Limb contractures are a common impairment in neuromuscular diseases. They contribute to increased disability from decreased motor performance, mobility limitations, reduced functional range of motion, loss of function for activities of daily living, and increased pain. The pathogenesis of contractures is multifactorial. Myopathic conditions are associated with more severe limb contractures compared with neuropathic disorders. Although the evidence supporting the efficacy of multiple interventions to improve range of motion in neuromuscular diseases in a sustained manner is lacking, there are generally accepted principles with regard to splinting, bracing, stretching, and surgery that help minimize the impact or disability from contractures.
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Known contributing extrinsic factors include decreased ability to actively move a limb through its full range of motion, static positioning for prolonged periods of time, and agonist-antagonist muscle imbalance.
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Known intrinsic factors contributing to contractures include fibrotic changes to the muscle resulting in reduced extensibility and disruption of muscle fiber architecture; thus, myopathic conditions are associated with more severe limb contractures compared with neuropathic disorders.
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A major rationale for controlling lower-limb contractures is to minimize their adverse effects on independent ambulation; however, the major cause of wheelchair reliance in neuromuscular diseases is generally weakness and not contracture formation.
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Static positioning of upper and lower limbs is an important cause of contracture formation.
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The primary focus of surgery has been on the management of lower-limb contractures to achieve a braceable lower extremity or plantigrade foot or because contractures of the arm and hand cause little functional deficit until the late stages of neuromuscular disease.
Introduction
Limb contractures are a common impairment in neuromuscular diseases (NMDs). They contribute to increased disability from decreased motor performance, mobility limitations, reduced functional range of motion (ROM), loss of function for activities of daily living, and increased pain. The pathogenesis of contractures is multifactorial. Known contributing extrinsic factors include decreased ability to actively move a limb through its full ROM, static positioning for prolonged periods of time, and agonist-antagonist muscle imbalance. Intrinsic factors include fibrotic changes to the muscle resulting in reduced extensibility. Contracture prophylaxis is important to maintain function, ROM, and skin integrity. Lower-limb contractures are much more prevalent than upper-limb contractures. Myopathic conditions are associated with more severe limb contractures compared with neuropathic disorders. The rate of NMD progression is also related to the frequency and severity of contractures with more rapidly progressive conditions resulting in earlier and more severe contracture formation. Bracing, stretching programs, and surgery have all been used in the prophylaxis and treatment of limb contractures.
Pathogenesis
A limb contracture is the lack of full passive ROM because of joint, muscle, or soft tissue limitations. Contractures in NMDs develop from intrinsic myotendinous structural changes and extrinsic factors.
Static Positioning
Weakness and inability to achieve active joint mobilization throughout the full normal range is the single most frequent factor contributing to the occurrence of fixed contractures. For example, less than antigravity knee extension strength places an individual at risk for knee flexion contractures, particularly if the patient no longer ambulates and spends most of their time seated with the knee joint positioned in flexion. The position in which a joint is statically positioned influences the number of sarcomeres present in any given muscle. A shortened muscle length may result in up to a 40% loss of sarcomeres. A statically positioned limb developing fibrotic changes within the muscle develops contracture formation in the position of immobilization. Contractures rapidly develop in many NMDs after transitioning to a wheelchair. The static nature of wheelchair mobility compared with the dynamic movement associated with gait contributes to the development of limb contractures. Compensatory strategies used to biomechanically stabilize joints to accommodate for muscle paresis result in reduced active ROM. For example, individuals with NMD resulting in proximal hip and knee extension weakness exhibit lumbar lordosis, diminished stance phase knee flexion, and equinus posturing at the ankle during stance and gait. The equinus posturing at the ankle is a compensation to keep the weight line and ground reaction force line anterior to the knee. The increased lumbar lordosis moves the weight line and ground reaction force line posterior to the hip. These compensations stabilize the lower limbs by creating a knee extension moment and a hip extension moment. However, these same compensations result in reduced active ROM of the same joints. This is likely why ankle plantar flexion contractures develop in Duchenne muscular dystrophy (DMD) before the onset of wheelchair reliance.
