Day 5 — FCPS Orthopaedic IMM
Module 1 Final Integration · FCPS Examiner Traps · Nonunion Algorithms · Graft Selection · Mechanobiology · Q201–Q250
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💎 Day 5 — High Yield Recall
Final Integration · FCPS Examiner Traps · Nonunion Algorithms · Graft Selection · Mechanobiology · Clinical Decision-Making — rapid recall, tables, pearls, traps & viva
⚡ Rapid Recall — One-Liners
| Concept | IMM answer |
|---|---|
| Primary healing | Absolute stability |
| Secondary healing | Relative stability |
| Primary healing callus | Minimal/absent external callus |
| Secondary healing | Callus expected |
| Strain | ΔL / original gap |
| Highest strain tolerance | Fibrous tissue |
| Mechanosensor | Osteocyte |
| Osteoblast lineage | Mesenchymal |
| Osteoclast lineage | Monocyte/macrophage |
| RANKL | ↑ osteoclastogenesis |
| OPG | RANKL decoy receptor |
| VEGF | Angiogenesis |
| BMP | Osteoinduction |
| Soft callus | Fibrocartilage |
| Cartilage → bone | Endochondral ossification |
| Hypertrophic nonunion | Biology good, mechanics poor |
| Oligotrophic | Little callus, often poor apposition/distraction |
| Atrophic | Biological deficiency ± mechanical problem |
| Communicating sinus | Confirmatory for FRI |
| Suspected infection | Multiple deep specimens |
| Cancellous autograft | Cells + signals + scaffold |
| Cancellous graft | Rapid revascularization |
| Cortical graft | Structural, slower incorporation |
| Vascularized fibula | Living structural graft |
| DBM | Conductive + variable inductive |
| HA | Slow-resorbing scaffold |
| Calcium sulfate | Rapidly resorbing scaffold |
| Critical-size defect | Unlikely to heal spontaneously |
| Masquelet Stage 1 | Debride + stabilize + spacer |
| Masquelet Stage 2 | Preserve membrane + graft |
| Distraction | ~1 mm/day classically |
| Too-fast distraction | Poor regenerate |
| Too-slow distraction | Premature consolidation |
| Bone transport endpoint | Docking site |
| Fatigue fracture | Excess repetitive load/normal bone |
| Insufficiency fracture | Normal load/weak bone |
| Early stress-fracture imaging | MRI |
| Anterior tibial cortex | High-risk stress fracture |
| Early scar collagen | Type III |
| Mature tendon/ligament | Type I |
| Proliferative wound phase | Fibroblast + angiogenesis |
| Smoking | Modifiable nonunion risk |
| Late implant breakage | Fatigue failure |
| Difficult nonunion framework | Infection + mechanics + biology + host + soft tissue |
📊 High-Yield Comparison Tables
Confusing Pairs — Final Integration
| Pair | Key Distinction |
|---|---|
| Primary vs secondary healing | Absolute stability vs relative stability |
| Hypertrophic vs atrophic nonunion | Mechanical failure vs biological deficiency |
| Oligotrophic vs atrophic | Little callus does not automatically mean avascular |
| Fatigue vs insufficiency fracture | Excess repetitive load on normal bone vs normal load on weak bone |
| Osteogenesis / Osteoinduction / Osteoconduction | Cells / Signals / Scaffold |
| Cancellous vs cortical graft | Biology vs structure |
| Bone transport vs Masquelet | Regenerate transport vs induced-membrane graft chamber |
| MRI vs CT in stress fracture | Early marrow biology vs cortical detail |
Nonunion Type → Dominant Problem → Fix
| Type | Dominant Problem | Primary Fix |
|---|---|---|
| Hypertrophic | Mechanics (biology intact) | Improve stability/compression |
| Oligotrophic | Apposition/distraction | Correct contact ± graft |
| Atrophic | Biology (necrosis/avascular) | Debride + stable fix + graft |
| Infected | Infection + biology + mechanics | Debride + stabilize + cover + reconstruct |
Graft Selection by Problem
| Problem | Preferred Graft |
|---|---|
| Small contained void, biology deficient | Cancellous autograft |
| Structural defect | Cortical allograft / strut graft |
| Hostile bed / large defect | Vascularized fibula |
| Osteoinductive stimulus (adjunct) | BMP |
| Scaffold for host ingrowth | DBM, HA, β-TCP |
| Local antibiotic delivery | Calcium sulfate / PMMA beads |
💡 Exam Pearls Wall
⚠️ Examiner Traps
🧠 Mnemonics & Memory Aids
🔢 Critical Numbers & Facts
🎤 Viva Rapid-Fire Q&A
What mechanical environment is required for primary bone healing?
Absolute stability with minimal interfragmentary motion.
