Comparison of Efficacy and Complications Between Negative Pressure Wound Therapy and Conventional Mechanical Fixation in Skin Grafts: A Retrospective Analysis

Introduction. Graft fixation is critical for the successful survival of a skin graft. Conventional mechanical fixation may induce inappropriate pressure and increase wound complications. Negative pressure wound therapy (NPWT) could be utilized to secure a skin graft and improve drainage. Limited quantitative data exist on the efficacy of NPWT for skin grafting. Objective. This retrospective study compares the efficacy and complications between NPWT and conventional mechanical fixation in skin grafts. Materials and Methods. Patients who underwent skin graft surgery from January 2015 to December 2016 at a large university hospital in southwest China were retrospectively analyzed. Characteristics, including wound pattern, skin graft type, surgical procedure, survival rate, and postoperative complication, were statistically analyzed by Pearson chi-square or Fisher’s exact test. Results. A total of 186 patients were included in the study; 72 received NPWT and 114 received conventional mechanical dressing fixation after skin grafting. Overall survival rate of full-thickness skin grafts was significantly higher in the NPWT group than the dressing group (P < .01). The NPWT group showed a higher survival rate than the dressing group for each anatomic site, but only patients who had skin grafts of the hand exhibited statistically significant results. Conclusions. This study reports a quantitative analysis of the efficacy of NPWT on skin graft fixation with NPWT providing consistent pressure and better drainage than conventional mechanical fixation. In addition, the use of NPWT also could increase graft take on the hand region.

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Skin grafting is the primary reconstructive measure used to cover small and large soft tissue defects. Graft fixation is essential for the successful survival of a skin graft. Conventionally, a skin graft could be secured by means of elastic dressing or tie-over bolsters.¹ Inappropriate pressure on the skin graft may lead to hematoma, infection, dislocation, or graft loss, reducing graft survival significantly.² Negative pressure wound therapy (NPWT) initially was introduced for suction therapy of various wounds. This technique could provide negative pressure to seal the space and secure the adherence of a skin graft with persistent, uniform pressure. It also offers continuous drainage of blood and exudate, minimizing infection and hematoma, and firm graft fixation on a complex wound surface.

In this study, in order to illuminate an appropriate fixation method for skin grafting, the outcomes of skin graft surgery with different types of fixation were retrospectively analyzed.

Patients who had skin graft surgeries in the Department of Plastic and Burn Surgery, First Affiliated Hospital of Chongqing Medical University, Chongqing, China, from January 2015 to December 2016 were retrospectively analyzed in the study. Research protocol was approved by the Ethical Committee of the First Affiliated Hospital of Chongqing Medical University. Patient data were collected from the electronic case records system. Medical data included age, sex, wound etiology, wound location, skin graft type, surgical method, surgical outcomes, and postoperative complications. 

Acute and chronic wounds due to trauma, soft tissue infection, burn injury, tumor resection, and scar plastic surgery were included in this study. Also, those with comorbidities, such as diabetes and hypertension, were included. Exclusion criteria consisted of patients who previously received a skin graft that had failed, had died, or were lost to follow-up before their wounds had healed.

Full-thickness skin grafts (FTSGs) were harvested from the abdomen or inner upper extremities with a scalpel. Grafts were punched with No. 11 blade scalpel (punch size, 1 cm x 0.5 cm) before applying to the wounds for better drainage. Split-thickness skin grafts (STSGs) were harvested from the scalp, abdomen, or thigh with a pneumatic-driven dermatome (Zimmer Biomet Air Dermatome; Zimmer Biomet, Warsaw, IN). The thickness of STSGs ranged from 0.02 cm to 0.03 cm. Split-thickness grafts were meshed 1.5:1 or 1:1 for coverage and drainage. After preparing the wound (thorough debridement, saline wash, and rinse with antibiotic fluids), a skin graft was applied and secured with intermittent nonabsorbable sutures as needed. Wash with saline was repeated, then the grafts were covered with nonadhesive petroleum jelly gauze. Skin grafts were fixed with either a conventional mechanical dressing or NPWT.

In the mechanical dressing group, the grafts were fixed with a bolster or elastic bandage (all gauze and bandages are from Cofoe Medical Products Co. Ltd, Jiangxi, China). Sterile cotton and gauze were placed above the petroleum jelly gauze. The elastic pressure dressing was changed 3 to 5 days postoperatively, and the bolster was replaced with an elastic bandage 5 to 7 days postoperatively.

In the NPWT group, the sponge (GRANUFOAM Dressing; KCI, an Acelity Company, San Antonio, TX) was trimmed to an appropriate contour to cover the grafted area. Suture was applied when needed to cover an extensive surface. The adhesive laminate was applied over the sponge and surrounding intact skin. Then, the sponge was connected to the portable unit (V.A.C. Ulta; KCI, an Acelity Company) after the seal coverage was secured. The vacuum mode was set at continuous -100 mm Hg for FTSGs and continuous -75 mm Hg for STSGs. The central wall vacuum was not used in any case. The NPWT unit could automatically detect leakage of the sponge, which would sound an alarm. The loss of vacuum pressure was managed with additional adhesive dressings. The sponge was kept on the grafts 5 to 7 days following surgery. After removal of the NPWT sponge, the grafts were covered with petroleum jelly gauze or antibiotic gauze and appropriate conventional fixations (dressing fixations applied once NPWT sponge was removed). Fixation included gauze, elastic and nonelastic bandage, and splint, if necessary; the pressure should not impair the blood supply of the grafts. 

