Orthopaedic Surgery - Muscular Dystrophies

Basics

Muscular dystrophies are a heterogeneous group of inherited muscle disorders characterized by progressive degeneration and weakness of skeletal muscle without a primary abnormality of the peripheral or central nervous system.

Although skeletal muscle is the principal tissue involved, many forms also affect:

Cardiac muscle

Respiratory function

The skeleton

Mobility and posture

Other organ systems

The various muscular dystrophies have traditionally been classified according to:

Distribution of weakness

Age at onset

Rate of progression

Associated systemic findings

Pattern of genetic inheritance

Because Duchenne muscular dystrophy has particularly important orthopaedic consequences, it is emphasized here.

Classification

Muscular dystrophies can be grouped according to their genetic inheritance and phenotype.

X-Linked Muscular Dystrophies

Important X-linked disorders include:

Duchenne muscular dystrophy

Becker muscular dystrophy

Emery–Dreifuss muscular dystrophy

Autosomal-Recessive Muscular Dystrophies

This group includes several forms of:

Limb-girdle muscular dystrophy

and other congenital or early-onset dystrophies.

The modern classification is increasingly based on the specific genetic or molecular defect rather than solely on clinical distribution.

Autosomal-Dominant Muscular Dystrophies

Examples include:

Facioscapulohumeral muscular dystrophy

Some distal muscular dystrophies

Oculopharyngeal muscular dystrophy

Certain other phenotypes may also follow dominant inheritance.

Epidemiology

Duchenne Muscular Dystrophy

Duchenne muscular dystrophy primarily affects boys.

Historically, the incidence has been approximately:

1 in 3,500 live male births.

Becker Muscular Dystrophy

Becker muscular dystrophy is less common, with an older estimated incidence of approximately:

1 in 30,000 live male births.

Risk Factors

For Duchenne and Becker muscular dystrophy, the major demographic risk factor is:

Male sex, because the disorders are inherited in an X-linked pattern.

A positive maternal family history also increases suspicion.

Genetics

Duchenne and Becker muscular dystrophies result from pathogenic variants in the DMD gene located on the short arm of the X chromosome.

This gene encodes:

Dystrophin, an important structural protein associated with the muscle-cell membrane cytoskeleton.

Dystrophin

Dystrophin helps stabilize the muscle-cell membrane during contraction.

Loss or marked reduction of functional dystrophin causes repeated muscle-fiber injury and progressive degeneration.

Duchenne Muscular Dystrophy

In Duchenne muscular dystrophy, functional dystrophin is:

Essentially absent or severely deficient.

The resulting phenotype is typically severe and begins early in childhood.

Becker Muscular Dystrophy

In Becker muscular dystrophy, dystrophin is:

Present in reduced quantity or abnormal form.

The clinical course is generally milder and more slowly progressive than Duchenne muscular dystrophy.

Etiology

The underlying cause is a genetic defect affecting structural proteins required for normal muscle function.

In Duchenne and Becker muscular dystrophy, abnormal dystrophin causes instability of the muscle-fiber membrane, leading to:

Repeated injury

Fiber necrosis

Replacement by fat and connective tissue

Progressive weakness

Diagnosis

Duchenne Muscular Dystrophy

Duchenne muscular dystrophy typically becomes clinically apparent between approximately 3 and 6 years of age.

Early Presentations

Common early findings include:

Delayed walking

Frequent falls

Difficulty running

Inability to hop or jump normally

Difficulty rising from the floor

Waddling gait

Trendelenburg gait

Exaggerated lumbar lordosis

Gower Maneuver

A classic finding is the Gower maneuver.

When rising from the floor, the child uses the hands to “climb” up the thighs because of marked weakness of the:

Hip extensors and proximal pelvic-girdle muscles.

Pattern of Weakness

Weakness is predominantly proximal and usually begins in the pelvic girdle.

Commonly affected muscle groups include:

Gluteal muscles

Quadriceps

Abdominal musculature

Hip abductors and extensors

Later, weakness progresses to the:

Shoulder girdle and upper extremities.

Gait

Pelvic-girdle weakness causes compensatory posture during walking.

The child may carry the:

Head and shoulders posterior to the pelvis, creating increased anterior pelvic tilt and lumbar lordosis.