What healing pattern is expected after IM nailing?
Secondary healing with callus.
Define interfragmentary strain.
ΔL divided by original gap.
Which tissue tolerates the greatest strain?
Fibrous tissue.
Why does a bigger callus promote healing?
Increases cross-sectional area → decreases local strain.
Origin of osteoclasts?
Hematopoietic monocyte/macrophage lineage.
What does RANKL do?
Promotes osteoclast differentiation and activation.
How does PTH increase bone resorption?
Acts on osteoblast-lineage cells → ↑RANKL.
What is the defect in osteomalacia?
Failure of osteoid mineralization.
What cell is the bone mechanosensor?
Osteocyte.
What does sclerostin do?
Inhibits Wnt signaling → suppresses bone formation.
Which factor drives angiogenesis?
VEGF.
What is BMP classified as?
Osteoinductive.
Mechanism of contact healing?
Osteoclast cutting cones crossing the fracture, followed by osteoblasts.
Histology of soft callus?
Fibrocartilaginous tissue.
Definition of nonunion?
~9 months with no progression for 3 months.
What does elephant-foot callus indicate?
Hypertrophic nonunion — good biology, poor mechanics.
Oligotrophic nonunion?
Little callus despite viable bone, often due to poor apposition/distraction.
Atrophic nonunion?
Minimal callus with sclerotic tapered ends; biological deficiency.
Confirmatory finding for FRI?
Communicating sinus/fistula.
Culture strategy for suspected FRI?
Multiple deep specimens with separate clean instruments.
When is CT useful in nonunion?
When cortical bridging or defect morphology is unclear on X-ray.
How to treat hypertrophic nonunion?
Improve mechanical stability/compression.
How to treat atrophic nonunion?
Debride + stable fixation + biological augmentation.
When is dynamization appropriate?
Selected axially stable nonunion where controlled compression helps.
Three properties of cancellous autograft?
Osteogenic + osteoinductive + osteoconductive.
Difference between autograft and allograft?
Autograft has cells; allograft lacks cells but offers quantity.
Which graft revascularizes fastest?
Cancellous autograft.
When is cortical structural graft preferred?
When structural support is needed.
Advantage of vascularized fibula?
Living bone with intrinsic blood supply.
What is creeping substitution?
Progressive resorption of graft and replacement by host bone.
What determines DBM osteoinductive activity?
Matrix-associated growth factors such as BMP.
HA vs calcium sulfate resorption?
HA slow; calcium sulfate fast.
Definition of critical-size defect?
Defect that will not reliably heal spontaneously without reconstruction.
Masquelet Stage 1?
Debride + stabilize + PMMA spacer.
Masquelet Stage 2?
Preserve membrane, remove spacer, fill with graft.
Classic distraction rate?
~1 mm/day in divided increments.
Consequence of fast distraction?
Poor/fibrous regenerate.
Consequence of slow distraction?
Premature consolidation.
What is docking site?
Where the transported segment meets the opposite bone end.
Fatigue vs insufficiency fracture?
Abnormal load/normal bone vs normal load/weak bone.
Best early stress-fracture imaging?
MRI.
Which stress-fracture site is highest risk?
Anterior tibial cortical stress fracture.
Collagen transition in scar maturation?
Type III early → organized type I mature.
Which cells dominate the proliferative wound phase?
Fibroblasts and endothelial cells.
Why does smoking impair union?
Vasoconstriction + impaired oxygen delivery + impaired cellular healing.
Why does a late plate break?
Fatigue from persistent nonunion.
Difficult nonunion framework?
Infection + mechanics + biology + host + soft tissue.
🩺 Clinical Decision Pearls
- Compression plating, no callus, no pain, progressive union → primary healing, no concern.
- IM-nailed shaft fracture with bridging callus → expected secondary healing.
- Small gap with residual motion → high strain; may prevent mineralized bridging.
- Hypertrophic nonunion with broken implant → improve mechanics; graft likely unnecessary.
- Atrophic nonunion with sclerotic ends → debride + stable fix + graft.
- Oligotrophic nonunion with distraction → correct apposition + stable fix ± graft.
- Draining sinus + nonunion → assume infection until excluded.
- Previous open fracture + slow union → consider occult infection even if markers normal.
- Contained void + biological deficiency → cancellous autograft.
- Segmental structural defect → cortical strut / vascularized graft.
- Infected defect after debridement → Masquelet, bone transport, or vascularized graft.
- Poor regenerate during lengthening → slow rate; check stability, host factors.
- Docking-site nonunion → freshen edges + compress + graft.
- Too-stiff bridge plate with no callus → consider increasing working length / reducing screw density.
- Complex tibial nonunion → Control infection → stabilize → cover → reconstruct biology.
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