Pathophysiology
I-34. Immobilization syndrome — effects on somatic functions
不動化症候群の体性機能への影響
Immobilization Syndrome — Overview
- Long-term bed rest/inactivity affects the whole body → immobilization syndrome.
- Similar clinical picture regardless of underlying cause. Some symptoms are reversible (but recovery takes longer than the immobilization itself), and can cause permanent damage → disability worse than original illness.
- Worse in: elderly, disabled, unconscious/anesthetized, chronically ill.
Central & Peripheral Nervous System
- CNS symptoms: sleep disorders, anxiety, emotional/behavioral illness, depression/apathy, intellectual deterioration.
- Causes: original disorder, insufficient blood supply (O₂/glucose deficit via cerebral atherosclerosis), psychological impact of prolonged bed rest.
- PNS: nerve compression (direct/contracture) → sensory disturbance (decubitus risk), motor impairment (→ more immobility).
Musculoskeletal System
- ↓Muscle strength/fatigue, muscle atrophy, contractures (fixed tightening ± heterotopic ossification), fibrotic degeneration, osteoporosis.
- Contractility: force depends on myofilament number (activity-dependent). Atrophy = ↓cross-sectional area + fewer nuclei + ↓myofibrillar proteins.
- Total inactivity → ↓strength 10–20%/week (halves in a month), worst in postural/lower-limb muscles (~3%/week thigh mass). Recovery is slow.
- Myostatin (key in atrophy): suppresses contractile-protein gene transcription, inhibits IGF-1, promotes protein degradation, activates autophagy/apoptosis (↓nuclei), induces mitochondrial dysfunction → ROS → apoptosis.
- Contracture causes: pain, paralysis (paralytic/spastic), plaster/splint. Sites: lower (hip/knee/ankle), upper (shoulder/elbow/wrist/finger). CT in muscle increases within days → dense CT → calcified (heterotopic ossification, worsened by bed-rest hypercalcemia).
- Prevent contracture: early mobilization, physiological joint positioning, active/passive movement therapy.
Disuse Osteoporosis
- Loss of postural/movement muscle activity → ↑sclerostin (osteocytes sense ↓canalicular fluid flow = ↓load) → ↓osteoblasts, ↑osteoclasts.
- Bone degradation → Ca²⁺ release → hypercalcemia → ↓PTH → ↓tubular Ca²⁺ reabsorption (↑urinary Ca → kidney/bladder stones) + ↓active vitamin D (↑fecal Ca).
- 3 months inactivity → →50% bone density (long bones, from medullary cavity). On remobilization, even normal contraction can cause pathological fractures.
Skin & Mucous Membranes
- Skin: pressure ulcers (decubitus), bacterial/fungal infections.
- Mucosa: “airway decubitus,” corneal ulcer.
- Pressure ulcer stages: 1) blanching + reactive hyperemia, 2) partial-thickness necrosis, 3) full-thickness skin loss, 4) subcutis necrosis with exposed bone/tendon/muscle.
- Etiology: tissue ischemia from compression exceeding capillary hydrostatic pressure (30 mmHg), then ↑vessel permeability → edema → further compression. Contributing factors: immobilization, hypotension, ↑blood viscosity, anemia, neuropathy, contractures, malnutrition, wound infection. Irreversible necrosis within 2 hrs → reposition regularly, use air mattresses. Common at bony prominences.
一問一答
▶What CNS effects occur in immobilization syndrome, and why?
Sleep disorders, anxiety, emotional/behavioral illness, depression/apathy, and intellectual deterioration — from the original disorder, insufficient cerebral blood supply (O₂/glucose deficit), and the psychological impact of bed rest.
▶What is immobilization syndrome?
A whole-body deterioration from long-term bed rest/inactivity that produces a similar clinical picture regardless of cause; some effects are reversible (recovery taking longer than the immobilization) but it can cause permanent disability.
▶How does immobilization affect the peripheral nervous system?
Nerve compression (direct or from contracture) → sensory disturbance (decubitus risk) and motor impairment (worsening immobility).
▶How quickly does muscle strength decline with total inactivity?
About 10–20% per week (halving in a month), worst in postural/lower-limb muscles (~3%/week of thigh mass), with slow recovery.
▶Who is most vulnerable to immobilization syndrome?
The elderly, disabled, unconscious/anesthetized, and chronically ill.
▶What characterizes muscle atrophy at the cellular level?
Decreased cross-sectional area, fewer nuclei, and decreased myofibrillar proteins (contractile force depends on activity-dependent myofilament number).
▶What is the mechanism of disuse osteoporosis?
Loss of postural/movement muscle activity → osteocytes sense ↓canalicular fluid flow (↓load) → ↑sclerostin → ↓osteoblasts and ↑osteoclasts → bone degradation.
▶What is the role of myostatin in disuse atrophy?
It suppresses contractile-protein gene transcription, inhibits IGF-1, promotes protein degradation, activates autophagy/apoptosis (↓nuclei), and induces mitochondrial dysfunction → ROS → apoptosis.
▶What causes contractures and how can they be prevented?
Causes: pain, paralysis (paralytic/spastic), plaster/splint immobilization (CT proliferates within days → dense → calcified/heterotopic ossification). Prevention: early mobilization, physiological joint positioning, and active/passive movement therapy.
▶How does disuse osteoporosis cause hypercalcemia and its renal consequences?
Bone degradation releases Ca²⁺ → hypercalcemia → ↓PTH → ↓tubular Ca²⁺ reabsorption (↑urinary Ca → kidney/bladder stones) and ↓active vitamin D (↑fecal Ca).
▶How much bone density can be lost after 3 months of inactivity, and what is the risk on remobilization?
Up to ~50% bone density loss (in long bones, from the medullary cavity); on remobilization, even normal contraction can cause pathological fractures.
▶What are the four stages of pressure ulcers (decubitus)?
1) Blanching + reactive hyperemia, 2) partial-thickness necrosis, 3) full-thickness skin loss, 4) subcutis necrosis with exposed bone/tendon/muscle.
▶What is the pathophysiology of pressure ulcer formation?
Compression exceeding capillary hydrostatic pressure (30 mmHg) causes tissue ischemia, then ↑vessel permeability → edema → further compression; irreversible necrosis occurs within 2 hours.
▶What factors contribute to pressure ulcer development, and how is it prevented?
Contributors: immobilization, hypotension, ↑blood viscosity, anemia, neuropathy, contractures, malnutrition, wound infection. Prevention: regular repositioning and air mattresses (ulcers form at bony prominences).
▶What musculoskeletal changes occur in immobilization syndrome?
Reduced muscle strength/fatigue, muscle atrophy, contractures (± heterotopic ossification), fibrotic degeneration, and osteoporosis.
▶What skin and mucous membrane complications arise from immobilization?
Skin: pressure ulcers and bacterial/fungal infections. Mucosa: "airway decubitus" and corneal ulcers.
▶How does bed-rest hypercalcemia worsen contractures?
It promotes calcification of the proliferating connective tissue in immobilized muscle, contributing to heterotopic ossification.
▶At which joints do contractures commonly develop during immobilization?
Lower limb (hip, knee, ankle) and upper limb (shoulder, elbow, wrist, finger).
▶Why is recovery from immobilization-related damage often prolonged?
Even reversible changes take longer to recover than the duration of immobilization, and some damage becomes permanent.
▶How does sclerostin link mechanical loading to bone mass?
Osteocytes sense reduced canalicular fluid flow (reduced load) and increase sclerostin, which inhibits osteoblasts → net bone loss during disuse.