This compensates for weak hip extensors.

Trendelenburg Gait

Weak hip abductors produce:

Pelvic instability and a waddling or Trendelenburg gait.

Calf Pseudohypertrophy

The calves commonly appear enlarged.

This is termed:

Pseudohypertrophy, because the increased bulk results largely from replacement of normal muscle by fat and connective tissue rather than true increased muscle strength.

Contractures

Contractures develop progressively, commonly involving:

Achilles tendons

Knees

Hips

Iliotibial bands

Upper-extremity contractures may develop later.

Shoulder-Girdle Weakness

Shoulder-girdle weakness typically develops several years after the initial lower-extremity symptoms.

The patient may be difficult to lift by supporting the axillae because the shoulder girdle fails to stabilize normally.

This historical finding has been called the Meryon sign.

Sensation

Sensory examination is usually normal.

The absence of sensory loss helps distinguish muscular dystrophy from many peripheral neuropathies.

Motor Development

Some children also demonstrate:

Developmental delay, learning difficulties, or cognitive impairment.

The degree varies considerably.

Loss of Ambulation

Historically, many boys with untreated or older-era Duchenne muscular dystrophy lost effective independent ambulation around the early adolescent years.

With contemporary corticosteroid therapy, cardiac care, respiratory support, rehabilitation, and disease-specific treatments, loss of ambulation may occur later and varies substantially among patients.

Cardiac Involvement

Cardiac involvement is common.

Potential abnormalities include:

Cardiomyopathy

Tachycardia

Conduction abnormalities

Progressive ventricular dysfunction

Cardiac surveillance is therefore essential even before symptoms develop.

Respiratory Involvement

Progressive respiratory muscle weakness leads to:

Reduced cough strength

Restrictive pulmonary dysfunction

Nocturnal hypoventilation

Respiratory insufficiency

Respiratory disease is a major determinant of long-term outcome.

Becker Muscular Dystrophy

Becker muscular dystrophy resembles Duchenne muscular dystrophy in:

Distribution of weakness and associated cardiac disease, but it is usually less severe.

Age at Onset

Symptoms generally begin later, often after approximately 7 years of age, although presentation is variable.

Progression

Muscle weakness progresses more slowly than in Duchenne muscular dystrophy.

Ambulation is often preserved for a much longer period.

Life expectancy is also generally greater, although significant cardiomyopathy may occur.

Physical Examination

The diagnosis begins with a careful history and examination.

Muscle Bulk

Assess for:

Calf pseudohypertrophy

Muscle wasting

Asymmetry

Gait Assessment

Observe for:

Waddling gait

Trendelenburg gait

Lumbar hyperlordosis

Toe walking

Difficulty rising from the floor

Proximal Weakness

Muscle strength should be tested systematically, beginning with proximal groups such as:

Hip abductors

Hip extensors

Quadriceps

Shoulder abductors

Scapular stabilizers

Gower Sign

Ask the patient to rise from the floor without assistance.

Use of the hands to push on the knees and thighs indicates proximal weakness.

Shoulder Stability

Assess scapular and shoulder-girdle control.

Difficulty supporting the upper trunk during lifting may reflect advanced proximal weakness.

Contractures

Examine for:

Achilles tightness

Knee flexion contractures

Hip flexion or abduction contractures

Elbow and wrist contractures

Spine

Examine for:

Scoliosis

Kyphosis

Pelvic obliquity

Spinal deformity becomes particularly important after loss of ambulation.

Laboratory Tests

Creatine Kinase

Serum creatine kinase is markedly elevated early in Duchenne muscular dystrophy.

Levels may be:

Many times above normal, sometimes reaching more than 100-fold elevation.

CK may decline later as functional muscle mass is progressively lost.

Genetic Testing

Molecular testing of the DMD gene is now a central component of diagnosis.

It can identify:

Deletions

Duplications

Point mutations

and other pathogenic variants.

Genetic confirmation also helps guide:

Family counseling and mutation-specific therapy.

Dystrophin Analysis

Muscle biopsy with dystrophin immunostaining is used less often now because genetic testing can establish the diagnosis in most patients.

When performed:

Duchenne muscular dystrophy shows absent or near-absent dystrophin.

Becker muscular dystrophy shows reduced or abnormal dystrophin.

