue technique in this population is a plantar fascial release. More formal plantarmedial stripping procedures have also been described. Transfers of multiple different tendons have also been applied to this patient population. Transfer of the tibialis posterior through the interosseous membrane to the dorsolateral foot (split or in isolation), transfer of the tibialis anterior centrally on the hindfoot, transfer of the extensor hallucis longus tendon to the neck of the first metatarsal done in concert with an interphalangeal fusion, transfer of the peroneus longus to the peroneus brevis, and flexor digitorum longus or Achilles tendon lengthening have been described. Younger and Hansen [25] published a thorough description of the in-phase and out-of-phase tendon transfers that can be considered in this scenario. The reader must be cautious in applying the specific capabilities of a given patient to this outline because of the phenotypic variability. Even in this population of patients who have often-inflexible cavus, soft tissues releases done with excessive vigor can result in profound collapse of the foot architecture, and a planus foot shape can develop (Fig. 5). In patients who have CMT, the method of osteotomy performed affects the ability to achieve deformity correction, and the relative movement of the architectural alignment of the skeleton will have an effect on the ability of various muscles to effect a moment arm. For example, dorsiflexion of the first ray will effectively lengthen the extensor hallucis longus and thereby may obviate the need for a formal correction of a cock up hallux (Jones procedure). Therefore, it is important that surgical reconstruction be done in a stepwise manner with reassessment throughout a procedure, rather than applying a given ‘‘recipe’’ of procedures to each foot with a cavovarus deformity. The degree and planes of correction of the hindfoot varus deformity that can be achieved through a translational or closing wedge (Dwyer) calcaneal osteotomy are more limited than those of more complex osteotomies, such as the one originally described by Pisani and modified by Hintermann [26,27]. The options for calcaneal osteotomy include a lateralizing translational tuberosity osteotomy with or without a closing wedge laterally; a Hintermann type Z osteotomy with closing wedge and lateral translation, which also shortens the hindfoot; or an ‘‘Italian-style’’ osteotomy, which additionally shortens and laterally translates the hindfoot and tips the tuberosity into a more valgus position [28]. Subtalar arthrodesis can also achieve a more valgus positioning with reduction through the subtalar joint, and triple arthrodesis is sometimes also required to put the foot in a proper position beneath the ankle. The ability to translate and rotate through the ‘‘Z’’ pattern of osteotomy appears to have increased our ability to address large deformities but it is
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Fig. 5. (A) Anteroposterior foot, (B) anteroposterior ankle, and (C) lateral views of a child with profound collapse of the arch after surgery to address a cavovarus deformity due to CMT 1A.
clearly a more technically demanding procedure with a greater risk to the remaining peroneal function (Fig. 6).
Outcomes of treatment Few studies have been published that assess the outcome of treatment of cavovarus foot deformities in patients who have CMT. In each of the cited studies, the reader is unable to draw definite conclusions because of the limited number of patients treated and variability in the patient groups. Nevertheless, each study offers some insight into the condition and the pitfalls of certain treatment choices. No randomized surgical studies have been done of defined subgroups of CMT. No prospective studies have been done either. The surgeon must thoughtfully apply the lessons learned from the available
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Fig. 6. Lateral weight-bearing view of a boy with CMT 1A treated with a ‘‘Z’’ calcaneal osteotomy, medial column dorsiflexion osteotomy, and posterior tibial tendon transfer.
literature, which is heavily weighted toward studies of young patients with short follow-up. Soft tissue procedures In 1980, Paulos and colleagues [29] described the results of soft tissue procedures alone in correcting pes cavovarus in children. Only 1 of the 27 patients had CMT. The outcomes of a complete plantarmedial release on these children who averaged 7 years of age at the time of surgery were subjectively improved at an average of 2 years follow-up. Coleman, who was the senior investigator on the paper, later advocated combined bony and soft tissue procedures for children with neuromuscular deformity. Six of 39 feet were noted to have residual cavus at the time of final evaluation. Isolated transfer of the posterior tibial tendon through the interosseous membrane has been studied in 43 children with overall good results. However, like most studies of a given procedure, few patients with CMT were included in the study. The outcome in these patients was not favorable and, indeed, the investigators recommended that the procedure be abandoned in patients who have CMT for whom a staged procedure including hindfoot stabilization is contemplated [30].
Osteotomies The results of osteotomies in the treatment of the cavovarus foot have been reported. Sammarco and Taylor [31] reported on 21 feet in 15 patients who underwent calcaneal osteotomy and one or more metatarsal osteotomies to correct their deformity. Fifteen of the feet were of patients who had CMT. The functional assessments, with commonly used instruments such as the American Orthopaedic Foot and Ankle Society ankle-hindfoot score and the Maryland Foot Score, showed improvements in outcome at an average of just less than 6 years. Although some complications were
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encountered, improvements in symptoms indicating the need for surgery such as ankle instability and forefoot metatarsalgia were documented. A lateral translational osteotomy of the calcaneus was done with closing wedge dorsolateral metatarsal osteotomies. Most feet underwent other procedures at the same time. The investigators emphasized the value of combining the osteotomies with plantar fascial release and the potential advantages over competing notions of hindfoot or tarsometatarsal arthrodeses, midtarsal osteotomies, and isolated forefoot or hindfoot procedures. One study of patients with CMT used dynamic pedobarography in nine children who had undergone joint-sparing corrective surgery that included a combination of osteotomies and tendon transfers; it was found that the degree of radiographic correction did not correlate with the degree of change in pedobarographic measurements [32]. The investigators reported preoperative increased heel pressure that was not improved significantly by surgical treatment. They emphasized that even if deformities appear to be corrected completely, pressure distribution is not normalized. Although the study assessed a small group of children who may not have been genetically dissimilar, the lack of correlation in functional parameters with commonly reported static measurements is cautionary and the investigators appropriately emphasized the need to make that clear to parents considering such surgery for their children. Midfoot osteotomy has been advocated in the treatment of cavovarus deformities. Japas [33] described a ‘‘V’’ osteotomy of the midfoot in combination with a Steindler plantarmedial stripping to address these deformities. He described his technique and experience with 17 feet observed for 2 to 6 years. By modern standards, the report is hard to assess, given the lack of weight-bearing radiographs and the use of antiquated assessment tools, but it does identify a logical framework for considering a midfoot osteotomy. The investigator notes the potential advantages of correcting the deformity at its most ‘‘prominent point’’ and he avoids the interference with tarsal motion seen with the competing arthrodesis operations that were common at the time. He described his paper as a ‘‘preliminary report,’’ and the lack of further follow-up may be telling in its absence. However, it remains a consideration for a rigid deformity and should be considered in a salvage situation.
