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Treatment of Large Canine Distal Limb Wounds via Full-thickness, Mesh-free Skin Graft Application and Negative Pressure Vacuum Therapy

Andrew Goodman, DVM, DACVS
Staff Surgeon
angell.org/surgery
surgery@angell.org
617-541-5048

 

Closure of large wounds of the distal limb is not always possible due either to a paucity of surrounding tissue or when tight skin apposition would result in a tourniquet effect. Treatment of these wounds can sometimes be successful via second-intention healing (i.e. bandage management), however this may require a prolonged course of treatment or be unsuccessful, especially should the defect approach 50% the circumference of the limb. A free skin graft can be considered as a technique to allow for closure of these defects in a timely and successful manner. Negative pressure vacuum system bandages are now also commonly used as an ancillary treatment to help improve wound bed quality pre-operatively and aid in survival of these grafts. The following article will review the technical aspects of free skin graft placement and will provide an introduction to negative pressure vacuum system bandage application.

The first step prior to successful free skin graft application is ensuring a healthy wound bed. This is important since for the first 48 hours after placement a graft’s nutrition is provided by fluid from the underlying tissue (called ‘plasmatic imbibition’) rather than a direct blood supply. A granulation bed is ideal, however muscle and tendon can also support graft survival. As an example, grafts have been successfully used for immediate wound closure at the time of surgical excision of tumors. It is imperative that infection be controlled prior to graft placement and topical wound treatment and bandage management should be used until grossly healthy tissue is present. Some surgeons will culture the wound bed prior to graft placement, however this is not typically necessary if the area is healing appropriately. Once a healthy wound bed has developed, the site should be bandaged with a non-adherent contact layer such as an Adaptic or Telfa pad. The addition of triple antibiotic ointment is also recommended due to its obvious antibacterial properties and to help avoid tissue desiccation.

A negative pressure vacuum system bandage involves application of a continuous level of suction to a porous foam padding which is applied over the wound and closed to the environment with adhesive plastic. These bandages are most easily created by using proprietary products available from companies such as 3M/KCI. The level of negative pressure elected (commonly -50 to -125mmHg) will vary based upon the indication for use and is programmable into the device. Benefits of these bandages compared to traditional dressings include evacuation of exudate, improvement of blood flow to damaged tissue, and decreased time to granulation bed formation. This latter attribute is especially appealing in the context of skin graft placement as we are able to more quickly develop a wound that is capable of sustaining the graft. These bandages can also be left in place for relatively long periods of time (typically 3 days) compared to the alternative of daily wet-to-dry bandage changes.

Once a healthy wound bed is present a plan can be developed for skin graft application. The wound diameter is measured and outlined on sterile surgical glove paper. This paper is cut to the shape of the wound and laid over the donor site to act as a guide. The donor tissue is typically removed from the lateral thorax or abdomen ensuring there is adequate skin to allow for primary closure of the resulting defect. The direction of hair growth is noted and the graft will eventually be placed in this appropriate orientation. The donor tissue excised should be a bit longer than the defect to be covered, but the width does not need to exceed that of the defect as the donor skin can expanded in this plane after it has been meshed. It is helpful, if available, to have a second surgeon close the donor defect during graft preparation to decrease total surgical time. After excision the donor tissue is laid over a sterile Vet Wrap cylinder with the subcutaneous tissue exposed. The edges of the tissue are stapled to the Vet Wrap for added stability and to apply tension to the graft during manipulation. A sharp pair of curved Metzenbaum scissors are used to remove the panniculus muscle and subcutaneous fat. An appropriate level of tissue removal is determined when a ‘cobblestone’ appearance to the graft is seen corresponding to the now exposed bases of hair follicles. The graft also becomes somewhat translucent when removal of the subcutaneous tissue is complete. The graft is then meshed by cutting full-thickness slits through the tissue which will allow exudate beneath the graft to escape. This is important since fluid or blood clots that remain between the graft and the wound bed will decrease adherence of the graft, interfere with absorption of nutrition by the graft, and block the eventual creation of new capillaries between the graft and wound (termed ‘inosculation’). The slits are typically 1cm long and less than 2cm apart in staggered parallel rows. The incisions are most easily created by stabbing through the graft into the Vet Wrap cylinder with a #15 blade. The graft is then laid on the wound bed ensuring there are no creases and even tension is applied. The edge of the graft is stapled or sutured to the edge of the wound bed, ideally overlapping the normal skin by approximately 5mm. This overlapped skin will eventually die and is peeled off during subsequent bandage changes. Additional staples or skin sutures can also be added to the center of the graft to further secure the tissue to the wound. Once the graft is secured, a sterile non-adherent material such as Adaptic with triple antibiotic ointment is placed over the site. It is important that this material not have creases that could apply unequal pressure to the graft. The Adaptic is then stapled around the periphery of the graft to limit motion.

