Day 2 — FCPS Orthopaedic IMM
Bone Metabolism & Fracture Healing Part II · 50-MCQ IMM–Part II Test · Q51–Q100
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💎 Day 2 — High Yield Recall
Bone Metabolism · Mineralization · Remodeling · Vascularity · Molecular Healing · Factors Affecting Union · Nonunion · Soft Tissue · Graft Biology — rapid recall, tables, pearls, traps & viva
⚡ Rapid Recall — One-Liners
| Concept | High-yield answer |
|---|---|
| Low serum Ca²⁺ | ↑ PTH |
| PTH | ↑ Ca, renal phosphate loss, ↑ vitamin-D activation |
| Vitamin D | ↑ intestinal Ca + phosphate |
| Calcitonin | ↓ osteoclast activity |
| Osteoid | Unmineralized organic matrix |
| Main organic matrix | Type I collagen |
| Main inorganic component | Hydroxyapatite |
| ALP | Osteoblast/mineralization marker |
| Osteoporosis | Reduced bone quantity |
| Osteomalacia | Defective mineralization |
| Remodeling | Activation → resorption → reversal → formation |
| Osteocyte | Mechanosensor |
| Sclerostin | Inhibits Wnt/osteoblast activity |
| Nutrient artery | Medullary + inner cortical supply |
| Periosteal blood supply | Important especially after fracture |
| VEGF | Angiogenesis |
| BMP | Osteoinduction |
| PDGF | Cell recruitment/proliferation |
| TGF-β | Matrix/cellular regulation |
| Smoking | Impairs union |
| Diabetes | Microvascular + cellular + infection problems |
| Steroids | Suppress bone formation |
| Severe malnutrition | Impairs repair |
| Radiation | Damages vascular/cellular biology |
| Hypertrophic nonunion | Good biology, bad mechanics |
| Atrophic nonunion | Poor biology ± mechanics |
| Oligotrophic nonunion | Little callus despite viable biology, often poor apposition |
| Normal ESR/CRP | Does not fully exclude infection |
| Suspected occult infection | Multiple deep cultures |
| Osteogenesis | Cells |
| Osteoinduction | Signals |
| Osteoconduction | Scaffold |
| Cancellous graft | Rapid incorporation/strong biology |
| Cortical graft | Structural support/slower incorporation |
📊 High-Yield Comparison Tables
Calcium-Regulating Hormones
| Hormone | Source | Principal Action |
|---|---|---|
| PTH | Parathyroid | ↑ serum Ca; ↑ RANKL signaling (indirect osteoclast activation) |
| Vitamin D (calcitriol) | Renal activation of skin-derived precursor | ↑ intestinal Ca + phosphate absorption |
| Calcitonin | Thyroid parafollicular C cells | ↓ osteoclast activity |
Osteoporosis vs Osteomalacia
| Feature | Osteoporosis | Osteomalacia |
|---|---|---|
| Quantity | Reduced | May be normal |
| Mineralization | Normal | Defective (unmineralized osteoid) |
| Definition | Quantity problem | Mineralization problem |
| Lab clue | Usually normal | ↑ ALP, ↓ Ca/phosphate in some cases |
Growth Factors in Fracture Healing
| Factor | Principal Role |
|---|---|
| VEGF | Angiogenesis |
| BMP | Osteoinduction (progenitor → osteoblast) |
| PDGF | Chemotaxis + proliferation of repair cells |
| TGF-β | Proliferation, differentiation, matrix synthesis |
Nonunion Types
| Type | Biology | Mechanics | Treatment Principle |
|---|---|---|---|
| Hypertrophic | Good (abundant callus) | Inadequate stability | Fix mechanics |
| Oligotrophic | Viable but little callus | Poor apposition/distraction | Correct apposition, stabilize ± graft |
| Atrophic | Poor (minimal callus, sclerotic) | Variable | Debride + graft + stability |
Bone Graft Properties
| Property | Meaning | Classic Example |
|---|---|---|
| Osteogenesis | Viable bone-forming cells | Fresh autograft |
| Osteoinduction | Signals recruit/differentiate progenitors | BMP |
| Osteoconduction | Scaffold for host bone ingrowth | Hydroxyapatite, allograft |
Cancellous vs Cortical Autograft
| Feature | Cancellous | Cortical |
|---|---|---|
| Biology | Stronger (rapid revascularization) | Weaker after processing |
| Structure | Weak | Strong |
| Incorporation | Faster | Slower (creeping substitution) |
| Best use | Biologically deficient nonunion | Structural defect/gap |
💡 Exam Pearls Wall
⚠️ Examiner Traps
🧠 Mnemonics & Memory Aids
🔢 Critical Numbers & Facts
🎤 Viva Rapid-Fire Q&A
Which hormone rises with low ionized calcium?