Arthrodesis Most studies that are referable to patients who have CMT are reviews subsequent to hindfoot fusion. Mann and Hsu [34] retrospectively reviewed 10 adolescent CMT patients who had had 12 foot operations that included triple arthrodesis. Each patient reportedly had a rigid hindfoot deformity. Five feet (50%) were plantigrade, fused at all joints, and asymptomatic at an average of 7.5 years. This group of patients, all treated with a single
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lateral incisional approach, included two talonavicular nonunions, one calcaneocuboid nonunion, and three nonplantigrade feet. In this small group of patients, who were followed for between 2 years 4 months and 18 years, three prior and nine subsequent surgeries were described. Clearly, adolescents surgically treated were likely to undergo more than one operation. Longer-term results from triple arthrodesis are the reports that have influenced most directly the surgical considerations in this patient population. The competing advantage of fairly reliable deformity correction with the disadvantage of lost motion, particularly in a younger patient population that has a normal life span, is a source of ongoing dialog for surgeons who treat these patients. Angus and Cowell [35] published a review of 80 feet with an average follow-up of 13 years after triple arthrodesis. They described a high incidence of arthritis of the ankle and midfoot. Understanding the numbers behind the widely touted conclusions is essential to appreciate the reported findings. The review was made of 62 patients, 18 of whom had bilateral triple arthrodeses. The initial study population included 302 patients, so it should be noted that only 20% of the patients were assessed. The average age of the patients was 14, and internal fixation was used in 12 of 80 feet. Three and one half months of casting, on average, was endured after surgery. Only a few of these patients had CMT, with most having cerebral palsy, idiopathic clubfoot, or poliomyelitis. Given the significant limitations in study design, the conclusions are limited, but arthrosis appeared frequently in these young people, who only averaged 27 years of age at follow-up. In 1989, Wetmore and Drennan [36] reported on 16 patients who had CMT, who had had a total of 30 triple arthrodeses. The average age at the time of operation was 15, and the average length of follow-up was 21 years. The results are sobering. The investigators described 77% of patients as having fair or poor outcomes and six limbs had also undergone an ankle fusion. Development of recurrent cavovarus deformity was thought to be the cause behind the poor outcomes. Saltzman and colleagues [37] also reported on the long-term outcome of patients who underwent a triple arthrodesis. Sixty-seven feet in 57 patients were reviewed. Nine percent of the patients in this study had CMT, with most (55%) due to polio. Seventy-eight percent of the patients had some residual deformity, but the deformities, in contrast to the findings of Wetmore and Drennan, were not progressive. At the final follow-up evaluation, all of the ankles in the study population showed degenerative changes on radiographs. Ninety-five percent of the patients were satisfied despite the concerning findings of progressive arthrosis of the ankle. One can also learn from nonneuromuscular patient groups. The results of the triple arthrodesis was studied in a group of 27 adult patients (31 feet) who had undergone triple arthrodesis for the treatment of chronic hindfoot pain and had been followed for a minimum of 10 years [38]. The mean age of the patients who were examined was 45 at the time of the surgery, and the
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mean duration of follow-up of those patients was 14 years. The investigators found that 25 (93%) of the patients were satisfied with the results of the treatment. However, only 11 (41%) reported that they could perform moderate activity with mild or no pain in the foot and ankle. Severe arthrosis developed in 7 of the 26 ankles, in 7 naviculocuneiform joints, and in 6 tarsometatarsal joints. Some patients had severe arthrosis at more than one level, and 3 patients later required an ankle arthrodesis.
Summary Understanding the cause of a disease will affect the understanding of the course and treatment of the condition. What is currently recognized by a characteristic phenotype may someday be recognized as distinct subsets of peripheral neurologic disease with molecular basis. The hope is that genetic subtyping will allow for better prediction of the development and progression of deformities of the foot and ankle, which can be translated into a more logical treatment method that will yield better functional outcomes for patients. The ability to weaken agonists during growth and development is within reach if astute clinicians can develop an understanding of the subtleties of a condition that appears to have a great deal of genetic and clinical variability. Joint-sparing operations tailored to the individual are an ideal to work toward, but currently, the best treatment comes from thoughtful consideration of the limited information that the reviewed investigators have provided. Key principles appear to be to understand the specific features of a given patient in detail when creating a customized surgical plan that uses bony reconstruction procedures to create a mechanically balanced foot, and then to apply soft tissue releases and tendon transfers as necessary to maintain functional control of the foot and ankle, while appreciating the likelihood of progression of the neuromotor imbalance.
