80 GRAFTS
# 81 GRAFTS
A graft is living tissue moved from one site to another and left to acquire a new blood supply from the recipient bed. A flap differs in that it carries its own vascular pedicle. MRCS Part A focuses on the vocabulary, the biology of graft "take", and the reconstructive ladder.
Classification by donor source
👩⚕️ Learn these four cold — they appear in almost every paper.
➡ Autograft — same individual (e.g. saphenous vein for CABG, STSG from thigh to chest). Most common. No rejection.
➡ Allograft — same species, different individual (e.g. cadaveric kidney or heart valve, donated bone for revision arthroplasty).
➡ Xenograft — different species (e.g. porcine or bovine heart valves, porcine skin as a temporary dressing).
➡ Isograft — genetically identical donor (identical twin). No rejection. Favourite SBA distractor.
➡ Synthetic / alloplastic — not strictly a graft but the term is used loosely. Includes polypropylene mesh, ePTFE, Dacron, silicone.
Skin grafts
A skin graft has no blood supply of its own and depends entirely on a clean, well-vascularised, infection-free bed. Grafts will not take on bare bone (without periosteum), bare tendon (without paratenon), bare cartilage (without perichondrium), or irradiated tissue.
Split-thickness vs full-thickness
| Feature | Split-thickness (STSG) | Full-thickness (FTSG) |
|---|---|---|
| Composition | Epidermis + part of dermis | Epidermis + entire dermis |
| Thickness | 0.2 – 0.4 mm | Full dermis |
| Harvest tool | Dermatome | Scalpel |
| Donor sites | Thigh, buttock, scalp | Postauricular, preauricular, supraclavicular, upper inner arm |
| Donor closure | Re-epithelialises from skin appendages (sweat glands, hair follicles) — heals like a graze | Primary closure required |
| Meshing | Yes (1.5:1 or 3:1) to expand area and allow exudate drainage | No |
| Contraction | Marked secondary contraction | Minimal contraction |
| Cosmesis | Poor — shiny, paler, no hair | Good — better colour match and texture |
| Sensation | Limited recovery | Better recovery |
| Take rate | Higher (thinner, easier nutrient diffusion) | Lower (thicker, more demanding bed) |
| Indication | Large surface area (burns, fasciotomy wounds, donor site for free flap) | Small defects of face, hand, fingertip |
Why STSG donor sites heal spontaneously — they retain dermal appendages (hair follicles, sebaceous and sweat glands). Keratinocytes migrate from these adnexal structures and resurface the wound, as in a superficial burn. FTSG takes the entire dermis with its appendages, so the donor must be closed primarily.
Why FTSGs contract less — the thicker dermis resists myofibroblast-driven contraction. This makes FTSG the choice over mobile or cosmetically critical areas (eyelid, fingertip, nasal tip).
Stages of graft take
The three I's — classic exam fact:
1. Imbibition (0 – 48 h) — plasmatic diffusion from the wound bed. Graft looks white and oedematous.
2. Inosculation (48 – 72 h) — recipient capillaries align end-to-end with cut graft vessels.
3. Revascularisation (4 – 7 days) — new vessels ingrow. Graft turns pink.
👩⚕️ Dusky on day 2 is normal. Purple on day 5 = failing graft, usually haematoma underneath.
Causes of graft failure
Commonest is haematoma, which lifts the graft off the bed and prevents inosculation. Others:
- Seroma — same mechanism
- Shear — disrupts new capillaries; prevented by tie-over or negative-pressure dressings
- Infection — especially beta-haemolytic Streptococcus, whose streptokinase dissolves the fibrin gluing the graft down
- Ischaemic bed — bare bone, bare tendon, irradiated tissue
- Technical error — graft placed upside-down
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Flaps
A flap carries its own arterial inflow and venous outflow. Because it does not rely on the recipient bed, flaps are the answer for bare bone, tendon, hardware, and irradiated wounds.
Classification
- Composition — cutaneous, fasciocutaneous, musculocutaneous, osseocutaneous
- Blood supply — random pattern (subdermal plexus) vs axial (named artery)
- Movement —
- Local — adjacent tissue: rotation (pivots), transposition (e.g. Z-plasty), advancement (e.g. V-Y for fingertip)
- Pedicled — moved while attached to its blood supply (e.g. pectoralis major for head and neck)
- Free — detached and microsurgically re-anastomosed (DIEP for breast, ALT for limb, fibula for mandible)
The reconstructive ladder
Pick the lowest rung that gives a durable, functional, cosmetically acceptable result.
1. Primary closure
2. Healing by secondary intention
3. Delayed primary closure
4. Split-thickness skin graft
5. Full-thickness skin graft
6. Local flap
7. Regional / pedicled flap
8. Distant or free flap
9. Vascularised composite allotransplantation (e.g. face, hand)
👩⚕️ Modern teaching favours a "reconstructive elevator" — sometimes a free flap is the right primary option (e.g. mandibular reconstruction). But the classical ladder is what SBAs test.
