Transient osteoporosis

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Epidemiology

  • M > F with a ratio of 3:1
  • Middle age men 40-50
  • Generally unilateral
  • Essentially 2 groups:
  1. Men aged 40-60
  2. 3rd trimester of pregnancy

Aetiology

  • Unknown

Clinical

History

  • ACUTE onset
  • 3 phases:
  1. Initial – rapid ­ in pain (1 month)
  2. Plateau – 1 month
  3. Resolution – 4 months
  • Patients usually complain from functional deficit more than pain.

Examination

  • ¯ Flexion and IR

Investigations

  1. X-ray
    • Osteopaenia
      • Can be very profound (“phantom head”)
      • Extends down metaphysis to intertrochanteric region
      • May involve the acetabulum
      • Takes 4 weeks to fully develop
    • NO subchondral collapse
  1. Bone scan
    • Always ­
      • Diffuse ­ uptake in head and metaphysis
      • No photopaenic areas (if they are present suspect AVN)
  1. MRI
    • Best way to differentiate from AVN
      • AVN – localised in head
      • Transient osteoporosis – diffuse marrow oedema, down into metaphysis
    • Effusion is common
    • Serial scan normalise around 6 months

Natural history

  • Self-limiting
    • Symptoms settle in ~ 6 months
    • In pregnant women symptoms settle after birth
  • Excellent prognosis
    • 2-5% develop AVN

Treatment

  1. Protected weight bearing
  2. Analagesia