Day 3 — FCPS Orthopaedic IMM · Bone Defects, Graft Incorporation, Distraction Osteogenesis & Masquelet — Q101–Q150

Day 3 — FCPS Orthopaedic IMM

Stress Fractures · Graft Incorporation · Critical Defects · Distraction Osteogenesis · Bone Transport · Masquelet · Q101–Q150

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Section 📚 All Sections (50 MCQs · Q101–Q150) 🦵 Stress Fractures 🧪 Bone Grafting 🔬 Bone Graft Incorporation 🧩 Bone Defects 📏 Distraction Osteogenesis 🚚 Bone Transport 🫧 Induced Membrane 🧱 Large Bone Defects 🚫 Nonunion 🔄 Graft Incorporation 🧬 Complex Nonunion

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💎 Day 3 — High Yield Recall

Stress Fractures · Graft Incorporation · Critical Defects · Distraction Osteogenesis · Bone Transport · Masquelet · Complex Nonunion — rapid recall, tables, pearls, traps & viva

⚡ Rapid Recall — One-Liners

Concept	High-yield answer
Fatigue fracture	Abnormal/repetitive load on normal bone
Insufficiency fracture	Normal load on weak bone
Stress-fracture mechanism	Microdamage > remodeling capacity
Cancellous graft	Fast incorporation, strong biology
Cortical graft	Structural, slow incorporation
Creeping substitution	Graft resorption + host replacement
Autograft	Cells + signals + scaffold
Allograft	Larger quantity, less biology
Structural graft	Mechanical support
Vascularized fibula	Living bone with intrinsic blood supply
Critical-size defect	Will not reliably heal spontaneously
Distraction osteogenesis	Controlled gradual separation creates new bone
Classic distraction rate	~1 mm/day in divided increments
Too-fast distraction	Poor/fibrous regenerate
Too-slow distraction	Premature consolidation
Distraction phases	Latency → distraction → consolidation
Corticotomy principle	Preserve vascularity
Bone transport	Move segment across defect while regenerate forms
Docking site	Interface where transported segment meets recipient bone
Bone transport complication	Pin-tract infection, docking nonunion, stiffness
Masquelet Stage 1	Debride + stabilize + cement spacer
Masquelet Stage 2	Preserve membrane + graft cavity
Induced membrane	Vascular biological chamber
Large defect strategy	Infection + mechanics + soft tissue + biology
Infected nonunion	Debride + stabilize + cover + reconstruct

📊 High-Yield Comparison Tables

Fatigue vs Insufficiency Fracture

Feature	Fatigue	Insufficiency
Bone quality	Normal	Weakened (osteoporosis, osteomalacia, radiation)
Load	Abnormal/repetitive	Normal physiological
Typical patient	Athlete, military recruit	Elderly, osteoporotic, post-radiation
Mechanism	Microdamage > remodeling	Normal load exceeds weakened bone capacity

Graft Types — Biological vs Structural

Graft	Biology	Structure	Incorporation
Cancellous autograft	Strongest (cells + signals + scaffold)	Weak	Fast
Cortical autograft	Moderate	Strong	Slow
Structural allograft	Weak (osteoconductive)	Strong	Slow, incomplete
Vascularized fibula	Strong (living bone)	Strong	Living incorporation

Distraction Osteogenesis — Phases

Phase	Key Principle	Complication if Wrong
Latency	Allow early reparative tissue to form	Too early → poor regenerate
Distraction	~1 mm/day in divided increments	Too fast → fibrous regenerate; too slow → premature consolidation
Consolidation	Regenerate matures until frame removal	Too early removal → fracture/deformity

Masquelet Technique — Two Stages

Stage	Key Steps	Biology
Stage 1	Debride + stabilize + PMMA spacer	Induces vascular membrane; controls dead space
Stage 2	Remove spacer + preserve membrane + bone graft cavity	Membrane acts as biological chamber supporting graft

Defect Reconstruction Options

Option	Best For	Drawback
Cancellous autograft	Contained voids, small defects	Limited structural support
Structural allograft	Metaphyseal structural defects	Slow incorporation, fatigue risk
Vascularized fibula	Large defects, hostile beds	Technically demanding
Bone transport	Large segmental diaphyseal defects	Long frame time, pin-tract infection
Masquelet	Infected defects, staged reconstruction	Two-stage procedure

💡 Exam Pearls Wall

▸ Fatigue fracture = abnormal load on normal bone. Insufficiency = normal load on weak bone.

