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🦴 Fragility Fractures, Osteoporosis & Bone Turnover: A Complete PLAB 2 Guide


Understanding fragility fractures and osteoporosis is essential for PLAB 2, not just for diagnosis, but for explaining conditions clearly to patients and managing them appropriately.

This guide simplifies the core concepts, clinical reasoning, and exam traps.


🔍 What is a Fragility Fracture?

A fragility fracture is:

A fracture that occurs from low-energy trauma, such as a fall from standing height or less.

👉 This type of injury should not normally cause a fracture in healthy bone.


📍 Common sites

  • Hip (neck of femur)

  • Vertebrae (compression fractures)

  • Distal radius (Colles’ fracture)

  • Proximal humerus


🎯 Key clinical point

Any fracture after minimal trauma in an older patient = fragility fracture until proven otherwise


🦴 What is Osteoporosis?

👉 Osteoporosis is a condition where:

  • Bone density decreases

  • Bone becomes fragile and prone to fractures


❗ Important concept

👉 Osteoporosis is not a blood disease👉 It is a bone structure problem



🧠 How Does Osteoporosis Happen?

This is the most important concept to understand.


Normal bone turnover

Bone is constantly being remodeled:

  • Osteoclasts → break down bone

  • Osteoblasts → build new bone

👉 In healthy individuals → balance


In osteoporosis

  • Bone breakdown increases

  • Bone formation decreases

➡️ Result: Net bone loss


🧠 Simple analogy

Think of bone as a bank account:

  • Deposits = bone formation

  • Withdrawals = bone breakdown

👉 In osteoporosis:

  • Withdrawals > deposits → savings (bone) decrease



🧪 Why Are Blood Tests Normal?

This is a common confusion.

👉 In primary osteoporosis:

  • Calcium → normal

  • Phosphate → normal

  • ALP → normal


❗ Why?

Because the body:

  • Maintains normal blood calcium at all costs

  • Pulls calcium from bone if needed

➡️ Blood looks normal➡️ Bone becomes weak


🎯 Exam point

“Normal blood tests do not rule out osteoporosis”

🧪 Then Why Do We Do Blood Tests?

👉 Not to diagnose osteoporosis

👉 But to exclude secondary causes


🔍 Examples of secondary causes

  • Vitamin D deficiency

  • Hyperparathyroidism

  • Thyroid disease

  • Chronic kidney disease



🧮 What is FRAX Score?

👉 FRAX estimates 10-year fracture risk

It helps decide:

  • Who needs reassurance

  • Who needs DEXA

  • Who needs treatment


What it includes

  • Age, sex

  • Previous fractures

  • Smoking, alcohol

  • Steroid use

  • (Optional) Bone density


⚠️ Important

👉 If patient already has a fragility fracture:

  • ❌ No need for FRAX

  • ✔ Treat directly



📉 Why Do We Do a DEXA Scan?

👉 DEXA = measures Bone Mineral Density (BMD)


📊 T-score interpretation

  • ≥ -1 → Normal

  • -1 to -2.5 → Osteopenia

  • ≤ -2.5 → Osteoporosis


🎯 Key difference

Test

Purpose

DEXA

Confirms diagnosis

Blood tests

Find cause


💊 Why Give Calcium & Vitamin D If Levels Are Normal?

This is a high-yield clinical concept.


Reasons:

1. Support bone health

Even if levels are normal, intake may not be optimal

2. Prevent further bone loss

Reduces need for body to pull calcium from bone

3. Required for treatment

Drugs like bisphosphonates need adequate calcium & vitamin D


🎯 Key takeaway

“Normal blood levels ≠ optimal bone support”

⚙️ Factors Affecting Bone Turnover

Understanding this helps explain why osteoporosis develops

1. Hormones (most important)

  • ↓ Estrogen → ↑ bone loss

  • ↑ Parathyroid hormone → ↑ resorption

  • ↑ Thyroid hormone → ↑ turnover

2. Age

  • Reduced bone formation

3. Mechanical factors

  • Exercise → strengthens bone

  • Immobilisation → bone loss

4. Nutrition

  • Calcium

  • Vitamin D

  • Protein

5. Lifestyle

  • Smoking

  • Alcohol

6. Medications

  • Steroids (very important)

7. Diseases

  • Endocrine disorders

  • Chronic illness


🎯 One-line summary

“Bone turnover is influenced by hormones, age, activity, nutrition, lifestyle, medications, and disease.”

🧠 Putting It All Together (Clinical Flow)

Step 1: Patient presents with fracture

→ Ask mechanism

Step 2: If low-energy trauma

→ Fragility fracture

Step 3: Assume osteoporosis

→ Start management

Step 4: Do:

  • Blood tests (rule out causes)

  • ± DEXA (if needed)

Step 5: Treat:

  • Lifestyle + supplements

  • Pharmacotherapy


🚨 Final PLAB 2 High-Yield Summary

  • Fragility fracture = low-energy injury

  • Osteoporosis = bone loss, not blood abnormality

  • Blood tests = usually normal

  • DEXA = diagnosis

  • FRAX = risk prediction

  • Calcium/Vit D = support treatment


🧠 Final One-Liner

“Osteoporosis is a disorder of increased bone resorption with normal blood tests, diagnosed by DEXA and often presenting as fragility fractures.”

📚 References



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