Imbalance of Agonist and Antagonist Muscles
Asymmetries of strength are an important determinant of contracture formation. The imbalance between flexor and extensor muscle groups has not been shown to be a major factor leading to contracture formation, but contractures are frequently observed when major muscle imbalance is present. This is likely caused by reduced active ROM because the movement is dominated by the stronger muscle group. For example, in several NMDs there is more pathologic involvement of the ankle dorsiflexors and evertors than the ankle plantarflexors and invertors. This imbalance in combination with intrinsic muscle changes leads to the frequently observed equinocavovarus foot deformities, which become exacerbated if the patient loses ambulation and is no longer weight bearing.
Fibrosis and Fatty Tissue Infiltration
Intrinsic muscle tissue alterations in dystrophic myopathies contribute to contracture formation. The most significant histologic changes are those of muscle fiber loss; abnormal residual dystrophic muscle fibers; segmental necrosis of muscle fibers; and increased amounts of adipose tissue, connective tissue, and fibrosis. Replacement of functioning muscle fibers with collagen and fatty tissue in concert with chronically shortened resting muscle length results in contracture formation. The collagen fibers undergo rearrangement and proliferation causing muscle fibrosis and resistance to passive stretch. Neurogenic atrophy typically results in a diminished degree of fibrosis, which lowers the risk of severe contracture formation.
Pathogenesis
A limb contracture is the lack of full passive ROM because of joint, muscle, or soft tissue limitations. Contractures in NMDs develop from intrinsic myotendinous structural changes and extrinsic factors.
Static Positioning
Weakness and inability to achieve active joint mobilization throughout the full normal range is the single most frequent factor contributing to the occurrence of fixed contractures. For example, less than antigravity knee extension strength places an individual at risk for knee flexion contractures, particularly if the patient no longer ambulates and spends most of their time seated with the knee joint positioned in flexion. The position in which a joint is statically positioned influences the number of sarcomeres present in any given muscle. A shortened muscle length may result in up to a 40% loss of sarcomeres. A statically positioned limb developing fibrotic changes within the muscle develops contracture formation in the position of immobilization. Contractures rapidly develop in many NMDs after transitioning to a wheelchair. The static nature of wheelchair mobility compared with the dynamic movement associated with gait contributes to the development of limb contractures. Compensatory strategies used to biomechanically stabilize joints to accommodate for muscle paresis result in reduced active ROM. For example, individuals with NMD resulting in proximal hip and knee extension weakness exhibit lumbar lordosis, diminished stance phase knee flexion, and equinus posturing at the ankle during stance and gait. The equinus posturing at the ankle is a compensation to keep the weight line and ground reaction force line anterior to the knee. The increased lumbar lordosis moves the weight line and ground reaction force line posterior to the hip. These compensations stabilize the lower limbs by creating a knee extension moment and a hip extension moment. However, these same compensations result in reduced active ROM of the same joints. This is likely why ankle plantar flexion contractures develop in Duchenne muscular dystrophy (DMD) before the onset of wheelchair reliance.
Imbalance of Agonist and Antagonist Muscles
Asymmetries of strength are an important determinant of contracture formation. The imbalance between flexor and extensor muscle groups has not been shown to be a major factor leading to contracture formation, but contractures are frequently observed when major muscle imbalance is present. This is likely caused by reduced active ROM because the movement is dominated by the stronger muscle group. For example, in several NMDs there is more pathologic involvement of the ankle dorsiflexors and evertors than the ankle plantarflexors and invertors. This imbalance in combination with intrinsic muscle changes leads to the frequently observed equinocavovarus foot deformities, which become exacerbated if the patient loses ambulation and is no longer weight bearing.