▸ Stress injury is fundamentally a microdamage–remodeling mismatch.

▸ Tension-side femoral neck stress fracture = high risk → may require surgery.

▸ Cancellous = fast biology, weak structure. Cortical = structural, slow incorporation.

▸ Autograft uniquely combines cells + signals + scaffold.

▸ Allograft = abundant quantity, weaker biology, small transmission/immunologic risk.

▸ Processed allograft is mainly osteoconductive — osteoinduction is variable (DBM).

▸ Creeping substitution = host resorbs graft and replaces it with new bone.

▸ Vascularized graft brings its own blood supply — useful in hostile beds.

▸ Critical-size defect = unlikely to heal spontaneously (biological, not fixed-size, definition).

▸ Distraction osteogenesis: latency → distraction → consolidation.

▸ Classic distraction rate ~1 mm/day in divided increments.

▸ Too fast → poor/fibrous regenerate. Too slow → premature consolidation.

▸ Regenerate forms predominantly via intramembranous ossification.

▸ Corticotomy must preserve vascularity — low-energy technique.

▸ Bone transport creates two biological problems: regenerate formation + docking-site union.

▸ Pin-tract infection is the classic long-frame complication.

▸ Masquelet Stage 1 = debride + stabilize + spacer; Stage 2 = preserve membrane + graft.

▸ Induced membrane is vascular and secretes growth factors — a biological chamber.

▸ Do not graft into uncontrolled infection — control it first.

▸ Implant failure often reflects failure of fracture healing, not just implant weakness.

▸ Complex tibial nonunion sequence: Debride → Stabilize → Cover → Reconstruct.

⚠️ Examiner Traps

Do not equate fatigue and insufficiency fractures — the bone quality and load differ.

Do not assume early radiographs exclude stress fracture — MRI is more sensitive.

Do not confuse cortical graft strength with biological activity.

Do not describe allograft as osteogenic — processing removes cells.

Do not quote a fixed universal critical defect size — definition is biological.

Do not turn ~1 mm/day into an absolute protocol — individualize.

Do not call a small delay in Masquelet Stage 2 a failure — timing is individualized.

Do not graft into active infection — debride and control first.

Do not assume docking-site nonunion will heal because regenerate looks good.

Do not fix an infected nonunion without addressing dead space and soft-tissue coverage.

Do not use one technique for all large defects — indication-based selection is key.

Do not forget host optimization (smoking, diabetes, nutrition) before reconstruction.

🧠 Mnemonics & Memory Aids

Stress fracture types: "Fatigue = bad load on good bone · Insufficiency = good load on bad bone"

Distraction phases: "L-D-C" → Latency, Distraction, Consolidation

Distraction rate: "One millimetre a day, split into four" (0.25 × 4)

Too fast/slow: "Fast = fibrous · Slow = fused"

Graft biology: "Cells · Signals · Scaffold"

Masquelet: "Debride + Spacer (Stage 1) · Membrane + Graft (Stage 2)"

Complex nonunion: "D-S-C-R" → Debride, Stabilize, Cover, Reconstruct

Bone transport: "Regenerate behind, docking ahead"

Vascularized graft: "Brings its own blood"

Critical defect: "Biological definition, not a fixed number"

🔢 Critical Numbers & Facts

Classic distraction rate~1 mm/day in divided increments

Distraction frequencyOften 4 increments of 0.25 mm

Distraction phasesLatency → distraction → consolidation

Regenerate ossificationPredominantly intramembranous

Masquelet stagesTwo (spacer → graft)

Classic Stage 2 intervalSeveral weeks (individualized)

High-risk stress fractureTension-side femoral neck

Vascularized graft of choice (tibia)Free fibula

🎤 Viva Rapid-Fire Q&A

Define a fatigue fracture.

