Effective Management of Major Lower Extremity Wounds Using an Acellular Regenerative Tissue Matrix: A Pilot Study

ABSTRACT

Wound healing is a significant problem in orthopedics. GraftJacket tissue matrix (Wright Medical Technology, Inc, Arlington, Tenn), a novel acellular regenerative tissue matrix, has been designed to aid wound closure. A prospective, randomized study was initiated to determine the efficacy of this tissue product in wound repair compared with conventional treatment. Lower extremity wounds are refractile to healing in patients with diabetes mellitus. Therefore, researchers used diabetic foot ulcers to evaluate the efficacy of GraftJacket tissue matrix in wound repair. Only a single administration of the tissue matrix was required. After 1 month of treatment, preliminary results demonstrate that this novel tissue matrix promotes faster healing at a statistically significant rate over conventional treatment. Because wounds in this series of patients are deep and circulation around the wound is poor, the preliminary results suggest that this tissue matrix will be applicable to other types of orthopedic wounds.

Successful orthopedic surgery involves not only the successful treatment of the affected bones, but also the healing of the wound as a result of trauma or surgery. With minimally invasive techniques, wound size can be kept to a minimum. However, additional factors, such as poor circulation, can compromise wound healing. As the population ages and the incidence of obesity increases, circulation complications secondary to diabetes mellitus are becoming more prevalent. Hard to heal, full thickness wounds, especially to the lower extremity, are a common and difficult problem to treat.¹ These wounds are often secondary to open fractures, postoperative wound dehiscence and, in many cases, diabetes mellitus.

Through tissue engineering, surgeons can transplant human tissues to assist in the closure of these wounds. Although little research has examined the efficacy of tissue-engineered skin in the treatment of open fractures or postoperative wound dehiscence, a significant amount of research focuses on tissue-engineered skin grafts in diabetic neurotrophic wounds.

Amputations secondary to foot ulcers are a major problem that affect 5%-10% of the diabetic population per year.^2-4 The diabetic foot is predisposed to wound development because of the abnormal fibroblast and matrix protein function found in the skin, the poor nutritional blood flow, peripheral neuropathy, and decreased inflammatory response found in the diabetic lower extremity.^3,5 The most common treatment for minor wounds is sharp debridement with moist wound dressing and standard offloading, with the treatment regimen becoming more difficult as the age and size of the wound increase.⁶ Research in tissue engineering has shown that there may be benefits to using allografts to achieve quicker wound healing as compared to local conservative care.^7,8

Several human skin matrixes are available for the treatment of wounds. GraftSkin (Novartis, New York, NY) was shown to reduce the time to heal diabetic foot ulcers compared to conventional treatment.⁸ Up to five applications of the skin matrix were needed. Falanga and Sabolinski⁷ used GraftSkin in hard to heal venous ulcers and determined that treatment with GraftSkin was more effective in wound closure compared with compression therapy alone. Naughton et al¹ demonstrated the benefits of a metabolically active human dermal replacement graft in the treatment of diabetic foot wounds; however, this graft material required up to eight applications.

GraftJacket tissue matrix (Wright Medical Technology, Inc, Arlington, Tenn) is a bilaminate acellular regenerative tissue matrix in which there is an intact woven collagen framework with the preservation of matrix proteins and vascular channels. The product is extensively tested after manufacturing for sterility and to ensure the preservation of the extensive collagen network.

Because of the abundance of research discussing the use of tissue engineered skin in treating diabetic foot wounds, GraftJacket tissue matrix was used in this same study group to assess its ability to promote healing. Results from this study may also apply to wounds found in trauma and reconstruction.

Materials and Methods

Patient Population

Between April 7, 2003 and June 27, 2003, 40 patients with full thickness wounds to the lower extremity secondary to either insulin dependent or noninsulin dependent diabetes mellitus were included in a study. A prospective, randomized, controlled single-blind design was performed. All wounds included were considered to be chronic nonhealing wounds, defined as present for at least 6 weeks without epidermal coverage. Patients in this study had wounds >1 cm²in size located on the leg or foot. Thirty-one men and nine women were included in the study. The average patient age was 58 years (range: 43-70 years). Twenty-four patients were using insulin as a hypoglycemic agent. The remaining 16 patients were taking daily oral hypoglycemics.

The patients randomly selected for control treatment (N520) received conventional therapy with sharp debridement, Curasol wound gel (Healthpoint, Ltd, Fort Worth, Tex) with gauze dressings, and standardized offloading. The patients randomly selected for GraftJacket tissue matrix application received the surgical application of the scaffold at day 0 and identical offloading of the wound as with the control group. Patients were evaluated weekly for 4 weeks. Reduction in wound length and width was measured using wound tracing on wound film. Digital calipers were used for exact measurement of the tracing. Wound depth was evaluated using disposable sterile rulers. All measurements were taken at the point of greatest length, width, and depth. Complete healing was defined as full epithelialization of wound with absence of drainage.

