A Biodegradable Polyurethane Dermal Matrix in Reconstruction of Free Flap Donor Sites

A Pilot Study

Marcus J.D. Wagstaff, BSc(Hons), MBBS, PhD, FRCS(Plast), FRACS; Bradley J. Schmitt, BAppSc, MPhys; Patrick Coghlan, MBBS; James P. Finkemeyer, BBioMedSci, BMBS; Yugesh Caplash, MBBS, MS, MCh, FRACS; John E. Greenwood, AM, BSc(Hons), MBChB, MD, DHlthSc, FRCS(Eng), FRCS(Plast), FRACS

Disclosures

ePlasty. 2015;15 

In This Article

Discussion

Safety

In all cases, BTM was tolerated without symptom or sign of adverse reaction or hypersensitivity. Surrounding inflammation was attributable to either infection (patient 2) or reaction to poliglecaprone sutures (patient 7). No pain was reported in any donor site that was attributable to the BTM. Infection is addressed in a later section.

Surgical Experience

The BTM implantation was straightforward, and fixation rapid with staples. Overdressing was determined by our routine protocols for existing dermal templates.

Integration and Donor Site Variability

Rate of BTM integration differed between patients and donor sites. The determination that vascular integration is complete was subjective and based on our experience of the appearance of the matrix after delamination in successful porcine studies.[4] Integrated BTM is adherent to its bed and displays a fine granulating superficial surface. The bonded seal is not designed to spontaneously delaminate once integration to the matrix surface has occurred. We had expected from these studies that the BTM would sustain skin grafting after 2 weeks. With patient 1, we learned that in humans this is not necessarily the case. In this case, the flap itself and the skin graft donor site healing were also delayed. Young, growing pigs with a strong immune system integrate BTM more rapidly than older, morbid, paraneoplastic human patients undergoing major and sometimes repeated surgical insult, enduring catabolic states and prolonged recovery times. We learned that longer times for integration are necessary in such patients.

The ALT and FOC donor sites appeared to integrate BTM at 3 to 4 weeks. The RF/UF donor sites required approximately 5 weeks to integrate over the volar wrist tendons.

The ALT donor site has a septum between rectus femoris and vastus lateralis opened to dissect free the perforators and pedicle of the flap. Such intra- and intermuscular dissection can traumatize and devascularize adjacent muscle. This open septum is sutured closed, prior to application of a split-skin graft routinely. Five days of bed rest allows skin graft to adhere to the bed; however, BTM appears to adhere more slowly. There may be a shear effect due to differential movement of the adjacent sutured muscles, inhibiting adherence of the BTM. Fluid can then collect underneath the BTM to form a small seroma (patient 1). We intervened in this situation with full-thickness BTM removal in this area. In patients 2 and 8 however, significant donor site complications secondary to underlying infection or necrotic muscle also required full-thickness removal of areas of BTM. We recommend careful debridement of any devitalized muscle at flap harvest, and closure of the septum over a drain.

The FOC donor site creates a deep cavity, which requires a drain and closure in layers. The BTM failed to adhere over the exposed distal peroneus longus tendon area in patient 3. This portion of the BTM was removed before grafting, leaving a defect over the tendon, which subsequently also failed to support overlying skin graft take. This was considered small enough to heal by secondary intention. This indicated that BTM integration over tendons takes longer, and further time should be allowed for this to occur, which modified our protocol for the later forearm flaps. In the authors' experience, skin grafts alone in this site can fail and this can be prevented with a fascial-sparing approach. This was performed with success for patients 4 and 5.

The RF/UF donor sites have a convoluted base over tendons with preserved paratenon. These patients usually receive a forearm splint for 5 days to protect the skin graft from shear stress due to movement and this was increased to 7 days in this series. There was a tendency for tissue fluid to collect under the seal, encouraging blebs of delamination from 2 weeks postapplication. Secondary infection occurred in 2 such patients (9 and 10). The seal was windowed allowing fluid escape, resulting in control of the infection and preservation of the BTM through to integration. While skin grafts are routinely fenestrated in flap donor sites, the BTM seal is not (to prevent tissue ingrowth beyond the superficial surface of the BTM, which led to contraction in earlier unsealed matrices).[1–4] In response to these findings, the BTM seal was hand-fenestrated for the second cohort (an ongoing trial).

Infection

Any open wound and long-term synthetic implant carry with it a risk of infection, particularly if it remains exposed to the outside world via dressings. The BTM is no exception, although this risk has not yet been quantified. Localized infection was confirmed in 4 cases (patients 2, 8, 9, and 10). While 1 infection appeared attributable to muscle necrosis, the other 3 involved the BTM itself. Only patient 8 described considerable discomfort in the donor site overlying the abscess deep to the necrotic muscle. In this case, the BTM did not adhere over necrotic tissue and 16% was excised to debride muscle and drain the abscess. The wound responded to topical negative pressure therapy, and the remaining adjacent BTM integrated and was successfully skin grafted 1 week later. Patient 2 suffered a significant infection, which was treated nonoperatively with partial full-thickness removal of BTM (37%) and daily dressing changes until eradicated. In patients 9 and 10, partial removal of the seal alone allowed fluid escape and integration to continue without removal of any BTM. In all of these cases, the remaining BTM persisted to integration and ultimately sustained split-skin graft take.