The negative pressure vacuum bandage is then placed over the site. The first bandage layer is sterile foam padding which is cut to size (typically slightly larger than the size of the graft) and stapled to the limb to maintain its position. It is ideal to not have foam directly contacting normal healthy skin, and if skin is exposed an Adaptic or Telfa pad can be placed over the site prior to foam application. Once the foam is secured, proprietary adhesive drapes are placed over the foam creating an air-tight seal. It is important that the underlying tissue be dry prior to application of the plastic drapes, otherwise the drapes will not stick to the skin creating a leak in the system. Various adhesive sprays can also be applied to the skin prior to drape placement to further improve this seal. A small hole is cut in the plastic and a suction attachment is secured to contact the underlying foam. The vacuum system is then activated and the desired pressure maintained. In our hospital we set the vacuum system to -75mmHg on continuous suction mode when placed over a free skin graft. A modified Robert-Jones bandage is often also placed over the vacuum bandage but is not always necessary. The patient will need to be hospitalized with the bandage in place until the first change, typically 3 days post-operatively. Studies have shown that percent free skin graft necrosis is decreased and time-to-healing of the mesh slits is improved via use of a vacuum bandage system versus traditional modified Robert Jones bandage placement alone. This is suspected to be due to increasing adherence of the graft to the wound bed, improved growth of granulation tissue through skin graft mesh slits, evacuation of fluid from under the graft, and improved blood supply to the site.

The owner should be made aware prior to the initial surgery that multiple sedated bandage changes will be required during the post-operative period. Changing the bandage without sedation is not recommended as any motion during the process could dislodge the graft and newly forming capillaries. The first bandage change is at day three post-operatively. The patient is sedated and the vacuum bandage and overlying non-adherent Adaptic material removed. The graft is evaluated and typically has a somewhat cyanotic color at this stage. The Adaptic dressing (with triple antibiotic ointment added) is replaced and stapled to the skin and a modified Robert-Jones bandage replaced. This process is completed again at days 7 and 14 post-op. The amount of graft survival is known by day 7 and the staples (donor and graft sites) can be removed by day 14. A protective e-collar is maintained for at least an additional week after staple removal as once nerve-endings are re-established a tingling sensation can develop at the graft and the patient may attempt to traumatize the area.

If close attention is paid to establishment of a healthy wound bed, the donor tissue is prepared carefully, and bandages are managed appropriately, the vast majority of dogs will have successful healing of even quite dramatic wounds via the use of free skin grafts. Negative pressure vacuum system bandages applied in the early post-operative period further improve the outcome of these cases.

 

References

  1. Stanley, BJ, et al. “Effects of negative pressure wound therapy on healing of free full-thickness skin grafts in dogs”. Veterinary Surgery, 2013, 42(5), pp. 511-522.
  2. Pavletic MM (2010). Atlas of Small Animal Wound Management and Reconstructive Surgery (3rd ed.). Ames, Iowa: Wiley-Blackwell
  3. Tong, T and Simpson DJ. “Free skin grafts for immediate wound coverage following tumour resection from the canine distal limb.” Journal of Small Animal Practice, vol. 53, 2012, pp. 520-525.
  4. Tobias KM & Johnston SA (2012). Veterinary Surgery: Small Animal. St. Louis, Missouri: Elsevier Saunders
  5. Demaria, M, Stanley, BJ, et al. “Effects of negative pressure wound therapy on healing of open wounds in dogs”. Veterinary Surgery, 2011, 40(6), pp. 658-669.
Image 1: Note the healthy wound bed. The area planned for graft donation is also draped into the surgical field.
Image 2: The graft has been prepared and laid on the recipient bed. The donor site is closed without tension.
Image 3: The graft has been secured to the wound bed with skin staples.
Image 4: A negative pressure vacuum bandage has been placed over the graft site immediately post-op.
Image 5: Day 3 post-op: Note the cyanotic/purple color to the graft which is typical at this time after surgery.
Image 6: Day 14 post-op: The mesh slits have closed and the staples will be removed.
Image 7: Day 21 post-op: The graft has healed and hair has begun to regrow.
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