BONE GRAFTS
Autograft | Allograft | Bone Substitutes | Biologics
Bone Graft Properties
Critical Must-Knows
- Autograft: ONLY graft with all 3 properties (osteogenic, osteoinductive, osteoconductive)
- Allograft: Osteoconductive ONLY (scaffold). No living cells. Minimal osteoinduction.
- DBM: Demineralized bone matrix. Osteoinductive + osteoconductive. Exposes BMPs.
- Ceramics (HA/TCP): Osteoconductive ONLY. Variable resorption rates.
- BMPs: Bone morphogenetic proteins. Pure osteoinduction. No scaffold.
Examiner's Pearls
- "Autograft = all 3 properties (GIC)
- "Allograft = scaffold only
- "DBM exposes BMPs = osteoinductive
- "ICBG donor site morbidity 10-30%
Clinical Imaging
Imaging Gallery
Critical Bone Graft Exam Points
Autograft Has All 3
Osteogenic + Osteoinductive + Osteoconductive. Only graft with living cells. Gold standard but limited quantity and donor site morbidity.
Allograft = Scaffold Only
Osteoconductive only. No living cells (processing kills them). Minimal osteoinduction. No disease transmission with proper processing.
BMP = Induction Only
Purely osteoinductive. rhBMP-2 and rhBMP-7. No scaffold - needs carrier. Complications: swelling, heterotopic bone.
Donor Site Morbidity
ICBG: 10-30% chronic pain. Nerve injury (LFCN), hematoma, fracture. Consider RIA for large volumes.
Quick Decision Guide - Graft Properties
| Graft Type | Osteogenic | Osteoinductive | Osteoconductive | Key Use |
|---|---|---|---|---|
| Autograft (ICBG, RIA) | YES | YES | YES | Gold standard for non-union |
| Fresh allograft | No | Minimal | YES | Large structural defects |
| Freeze-dried allograft | No | Minimal | YES | Impaction grafting |
| DBM | No | YES | YES | Graft extender with autograft |
| Ceramics (HA/TCP) | No | No | YES | Metaphyseal defects |
| BMP (rhBMP-2) | No | YES | No | Non-union, spine fusion |
GICThree Properties of Bone Graft
Memory Hook:GIC = osteogenic (living cells), osteoinductive (growth factors), osteoconductive (scaffold). Only AUTOGRAFT has all 3!
ILDRAutograft Sources
Memory Hook:ILDR = Iliac crest (most common), Local bone, Distal radius, RIA from femur!
SCHOBMP Complications
Memory Hook:SCHO = Swelling, Cancer concerns, Heterotopic ossification, Osteolysis - know BMP complications!
Overview and Epidemiology
Why Bone Grafts Matter
Bone graft science is essential basic science for the exam. You must know the three properties (osteogenic, osteoinductive, osteoconductive) and which grafts possess which properties.
Bone Grafts are materials used to fill defects, augment healing, and reconstruct bone.
Indications
- Non-union: Augment biology
- Bone defects: Fill segmental loss
- Arthrodesis: Promote fusion
- Augmentation: Enhance fixation
- Revision surgery: Restore bone stock
Graft choice depends on indication and defect size.
Types
- Autograft: Patient's own bone
- Allograft: Human donor bone
- Xenograft: Animal bone (rare)
- Synthetic: Ceramics, polymers
- Biologics: DBM, BMPs, PRP
Multiple options with different properties.
Pathophysiology and Mechanisms
Bone Healing Biology
Bone healing requires: (1) Cells to form bone (osteogenic), (2) Signals to induce bone formation (osteoinductive), and (3) Scaffold for bone to grow into (osteoconductive). Autograft provides all three; other grafts provide only some.
Bone Healing Physiology:
- Inflammation: Hematoma forms, cytokines released
- Repair: Callus formation (soft then hard)
- Remodeling: Wolff's law - bone remodels to stress
Graft Incorporation:
- Creeping substitution: Host bone resorbs graft and replaces
- Cancellous: Faster incorporation (more surface area)
- Cortical: Slower incorporation (dense structure)
Understanding biology guides graft selection.