Fibrosis and Fatty Tissue Infiltration
Intrinsic muscle tissue alterations in dystrophic myopathies contribute to contracture formation. The most significant histologic changes are those of muscle fiber loss; abnormal residual dystrophic muscle fibers; segmental necrosis of muscle fibers; and increased amounts of adipose tissue, connective tissue, and fibrosis. Replacement of functioning muscle fibers with collagen and fatty tissue in concert with chronically shortened resting muscle length results in contracture formation. The collagen fibers undergo rearrangement and proliferation causing muscle fibrosis and resistance to passive stretch. Neurogenic atrophy typically results in a diminished degree of fibrosis, which lowers the risk of severe contracture formation.
Contractures in specific NMDs
Duchenne and Becker Muscular Dystrophies
The most common contractures observed in dystrophinopathies in the order of frequency are ankle plantar flexion, knee flexion, hip flexion, hip abduction, elbow flexion, and wrist flexion contractures. Proximal lower-extremity contractures are rare while subjects with DMD are ambulatory, but develop soon after they transition to a sitting position in a wheelchair for most of the day. The occurrence of elbow flexion contractures also seems to be directly related to prolonged static positioning of the limb flexed because these contractures develop soon after full-time wheelchair reliance ( Fig. 1 ). The relationship between wheelchair reliance and hip and knee flexion contractures has been noted by multiple authors. Given the tremendous replacement of muscle by fibrotic tissue in individuals with DMD, it is not surprising that a muscle with less than antigravity strength statically positioned in a wheelchair would develop a contracture. Although 20% of subjects with DMD in the study by McDonald and colleagues developed ankle plantar flexion contractures of greater than 5 degrees before wheelchair reliance, there was a rapid acceleration in severity of these contractures after transition to wheelchair reliance (see Fig. 1 ). Ankle plantar flexion contractures were not likely a significant cause of wheelchair reliance because less than 10% of subjects had plantar flexion contractures of greater than or equal to 15 degrees before their transition to the wheelchair. The natural history data for DMD was described by McDonald and colleagues. The cause and frequency of contractures in Becker muscular dystrophy is similar to DMD when comparing individuals of similar function. As a result, contractures are rare in ambulatory boys with Becker muscular dystrophy with exception to ankle plantar flexion. As they transition to a wheelchair, the prevalence of contractures increases.
Emery-Dreifuss Muscular Dystrophy
Emery-Dreifuss muscular dystrophy (EMD) is a group of muscular dystrophies with early and extreme contracture formation disproportional to the degree of muscle weakness and immobility. EMD deserves special attention because of the notorious presence of limb contractures despite the presence of functional strength. EMD results from a group of genes that encode for nuclear proteins. The exact mechanisms of such profound contracture formation in EMD are not fully understood. The condition usually presents in adolescence or early adult life, and many clinical features may be seen in early childhood. An associated cardiomyopathy usually presents with arrhythmia and may lead to sudden death in early adult life. A hallmark of EMD type 1 is the early presence of contractures of the elbow flexors with limitation of full extension. Patients often have striking wasting of the upper arms accentuated by sparing of the deltoids and forearm muscles. The early presence of contractures of the elbow flexors is contrasted by focal wasting of the biceps brachii muscles. Heel cord tightness may be present early in the disorder concomitant with ankle dorsiflexion weakness and toe walking. Unlike DMD, the toe walking in EMD usually is secondary to ankle dorsiflexion weakness and contracture formation, and it is not a compensatory strategy to stabilize the knee because of proximal limb weakness. Tightness of the cervical and lumbar spinal extensor muscles or rigid spine results in limitation of neck and trunk flexion.
Slowly Progressive Muscular Dystrophies
The slowly progressive muscular dystrophies are a heterogeneous group of muscular dystrophies with a slower progression, with a life expectancy into later adulthood. Limb-girdle muscular dystrophies, facioscapulohumeral muscular dystrophy, and myotonic muscular dystrophy types 1 and 2 can all be associated with contracture formation. The severity of contractures coincides with the degree of muscle weakness. Severe contractures are infrequent in ambulators but are more prevalent in full-time wheelchair users. Contractures in congenital myotonic dystrophy are common affecting greater than 70% of individuals and most commonly affect the ankle but rarely the knees or hips. Patients with congenital myotonic muscular dystrophy may be born with clubfoot deformities. Scoliosis is also commonly observed.