Parathyroid hormone.
How does PTH activate osteoclasts?
Indirectly, via osteoblast-lineage RANKL signaling.
Principal intestinal effect of calcitriol?
Increased absorption of both calcium and phosphate.
Where is calcitonin produced?
Thyroid parafollicular C cells.
Difference between osteoporosis and osteomalacia?
Osteoporosis = reduced quantity with normal mineralization. Osteomalacia = defective mineralization of osteoid.
What is osteoid?
Unmineralized organic bone matrix, predominantly type I collagen.
Marker of osteoblast activity?
Bone-specific alkaline phosphatase.
Which component gives bone compressive stiffness?
Hydroxyapatite.
Remodeling sequence?
Activation → Resorption → Reversal → Formation.
What does sclerostin do?
Osteocyte-derived inhibitor of Wnt signaling, suppressing osteoblast bone formation.
Nutrient artery supply?
Medullary cavity and a substantial portion of the inner cortex.
Which factor drives angiogenesis?
VEGF.
What are BMPs?
Osteoinductive signaling proteins that drive progenitor differentiation toward osteoblasts.
Role of PDGF in fracture healing?
Chemotaxis and proliferation of repair cells.
Role of TGF-β?
Regulates cell proliferation, differentiation and extracellular matrix synthesis.
Why is fracture hematoma important?
It contains inflammatory cells, cytokines and signaling molecules that initiate healing.
How does smoking affect union?
Impairs vascular and cellular healing, increasing delayed union and nonunion risk.
Effect of chronic steroids on bone?
Suppress osteoblast function and impair bone formation.
Hypertrophic vs atrophic nonunion?
Hypertrophic = good biology, poor mechanics. Atrophic = poor biology ± poor mechanics.
What is oligotrophic nonunion?
Little callus despite viable biology — often poor apposition or distraction.
Best test when union is unclear?
CT for cortical bridging.
Cultures in suspected occult FRI?
Multiple deep tissue samples with separate clean instruments.
Why does articular cartilage heal poorly?
It is avascular with limited cellular regenerative capacity.
Osteogenesis vs osteoinduction vs osteoconduction?
Cells vs signals vs scaffold.
Cancellous vs cortical graft?
Cancellous = biologically strong, weaker structurally, faster incorporation. Cortical = structurally strong, slower incorporation.
Why can union fail with good biology?
Because bone regeneration is mechanobiological — excessive strain prevents mineralized bridging.
🩺 Clinical Decision Pearls
- Low serum Ca²⁺ → think PTH first.
- Adult diffuse bone pain + unmineralized osteoid → osteomalacia.
- Bone density low but mineralization normal → osteoporosis.
- Isolated raised ALP after fracture → consider osteoblastic activity, but exclude hepatic source.
- Comminuted fragment attached to soft tissue → preserve it; avoid stripping.
- Comminuted tibial fracture + weak construct → bridge plating, not fragment-by-fragment compression.
- Abundant callus + persistent motion → hypertrophic nonunion → fix mechanics.
- Minimal callus + sclerotic ends → atrophic nonunion → debulk + graft + stabilize.
- Little callus but viable bone + distraction → oligotrophic → correct apposition.
- Open fracture + slow union → always consider occult infection.
- Smoker with nonunion → cessation is part of treatment.
- Diabetic with nonunion → optimize glycemia; watch infection.
- Irradiated bone fracture → biologically hostile; consider vascularized reconstruction.
- Fracture gap after fixation → assess biology and mechanics before adding graft.
- Tendon/ligament injury → protect first, then controlled loading.
- Full-thickness cartilage defect → can access marrow; purely chondral defects heal poorly.
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