Bone grafts
Three biological properties decide what a bone graft can do:
- Osteogenic — living osteoblasts that lay down new bone
- Osteoinductive — growth factors (BMPs) recruit host mesenchymal stem cells
- Osteoconductive — scaffold for ingrowth of host vessels and bone
| Graft | Osteogenic | Osteoinductive | Osteoconductive | Use |
|---|---|---|---|---|
| Autograft (iliac crest — gold standard) | Yes | Yes | Yes | Non-unions, spinal fusion, small defects |
| Allograft (cadaveric) | No | Limited | Yes | Revision arthroplasty, structural defects |
| Synthetic (hydroxyapatite, tricalcium phosphate) | No | No | Yes | Void fillers |
| BMP (recombinant) | No | Yes | No | Selected non-unions, fusions |
➡ Morselised (cancellous chips) — revascularises quickly, fills cavities.
➡ Structural (cortical strut) — mechanical support, slower to incorporate.
Iliac crest causes chronic donor-site pain in up to a quarter of patients — a popular distractor.
Vascular grafts
- Autogenous — reversed long saphenous vein for CABG and distal lower-limb bypass; superior below-knee patency. LIMA-to-LAD has the best long-term patency of any CABG conduit.
- Synthetic — Dacron (woven polyester) for aortic and aorto-bifemoral grafts; ePTFE ("Gore-Tex") for above-knee fem-pop and AV access.
👩⚕️ Below the knee, vein beats prosthetic every time — synthetic patency is poor in small-calibre, low-flow vessels.
Nerve and tendon grafts
- Nerve grafts — bridge a gap when tension-free primary repair is impossible. Sural nerve is the classic donor (purely sensory to the lateral foot). The graft acts as a conduit for axonal regrowth at ~1 mm/day.
- Tendon grafts — palmaris longus (absent in ~15%) and plantaris are the standard donors. Used in flexor tendon and ligament reconstruction (e.g. UCL "Tommy John").
Organ transplant grafts
Covered in detail in Lesson 56. For this lesson, remember the rejection timeline:
| Type | Timing | Mechanism |
|---|---|---|
| Hyperacute | Minutes | Preformed antibodies (ABO mismatch) → complement activation, thrombosis. Prevented by crossmatch. Untreatable once it occurs. |
| Acute | Days – weeks | T-cell mediated cellular rejection. Treated with steroids and increased immunosuppression. |
| Chronic | Months – years | Vasculopathy and fibrosis, multifactorial. Largely irreversible. |
[Image: MCQs banner]
Test yourself
A man is receiving a human heart valve for rheumatic heart disease. What kind of graft is this?
- ((Autograft::Tissue from the same person — not the case here.))
- ((Allograft::☑️ Tissue from another human (living or cadaveric) within the same species.))
- ((Xenograft::Would be from an animal source, e.g. porcine valve.))
- ((Isograft::Requires a genetically identical donor (identical twin).))
A porcine skin graft is classified as which type of graft?
- ((Autograft::From the same individual.))
- ((Allograft::From another human, not another species.))
- ((Xenograft::☑️ Pig (porcine) tissue into a human crosses species — xenograft.))
- ((Isograft::From a genetically identical donor.))
A patient receives a cadaveric kidney transplant. What type of graft is this?
- ((Autograft::From the same individual.))
- ((Allograft::☑️ Cadaveric human tissue into another human is an allograft.))
- ((Xenograft::From another species.))
- ((Isograft::From an identical twin.))
A woman undergoes a mastectomy and a split-thickness skin graft is taken from her thigh for reconstruction. What type of graft is this?
- ((Autograft::☑️ Tissue moved from one site to another in the same patient.))
- ((Allograft::From another person.))
- ((Xenograft::From another species.))
- ((Isograft::Requires an identical twin donor.))
A patient undergoing renal transplant develops sudden graft swelling, cyanosis and thrombosis on reperfusion. What is the most likely cause?
- ((Hyperacute rejection from ABO incompatibility::☑️ Preformed antibodies trigger complement and thrombosis within minutes of reperfusion.))
- ((Acute cellular rejection::T-cell mediated; takes days to weeks to develop.))
- ((Chronic rejection::Develops over months to years with vasculopathy.))
- ((Ischaemia–reperfusion injury::Causes ATN, not the swelling–cyanosis–thrombosis triad.))
👩⚕️ The crossmatch is designed precisely to prevent hyperacute rejection — once it happens, the graft cannot be salvaged.
Acute graft rejection is primarily mediated by which cells?
- ((B lymphocytes::Antibody producers — more relevant to hyperacute and chronic rejection.))
- ((T lymphocytes::☑️ CD4+ and CD8+ T cells recognise donor MHC and drive acute rejection.))
- ((Natural killer cells::Contribute via innate immunity but are not the primary driver.))
- ((Macrophages::Effectors downstream of T-cell activation.))