Electromyography

Electromyography demonstrates a myopathic pattern characterized by:

Low-amplitude

Short-duration

Polyphasic motor-unit potentials

EMG is less important than genetic testing in modern diagnostic pathways but can help when the diagnosis is uncertain.

Cardiac Assessment

Cardiac evaluation should be performed regularly.

Monitoring may include:

Electrocardiography

Echocardiography

Cardiac MRI

depending on age and disease stage.

Imaging

Spine Imaging

Patients should be screened clinically for scoliosis.

Once deformity is suspected or identified, radiographs are used to:

Measure curve magnitude and monitor progression.

Characteristic Scoliosis

The scoliosis associated with Duchenne muscular dystrophy is typically a:

Long, collapsing thoracolumbar curve, often accompanied by pelvic obliquity.

Unlike idiopathic scoliosis, the deformity may involve most of the spine as a single sweeping curve.

Pathological Findings

Muscle pathology demonstrates:

Progressive degeneration and necrosis of muscle fibers

Variation in muscle-fiber size

Regeneration of some fibers

Replacement by connective tissue

Fatty infiltration

These changes account for progressive weakness and pseudohypertrophy.

Differential Diagnosis

Important differential diagnoses include:

Peripheral neuropathy

Anterior horn cell disease

Spinal muscular atrophy

Poliomyelitis

Congenital myopathy

Metabolic myopathy

The absence of sensory loss, markedly elevated CK, characteristic weakness pattern, and genetic testing help distinguish Duchenne muscular dystrophy.

Treatment

General Principles

There is no simple curative therapy for most muscular dystrophies.

Management is multidisciplinary and aims to:

Preserve mobility

Prevent contractures

Maintain respiratory and cardiac function

Manage skeletal deformity

Improve quality of life and independence

Modern treatment has substantially extended survival compared with historical series.

Activity

Physical activity should be encouraged within the patient’s capabilities.

The aim is to maintain:

Mobility, joint motion, conditioning, and participation.

Excessive high-resistance or eccentric exercise that causes prolonged muscle damage should be avoided.

Physical Therapy

Physical therapy is central to management.

Strength Monitoring

Serial muscle-strength assessment helps document progression.

Stretching

Daily stretching is used to reduce development of contractures.

Particular attention is given to:

Achilles tendons

Hamstrings

Hip flexors

Iliotibial bands

Upper-extremity joints

Orthoses

Ankle-foot orthoses may help:

Maintain ankle position

Delay equinus contracture

Improve nighttime stretching

They are most useful when deformity remains flexible.

Mobility Support

As weakness progresses, patients may require:

Walking aids

Standing devices

Wheelchairs

Positioning systems

The goal is to preserve function and independence rather than simply prolong ambulation at all costs.

Fractures

Lower-extremity fractures occur relatively frequently, especially in patients with:

Reduced mobility, osteoporosis, or chronic corticosteroid exposure.

Stable fractures should be treated in a manner that minimizes prolonged immobilization whenever possible because loss of mobility can lead to permanent functional decline.

Contracture Management

Contractures should initially be managed with:

Stretching

Positioning

Orthoses

Surgical release may occasionally be considered when a contracture interferes with:

Positioning, footwear, standing, hygiene, or function.

Achilles and Fascia Lata Release

Selected procedures may include:

Achilles tendon lengthening

Release of fascia lata or other contracted structures

These procedures are performed selectively because weakening an already weak muscle group can impair function.

Scoliosis

Progressive scoliosis is common in nonambulatory Duchenne muscular dystrophy.

Older series reported progression in the great majority of untreated patients.

The risk and rate may be reduced by contemporary corticosteroid therapy.

Nonoperative Spine Management

Management includes:

Postural support

Wheelchair seating optimization

Monitoring of pelvic obliquity

Respiratory assessment

Bracing has limited ability to permanently control progressive neuromuscular scoliosis.

Spinal Surgery

Spinal fusion may be considered for significant progressive deformity that compromises:

Sitting balance

Comfort

Pelvic alignment

Pulmonary mechanics

Historically, surgery was recommended for curves progressing beyond approximately 20–30°, while older operative thresholds such as 45° were also used.

Current decisions are individualized according to curve progression, remaining function, pulmonary reserve, cardiac status, and overall goals.