References [1] Charcot JM, Marie P. Sure one former particular d’atrophie musculaire progressive, souvent familiale de´butant par les pieds et les jambes et atteignant plus tard les mains. Revue Me´dicale Paris 1886;6:97–138. [2] Tooth HH. The peroneal type of progressive muscular atrophy. London (UK): H.K. Lewis; 1886 [dissertation]. [3] Dyck PJ, Lambert EH. Lower motor and primary sensory neuron diseases with peroneal muscular atrophy. II. Neurologic, genetic, and electrophysiologic findings in various neuronal degenerations. Arch Neurol 1968;18:619–25. [4] Dyck PJ, Lambert EH. Lower motor and primary sensory neuron diseases with peroneal muscular atrophy. I. Neurologic, genetic, and electrophysiologic findings in hereditary polyneuropathies. Arch Neurol 1968;18:603–61. [5] Roa BB, Garcia CA, Suter U, et al. Charcot-Marie-Tooth disease type 1A. Association with a spontaneous point mutation in the PMP22 gene. N Engl J Med 1993;329(2):96–101.
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[6] Lawson VH, Graham BV, Flanigan KM. Clinical and electrophysiologic features of CMT2A with mutations in the mitofusin 2 gene. Neurology 2005;65:197–204. [7] Teunissen LL, Notermans NC, Franssen H, et al. Disease course of Charcot-Marie-Tooth disease type 2: a 5-year follow-up study. Arch Neurol 2003;60(6):823–8. [8] Schwend RM, Drennan JC. Cavus foot deformity in children. J Am Acad Orthop Surg 2003; 11(3):201–11. [9] Gallardo E, Garcı´ a A, Combarros O, et al. Charcot-Marie-Tooth disease type 1A duplication: spectrum of clinical and magnetic resonance imaging features in leg and foot muscles. Brain 2006;129(Pt 2):426–37. [10] Burns J, Redmond A, Ouvrier R, et al. Quantification of muscle strength and imbalance in neurogenic pes cavus, compared to health controls, using hand-held dynamometry. Foot Ankle Int 2005;26(7):540–4. [11] Berciano J, Garcı´ a A, Combarros O. Initial semeiology in children with Charcot-MarieTooth disease 1A duplication. Muscle Nerve 2003;27(1):34–9. [12] Beals TC, Manoli A II. The peek-a-boo heel sign in the evaluation of hindfoot varus. Foot 1996;6:205–6. [13] Aktas S, Sussman MD. The radiological analysis of pes cavus deformity in Charcot Marie Tooth disease. J Pediatr Orthop B 2000;9(2):137–40. [14] Coleman SS, Chesnut WJ. A simple test for hindfoot flexibility in the cavovarus foot. Clin Orthop Relat Res 1977;123:60–2. [15] Tynan MC, Klenerman L, Helliwell TR, et al. Investigation of muscle imbalance in the leg in symptomatic forefoot pes cavus: a multidisciplinary study. Foot Ankle 1992;13(9):489–501. [16] Mann RA, Missirian J. Pathophysiology of Charcot-Marie-Tooth disease. Clin Orthop Relat Res 1988;(234):221–8. [17] Guyton GP. Current concepts review: orthopaedic aspects of Charcot-Marie-Tooth disease. Foot Ankle Int 2006;27(11):1003–10. [18] Holmes JR, Hansen ST Jr. Foot and ankle manifestations of Charcot-Marie-Tooth disease. Foot Ankle 1993;14(8):476–86. [19] Sabir M, Lyttle D. Pathogenesis of pes cavus in Charcot-Marie-Tooth disease. Clin Orthop Relat Res 1983;175:173–8. [20] Sackley C, Disler PB, Turner-Stokes L, et al. Rehabilitation interventions for foot drop in neuromuscular disease. Cochrane Database Syst Rev 2007;18(2):CD003908. [21] Guzian MC, Bensoussan L, Viton JM, et al. Orthopaedic shoes improve gait in a CharcotMarie-Tooth patient: a combined clinical and quantified case study. Prosthet Orthot Int 2006;30(1):87–96. [22] Refshauge KM, Raymond J, Nicholson G, et al. Night splinting does not increase ankle range of motion in people with Charcot-Marie-Tooth disease: a randomized, cross-over trial. Aust J Physiother 2006;52(3):193–9. [23] Jahss MH. Evaluation of the cavus foot for orthopedic treatment. Clin Orthop Relat Res 1983;181:52–63. [24] Alexander IJ, Johnson KA. Assessment and management of pes cavus in Charcot-MarieTooth disease. Clin Orthop Relat Res 1989;246:273–81. [25] Younger AS, Hansen ST Jr. Adult cavovarus foot. J Am Acad Orthop Surg 2005;13(5): 302–15. [26] Hinterman B. Surgical techniques. In: Total ankle arthroplasty: historical review, current concepts and future perspectives. Vienna (Austria): Springer; 2005. p. 105–26. [27] Pisani G. Osteotomie sous-talamique par la correction chirurgicale des deformitions du calcaneum dans la plan frontal (varu, valgus). [Subtalar Ostotomy for the correction of the deformities of the calcaneus in the frontal plane]. France (Paris): Podologie 85 – Expan Scient; 1985 [in French]. [28] Malerba F, De Marchi F. Calcaneal osteotomies. Foot Ankle Clin N Am 2005;10:523–40. [29] Paulos L, Coleman SS, Samuelson KM. Pes cavovarus. J Bone Joint Surg Am 1980;62: 942–53.