The outcomes of the grafts were analyzed by the attending surgeons and recorded. The qualitative evaluations included full graft survival, partial graft failure, total graft failure, hematoma formation, and graft infection. Full graft survival healed with primary complete epithelialization while a total graft failure usually needed an additional skin grafting procedure. Partial graft failure meant a small portion of the graft was lost. Follow-up ended when complete epithelialization was achieved, and the dressing was changed to moisturizing cream (Erythromycin ointment; Ma Ying Long Pharm, Wuhan, China).

For the data analysis and report, all discrete variables were reported as numbers and percentages. Statistical significance of the results was assessed using Fisher’s exact test or Pearson chi-square. A P value < .05 was considered to be statistically significant.

During the 2-year study timeframe, 231 patients had skin graft surgery, of which 186 patients were included in this study. Patient characteristics are detailed in Table 1. The mean age of the NPWT group was younger than the dressing group. Of the 186 wounds, 77 received a FTSG and 109 received a STSG. Inguinal crease and inner extremities were the main FTSG donor sites. Recipient sites include hand, foot, lower extremities, upper extremities, and posterior and anterior trunk (Table 2). Facial and neck wounds were not included because of the difficulty in applying NPWT on these anatomic sites. 

For FTSGs, the overall full graft survival rate was greater in the NPWT group (88.2%, n = 51) than the dressing group (57.7%, n = 26). The outcome was statistically significant (P < .01). For STSGs, the overall full graft survival rate also was greater in the NPWT group (58.4%, n = 45) than the dressing group (19.5%, n = 15); however, this result was not statistically significant (P = .052). The overall graft failure was 33% and 16.1% for foot wounds in the dressing and NPWT groups, respectively (P = .054). Infection rate was higher in the lower extremity wounds receiving the dressing (18.2%, n = 22) than those that received NPWT (6.7%, n = 30). Hand wounds treated with the dressing showed the highest complication rate among all anatomic groups (54.5%, n = 11). More detailed data regarding outcomes is shown in Table 2. On each anatomic recipient site, the NPWT group showed a better total survival rate than the dressing group (Figure 1), but only results of hand wounds appeared statistically significant.

Case 1
A 59-year-old man with diabetes presented with plantar necrotizing fasciitis of the right foot, measuring 7 cm x 9 cm. After undergoing surgical drainage for 2 weeks, local infection was controlled and granulation tissue began to grow. An autologous STSG from the right upper thigh (measuring 7 cm x 8 cm) was harvested to cover the wound. Negative pressure wound therapy was utilized to secure the graft and provide drainage. The NPWT sponge was removed on postoperative day 6, at which time full graft take was observed. The wound was covered completely by epithelialization from peripheral STSG in another 7 days (Figure 2). 

Case 2
A 23-year-old woman presented for plastic surgery to correct a scar contracture deformity (post resection and release the wound measured about 1.5 cm x 3.5 cm on each finger) on her left hand. The hypertrophic scar was resected and the contracted interphalangeal joints were released. A FTSG was harvested from her left upper inner arm. The graft was placed on the wound and secured with NPWT. Full graft survival was observed on postoperative day 8 (Figure 3).

Case 3
A 38-year-old man sustained critical injury on his right arm following a car accident. Multiple fractures and tendon ruptures developed on his right forearm along with soft tissue laceration. Internal and external fixations were performed by orthopedic surgeons, then the patient was transferred to the authors’ department for soft tissue reconstruction. Since there was exposed bone and tendon, the wound initially was covered with a dermal substitute (PELNAC; Gunze Ltd, Kyoto, Japan) after debridement. The dermal substitute was kept on with NPWT for 8 days. As granulation tissue filled the wound, a STSG was harvested from the right thigh and applied and secured by NPWT sponge for 7 days. Full graft take was observed on postoperative day 10 (Figure 4).

For any skin graft surgery, graft fixation is especially critical for graft survival. It requires appropriate pressure, stable tension, and adequate drainage. Conventionally, the tie-over bolster dressing and elastic bandage dressing are the most commonly used methods for securing skin grafts. The use of bolster fixation requires experience and well-trained surgical skill to make skin grafts adhere closely to a recipient wound with an irregular surface. Surgical fixation with tie-over bolster and elastic bandage may lead to inappropriate tension and pressure, and their drainage effects are limited and not expectable, because the gauze dressing possibly could impair the draining pathway. Thus, excessive pressure may cause skin necrosis and insufficient drainage may facilitate infection, both of which could impair the graft take. For certain anatomic sites such as the foot or hand, a wound’s shape could be complicated and irregular, requiring delicate adjustments in pressure.

