Primary generalised osteoporosis

The most prevalent metabolic bone disease and a leading cause of insufficiency fracture / fragility fracture → fractures of the proximal femur have a major impact on the quality of life of both patients and caregivers.

Biology

• Peak bone mass is achieved in the late teens to early 3rd decade; males > females; Black > other races.
• After peak bone mass, bone mass gradually decreases with age in all populations:
  • In women, loss accelerates after the 4th–5th decade (post-menopause).
  • In men, loss starts later (around the 5th decade) and is more gradual.
  • A similarly sharp fall in bone mass is seen earlier in women with bilateral oophorectomy, athletes with secondary amenorrhoea, hyperprolactinaemia, and Turner syndrome.
  • Comparable bone loss can also occur in men with hypogonadism.
  • These observations support a major role of sex hormones (oestrogen, testosterone) in preserving bone density.
• Beyond sex hormones, age-related generalised bone loss is multifactorial and not fully explained by routine laboratory tests. Conventional lab results are typically normal.
• Both trabecular (more severe) and cortical bone loss occur and contribute to increased risk of insufficiency fracture:
  • Trabecular bone loss → ↑ vertebral insufficiency fracture, distal radius fractures.
  • Cortical bone loss → ↑ proximal femur fractures.

Clinical

• Often asymptomatic until fracture.
• Back pain due to:
  • Vertebral insufficiency fracture →
    • Height loss
    • Increased thoracic kyphosis (ddx senile kyphosis)
    • Usually no neurological complications
  • Pelvic and sacral fractures
• Atraumatic or fragility fractures of ribs, proximal femur, humerus, radius.

Diagnosis

• Normal bone mineralisation but reduced bone density compared with individuals of the same sex and race, with or without evidence of insufficiency fracture.
• For technical details and diagnostic criteria → see DXA scan for osteoporosis.
• Various other methods to measure bone mineral density are being investigated but are not standard practice.

Radiological findings

• Changes predominate in the axial skeleton and proximal portions of long bones of the appendicular skeleton.
• Expansion of the medullary cavity at the expense of cortical thickness due to greater increase in endosteal diameter than periosteal diameter.
• Reduction of trabecular bone (some trabeculae are thinned, others lost) → accentuation/unmasking of remaining trabecular patterns:
  • Vertebral bodies: accentuated vertical striations (can simulate the appearance of a vertebral haemangioma)
    • Due to preferential resorption of the horizontal trabeculae.
  • Proximal femur: more prominent Ward’s triangle; basis of the Singh index.
• Linear or band-like sclerosis oriented perpendicular to the long axis of long bones in periarticular regions = “reinforcement lines” / “bone bars”
  • Due to remodelling of trabecular bone.
• Insufficiency fracture typical sites by frequency:
  • Vertebral insufficiency fracture
  • Symphysis pubis, pubic rami, sacrum
  • Other regions of the bony pelvis, femoral neck, proximal and distal tibia, sternum