Skin grafting

SKIN grafting in detail

1. SKIN GRAFTING DR.Punithavasanthan.B FNB(Hand and microsurgery) SKIMS-Srinagar

2. EPIDERMIS No blood vessels. Relies on diffusion from underlying tissues. Stratified squamous epithelium composed primarily of keratinocytes . Separated from the dermis by a basement membrane. protective barrier (against mechanical damage, microbe invasion, & water loss) high regenerative capacity

3. DERMIS Composed of two “ sublayers ”: superficial papillary & deep reticular. The dermis contains collagen, capillaries, elastic fibers, fibroblasts, nerve endings, etc. mechanical strength (collagen & elastin ) Barrier to microbe invasion Sensation (point, temp, pressure, proprioception ) Thermoregulation (vasomotor activity of blood vessels and sweat gland)

4. Grafts are typically described in terms of thickness or depth. Split Thickness(Partial): Contains 100% of the epidermis and a portion of the dermis. Split thickness grafts are further classified as thin or thick. Full Thickness : Contains 100% of the epidermis and dermis.

5. . Split-thickness skin grafts classify according to their thickness into thin STSGs (0.15 to 0.3mm), intermediate STSGs (0.3 to 0.45mm), and thick STSGs (0.45 to 0.6mm).

6. Skin Grafts: “Process of Take” 4 Phases: – Fibrin adhesion – Plasmatic imbibition – Revascularization: Inosculation & capillary ingrowth – Remodelling : Revascularization & fibrous attachment in restoring normal histological architecture

7. The graft becomes incorporated in the host bed through the process of graft “take”. The success of a graft depends primarily on the extent and speed at which vascular perfusion is restored to this parasitic, ischemic tissue.

8. Plasmatic imbibition Grafts placed on poorly vascularized beds will be ischemic for a longer time than those placed on wounds with good blood supply. FTSGs seem to tolerate ischemia for up to 3 Split-thickness grafts take well even after 4 days of ischemia. Plasmatic imbibition allows a graft to survive this immediate postgraft ischemic period until such time as graft vasculature is reestablished

9. Grafts gain weight during the phase of plasmatic imbibition,33–35 adding as much as 40% to their pregraft weight through fluid movement from bed to graft.

10. Revascularization-Inosculation and Capillary Ingrowth At the end of 48 hours, a fine vascular network is established in the fibrin layer between the graft and its recipient bed. Capillary buds from the blood vessels in the recipient bed make contact with the graft vessels and open channels are formed . Blood flow is established and the skin graft becomes pink

11. Remodelling -Revascularization & fibrous attachment: Connection of graft & host vessels via anastomoses (inosculation) Formation of new vascular channels by invasion of graft ( neovascularisation ) Combination of old & new vessels ( revascularisation ) Fibroblast proliferation: conversion of fibrin Adhesion to fibrous tissue attachment ( anchorage within 4 days)

12. Histological changes 0 to 4- Epithelium doubles; crusting, scaling of epidermis; swelling of nuclei & cytoplasm; epithelial cellmigration to surface; mitosis of follicular & granular cells 3- ++ mitotic activity in SSG not FTSG 4 – 8 Proliferation & thickening of epithelium (up to 7x) Week 4 Epidermis returned to normal thickness

13. Fibrous component: Collagen - Hyalinized early and progressively replaced with new fibres by 6 weeks; Turned over 3-4X faster than normal skin. Elastin -Accounts for resilience; Days 3-7 fragment; Replaced 4-6 weeks.

14. Appendages: sweating dependent on no. of transplanted sweat glands & degree of sympathetic reinnervation ; sweat like recipient site in FTSG only sebaceous gland activity mostly in thicker grafts: STSG usually dry & shiny hair grows from FTSG if well taken with no complications

15. Skin Graft Healing Initially white then pinkens with new blood supply Lymphatic drainage by day 6 Collagen replacement from day 7 to week 6 Vascular remodelling for months Reinnervation : from margins to bed; 4 week to 2 years; Depends on graft thickness and bed; Uneventful healing leads to near normal 2PD; Cold sensitivity can be a problem.

16. Indications , indicated when simpler methods of wound closure will not suffice, such as healing by secondary intention, primary closure, or negative pressure wound therapy. A prerequisite of skin grafting includes available donor sites and recipient sites that are well- vascularized and clean.

17. Typically skin grafts are used to cover skin defects, or placement over muscle; however, they can survive on any wound bed with vascularity including tendon with intact paratenon , cartilage with intact perichondrium , bone with intact periosteum , If these thin vascular layers are not in place, STSGs will fail. Split-thickness skin grafts are otherwise indicated in acute skin loss (burn wounds, traumatic wounds, infection), chronic skin loss (leg ulcers), and as adjuncts to other procedure).

18. Contraindications Absolute contraindications : wounds with an active infection, active bleeding, or known cancer. Wounds with exposed bone, tendon, nerve, or blood vessel without appropriate vascular layer.