- ((Neutrophils::Dominant in hyperacute rejection, not acute.))
Which is the commonest cause of skin graft failure?
- ((Haematoma under the graft::☑️ Lifts the graft off the bed and prevents inosculation — number one cause.))
- ((Infection::Important, especially beta-haemolytic Streptococcus, but less common.))
- ((Shear::Prevented by tie-over or negative-pressure dressings.))
- ((Seroma::Same mechanism as haematoma but less frequent.))
- ((Graft placed upside-down::A technical error, rare in practice.))
A skin graft survives in the first 48 hours by which mechanism?
- ((Plasmatic imbibition::☑️ Diffusion of nutrients from the recipient bed before any vascular connection.))
- ((Inosculation::Capillary alignment occurs from 48–72 hours.))
- ((Revascularisation::New vessel ingrowth occurs from day 4–7.))
- ((Lymphatic drainage::Re-establishes later and is not the source of nutrition.))
Which property of an iliac crest autograft is NOT shared by a cadaveric bone allograft?
- ((Osteogenic::☑️ Only fresh autograft contains living osteoblasts; allograft is processed and acellular.))
- ((Osteoconductive::Both autograft and allograft provide a scaffold for bone ingrowth.))
- ((Mechanical strength::Allografts can be structural, e.g. femoral head in revision arthroplasty.))
- ((Sterility::Allografts are processed to be sterile.))
👩⚕️ Autograft = all three (osteogenic, osteoinductive, osteoconductive). Allograft = mainly osteoconductive.
A surgeon plans a fingertip reconstruction and wants minimal contraction and good colour match. Which graft is most appropriate?
- ((Split-thickness skin graft from the thigh::Contracts and gives a poor cosmetic result.))
- ((Full-thickness skin graft from the postauricular area::☑️ Less contraction, better colour and texture for face and hand.))
- ((Meshed STSG::Designed for large surface area coverage, not cosmetic reconstruction.))
- ((Xenograft::Used as a temporary biological dressing only.))
Which vessel provides the best long-term patency in CABG?
- ((Left internal mammary artery to LAD::☑️ Highest patency of any conduit at 10+ years.))
- ((Reversed long saphenous vein::Workhorse but lower patency than LIMA.))
- ((Radial artery::Used as a secondary arterial conduit; patency intermediate.))
- ((ePTFE synthetic graft::Not used in CABG — poor patency in small coronary vessels.))
Which donor nerve is most commonly used as an autograft to bridge a peripheral nerve gap?
- ((Median nerve::Functionally critical — never harvested.))
- ((Sural nerve::☑️ Purely sensory to the lateral foot; minimal morbidity, long usable length.))
- ((Ulnar nerve::Mixed motor and sensory — too much functional loss.))
- ((Posterior interosseous nerve::Used in selected hand reconstruction, not standard for grafting.))
A Z-plasty is best described as which type of flap?
- ((Local transposition flap::☑️ Two triangular flaps interdigitated to lengthen and reorient a scar.))
- ((Advancement flap::Slides tissue forward without rotation, e.g. V-Y.))
- ((Rotation flap::Pivots tissue around an arc into the defect.))
- ((Free flap::Detached and microsurgically anastomosed to recipient vessels.))
Which is true of a free flap (e.g. DIEP for breast reconstruction)?
- ((It survives by plasmatic imbibition from the recipient bed::Describes a graft, not a flap.))
- ((It carries its own arterial inflow and venous outflow, anastomosed microsurgically::☑️ Defining feature of any free flap.))
- ((It must remain attached to its donor site::Describes a pedicled flap.))
- ((It is contraindicated over irradiated tissue::Flaps are in fact the preferred option in irradiated beds.))
Revision summary
- Auto (self) — Allo (same species) — Xeno (different species) — Iso (identical twin).
- Graft relies on recipient bed for blood supply; flap brings its own.
- STSG — epidermis + partial dermis; thigh; donor heals from appendages; meshed for large areas; contracts.
- FTSG — epidermis + full dermis; postauricular; donor closed primarily; less contraction; face and hand.
- Graft take — imbibition (0–48 h) → inosculation (48–72 h) → revascularisation (4–7 days).
- Commonest cause of graft failure = haematoma. Worst infection = beta-haemolytic Strep.
- Reconstructive ladder — primary closure → secondary intention → STSG → FTSG → local flap → pedicled flap → free flap.
- Bone graft — autograft (iliac crest) is osteogenic + osteoinductive + osteoconductive; allograft is mainly osteoconductive.
- Vascular — saphenous vein autograft for distal bypass and CABG; LIMA–LAD best long-term patency; Dacron for aorta; ePTFE for above-knee fem-pop and AV fistulas.
- Nerve graft — sural. Tendon graft — palmaris longus, plantaris.
- Rejection — hyperacute (minutes, preformed Ab) / acute (days–weeks, T cells) / chronic (months–years, vasculopathy).