Courtesy: Prof Nabil Ebraheim, University of Toledo, Ohio, USA

 

Osteoporosis: Causes, Pathophysiology, and Clinical Impact

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Overview

Osteoporosis is a common skeletal disorder characterized by:

• Decreased bone mass
• Deterioration of bone microarchitecture
• Reduced bone strength

 Leads to an increased risk of fractures

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Bone Strength Depends On

• Bone mineral density (BMD)
• Bone quality:
  • Microarchitecture
  • Bone turnover
  • Mineralization

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Common Osteoporotic Fractures

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Typical Sites

• Distal radius (wrist)
• Vertebral spine
• Hip

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Age-Related Pattern

• Younger postmenopausal women:
  • Wrist fractures first
• Elderly:
  • Hip fractures more common

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Risk of Subsequent Fractures

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After Vertebral Fracture

• -5× increased risk of:
  • Another vertebral fracture
• Increased risk of:
  • Hip fracture

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After Hip Fracture

• 8–10× increased risk of:
  • Second hip fracture

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Important Clinical Insight

• Higher mortality in men after hip fracture compared to women

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Mortality Associated with Osteoporosis

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• 20–25% of elderly patients die within 1 year after hip fracture

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Common Causes

• Immobility
• Infection
• Thromboembolism

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Lifetime Risk of Fracture

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• Women: -40–50%
• Men: -13–22%

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Bone Physiology

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Bone Remodeling Cells

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Osteoclasts

• Function:
  • Bone resorption
• Remove old bone

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Osteoblasts

• Function:
  • Bone formation
• Produce new bone matrix

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Normal Bone Balance

• Bone health depends on balance between:
  • Resorption (osteoclasts)
  • Formation (osteoblasts)

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Pathophysiology of Osteoporosis

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Key Mechanism

• Bone mineralization: Normal
• Problem:
  • Reduced bone mass (quantity)

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Result

• Increased osteoclastic activity
  OR
• Decreased osteoblastic activity

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Outcome

• Progressive bone loss
• Structural weakening

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Important Concept

• Osteoporosis is a quantitative bone disorder
• Not a defect in mineralization

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Osteoporosis vs Osteomalacia

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Peak Bone Mass

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• Achieved between:
  • 16–25 years

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Clinical Importance

• Higher peak bone mass — lower fracture risk later

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Age-Related Bone Loss

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In Men

• Begins after -25 years
• Rate: -0.3% per year

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In Women

• Rate: -0.5% per year

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Postmenopausal Bone Loss

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Cause

• Estrogen deficiency

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Rate

• 2–3% per year

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Duration

• Rapid phase lasts:
  • 5–10 years

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Types of Osteoporosis

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Type I – Postmenopausal Osteoporosis

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Features

• Occurs 15–20 years after menopause
• Caused by estrogen deficiency
• Affects:
  • Trabecular bone

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Common Fractures

• Vertebral fractures
• Wrist fractures

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Type II – Senile Osteoporosis

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Features

• Occurs after age 70
• Affects both sexes
• Causes:
  • Aging
  • Calcium & vitamin D deficiency

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Bone Involvement

• Cortical + trabecular bone

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Common Fractures

• Hip fractures
• Vertebral fractures

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Structural Changes in Aging Bone

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• Increased medullary cavity
• Reduced cortical thickness

 Leads to reduced mechanical strength

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Epidemiology

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• Affects:
  • 45–50% of women >50 years
• Lower but significant in men

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Gender Ratio

• Female : Male –2 : 1

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Risk Factors for Osteoporosis

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Non-Modifiable Factors

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• Female sex
• Increasing age
• Family history
• Caucasian / Northern European ancestry
• Low body weight

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Lifestyle Factors

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• Sedentary lifestyle
• Smoking
• Excess alcohol
• Poor calcium / vitamin D intake

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Medication-Related Factors

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• Long-term use of:
  • Glucocorticoids
  • Anticonvulsants (e.g., phenobarbital)
  • Other drugs affecting bone metabolism

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Key Takeaways

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• Osteoporosis is a silent disease until fracture occurs
• Bone mineralization is normal — problem is loss of bone mass
• Hip fractures carry high mortality
• Peak bone mass in youth is critical for prevention
• Early identification of risk factors is essential