Surgical Technique

After the wound was evaluated for length, width, and depth, the GraftJacket tissue matrix was measured and cut to fit the defect. When cutting the graft, it was important to accommodate for the depth of the wound. The GraftJacket tissue matrix was then prepared for implantation. A 10-minute bath in sterile saline was used to rehydrate the scaffold. The graft was noted to be ready for application when the paper covering the basement membrane surface of the scaffold detached from the graft. While the graft was rehydrating, the wound bed was prepared for graft application using typical full thickness wound debridement (Figure 1A). All necrotic tissue was removed from the wound, and a bleeding wound base was created. The graft was then applied with the reticular surface (shiny side) toward the wound bed. The basement membrane surface (dull surface) was superficial and exposed to the compression dressing. Using skin staples or sutures, the scaffold was circumferentially affixed to the wound margins (Figure 1B). To maintain a moist environment for healing, a mineral oil-soaked fluff compressive dressing was applied as the postoperative dressing. This dressing was changed and reapplied at days 5, 10, and 15 (Figures 1C-E). After day 15, the wound was covered with a dry sterile dressing.



Figure 1: AP radiograph of a tibia in an 8-year-old child. The lesion (aneurysmal bone cyst) of the upper tibia is expanded (A). Lateral radiograph (B). Axial T2-weighted MRI. There are numerous fluid levels (C). Postoperative radiograph after tumor excision and grafting with AlloMatrix and OsteoSet (D). Postoperative radiograph. Note the dissolution of the OsteoSet and AlloMatrix and filling of the defect with bone. This patient’s functional score was 30 points (E).

Results

To ensure accurate comparison between subject groups, statistical analysis was performed on the following parameters: average age of wound at day 0, and difference in length, width, area, and depth of wound at day 0 between the two subject groups. The average timespan of the wound was 25 weeks in the GraftJacket tissue matrix subject group and 27 weeks in the control group. A Mann-Whitney statistical analysis demonstrated no statistical difference (P=.695) between the two groups. There was no statistical significance between the two groups in wound length, width, area, and depth (Table 1).

Four weeks after treatment, the following end points were assessed: average wound reduction per week (millimeters), percent closure at 4 weeks, and average number of applications. Average wound reduction per week demonstrated both statistically and clinically significant results across the two treatment groups (Table 1). In the GraftJacket tissue matrix treatment group, wound length decreased by an average 3.4 mm per week as compared to the control group that decreased by 1.0 mm per week. Wound width decreased by an average of 2.3 mm per week in the GraftJacket tissue matrix group as compared to 1.0 mm in the control group. In the GraftJacket tissue matrix group, the wound area decreased by 1.5 cm² per week compared with 0.5 cm² per week in the control group. Finally, depth in the GraftJacket tissue matrix group decreased by an average of 1.9 mm per week, as compared to 0.4 mm per week in the control group. For all of these parameters, a Mann-Whitney Rank Sum Test was performed and there was a statistically significant difference between the two groups (Table 1).

Table 1 The percent of wound closure at 4 weeks showed significant differences between the two treatment arms using the Mann-Whitney Rank Sum Test (Table 2). At 4 weeks, the GraftJacket tissue matrix patient group showed an average reduction in wound depth by 89.1% as compared to 25% in the control group. Grafted patients showed a decrease in wound area by 67.4%, while patients treated with traditional local care showed a decrease in wound area by 34%. Differences in rates of healing were also observed for the wound length and depth.

One graft application was necessary after the initial application for all patients in the GraftJacket tissue matrix treatment group. No patients in the study experienced any serious adverse effects to the implanted graft. In the GraftJacket-treated patient group, the most common postoperative complication included “drying” of the superficial portion of the graft. This occurred in four of the 20 GraftJacket-treated patients, all secondary to an insufficiently mineral oil soaked compressive dressing. All of the four grafts incorporated into the host tissue and were not considered surgical failures. One patient developed a seroma that was aspirated at the first postoperative visit. This graft also incorporated with the host tissue and was not considered a host failure.

Discussion

This prospective study demonstrates the ability of an acellular dermal regeneration matrix to stimulate healing in chronic full thickness wounds. Significant differences between GraftJacket-treated patients and control-treated patients were found for the average closure rate per week (millimeters) and percent reduction in wound area. The following treatment rates were noted: the length of the GraftJacket-treated wound healed 3.3 times faster than with conventional treatment over the course of 4 weeks, the width of the graft-treated wounds healed 2.1 times faster than conventional treatment, the area healed three times faster than conventional treatment, and the depth healed 3.6 times faster than the control group. Healing rates can depend on the control of external variables that may influence the defined protocol. Therefore, before randomization, each wound received a similar treatment regimen. This allowed for a decrease in variability in wounds and wound healing rate.

The percent change in wound area over a 4-week period has been shown to be a robust predictor of complete healing in a 12-week prospective trial.⁹ In that trial, the level of wound reduction between patients who had healed by 12 weeks and patients who had not healed by 12 weeks at the 4-week period revealed a striking difference. Healed patients had a mean wound healing rate of 82% compared to a mean wound healing rate of 25% in the nonhealers. The midpoint between these two mean healing rates is 53%. Extrapolating this information into the present population, it is predicted that 18 of 20 GraftJacket-treated patients would be healed by 12 weeks compared with two of 20 conventional-treated patients.