Unlike manual fixation techniques, NPWT applies negative pressure to the space between the skin graft and recipient site. It removes space and pulls the entire skin graft with uniform pressure. Laboratory and clinical studies have shown NPWT could increase wound blood flow, oxygen concentration, and granulation tissue formation as well as decrease accumulation of fluid and bacteria.^3,4 Several studies^5-9 demonstrated that NPWT could be used successfully for securing skin grafts, especially in an exudative, irregular, or mobile recipient wound and in complex anatomic sites. Rozen et al¹⁰ introduced the use of simple suction drain as a cheap and safe alternative to commercial NPWT dressings for the treatment of lower limb STSGs. Their results¹⁰ showed full take of skin grafts with no complications. An additional study by Lee and Kim¹¹ shows a shorter time of graft take with NPWT use, reducing patients’ need for immobilization and hospital days consequently. The advantages of NPWT over mechanical dressings include improved graft survival and decreased complications, mainly due to the removal of fluid beneath the graft, reliable and subtle pressure, and prevention of shear forces.

Negative pressure wound therapy could stabilize the skin graft and conform well to the shape of recipient bed, remove fluid, decrease bacterial counts, and provide a secured dressing. Improved graft survival and reduced need for repeat skin grafting were noted in a retrospective study by Isago et al.¹² The authors¹² used NPWT for skin graft fixation in 10 patients and confirmed its high utility as evidenced by a 95% or higher survival rate of the grafted areas. Negative pressure wound therapy is a highly reliable method to bolster a STSG in the burn population. The observed rate of 0 returns to the operating room for repeat grafting was especially encouraging.¹³ Some surgeons introduced the use of NPWT in skin graft surgery for patients with large area (> 25% total body surface area) burns and noticed STSG fixation with NPWT was an efficient method in major burn reconstruction, notably in areas with irregular wound surfaces or subject to movement.¹⁴ 

The present results showed graft survival rate with NPWT was significantly higher in the FTSG group. This finding may be due to the reason that FTSGs require more consistent and stable pressure, and any shear force or pressure shift may lead to partial or total graft failure. In addition, NPWT helps maintain secured adhesion, even at sites where it is difficult to maintain stable pressure. The authors believe this technique can be used at any graft recipient site if there is enough space to place a film dressing securely around the site. This may explain why NPWT is significantly helpful for the survival of skin grafts of the hand, because hand wounds often appear irregular and complex. The manufacturer guidelines recommend continuous negative pressure of -75 mm Hg to -125 mm Hg,¹⁵ though the present authors routinely used -100 mm Hg for FTSG and -75 mm Hg for STSG fixation. A previous study¹⁶ has claimed negative pressure may be used as low as -50 mm Hg without compromising skin graft incorporation. The application of NPWT is technically easier than performing a tie-over technique using gauze, therefore saving surgical time and relevant expenditure for patients. Research has found patients with STSGs secured with NPWT showed fewer repeated grafting procedures and a very high initial graft survival with complete recipient bed coverage.¹⁷

Some NPWT devices restrict patient activity because the suction tube needs to connect to a central negative pressure on a wall, but a portable NPWT device can facilitate patient movement. It can be difficult to apply NPWT on certain anatomic sites if there is inadequate space for placing a film dressing, such as the face and perianal region. Use of NPWT also may increase disposable material costs, but it will reduce length of hospitalization and surgery time, which may save considerable expense for the patients and hospital. 

The limitations of this study are related to the multiple wound locations and etiology as well as the mix of STSG and FTSG harvesting. Each limitation could be a valuable clinical or statistical variable. All cases presented at a single institution, and descriptions of the wounds are limited. No detailed information, such as wound surface area, pathological examination, and overall healing time, are provided. 

Graft fixation is critical for graft survival. Negative pressure wound therapy is an alternative approach for skin graft fixation. In comparison with conventional tie-over bolster or dressing methods, NPWT offers consistent pressure, better drainage, and less operation time. Complications like hematoma and infection rate were lower in patients who received NPWT. The graft survival rate with NPWT was significantly higher for FTSGs. For certain anatomic regions, such as the hands, NPWT could increase the overall graft take to the wound. 

Note: Dr. Shen initiated the design of this study; wrote most of the manuscript, including figures modeling; and obtained patient photos. Dr. Zhan conducted the literature search, patient data extraction, and created the tables. Dr. Wei provided primary statistical analysis and literature search. Dr. Zhang consulted in the study design, data analysis, and article review.

Authors: Xiao Shen, MD; Tianfu Zhan, MD; Dayong Wei, MD; and Hengshu Zhang, MD

Affiliation: Department of Plastic and Burn Surgery, The First Affiliated Hospital of Chongqing Medical University, Chongqing, China

Correspondence: Hengshu Zhang, MD, Department of Plastic and Burn Surgery, 4 No.1 You Yi Road, Chongqing, China; 42019142@qq.com

Disclosure: The authors disclose no financial or other conflicts of interest.