Classification Systems
The Three Properties
| Property | Definition | Which Grafts | Example |
|---|---|---|---|
| Osteogenic | Contains living cells that can form bone | Autograft, BMA | Osteoblasts, MSCs |
| Osteoinductive | Contains signals that induce new bone | Autograft, DBM, BMP | BMPs, growth factors |
| Osteoconductive | Provides scaffold for bone ingrowth | All grafts, ceramics | HA, TCP, allograft |
Only autograft has ALL THREE properties.
Clinical Assessment
Patient Assessment
- Comorbidities: Diabetes, smoking, vascular disease
- Prior surgery: Available bone stock
- Infection: Must be excluded
- Soft tissue: Adequate coverage
- Host factors: Malnutrition, immunosuppression
Optimize patient factors before grafting.
Defect Assessment
- Size: Determines volume needed
- Location: Metaphyseal vs diaphyseal
- Biology: Atrophic vs hypertrophic non-union
- Vascularity: Deficient may need vascularized graft
- Structural needs: Load-bearing vs non-structural
Match graft to defect requirements.
Graft Selection Principles
Consider: (1) Defect size and location, (2) Structural requirements, (3) Biological requirements, (4) Donor site morbidity, (5) Cost and availability. For non-union, autograft + stable fixation is gold standard.
Investigations
Pre-Graft Investigation
Assess defect accurately. Size, location, bone stock. Plan graft volume and type.
For free vascularized grafts. Assess recipient vessels. Fibular flap planning.
ESR, CRP, aspiration. Grafting into infected bone will fail. Two-stage if needed.
Albumin, prealbumin, vitamin D, calcium. Malnutrition impairs graft incorporation.
Thorough pre-operative assessment guides graft selection.
Management Algorithm
Graft Selection for Non-Union
Non-Union Approach
Atrophic vs hypertrophic. Atrophic needs biology. Hypertrophic needs stability only.
Stable fixation is prerequisite. Exchange nailing, plate revision, external fixation.
Autograft is gold standard. ICBG or RIA depending on volume. DBM as extender.
rhBMP-2 for difficult cases. Alternative to autograft. Consider cost and complications.
Biological non-union requires both stable fixation AND biological augmentation.
Surgical Technique
Iliac Crest Bone Graft Harvest
Anterior ICBG Technique
Supine. Bump under ipsilateral hip. Prep iliac crest.
2-3cm posterior to ASIS. Parallel to crest. Protects LFCN (runs 1-2cm medial to ASIS).
Split iliac apophysis. Subperiosteal elevation exposes outer table.
Curettes for cancellous. Osteotome for corticocancellous. Stay 2cm from ASIS and AIIS.
Haemostasis. Consider drain. Close in layers. Leave cancellous bed exposed.
Careful technique minimizes donor site morbidity.
Complications
Complications of Bone Grafting
| Complication | Incidence | Prevention/Management |
|---|---|---|
| ICBG donor site pain | 10-30% | Meticulous technique, minimize disruption |
| LFCN injury (anterior ICBG) | 5-15% | Incision 2cm posterior to ASIS |
| Hematoma | 2-5% | Haemostasis, consider drain |
| Iliac crest fracture | Less than 1% | Leave 2cm anterior margin |
| Graft failure/resorption | 5-15% | Adequate fixation, optimize biology |
| Infection | 1-5% | Sterile technique, prophylactic antibiotics |
| Disease transmission (allograft) | Very rare | Proper screening and processing |
Donor site morbidity is the main disadvantage of autograft. Consider RIA or synthetic alternatives if significant.
Postoperative Care
Post-Graft Management
Standard wound care. Watch for hematoma at donor site. Donor site often more painful than recipient.
Protected weight-bearing as per fixation. Donor site pain usually settles by 2-6 weeks.
Serial X-rays. Cancellous grafts incorporate faster than cortical. CT if union unclear.
Once incorporated. Graft remodels over months to years.
Graft incorporation takes 3-6 months for cancellous, longer for cortical.
Outcomes and Prognosis
Union Rates with Grafting:
- Autograft for non-union: 85-95%
- Allograft alone: 60-80%
- DBM + autograft: 85-90%
- BMP + fixation: 80-90%
Prognostic Factors:
| Factor | Better Outcome | Worse Outcome |
|---|---|---|
| Patient | Non-smoker, healthy | Smoker, diabetic |
| Defect | Small, contained | Large, segmental |
| Vascularity | Good soft tissue | Scarring, irradiation |
| Fixation | Rigid stability | Motion at site |
Optimize modifiable factors for best outcomes.