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[30] Miller GM, Hsu JD, Hoffer MM, et al. Posterior tibial tendon transfer: a review of the literature and analysis of 74 procedures. J Pediatr Orthop 1982;2(4):363–70. [31] Sammarco GJ, Taylor R. Cavovarus foot treated with combined calcaneus and metatarsal osteotomies. Foot Ankle Int 2001;22(1):19–30. [32] Chan G, Sampath J, Miller F, et al. The role of the dynamic pedobarograph in assessing treatment of cavovarus feet in children with Charcot-Marie-Tooth disease. J Pediatr Orthop 2007;27(5):510–6. [33] Japas LM. Surgical treatment of pes cavus by tarsal v-osteotomy. J Bone Joint Surg Am 1968;50:927–44. [34] Mann DC, Hsu JD. Triple Arthrodesis in the treatment of fixed cavovarus deformity in adolescent patients with Charcot-Marie-Tooth disease. Foot Ankle 1992;13:1–6. [35] Angus PD, Cowell HR. Triple arthrodesis. J Bone Joint Surg Br 1986;68:260–5. [36] Wetmore RS, Drennan JC. Long-term results of triple arthrodesis in Charcot-Marie-Tooth disease. J Bone Joint Surg Am 1989;71:417–22. [37] Saltzman CL, Fehrle MJ, Cooper RR, et al. Triple arthrodesis: twenty-five and forty-fouryear average follow-up of the same patients. J Bone Joint Surg Am 1999;81(10):1391–402. [38] Smith RW, Shen W, Dewitt S, et al. Triple arthrodesis in adults with non-paralytic disease. A minimum ten-year follow-up study. J Bone Joint Surg Am 2004;86(12):2707–13.
Charcot-Marie-Tooth Disease and the Cavovarus Foot Timothy C. Beals, MD*, Florian Nickisch, MD University of Utah School of Medicine, University Orthopaedic Center, 590 Wakara Way, Salt Lake City, UT 84108, USA
The purpose of this article is to focus on the cavovarus foot shape, with particular emphasis on those patients who have Charcot-Marie-Tooth disease (CMT). The features of the cavovarus foot deformity have received more attention in the last few years. This understanding has led to a greater appreciation of how the underlying condition drives deformity progression and treatment of the problems associated with cavovarus foot deformity. For example, the unilateral cavovarus foot due to an asymmetric spinal cord or peripheral nerve compression phenomenon is unlikely to progress significantly in terms of the deformity once the underlying problem is identified and treated. In contrast, CMT is typically a progressive condition, so the treating physician must factor in the likelihood of deformity progression into the treatment plan. Additionally, because CMT characteristically manifests in the growing child, the resultant shape of bones and the planes of motion of joints are recognized to be atypical in many cases, which affects the predictability of the application of standardized treatment ‘‘recipes’’ for particular patterns of foot deformity. For example, the plantar-flexed first ray that is the sine quo non of the cavus portion of the deformity in a cavus-shaped and flexible foot will respond to either a laterally posted forefoot orthosis or dorsiflexion osteotomy of the first ray. However, in the patient who has CMT, the predictability of that correction is compromised. It is the nuances of CMT that are emphasized here. Pertinent history and genetics In 1884, Friedrich Schultze initially described what is now known as CMT. The early descriptions of the phenotypic syndrome by Jean-Martin * Corresponding author. E-mail address: [email protected] (T.C. Beals). 1083-7515/08/$ - see front matter Ó 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.fcl.2008.02.004 foot.theclinics.com
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Charcot and Pierre Marie in France in 1886 and Howard Henry Tooth in London the same year established an understanding of the condition as being based on abnormal peripheral nervous system function [1,2]. These investigators recognized that the condition manifested itself through a neuropathic, rather than a myopathic, process. Through the years, it was learned that the condition was based on genetic mutations. The past 2 decades have seen a dramatic increase in the number of defined genetic abnormalities that lead to what is still referred to as CMT. However, as an understanding of the heterogeneity of the condition has progressed, the dogma of diagnosis and treatment has become challenged. At this time, it is important that the treating physician recognize the different types of CMT from a genetic standpoint because the risk of progression and deformity may not be the same for different mutations. For the practicing orthopedic surgeon, it is important to recognize CMT as a condition with a more or less typical phenotypic manifestation of a complex genetic disorder, with variable underlying causative genetic abnormalities resulting in greatly variable clinical severity. The most common segmentation of CMT patients is into so-called ‘‘type 1’’ and ‘‘type 2’’ patients. Classically, type 1 is a condition in which the myelin surrounding the nerve is abnormal, whereas the axonal function is abnormal in patients who have type 2 disease. Electrophysiologic nerve testing demonstrates that the speed of impulse transfer is slowed in type 1 because of the nerve sheath dysfunction. In type 2, the rate of impulse transfer is normal but the magnitude of the impulse is decreased, as manifested by the loss of sensory- and motor nerve–evoked response amplitudes. Roughly two thirds of patients who have CMT have type 1 and one third have type 2 [3,4]. About 37 in 100,000 people are affected. The term ‘‘type 3’’ has been applied to Dejerine-Sottas disease, which is a form of hereditary peripheral neuropathy that is severe in its clinical manifestations but results in a similar phenotype. The understanding of the genetic abnormalities underpinning the different types of CMT is well beyond our ability to apply that knowledge in the clinical setting. The most common genetic abnormality that has been identified as causative of CMT is a gene defect on chromosome 17, known as CMT 1A. CMT 1B is caused by a gene defect identified on chromosome 1. Genetic testing is currently commercially available for CMT 1A. The most common abnormality identified on chromosome 17 is a duplication of a part of the PMP22 gene, but other variants have been identified. Both the gene defects on chromosome 17 and 1 are inherited in an autosomal dominant pattern. An X-linked form of type 1 CMT disease with a known gene defect also exists [5]. Autosomal recessive forms of CMT have also been identified. The genetic underpinning of CMT type 2 is less well understood but it is important to recognize it as a distinct condition, particularly as it relates to foot deformities and treatment. Like type 1, it is inherited in an autosomal dominant pattern. Defects in chromosomes 1 and 3 have been associated
