🔑 Key Learning

  • Osteomalacia/rickets = defective bone mineralisation due to vitamin D deficiency
    • Rickets occurs in children (bow legs, short stature)
      Osteomalacia in adults (bone pain, fractures)
    • Classic biochemistry = low vit D, low calcium/phosphate, high PTH and ALP
  • Other important bone disorders:
    • Osteopetrosis – dense, brittle bones due to osteoclast dysfunction
    • Osteitis fibrosa cystica – high PTH bone disease with cysts and brown tumours
    • Osteogenesis imperfecta – brittle bone disease due to type I collagen defect

🧬 Pathophysiology

Osteomalacia / Rickets

  • Inadequate bone mineralisation due to:
    • ↓ Calcium and/or phosphate
    • ↓ Vitamin D (most common cause)
    • Chronic renal failure (secondary hyperparathyroidism)
    • Rarely, Vitamin D–resistant rickets

👀 Clinical Features

Rickets (Children)

  • Bone pain, skeletal deformities:
    • Knock knees, bow legs, scoliosis
    • Waddling gait
    • Short stature
  • ⚠️ Physiological genu varum is normal under age 4 in healthy children

Osteomalacia (Adults)

  • Diffuse bone pain (esp. back, legs, pelvis)
  • Muscle weakness
  • Fragility fractures
  • Bony tenderness (e.g. shins)

🧪 Investigations

Bloods

  • ↓ Calcium, ↓ Phosphate
  • ↑ PTH, ↑ ALP
  • Check Vitamin D levels

Imaging

  • X-ray: Looser zones (pseudofractures)

💊 Management

  • Treat underlying cause
  • Vitamin D replacement:
    • Colecalciferol / ergocalciferol
    • Adcal-D3 (Vit D + calcium) if low dietary intake
  • Address chronic renal failure or other underlying causes if relevant

🧬 Other Bone Disorders

🧱 Osteopetrosis (Marble Bone Disease)

  • Rare disorder of osteoclast dysfunction
  • Bones become thick and dense but are fragile
  • Normal calcium, phosphate, PTH, ALP

💀 Osteitis Fibrosa Cystica

  • Caused by advanced hyperparathyroidism
  • Bone resorption leads to:
    • Osteopenia
    • Brown tumours, cystic lesions
    • Skeletal deformity and fractures
  • Bloods:
    • ↑ PTH, ↑ Calcium, ↑ ALP
    • ↓ Phosphate

🧬 Osteogenesis Imperfecta

  • Autosomal dominant disorder of type I collagen
  • Classic triad:
    • Recurrent childhood fractures
    • Blue sclera
    • Hearing loss / dental abnormalities

📝 Exam Clues & Clinchers

  • Looser zones on X-ray = osteomalacia
  • Bow legs + short stature + low Ca/phosphate = rickets
  • High PTH + brown tumours = osteitis fibrosa cystica
  • Fractures + blue sclera + hearing loss = osteogenesis imperfecta
  • Dense, brittle bones on XR = osteopetrosis
Condition Pathophysiology Key Features Bloods Imaging
Osteomalacia / Rickets ↓ Bone mineralisation (usually ↓ Vit D) Bone pain, deformities (rickets), Looser zones ↓ Ca, ↓ PO₄, ↑ PTH, ↑ ALP Looser zones on X-ray
Osteopetrosis Osteoclast dysfunction Brittle, dense bones, fractures Normal Sclerosis on XR (‘marble bones’)
Osteitis Fibrosa Cystica Bone changes due to ↑ PTH Bone pain, cysts, brown tumours ↑ Ca, ↓ PO₄, ↑ PTH, ↑ ALP Bone cysts, subperiosteal erosion
Osteogenesis Imperfecta ↓ Type I collagen (AD inheritance) Childhood fractures, blue sclera, hearing loss, dental problems Normal Generalised osteopenia, fractures