Delamination

The BTM seal was removed (delamination), by peeling with nontoothed forceps. The seal fragmented, requiring piecemeal removal in all patients. In a small wound, piecemeal delamination merely lengthened the process. However, this material is designed for use in major burn injury, where prolonged delamination might result in patient morbidity. This prompted immediate investigation into newer seals and seal-bonding methods in separate in vitro and in vivo animal studies. These improvements have already been tested in vivo in our porcine model, where rapid and single action delamination was observed.[7] These new BTMs have been introduced in the human pilot burn trial and during their ongoing use in free flap donor site reconstruction.

Skin Grafting

Skin grafts were fixed over the integrated BTM with either suture or staples. The choice did not affect graft-take. Like other dermal templates, graft adherence is slightly delayed (compared to routine wound skin grafting) by 24 to 36 hours. We would recommend leaving the postsurgical dressing intact for 5 days, and delaying the commencement of physiotherapy, to accommodate this.

Wound Area

With a small number of patients, further separated into donor site groups, meaningful interpretation is difficult. Overall, the mean initial wound area decreases by 3.87% by the time of grafting (20–50 days). In our experience, this is less than wounds left to heal over these periods by secondary intention, supported by our research experience with control wounds in animals.[9,14]

The FOC and ALT donor sites initially increased in area. The wound bed muscles appeared to swell initially and then subside, and changes in measured wound area might be due to muscle volume changes altering the convexity of the limb and the measurement. After about 50 days in all 3 ALT patients, wound areas started to increase again, with the sole patient to survive to 12 months having a final wound area 118.6% of the original. Wound areas appeared to stabilize in the FOC patients after around day 80.

The RF/UF donor sites are flat or concave, with deeper grooves around the tendons. In these, the need for early, partial delamination in 3 patients facilitated granulation tissue formation and wound contraction.[4] In all but the final patient (who suffered some graft loss over the tendon that healed by secondary intention and underwent more marked contraction), wound areas stabilized after around day 80.

These results are in keeping with our anecdotal experience of wound contraction, which tends to be at its most marked up to 90 days after split-skin grafting. With the exception of the ALT donor sites, even in an uneventful course, these data suggest that some wound contraction does occur, however without a larger scale randomized controlled trial comparison against an alternative dermal substitute, or immediate split-skin grafting, interpretation regarding resistance to contraction is not possible.

Scar Outcomes

Results for both the POSAS and MAPS scales favored the lower end of the scales indicating good scar characteristics and cosmetic outcome. A mean MAPS score of 1.88 in this study falls within mean scores of 1.5 (<10% grafting) and 2.4 (>10% grafting) previously reported by Jarrett et al[26] 1 year after split-skin grafting of burn injuries. In a previous study, a mean Vancouver Scar Scale score of 4.2 was reported among 13 patients who underwent radial free flap donor site coverage with Integra and split-skin graft (mean follow-up of 23.8 months).[27] Although comparison is difficult between scales, a mean MAPS score of 1.88 compares favorably. Mean follow-up time in this study was 370.88 days, indicating that there could also be more improvement as each scar matures and consequent further reduction in MAPS scores.

Mean POSAS total scores of 11.5 (Patient) and 15.75 (Observer) are lower than those reported for straight-line caesarean scars 1 year after wound closure.[28] Average scores of 2.63 (Observer) and 1.88 (Patient) in the current study are also lower than those reported 12 months after full-thickness burn injury.[29] These studies report on very different patient cohorts, with different etiologies and possibly different expectations.

Pain and itching have been reported to be a concern post–radial free flap donor site reconstruction. One study reported that 22% (patient group of 50) still had itching in their donor site over 6 months postprocedure,[30] while another found 26% of patients with pain 1 year postoperatively following radial free forearm flap, albeit a low rating (0.5) on a visual analogue scale.[31] Among the small sample in the present study, no patient reported itch or pain in their donor sites in the few weeks before undertaking the POSAS assessment.

Polymer Degradation and Histopathology

The NovoSorb biodegradable polyurethane has been designed to maintain physical strength and structure until 3 months postapplication. After this time point, progressive hydrolysis of the material results in matrix degradation and absorption. This process is illustrated in Fig 5.

Figure 5.

Punch biopsy sampling of integrated/overgrafted BTM. At 6 months (a), the 2-mm-thick material has undergone significant degradation and appears eroded with "rounded corners." By 9 months (b), degradation has progressed, the polymer fragments are smaller and appear more—"spaced out" and rounded. At 12 months (c), degradation and absorption are almost complete with microscopic remnants remaining. The remnants (boxed) are no larger than the multinucleate macrophages surrounding them. By 18 months (d), there is no residual polymer.

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