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with this condition [6]. More information is being accumulated that documents that the progression of type 2 disease is not as relentless as has been assumed in the past. A prospective study of patients over a 5-year period who had the axonal (type 2) form of CMT did not demonstrate an increase in the number of patients who had a cavus foot shape, and only slow progression of the disease was observed [7]. More than 30 different gene defects have been identified as being related to different forms of what clinicians refer to as ‘‘Charcot-Marie-Tooth disease.’’ Clinical examination of patients who have Charcot-Marie-Tooth disease When evaluating a patient who has a cavovarus foot deformity, it is important to determine the underlying cause of the condition [8]. When a patient presents with a known diagnosis of CMT, the physician has a tendency to confirm the classic clinical findings because they are emphasized throughout medical education as being so characteristic of the disease. Classically, the clinical findings of CMT include weakness of the intrinsic muscles of the hands and feet, and peroneal muscle atrophy and weakness. However, one of the keys to proper evaluation of such patients is to appreciate the individuality of the patients who have this condition. In recent years, the examination of patients has been reassessed in light of the improved understanding of the genetic variability of the disease. Although many articles have been written that parrot the historical descriptions of the classic findings, senior clinicians often remark on the variability in presentation and outcomes of treatment. A recent MRI study of a small sample of patients who had CMT type 1A demonstrated consistent abnormalities of the intrinsic muscles of the foot and a notable variability in the MRI findings of fatty infiltration of leg muscles. The investigators felt their results help explain the development of the cavus deformity but, more importantly, demonstrated abnormalities in what otherwise appeared to be clinically normal muscles and variability among patients [9]. Documentation of the strength of all the muscle groups of the lower extremities is important because it allows an assessment of the progression of the disease over time and helps the surgeon best understand the options for surgical reconstruction, if the symptoms warrant intervention. Burns and colleagues [10] studied the reliability of a hand-held dynamometry unit in the evaluation of CMT patients and compared the patients to normal controls. They concluded that such testing provided a reliable and objective measure of muscle strength, which further allowed them to understand the degree of muscle imbalance. The clinical findings of CMT can be appreciated in young patients. Given the autosomal dominant pattern of inheritance and the ability to test genetically for CMT 1A, it is possible to evaluate children at risk from an early age. Berciano and colleagues [11] serially evaluated a group of 12 children known to have this condition and found that each of the children demonstrated a lack of lower limb reflexes
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and a subtle weakness most often demonstrated by a difficulty with heel walking. Physical examination of the patient who has CMT includes observation of standing posture and assessment of the ability to walk on the heels and toes. Such efforts allow the clinician to appreciate the degree of difficulty with balance and to assess for other associated deformities of the spine or hips (Fig. 1). An assessment of the range of motion of the ankle is important, with particular attention to determining if the ankle rolls normally or whether it functions more as a hinge. This assessment is particularly important in patients who have undergone prior surgical treatment. The ankle must be assessed for evidence of ligamentous instability, which is a common presenting symptom of patients presenting with CMT. In all patients who have ankle instability, it is wise to assess for the presence of a contributory cavus or cavovarus deformity and, if present, to consider the diagnosis of an underling neuromotor dysfunction. Although no practical way to quantify rotatory ankle instability exists at present, the examiner should be cognizant that patients who have CMT have rotatory asymmetries of the ankle region and may manifest a degree of rotatory instability. The shape of the foot must be characterized, noting the presence or absence of clawing of the toes and the presence or absence of a varus hindfoot. The so-called ‘‘peek-a-boo’’ heel sign is readily observed when viewing the patient from the front. Normally, the heel is hidden behind the foot, but its medial side is readily observed when the patient has a cavus foot shape [12]. The degree of flexibility of the forefoot and hindfoot must be assessed and a determination made of the presence or absence of an equinus
Fig. 1. (A) Bilateral anteroposterior weight-bearing radiographs of a 65-year-old woman with CMT 1A who had limited surgical treatment. Deformity was severe and walking capacity was limited with the use of a walker. (B) Same patient 6 years later after ankle fusion, calcaneal osteotomy, and forefoot dorsiflexion osteotomy. Deformity was moderate but the patient was fully ambulatory without assistive devices.
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contracture. As one considers the position of the hindfoot, it is worth noting that in patients who have known CMT 1A, a review of weight-bearing lateral foot radiographs demonstrated that the hindfoot was actually in dorsiflexion and that the apparent foot equinus observed was caused by the plantar flexion of the first ray [13]. Perhaps Coleman and Chestnut [14] presented the single most important contribution to the development of a salient methodology for the assessment of the cavovarus foot in 1977. In their classic manuscript, they described an elegant and simple method to assess the degree of flexibility of the hindfoot in a patient who has a cavus deformity. The ‘‘Coleman block test’’ requires a patient to stand on a block of wood with the heel and the lateral forefoot supported by the block, which allows the plantar-flexed first ray to drop. This test allows the examiner, positioned behind the patient, to determine if the hindfoot varus deformity is corrected by this maneuver. Simply put, if dropping the first ray over the edge of the block allows the hindfoot to correct to a valgus position, the hindfoot is flexible. If correction of the varus is not observed, the hindfoot is rigid (Fig. 2). This single determination drives the decision making for treatment, whether it is for the manufacture of an orthosis or for surgical treatment. The phenotypic expression of CMT is known to be variable even among families with similar genotypes, but the physical examination helps define the subtle differences of this condition. Carefully identifying the static and dynamic characteristics described earlier and assessing the reflexes of the lower extremities should allow the identification of patients who have this condition and lead the clinician to a logical conclusion about the options for management. The phenotypic expression of this genetic disorder is
Fig. 2. Patient who has cavovarus foot shape with apparent hindfoot varus. (A) Standing appearance of a patient who has bilateral cavovarus feet. Note hindfoot varus. (B) Same patient standing on a Coleman block supporting the lateral forefoot and heel, allowing the first metatarsal to drop to the floor, enabling the hindfoot to correct passively into a valgus position.