Evidence Base
- rhBMP-7 (OP-1) vs autograft for tibial non-union
- Similar union rates (81% vs 85%)
- BMP avoids donor site morbidity
- Comparable clinical outcomes
- rhBMP-2 for open tibial fractures
- Reduced secondary interventions
- Faster radiographic healing
- Lower infection rate with BMP
- RIA provides large graft volumes (40-90cc)
- Comparable or superior cellular content
- Reduced donor site pain vs ICBG
- Similar union rates
- Induced membrane technique for large defects
- 70-90% union rates for defects 4-25cm
- Two-stage procedure
- Membrane provides growth factors and vascularization
- Ceramic bone substitutes in metaphyseal defects
- Similar outcomes to autograft
- Avoid donor site morbidity
- Variable resorption rates
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Non-Union Graft Selection
"You are treating an atrophic tibial non-union. The patient is a 45-year-old non-smoker. What graft would you use and why?"
Scenario 2: Large Segmental Defect
"A 30-year-old motorcyclist has a 10cm tibial bone defect after debridement of an open fracture. How would you manage the bone defect?"
Scenario 3: Allograft vs Autograft
"What are the differences between autograft and allograft? When would you use each?"
MCQ Practice Points
Three Properties Question
Q: Which bone graft has all three properties (osteogenic, osteoinductive, osteoconductive)? A: Autograft. Only autograft has living cells. Allograft lacks cells. DBM has induction+conduction. BMPs have induction only.
Allograft Properties
Q: What is the main property of allograft? A: Osteoconductive (scaffold only). Processing removes cells. Provides structure for bone ingrowth but no biological activity.
DBM Mechanism
Q: Why is demineralized bone matrix (DBM) osteoinductive? A: Removing mineral exposes BMPs. The demineralization process exposes bone morphogenetic proteins that were embedded in the mineral matrix.
ICBG Donor Site Pain
Q: What is the incidence of chronic donor site pain after ICBG harvest? A: 10-30%. This is the main disadvantage of autograft. Consider RIA or alternatives if significant concern.
Masquelet Technique
Q: What is the Masquelet technique? A: Two-stage induced membrane technique. Stage 1: cement spacer placement. Stage 2 (6-8 weeks): membrane preserved, cement removed, cavity filled with autograft.
BMP Complications
Q: What are the main complications of BMP use? A: Significant swelling, heterotopic ossification, osteolysis. Contraindicated near neural structures (spinal canal). Very expensive.
Australian Context
Australian Practice:
- Autograft remains gold standard for non-union
- Allograft from ATBA (Australian Tissue Banks Association) screened tissue banks
- BMPs (rhBMP-2) TGA-approved with specific indications
- PBS does not subsidize BMPs - significant cost consideration
Medicolegal Considerations:
- Document informed consent for donor site morbidity (ICBG)
- Discuss risks of allograft (disease transmission - very low but must mention)
- Document rationale for graft selection
Cost Considerations:
- Autograft: No product cost but OR time for harvest
- Allograft: Moderate cost through tissue banks
- BMP: Expensive (multiple thousand dollars)
- Ceramics: Variable cost
Australian surgeons should document graft selection rationale and obtain informed consent for harvest site.
BONE GRAFTS
High-Yield Exam Summary
Three Properties (GIC)
- •osteoGenic: Living cells
- •osteoInductive: Growth factors, BMPs
- •osteoConductive: Scaffold
- •Only AUTOGRAFT has all 3
Autograft
- •Gold standard - all 3 properties
- •ICBG most common source
- •RIA for large volume
- •10-30% donor site pain
Allograft
- •Osteoconductive ONLY
- •No living cells
- •Fresh-frozen or freeze-dried
- •Structural or morselized
Synthetics and Biologics
- •Ceramics (HA, TCP): Scaffold only
- •DBM: Inductive + conductive
- •BMPs: Pure induction, no scaffold
- •Combine with autograft to enhance
Complications
- •ICBG: Pain, LFCN injury, fracture
- •BMP: Swelling, heterotopic ossification
- •Allograft: Very low disease transmission
- •All: Infection, non-incorporation