19. Relative contraindications: wounds over joints or key anatomic landmarks in which contraction would reduce mobility and/or aesthetics (i.e., wrist, elbow, eyelid), previously irradiated wounds. tobacco use, anti-coagulant use, bleeding disorder, chronic steroid use, or malnutrition. wounds contaminated with beta-hemolytic streptococci

20. instruments for harvest of the skin grafts

21. during World War II, a young American surgeon, Harry M. Brown, conceived the idea of a new instrument, the electric dermatome

22. Donor sites. The ideal donor site would provide skin that is identical to the skin surrounding the recipient area. Unfortunately, skin varies dramatically from one anatomic site to another in terms of: - Colour - Thickness - Hair - Texture

23. Graft Fixation inspect for hematoma formation. In graft fixation, the first step is to apply a nonadherent dressing. Then, a dressing should be applied to the graft with gentle pressure (10–20 mmHg) to promote graft adherence without causing pressure necrosis . “Tie-over dressing” minimizes the risk of hematoma or seroma formation and also prevents shearing forces from outside. Many fixation techniques have been reported, such as reverse tie-over fixation, use of a wire frame or stoppers in tie-over fixation or quilting sutures, use of fibrin glue and dermabond , and negative pressure dressing without tie-over dressing .

24. Donor site healing and maintenance The healing of the donor site occurs by epithelial migration from the epithelial remnants in the dermis such as hair follicles, sebaceous gland, and sweat glands. Epithelial migration also occurs at the wound margins. The more superficial a STSG is cut, the faster the donor site will heal. The healing of the STSGs donor sites take place over seven to fourteen days. Donor sites from which thicker split grafts are cut may not heal for several weeks

25.  it is effective to take grafts from a hair-bearing region, because the scarring after skin harvesting can be hidden in the hair. In addition, re- epithelialization is faster, because of the hair follicles. When taking a graft from a hair-bearing region, it is important to take a thin graft, because thicker split-thickness grafts will contain undesired hair follicles and eventually lead to hair in the graft and hair loss in the donor site. 

26. Graft preparation Defat FTSG Fenestrate STSG Mesh

27. Meshing is the term used for cutting slits into a sheet graft and stretching it open prior to transplantation. Advantages: meshed grafts will cover a larger area with less morbidity than non-meshed grafts; the contour of the meshed graft can be adapted to fit in a regular recipient bed; blood and exudate can drain freely through the interstices of a meshed graft; in the event of localized bacterial contamination, only a small area of meshed graft will be jeopardized; a meshed graft offers multiple areas of potential reepithelialization .

28. Disadvantages Much of wound heal by contracture Cobble stone appearance

29. Aftercare STSG Donor site (inspect @ 2weeks) Recipient site (5th day) FTSG Donor site (depends on the site, 1week) Recipient site (1week)

30. GRAFT FAILURE A meticulous surgical technique contributes greatly to the survival of a skin graft. Particular attention should be paid to ensuring atraumatic graft handling a well- vascularized , scar-free bed careful hemostasis and removal of accumulated blood before dressing the wound postoperative immobilization of the graft recipient site use of a tourniquet during graft harvest and transfer no proximal constricting bandages

31. The most common cause of autologous skin graft failure is hematoma. The clot isolates the undersurface of the graft from the endothelial buds of the recipient site so that revascularization cannot take place The second most common cause of graft loss is infection. .

32. Fluid beneath the graft can also cause graft necrosis. Areas rich in lymphatics such as the supraclavicular , inguinal, and axillary regions are particularly prone to develop seromas . Atraumatic tissue handling, cauterization of lymphatic vessels, limited use of electrocautery in the graft bed, and a light pressure dressing or VAC technique minimizes the risk of fluid accumulation under the graft

33. Excessive pressure on a fresh graft may also cause it to die. The applied pressure should never exceed 30 mmHg. Other causes of graft failure include gravitational dependency, movement of the area, arterial insufficiency, venous congestion, lymphatic stasis, and surgeon error.

34. Dirty wounds had high bacterial counts and increased levels of active plasmin . High plasmin and proteolytic enzyme activity was generally seen in wounds contaminated with beta-hemolytic streptococci and various species of Pseudomonas. The presence of fibrin under autografts was associated with success in 17 of 21 ulcers, and the absence of fibrin was associated with graft failure. dissolution of fibrin by plasmin and proteolytic enzymes is the probable mechanism in graft failure secondary to microorganisms

35. Contraction (1˚ & 2˚): 1° contraction is due to elastic recoil: o FTSG 40% o Medium SSG 20% o Thin SSG 10% 2˚ contraction as the graft heals: o FTSG do not undergo 2ndary contraction SSG will contract as much as possible dermis in FTSGs is resistant to the pull of myofibroblasts   immobilization with a splint

36. PIGMENTATION Skin grafts change color during healing.10 Grafts harvested from the abdomen, buttocks, and thigh become darker as they heal, while grafts taken from the palm tend to lighten. Dermaabrasion,hydroquine creams Prevent Sunlight exposure for first 6 months

37. Hypertrophic Scarring All grafted areas will scar to some extent, and a scar is not deemed “mature” until a year after grafting. Any scar that is raised above skin level is considered hypertrophic. After about 2 weeks,scar prevention measures begin.  Silicone covering and pressure therapy are applied to prevent hypertrophy. This protocol should be continued for 3 months

38. Preservation of split-thickness skin grafts Skin grafts can be stored by being refrigerated. Such grafts may be moistened in sterile saline and then placed in a refrigerator at 4 ºC It may be wise to discard grafts after 8 days, Freezing causes tissue death because of concentration within the cell, leaving behind a lethal concentration of salts. Protective agents such as 15% glycerol or 10% dimethyl sulfoxide (DMSO) in Ringer’s solution and storage at -70 ºC with liquid nitrogen help to protect against this type of injury and allow viable skin to be preserved for up to 28.   freeze-drying  of skin for storage at room temperature.

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