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variable and this should be expected, given the other phenotypic variability seen in siblings (Fig. 3). Pathogenesis of deformity Several insightful manuscripts make an effort to describe the pathogenesis of the deformities characteristic of this group of diseases. Tynan and colleagues [15] reviewed 41 leg MRI scans in patients who had neuromuscular disorders and cavus feet. They concluded that in most of the patients who had forefoot cavus, the peroneal compartment was enlarged relative to normal controls, with biopsies confirming the absence of pseudohypertrophy of the peroneus longus. The peroneus longus muscle is thought to be selectively spared in the development of the cavovarus deformity, with wasting of the peroneus brevis being evident early in the disease. Mann and Missirian [16] made this clinical observation in 1988. Characteristically, muscle involvement in CMT progresses from distal to proximal. However, the described patterns of muscle function have limitations. Relative sparing of the extensor hallucis longus can be observed, which is felt to be contributory to the development of the clawed hallux. Because the innervation of this muscle is more distal to the characteristically weak anterior tibialis, it is not clear why it would be spared. It is the ‘‘push me, pull you’’ relationship of weak dorsiflexion power of the anterior tibialis and the strongly plantar-flexing peroneus longus acting on the
Fig. 3. Siblings with CMT demonstrating significant differences in many phenotypic features.
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medial midfoot that is felt to be the primary driver of the cavus deformity once the intrinsic musculature is dysfunctional. Despite the original descriptions of early functional loss of the peroneal and anterior compartments of the leg, it is the tibial nerve–innervated intrinsic musculature that fails first in this family of disorders. Despite the thorough description of the patterns of weakness in specific muscle groups, no mention is typically made of a side-to-side difference in strength. The authors routinely note an asymmetry of the severity of involvement of the lower extremities in terms of strength and deformity. The characteristic deformities of the cavovarus foot in CMT are accepted to be the result of motor imbalance. Ankle dysfunction, most commonly manifested by a foot drop, is due to the relative loss of strength of the tibialis anterior relative to the superficial posterior compartment muscles. Despite the relative weakness of the tibialis anterior, it can continue to be a powerful deforming force because of its static resistance to eversion in a patient who has a varus hindfoot. The hindfoot varus is presumed to be developing passively, secondary to the forefoot cavus from the described first ray plantar flexion (forefoot-driven hindfoot varus) and the imbalance between the strong posterior tibialis and the weak peroneus brevis that serves as its antagonist in balancing the foot (Fig. 4). The forefoot deformities appear to develop after loss of the function of the intrinsic muscles and, once again, an imbalance of the extrinsic muscles. Lesser toe clawing develops after the intrinsic function of plantar flexion of the metatarsophalangeal joints and interphalangeal extension is lost. The development of the clawed hallux may be caused by the spared extensor hallucis longus muscle, which is often described as serving as an ankle extensor in the absence of the other anterior compartment muscles [17–19]. Nonsurgical treatment Little literature describes the outcome of nonsurgically treated patients who have CMT. Specifically, no large natural history studies of this
Fig. 4. (A) Left and (B) right weight-bearing lateral radiographs of a child with CMT demonstrating high arches, clawing of toes, and plantar-flexed first metatarsal. Note the asymmetry in the two sides.
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population exist. Despite that, most patients are indeed treated nonsurgically with shoe modifications, orthoses, braces, and physical therapy. A review article that attempted to evaluate the efficacy of surgical and nonsurgical care for patients who had drop foot from neuromuscular causes identified only one study that demonstrated a positive effect on the ability to walk, and that was an exercise program for people with CMT [20]. An anecdotal report of improvement in a patient who had CMT with orthopedic shoes has been published but no significant studies on orthosis use in this population [21]. One randomized trial assessing nighttime ankle bracing in patients who had CMT 1A has been published and it demonstrated no benefit [22]. Because of the cavovarus foot shape, the development of ankle instability is common in patients who have CMT. For many patients, ankle instability is often their initial presenting clinical concern. Because of the cavovarus foot shape, excess stress is placed on the lateral hindfoot structures, particularly given the progressive weakness of the peroneus brevis. The relative overpull of the more medially inserting tendons leads to a progressive tendency toward inversion, and then the progressive static deformities of a cavus foot shape accentuate that tendency, with patients developing lateral instability. Classic therapy with peroneal strengthening and proprioceptive retraining are likely less effective in this patient population that has sensory and motor deficits, particularly with regard to eversion strength, but it can be attempted. Some patients, especially adolescents with milder deformities who are still flexible, as determined by a Coleman block test, can be treated initially with foot orthoses, which elevate the lateral forefoot, allowing the first ray to drop effectively into a hole and keep the subtalar joint in a more neutral position.
