Arthrogryposis

Definition: Arthrogryposis Multiplex Congenita (AMC) is a descriptive term for conditions characterized by multiple congenital joint contractures affecting two or more body areas. It is NOT a specific diagnosis but a clinical finding.

Epidemiology:

• Incidence: 1 in 3000 live births.
• Amyoplasia: ~30% of AMC cases (most common recognizable type).

Pathogenesis (Fetal Akinesia): Any condition causing decreased fetal movement leads to contractures:

• Neurogenic: Spinal muscular atrophy, Myelomeningocele.
• Myopathic: Congenital myopathies, Muscular dystrophies.
• Connective Tissue: Diastrophic dysplasia.
• Mechanical: Oligohydramnios, Multiple pregnancy.
• Vascular: Anterior horn cell ischemia (Amyoplasia).

The Central Mechanism: Fetal Immobility

All forms of arthrogryposis share a common final pathway: fetal akinesia (decreased fetal movement) during critical periods of joint development.

Normal Joint Development (Weeks 8-12):

• Joints form through cavitation of mesenchyme
• Movement is essential for normal joint cavity formation
• Fetal movement shapes articular surfaces and prevents contractures
• Muscles develop in response to neural input and use

Consequences of Akinesia:

Causes of Fetal Akinesia

1. Neurogenic Causes (Most Common)

• Anterior horn cell dysfunction (Amyoplasia - vascular insult)
• Spinal muscular atrophy
• Myelomeningocele
• CNS malformations

2. Myopathic Causes

• Congenital myopathies (Nemaline, Central Core)
• Congenital muscular dystrophy
• Myotonic dystrophy (maternal)

3. Mechanical Restriction

• Oligohydramnios (renal agenesis, PROM)
• Multiple pregnancy
• Uterine anomalies
• Amniotic bands

4. Connective Tissue Disorders

• Diastrophic dysplasia
• Larsen syndrome

Amyoplasia-Specific Pathophysiology

Amyoplasia is caused by anterior horn cell ischemia during early gestation:

• Sporadic occurrence (no inheritance)
• Symmetric involvement suggests vascular etiology
• Anterior horn cells are particularly vulnerable to hypoxia
• Results in muscle hypoplasia/aplasia with fatty replacement
• Preserved sensory function (posterior horn spared)

The pathology is periarticular soft tissue, not bone. Fibro-fatty replacement of muscle, capsular fibrosis, and ligamentous shortening fix the joint, while the underlying articular surfaces and ossification centres are usually structurally normal at birth. Bony deformity is secondary and develops with growth against unbalanced soft tissues.

Joint-by-joint pattern (classic Amyoplasia):

Pathomechanics: Because muscle is deficient rather than merely tight, deforming forces are weak but corrected positions are also poorly maintained by active power. This dual problem (rigid contracture plus weak motors) is why recurrence is high and why surgery aims for a balanced, braceable position rather than a normal arc of motion.

History:

• Pregnancy: Decreased fetal movements? Oligohydramnios?
• Birth: Breech? Complications?
• Family History: Any inheritance pattern?
• Development: Milestones? Intelligence?

Physical Examination:

• General: Facies (Micrognathia), Skin (Dimpling, Lack of creases).
• Upper Limb:
  • Shoulder: Internal rotation contracture.
  • Elbow: Extension contracture (most common) or Flexion.
  • Wrist: Flexion/Ulnar deviation.
  • Hand: Thumb-in-palm, Camptodactyly.
• Lower Limb:
  • Hip: Dislocated (30% in Amyoplasia), Flexion contracture.
  • Knee: Extension or Flexion contracture.
  • Foot: Clubfoot (rigid), Vertical Talus, Congenital Knee dislocation.
• Spine: Scoliosis (common).
• Neurological: Assess muscle bulk, Tone, Reflexes.

Differential Diagnosis

Arthrogryposis is a sign, not a diagnosis. The task is to place the child into a prognostic and genetic category.

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Diagnosis (Clinical):

• Diagnosis is clinical (multiple congenital contractures).
• Investigations aim to find the underlying cause.

Investigations:

1. Genetic Testing: Gene panels for distal arthrogryposis, SMA, etc.
2. MRI Brain/Spine: If neurogenic cause suspected.
3. EMG/NCS: Differentiate myopathic vs neurogenic.
4. Muscle Biopsy: If myopathy suspected.
5. Ophthalmology Review: Associated eye anomalies.
6. Cardiac Echo: Associated cardiac anomalies.

Orthopaedic Imaging:

• Hip X-ray/Ultrasound: Assess dislocation.
• Spine X-ray: Scoliosis.
• Foot X-ray: Clubfoot assessment.

After Clubfoot Surgery:

• Cast 6-8 weeks.
• Bracing long-term (AFO, UCBL).
• Monitor for recurrence.

After Elbow Surgery:

• Splint in flexion 6 weeks.
• Gradual ROM.
• Long-term PT.

• Amyoplasia: Excellent outcomes. Most walk. Normal intelligence and lifespan.
• Syndromic: Depends on underlying condition.
• Function: Children adapt remarkably and achieve independence.

Global epidemiology: Arthrogryposis affects roughly 1 in 3,000 to 1 in 5,000 live births worldwide; amyoplasia is the most common recognisable form (Hall 2014, N=560). Distribution is broadly similar across regions; apparent variation reflects ascertainment rather than true geography.

Side-by-side guidance:

Registry context: There is no dedicated AMC implant registry; arthroplasty registries (NJR, AJRR, AOANJRR) are not relevant in childhood. Outcome data come from specialist-centre cohorts and clubfoot relapse audits, which consistently identify brace non-compliance as the dominant predictor of recurrence.

High- vs limited-resource practice: In high-resource settings, early MDT clinics (orthopaedics, physiotherapy, occupational therapy, genetics) and serial casting from the neonatal period are standard. In limited-resource settings, late presentation is common, Ponseti programmes are the most scalable and cost-effective intervention, and talectomy remains a valuable single-stage salvage where staged reconstruction and long-term bracing are impractical.