What are the different classifications of grafts?

Classification of Grafts

Grafts are classified into four main categories based on their origin: autografts (from the same individual), allografts (from a different individual of the same species), xenografts (from a different species), and alloplasts (synthetic materials). 1

Primary Classification System by Origin

Autografts (Autologous/Autogenous Grafts)

• Tissue transferred from one site to another within the same individual 1, 2
• Represents the "gold standard" for bone grafting due to possessing all three critical properties: osteoconduction, osteoinduction, and osteogenesis 3
• Contains viable osteoprogenitor cells that directly contribute to new bone formation 3
• For bone applications, can be harvested as block grafts or particulate grafts from sites like mandibular symphysis, ramus, retromolar area, or iliac crest 1
• Main disadvantage is donor site morbidity, with 34% of patients reporting iliac crest harvest pain on independent assessment 1

Allografts (Allogeneic Grafts)

• Tissue transferred between genetically different individuals of the same species 4, 2
• Lacks osteogenic properties (no viable cells) but retains some osteoinductive potential, particularly with demineralized bone matrix 3
• Associated with higher non-union rates and significantly increased graft collapse (30%) compared to autograft (5%) in multiple-level procedures 3
• Smoking has more significant negative impact on fusion success with allograft versus autograft 3
• Common forms include freeze-dried bone allografts (FDBAs) and demineralized freeze-dried bone allografts (DFDBAs) 5
• Healing time for allograft block grafts is 5-6 months before implant placement 1

Xenografts (Xenogeneic Grafts)

• Tissue from one species implanted into a member of a different species 6, 2
• Commonly bovine or porcine materials used in clinical practice 1, 5
• Nonresorbable properties due to sintering technique and heating during processing, which changes hydroxyapatite dissolution rate and prevents osteoclastic resorption 5
• Often combined with allografts in 50/50 or 70/30 ratios for various grafting procedures 5
• Provides osteoconductive scaffold but lacks osteoinductive and osteogenic properties 7

Alloplasts (Synthetic Grafts)

• Synthetic materials including calcium phosphate salts, hydroxyapatite, β-tricalcium phosphate, and wollanosite 1
• Provide osteoconductive scaffold for bone growth 1
• Generally not recommended for vascular applications due to infection risks 1

Secondary Classification Systems

By Thickness (Skin Grafts)

• Split-thickness (partial) grafts: Further divided into thin, intermediate, and thick varieties; usually take well 6
• Full-thickness grafts: Only take if relatively small 6

By Form (Bone Grafts)

• Block grafts: Solid pieces requiring 4-6 months healing for autografts, 5-6 months for allografts, with expected lateral bone gain of 4-6 mm 1
• Particulate grafts: Morselized bone used alone or combined with other materials 1

By Biological Properties (Bone Grafts)

• Osteogenic: Contains living cells capable of forming bone (autografts only) 3, 7
• Osteoinductive: Contains growth factors that induce bone formation (autografts, some allografts like demineralized bone matrix) 3, 7
• Osteoconductive: Provides scaffold for bone growth (all graft types) 7

Special Graft Categories for Vascular Applications

For Infected Vascular Graft Reconstruction

• Rifampin-bonded or silver-coated synthetic grafts: Preferable for patients unable to tolerate prolonged surgery, though less resistant to infection than biological grafts 1
• Cryopreserved or fresh arterial allografts: Associated with lower infection rates than synthetic materials but subject to graft degeneration over time 1
• Autogenous superficial femoral venous grafts: Highest long-term patency due to lack of HLA class II antigen expression, but requires prolonged operative time and carries risk of venous stasis morbidity 1

Critical Clinical Distinctions

Graft Acceptance

• Only autografts permanently take and integrate 6
• Allografts and xenografts provoke immunological responses leading to rejection unless in specific applications (e.g., temporary coverage in burns or as scaffold materials) 6, 4
• Isografts (syngeneic grafts between genetically identical individuals) are readily accepted 4

For Peyronie's Disease Surgery

Grafts classified into four types for tunical lengthening procedures 1:

• Type 1 (Autografts): Dermis, vein, fascia, buccal mucosa from patient
• Type 2 (Allografts): Pericardium and fascia lata from donors
• Type 3 (Xenografts): Bovine/porcine materials and small intestinal submucosa
• Type 4 (Synthetic): Generally not recommended due to infection risks