Surgical options Several different operations have been described in isolation and in combination in the treatment of patients who have cavovarus foot deformities secondary to CMT. The broad categories of ‘‘bony’’ and ‘‘soft tissue’’ procedures have been described, with a progressive realization that the combination of both is typically necessary for optimal outcome [23,24]. It appears that soft tissue procedures alone do not offer significant lasting benefit. Bony procedures include the use of fusion of the ankle, hindfoot, midfoot, or the great toe interphalangeal joint, and all are performed in concert with deformity correction. Joint-sparing osteotomies, most commonly of the calcaneus and metatarsals or medial midfoot, have the same goals. The recent drift to joint-sparing procedures is driven by an appreciation that a significant degree of deformity correction can be achieved through osteotomy and an acknowledged concern about ‘‘adjacent joint arthritis’’ that has been observed primarily in patients undergoing triple arthrodesis. Given the young age of
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so many of the patients treated for deformities associated with CMT, this consideration is logical. Soft tissue operations that have been described in the treatment of patients who have CMT include various procedures. A common soft tissue technique in this population is a plantar fascial release. More formal plantarmedial stripping procedures have also been described. Transfers of multiple different tendons have also been applied to this patient population. Transfer of the tibialis posterior through the interosseous membrane to the dorsolateral foot (split or in isolation), transfer of the tibialis anterior centrally on the hindfoot, transfer of the extensor hallucis longus tendon to the neck of the first metatarsal done in concert with an interphalangeal fusion, transfer of the peroneus longus to the peroneus brevis, and flexor digitorum longus or Achilles tendon lengthening have been described. Younger and Hansen [25] published a thorough description of the in-phase and out-of-phase tendon transfers that can be considered in this scenario. The reader must be cautious in applying the specific capabilities of a given patient to this outline because of the phenotypic variability. Even in this population of patients who have often-inflexible cavus, soft tissues releases done with excessive vigor can result in profound collapse of the foot architecture, and a planus foot shape can develop (Fig. 5). In patients who have CMT, the method of osteotomy performed affects the ability to achieve deformity correction, and the relative movement of the architectural alignment of the skeleton will have an effect on the ability of various muscles to effect a moment arm. For example, dorsiflexion of the first ray will effectively lengthen the extensor hallucis longus and thereby may obviate the need for a formal correction of a cock up hallux (Jones procedure). Therefore, it is important that surgical reconstruction be done in a stepwise manner with reassessment throughout a procedure, rather than applying a given ‘‘recipe’’ of procedures to each foot with a cavovarus deformity. The degree and planes of correction of the hindfoot varus deformity that can be achieved through a translational or closing wedge (Dwyer) calcaneal osteotomy are more limited than those of more complex osteotomies, such as the one originally described by Pisani and modified by Hintermann [26,27]. The options for calcaneal osteotomy include a lateralizing translational tuberosity osteotomy with or without a closing wedge laterally; a Hintermann type Z osteotomy with closing wedge and lateral translation, which also shortens the hindfoot; or an ‘‘Italian-style’’ osteotomy, which additionally shortens and laterally translates the hindfoot and tips the tuberosity into a more valgus position [28]. Subtalar arthrodesis can also achieve a more valgus positioning with reduction through the subtalar joint, and triple arthrodesis is sometimes also required to put the foot in a proper position beneath the ankle. The ability to translate and rotate through the ‘‘Z’’ pattern of osteotomy appears to have increased our ability to address large deformities but it is
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Fig. 5. (A) Anteroposterior foot, (B) anteroposterior ankle, and (C) lateral views of a child with profound collapse of the arch after surgery to address a cavovarus deformity due to CMT 1A.
clearly a more technically demanding procedure with a greater risk to the remaining peroneal function (Fig. 6).
Outcomes of treatment Few studies have been published that assess the outcome of treatment of cavovarus foot deformities in patients who have CMT. In each of the cited studies, the reader is unable to draw definite conclusions because of the limited number of patients treated and variability in the patient groups. Nevertheless, each study offers some insight into the condition and the pitfalls of certain treatment choices. No randomized surgical studies have been done of defined subgroups of CMT. No prospective studies have been done either. The surgeon must thoughtfully apply the lessons learned from the available
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Fig. 6. Lateral weight-bearing view of a boy with CMT 1A treated with a ‘‘Z’’ calcaneal osteotomy, medial column dorsiflexion osteotomy, and posterior tibial tendon transfer.
literature, which is heavily weighted toward studies of young patients with short follow-up. Soft tissue procedures In 1980, Paulos and colleagues [29] described the results of soft tissue procedures alone in correcting pes cavovarus in children. Only 1 of the 27 patients had CMT. The outcomes of a complete plantarmedial release on these children who averaged 7 years of age at the time of surgery were subjectively improved at an average of 2 years follow-up. Coleman, who was the senior investigator on the paper, later advocated combined bony and soft tissue procedures for children with neuromuscular deformity. Six of 39 feet were noted to have residual cavus at the time of final evaluation. Isolated transfer of the posterior tibial tendon through the interosseous membrane has been studied in 43 children with overall good results. However, like most studies of a given procedure, few patients with CMT were included in the study. The outcome in these patients was not favorable and, indeed, the investigators recommended that the procedure be abandoned in patients who have CMT for whom a staged procedure including hindfoot stabilization is contemplated [30].