Fusion Levels

Correction often involves long posterior fusion extending through most of the thoracic and lumbar spine.

Instrumentation may extend to the:

Pelvis or sacrum when substantial pelvic obliquity is present.

Timing of Spine Surgery

If surgery is required, it is preferable to intervene before:

Severe pulmonary compromise or advanced cardiomyopathy

makes anesthesia and recovery excessively hazardous.

Respiratory Therapy

Respiratory management is essential.

Treatment may include:

Assisted coughing

Airway-clearance techniques

Inspiratory or expiratory muscle support

Noninvasive positive-pressure ventilation

Nocturnal ventilatory support

These interventions can substantially improve quality of life and survival.

Cardiac Management

Patients require regular cardiology follow-up.

Treatment of cardiomyopathy may include:

ACE inhibitors

Angiotensin-receptor blockers

Beta-blockers

Mineralocorticoid receptor antagonists

according to cardiac findings.

Genetic Counseling

Families should receive genetic counseling regarding:

X-linked inheritance

Carrier testing

Risk to future children

Testing of female relatives when appropriate

Medication

Corticosteroids

Corticosteroids such as:

Prednisone or deflazacort

can prolong motor function and may delay:

Loss of ambulation

Contracture development

Scoliosis progression

They may also have favorable effects on pulmonary function.

Corticosteroid Adverse Effects

Potential long-term complications include:

Weight gain

Cushingoid appearance

Growth suppression

Cataracts

Hypertension

Osteoporosis

Fracture risk

These effects require monitoring.

Disease-Specific Therapies

Some patients with Duchenne muscular dystrophy may be eligible for mutation-specific or gene-directed treatment.

These therapies depend on:

The exact DMD mutation, age, disease stage, and regulatory availability.

They complement rather than replace multidisciplinary supportive care.

Surgery

Orthopaedic surgery may be required for:

Selected contractures

Severe progressive scoliosis

Fractures requiring stabilization

Rare positioning or functional problems

Follow-Up

Patients should be followed regularly by a multidisciplinary team.

Neurologic and functional reassessment is commonly performed approximately every 4–6 months, or more often when clinically necessary.

Prognosis

Duchenne Muscular Dystrophy

Historically, Duchenne muscular dystrophy was often fatal in the second or third decade because of respiratory and cardiac failure.

With modern:

Corticosteroids, cardiac surveillance, assisted ventilation, rehabilitation, and newer disease-modifying therapies, survival has improved markedly, and many patients now survive well into adulthood.

Becker Muscular Dystrophy

Becker muscular dystrophy progresses more slowly.

Ambulation is usually maintained longer, and life expectancy is generally greater, although cardiomyopathy can still be severe.

Complications

Major complications include:

Respiratory insufficiency

Cardiomyopathy and heart failure

Fractures

Scoliosis

Joint contractures

Osteoporosis

Loss of mobility

Pressure-related skin problems in advanced disease

Respiratory Failure

Progressive respiratory muscle weakness can ultimately cause:

Hypoventilation, recurrent respiratory infection, ineffective coughing, and respiratory failure.

Cardiac Failure

Dilated cardiomyopathy and progressive ventricular dysfunction are major causes of morbidity and mortality.

Fractures

Reduced mobility, poor bone density, and corticosteroid exposure increase the risk of fractures.

Loss of ambulation after a fracture should be minimized whenever possible through prompt rehabilitation and appropriate stabilization.

Scoliosis

Spinal deformity may impair:

Sitting balance, comfort, pulmonary mechanics, and pelvic alignment.

Careful surveillance after loss of ambulation is particularly important.

Patient Monitoring

Regular multidisciplinary monitoring should include:

Muscle strength and motor milestones

Range of motion and contractures

Ambulatory status

Spinal alignment

Bone health

Pulmonary function

Cardiac function

Nutritional status

Psychosocial and developmental needs

Key Principle

Muscular dystrophies are progressive inherited disorders of muscle, and Duchenne muscular dystrophy has particularly important orthopaedic consequences.

Optimal management focuses on:

Preserving mobility, preventing contractures, monitoring scoliosis, protecting bone health, supporting cardiac and respiratory function, and coordinating long-term multidisciplinary care.