Abnormal/repetitive loading of structurally normal bone exceeds remodeling capacity.

Define an insufficiency fracture.

Normal physiological loading of weakened abnormal bone.

Mechanism of stress injury?

Microdamage accumulation exceeding remodeling repair.

Which stress fracture site is high risk?

Tension-side femoral neck stress fracture.

Why does cancellous graft incorporate faster?

Porous architecture permits rapid vascular ingrowth and remodeling.

Why is cortical graft stronger but slower?

Dense structure gives strength but limits rapid vascular penetration.

What is creeping substitution?

Progressive host resorption of graft with replacement by new host bone.

Main advantage of autograft?

Provides viable osteogenic cells; combines cells + signals + scaffold.

Main advantage of allograft?

Availability in large quantity without donor-site morbidity.

Main disadvantage of allograft?

Less biological activity; potential transmission/immunologic risk.

Define critical-size defect.

A defect that will not reliably heal spontaneously without reconstruction.

Principle of distraction osteogenesis?

Controlled gradual distraction after corticotomy generates new bone (tension-stress principle).

Classic distraction rate?

~1 mm/day in divided increments.

Consequence of too-fast distraction?

Poor/fibrous regenerate with risk of nonunion.

Consequence of too-slow distraction?

Premature consolidation.

Phases of distraction osteogenesis?

Latency → distraction → consolidation.

Why corticotomy not osteotomy?

Preserves medullary/periosteal blood supply.

What is bone transport?

Gradual movement of a vascular segment across a defect while regenerate forms behind it.

What is the docking site?

Interface where the transported segment meets the opposite bone end.

Classic long-frame complication?

Pin-tract infection.

Masquelet Stage 1?

Debride, stabilize, place PMMA spacer.

Masquelet Stage 2?

Remove spacer, preserve membrane, fill with bone graft.

Role of induced membrane?

Vascular biological chamber that supports graft incorporation.

When would you delay Stage 2?

Persistent infection, poor soft tissue, host factors not optimized.

When is a vascularized graft useful?

Large defect in a hostile/poorly vascularized recipient bed.

Why can a strong implant fail?

Repeated cyclic loading when bone never regains load transmission — fatigue failure.

Complex infected nonunion sequence?

Debride → Stabilize → Cover → Reconstruct.

🩺 Clinical Decision Pearls

• Sudden increase in training + progressive tibial pain → fatigue stress fracture.
• Elderly osteoporotic sacral pain → insufficiency fracture.
• High-risk stress fracture site (tension-side femoral neck) → surgical stabilization.
• Contained metaphyseal void → cancellous autograft.
• Structural defect needing support → cortical/corticocancellous graft or allograft.
• Biologically deficient nonunion → autograft (cells + signals + scaffold).
• Hostile/irradiated bed with large defect → vascularized fibula.
• Critical-size segmental diaphyseal defect → bone transport, Masquelet, or vascularized graft.
• Infected tibial nonunion with defect → debride, stabilize, cover, then reconstruct.
• Docking-site nonunion → freshen edges, compress, augment biology.
• Poor regenerate during lengthening → check rate, rhythm, stability, host factors.
• Persistent infection at Stage 2 planning → delay grafting, re-debride.
• Broken plate at 10 months → assume nonunion until proven otherwise.
• Exposed tibial bone/implant → flap coverage essential for infection control and healing.

Golden rule: In complex bone reconstruction: Debride → Stabilize → Cover → Reconstruct — in that order.

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