Osteotomies The results of osteotomies in the treatment of the cavovarus foot have been reported. Sammarco and Taylor [31] reported on 21 feet in 15 patients who underwent calcaneal osteotomy and one or more metatarsal osteotomies to correct their deformity. Fifteen of the feet were of patients who had CMT. The functional assessments, with commonly used instruments such as the American Orthopaedic Foot and Ankle Society ankle-hindfoot score and the Maryland Foot Score, showed improvements in outcome at an average of just less than 6 years. Although some complications were
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encountered, improvements in symptoms indicating the need for surgery such as ankle instability and forefoot metatarsalgia were documented. A lateral translational osteotomy of the calcaneus was done with closing wedge dorsolateral metatarsal osteotomies. Most feet underwent other procedures at the same time. The investigators emphasized the value of combining the osteotomies with plantar fascial release and the potential advantages over competing notions of hindfoot or tarsometatarsal arthrodeses, midtarsal osteotomies, and isolated forefoot or hindfoot procedures. One study of patients with CMT used dynamic pedobarography in nine children who had undergone joint-sparing corrective surgery that included a combination of osteotomies and tendon transfers; it was found that the degree of radiographic correction did not correlate with the degree of change in pedobarographic measurements [32]. The investigators reported preoperative increased heel pressure that was not improved significantly by surgical treatment. They emphasized that even if deformities appear to be corrected completely, pressure distribution is not normalized. Although the study assessed a small group of children who may not have been genetically dissimilar, the lack of correlation in functional parameters with commonly reported static measurements is cautionary and the investigators appropriately emphasized the need to make that clear to parents considering such surgery for their children. Midfoot osteotomy has been advocated in the treatment of cavovarus deformities. Japas [33] described a ‘‘V’’ osteotomy of the midfoot in combination with a Steindler plantarmedial stripping to address these deformities. He described his technique and experience with 17 feet observed for 2 to 6 years. By modern standards, the report is hard to assess, given the lack of weight-bearing radiographs and the use of antiquated assessment tools, but it does identify a logical framework for considering a midfoot osteotomy. The investigator notes the potential advantages of correcting the deformity at its most ‘‘prominent point’’ and he avoids the interference with tarsal motion seen with the competing arthrodesis operations that were common at the time. He described his paper as a ‘‘preliminary report,’’ and the lack of further follow-up may be telling in its absence. However, it remains a consideration for a rigid deformity and should be considered in a salvage situation.
Arthrodesis Most studies that are referable to patients who have CMT are reviews subsequent to hindfoot fusion. Mann and Hsu [34] retrospectively reviewed 10 adolescent CMT patients who had had 12 foot operations that included triple arthrodesis. Each patient reportedly had a rigid hindfoot deformity. Five feet (50%) were plantigrade, fused at all joints, and asymptomatic at an average of 7.5 years. This group of patients, all treated with a single
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lateral incisional approach, included two talonavicular nonunions, one calcaneocuboid nonunion, and three nonplantigrade feet. In this small group of patients, who were followed for between 2 years 4 months and 18 years, three prior and nine subsequent surgeries were described. Clearly, adolescents surgically treated were likely to undergo more than one operation. Longer-term results from triple arthrodesis are the reports that have influenced most directly the surgical considerations in this patient population. The competing advantage of fairly reliable deformity correction with the disadvantage of lost motion, particularly in a younger patient population that has a normal life span, is a source of ongoing dialog for surgeons who treat these patients. Angus and Cowell [35] published a review of 80 feet with an average follow-up of 13 years after triple arthrodesis. They described a high incidence of arthritis of the ankle and midfoot. Understanding the numbers behind the widely touted conclusions is essential to appreciate the reported findings. The review was made of 62 patients, 18 of whom had bilateral triple arthrodeses. The initial study population included 302 patients, so it should be noted that only 20% of the patients were assessed. The average age of the patients was 14, and internal fixation was used in 12 of 80 feet. Three and one half months of casting, on average, was endured after surgery. Only a few of these patients had CMT, with most having cerebral palsy, idiopathic clubfoot, or poliomyelitis. Given the significant limitations in study design, the conclusions are limited, but arthrosis appeared frequently in these young people, who only averaged 27 years of age at follow-up. In 1989, Wetmore and Drennan [36] reported on 16 patients who had CMT, who had had a total of 30 triple arthrodeses. The average age at the time of operation was 15, and the average length of follow-up was 21 years. The results are sobering. The investigators described 77% of patients as having fair or poor outcomes and six limbs had also undergone an ankle fusion. Development of recurrent cavovarus deformity was thought to be the cause behind the poor outcomes. Saltzman and colleagues [37] also reported on the long-term outcome of patients who underwent a triple arthrodesis. Sixty-seven feet in 57 patients were reviewed. Nine percent of the patients in this study had CMT, with most (55%) due to polio. Seventy-eight percent of the patients had some residual deformity, but the deformities, in contrast to the findings of Wetmore and Drennan, were not progressive. At the final follow-up evaluation, all of the ankles in the study population showed degenerative changes on radiographs. Ninety-five percent of the patients were satisfied despite the concerning findings of progressive arthrosis of the ankle. One can also learn from nonneuromuscular patient groups. The results of the triple arthrodesis was studied in a group of 27 adult patients (31 feet) who had undergone triple arthrodesis for the treatment of chronic hindfoot pain and had been followed for a minimum of 10 years [38]. The mean age of the patients who were examined was 45 at the time of the surgery, and the
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mean duration of follow-up of those patients was 14 years. The investigators found that 25 (93%) of the patients were satisfied with the results of the treatment. However, only 11 (41%) reported that they could perform moderate activity with mild or no pain in the foot and ankle. Severe arthrosis developed in 7 of the 26 ankles, in 7 naviculocuneiform joints, and in 6 tarsometatarsal joints. Some patients had severe arthrosis at more than one level, and 3 patients later required an ankle arthrodesis.
Summary Understanding the cause of a disease will affect the understanding of the course and treatment of the condition. What is currently recognized by a characteristic phenotype may someday be recognized as distinct subsets of peripheral neurologic disease with molecular basis. The hope is that genetic subtyping will allow for better prediction of the development and progression of deformities of the foot and ankle, which can be translated into a more logical treatment method that will yield better functional outcomes for patients. The ability to weaken agonists during growth and development is within reach if astute clinicians can develop an understanding of the subtleties of a condition that appears to have a great deal of genetic and clinical variability. Joint-sparing operations tailored to the individual are an ideal to work toward, but currently, the best treatment comes from thoughtful consideration of the limited information that the reviewed investigators have provided. Key principles appear to be to understand the specific features of a given patient in detail when creating a customized surgical plan that uses bony reconstruction procedures to create a mechanically balanced foot, and then to apply soft tissue releases and tendon transfers as necessary to maintain functional control of the foot and ankle, while appreciating the likelihood of progression of the neuromotor imbalance.
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