Congenital Muscular Dystrophies and Congenital Myopathies
Congenital muscular dystrophies and congenital myopathies represent groups of congenital or infant-onset myopathies. These disorders present with hypotonia and early presence of contractures. Subjects with congenital muscular dystrophies or myopathies often exhibit early contractures including ankle plantarflexion, knee flexion, hip flexion, wrist flexion, and long finger flexion. These myopathies have been reported to be fairly slowly progressive or relatively static; however, the contractures become more severe over time with prolonged static positioning and lack of active ROM. Patients with Ullrich congenital muscular dystrophy have a primary defect in collagen VI in addition to a dystrophic myopathy. These patients have the unique combination of distal ligamentous laxity with hypermobile joints and proximal contractures.
Arthrogryposis
Arthrogryposis is a symptom complex characterized by congenital rigidity of the joints and is not a specific diagnostic entity. By definition, arthrogryposis involves multiple joints, with distal joints more often affected than proximal joints. The feet, ankles, hands, and wrists are most commonly affected. A variety of central nervous system disorders, such as chromosomal syndromes, developmental disorders, and congenital malformations of the central nervous system, may result in arthrogryposis. Alternatively, focal and segmental vascular insufficiency during embryonic development may lead to a focal loss of anterior horn cells and hypomyoplasia or amyoplasia. Arthrogryposis caused by amyoplasia leads to embryonic strength imbalance around joints, which results in congenital contractures.
Spinal Muscular Atrophy
Spinal muscular atrophy (SMA) is a term used to describe a varied group of inherited disorders characterized by weakness and muscle wasting secondary to degeneration of both anterior horn cells of the spinal cord and brainstem motor nuclei without pyramidal tract involvement. The most common SMA syndrome is predominantly proximal, autosomal-recessive, and linked to chromosome 5q. Contractures are problematic in patients with SMA who have lost ambulation or never obtained ambulation. One study found reductions in ROM by more than 20 degrees among 22% to 50% of subjects with SMA II depending on the joint. Hip, knee, and wrist contractures were most common. Lower-extremity contractures have been found to be rare in ambulatory patients with SMA. Patients with SMA perceive their elbow flexion contractures to hinder one or more daily functions, and the contractures were reported to be associated with greater discomfort. Contractures are very common in SMA II. In the lower limbs, the knees are most affected followed by the hips and ankles. The shoulders are the most severely affected in the upper limbs followed by the elbows and wrists.
Amyotrophic Lateral Sclerosis
Amyotrophic lateral sclerosis is a rapidly progressive motor neuron disorder that results in profound appendicular, bulbar, and respiratory muscle weakness, but only mild joint contractures. In one study, only 26% of subjects with amyotrophic lateral sclerosis had ankle plantar flexion contractures, 13% had shoulder contractures, and 20% had contractures of any joint measuring greater than or equal to 20 degrees by goniometry. The low prevalence and mild severity of contractures in amyotrophic lateral sclerosis is likely caused by the neurogenic nature of the muscle wasting with less severe fibrosis and fatty tissue infiltration.
Charcot-Marie-Tooth Disease
Multiple subtypes of Charcot-Marie-Tooth (CMT) or hereditary motor sensory neuropathy exist with genetic heterogeneity among the primarily demyelinating forms and the primarily axonal forms. In a study of 53 subjects, reduction in ROM by 20 degrees or more was seen in 9% at the ankle, 8% at the knee, 2% at the elbow, 14% at the hip, and 19% at the wrist. Focal wasting of intrinsic foot and hand musculature is common, and the most common lower-limb contracture is an equinocavovarus deformity. Cavus foot deformities associated with hindfoot varus and a variety of complex foot deformities caused by muscle imbalance is common in CMT with disease progression.
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