The mechanism at which the graft scaffold works to promote a healthy granular bed in hard-to-heal wounds is still under investigation. This scaffold is made of interwoven collagen, laminen, and elastin fibers that are preserved during a proprietary cryofreezing process to render the graft acellular. After the graft is rid of its cellular components, the remaining matrix of intact connective tissue and preserved vascular channels act as a scaffold to allow the cells of wound healing to migrate. The authors hypothesize that the vascular channels that are preserved in the freeze-drying process are of the utmost importance in the process of wound healing. This allows for an intact support structure for the microvascular supply of the wound bed to incorporate within the first 5-7 postoperative days. This characteristic may allow this scaffold to be placed in areas in which bone and/or tendon are exposed.

The orientation of the collagen fibers in the scaffold is also of great importance in treating lower extremity wounds. The “lattice-like” structure of the collagen fibers allows for a tensile strength greater than that of fascia lata. Diabetic patients with neurotrophic wounds often have a decreased proprioceptive awareness. This can cause inadvertent collisions to the affected lower extremity creating a difficult environment for graft healing. The added tensile strength of the GraftJacket tissue matrix creates for a stronger product with a better chance for positive surgical outcomes in this situation.

Although there have been advances in tissue engineering for the treatment of chronic, nonhealing wounds, many of these allografts are fragile and require multiple applications.^1,3,4,6,8 Only a single application of the GraftJacket tissue matrix acellular regenerative tissue matrix was required.

It is difficult to compare the preliminary results of this study with the results of treating diabetic ulcers by other tissue products.^1,8 The diabetic wounds in this study are significantly larger than in the GraftSkin study.⁸ The average starting wound area in this study was 9.7 cm² compared with 3.0 cm² in the GraftSkin study.⁸ It has been shown that there is a direct correlation between ulcer area and the time it takes to heal.¹⁰

Furthermore, neither of the other studies using other tissue products discussed the depth of the diabetic foot ulcer wound.^1,8 This parameter can have a significant effect on the time to healing.¹¹

This pilot study has defined the surgical application of the GraftJacket tissue matrix acellular regenerative tissue matrix for foot and leg ulcers and has shown that GraftJacket tissue matrix may be beneficial in treating complex, full thickness lower extremity wounds in the diabetic patient. Although using 4-week predictors suggest that there will be a significant difference in the healing rate between the two treatment groups, further study with 12-week follow-up data are needed.

References

Naughton G, Mansbridge J, Gentzkow G. A metabolically active human dermal replacement for the treatment of diabetic foot ulcers. Artif Organs. 1997; 21:1203-1210.
Gentzkow GD, Iwasaki SD, Hershon KS, et al. Use of dermagraft, a cultured human dermis, to treat diabetic foot ulcers. Diabetes Care. 1996; 19:350-354.
Gentzkow GD, Jensen JL, Pollak RA, et al. Improved healing of diabetic foot ulcers after grafting with a living human dermal replacement. Wounds. 1999; 11:77-84.
Armstrong DG, Nguyen HC, Lavery LA, et al. Off-loading the diabetic foot wound: a randomized clinical trial. Diabetes Care. 2001; 24:1019-1022.
Newton DJ, Khan F, Belch JJ, Mitchell MR, Leese GP. Blood flow changes in diabetic foot ulcers treated with dermal replacement therapy. J Foot Ankle Surg. 2002; 41:233-237.
Gentzkow GD, Iwasaki SD, Hershon KS, et al. Use of dermagraft, a cultured human dermis, to treat diabetic foot ulcers. Diabetes Care. 1996; 19:350-254.
Falanga V, Sabolinski M. A bilayered living skin construct (APLIGRAF) accelerates complete closure of hard-to-heal venous ulcers. Wound Repair Regen. 1999; 7:201-207.
Veves A, Falanga V, Armstrong DG, Sabolinski ML. Graftskin, a human skin equivalent, is effective in the management of noninfected neuropathic diabetic foot ulcers: a prospective randomized multicenter clinical trial. Diabetes Care. 2001; 24:290-295.
Sheehan P, Jones P, Caselli A, Giurini JM, Veves A. Percent change in wound area of diabetic foot ulcers over a 4-week period is a robust predictor of complete healing in a 12-week prospective trial. Diabetes Care. 2003; 26:1879-1882.
Oyibo SO, Jude EB, Tarawneh I, et al. The effects of ulcer size and site, patient’s age, sex and type and duration of diabetes on the outcome of diabetic foot ulcers. Diabet Med. 2001; 18:133-138.
Margolis DJ, Allen-Taylor L, Hoffstad O, Berlin JA. Diabetic neuropathic foot ulcers: the association of wound size, wound duration, and wound grade on healing. Diabetes Care. 2002; 25:1835-1839.

Authors

From St. Agnes Medical Center, Philadelphia, Pa.