Palmar Resurfacing of the Hand With Porcine Urinary Bladder Extracellular Matrix Following Traumatic Injury

Soft tissue defects are common in traumatic injuries of the hand. These defects can vary in size and complexity.^1,2 Small defects and those that involve fewer layers of tissue can frequently be addressed using techniques at lower rungs on the reconstructive ladder, such as primary closure, vacuum-assisted closure, and tissue expansion. However, larger defects involving multiple organ systems often require complex reconstruction. Treatment decisions concerning larger defects depend on what type of functional tissue is needed to cover the deficit. 

Traditional techniques for soft tissue coverage of complex hand injuries include split-thickness skin grafts, reverse posterior interosseous artery flaps, sandwich temporoparietal free fascial flaps, composite osteocutaneous free flaps, radial forearm fascial-only flaps, and pedicled flaps.^3-5

Split-thickness skin grafts are often used owing to their accelerated graft take and low rates of primary contraction. Despite these advantages, split-thickness grafts do not provide specialized skin and exhibit decreased durability compared with full-thickness grafts. Thick, glabrous skin is required to sustain shearing forces at the palm; thus, split-thickness skin grafting is an unfavorable coverage option for palmar deficits. 

In an effort to address functional requirements of palmar reconstruction, full-thickness skin grafts have been used for their durability and improved functional approximation of the target tissue. With free flaps, the aim is to preserve exposed vital structures, allow for earlier mobilization, and improve aesthetic outcomes. Because of these advantages, free flaps have been associated with fewer operations and shorter hospital stay.^6-8 There is, however, a sharp learning curve associated with free flap reconstruction, and current techniques may not be practical at many institutions.⁹ The extensive monitoring required may prove resource prohibitive, even if surgeons are capable of performing the procedures.¹⁰ Free flaps are a high-risk, high-reward reconstructive option best suited to specialized centers. When an injury precludes other reconstructive options, the patient should be transferred to a facility with the resources to both perform the procedure and monitor the flap postoperatively.

Pedicled flaps have also been used in severe deficits involving multiple layers of soft tissue as they are thicker and vascularized. While structural features of free and pedicled flaps improve motor function compared with split-thickness grafting, adequate sensation is rarely achieved. Additionally, both free and pedicle flaps require a risk-benefit analysis given the incidence of flap failure and associated donor site morbidity.¹¹

More recently, acellular templates have become available as adjuncts to assist the body in healing soft tissue defects. In areas requiring highly specialized skin, such as the fingertips, dermal substitutes have been shown to facilitate regeneration of native tissue, leading to improved functional and sensory outcomes compared with flap coverage.¹² Palmar skin, much like the fingertips, is highly specialized with respect to durability and sensation. Compromises in either domain could lead to functional deficits in the affected hand. Given the similarity of the skin on the volar digits to that of the palmar surfaces, in the case reported herein acellular dermal matrix (ADM) was used to reconstruct a large palmar defect. 

Use of urinary bladder extracellular matrix (UBM) is increasing and more published literature on its use is available, with noted case studies of UBM used for definitive closure in the lower extremity^13,14; however, only one article details the use of extracellular matrix (ECM) on complex, traumatic injuries of the hand and upper extremity.² None of the cases published on ECM addresses coverage of the palmar surface of the hand. This case presents a novel use of this product in resurfacing 80% of a palm after postoperative necrosis following a table saw injury to the right volar palm at the distal crease.^13,14

A 43-year-old, right-hand dominant male presented with a table saw injury to the right volar palm at the level of the distal crease, with bony injury to the base of the right index finger (Figure 1). Hypertension was the only preexisting risk factor for postoperative complications. At the time of the injury, the patient had neurovascular injuries to the index, middle, ring, and small fingers; however, he had intact motor and sensory function as well as vascularity to the uninjured thumb. The patient initially underwent 2 revascularization procedures; open reduction and internal fixation of the fracture of the second metacarpophalangeal (MCP) joint; nerve repair with conduits for the digital nerves; repair of the flexor tendons in zone 2 to the index, middle, ring, and small fingers; and zone 5 extensor tendon repair of the index finger.

At 2 weeks postoperatively, wound necrosis was evident, ranging from epidermolysis to full-thickness skin necrosis along the central portion, with no evidence of infection (Figure 2). The patient was returned to the operating room for irrigation and debridement. The proximal aspect of the wound was closed with interrupted polypropylene suture. The remainder of the wound was not amenable to closure and was treated with topical application of micronized (or microparticle) UBM powder followed by application of a 5-cm × 7-cm sheet of UBM, effectively filling all areas with full-thickness defects along the distal palmar crease. The sheets were then covered with Xeroform (DeRoyal), Surgilube (HR Pharmaceuticals), and Telfa (Covidien), supplemented with light compressive dressing and splint. 

Several steps were performed in the first 6 weeks postoperatively. The UBM microparticles and UBM sheet were reapplied at 1 week postoperatively (Figure 3), followed by repeat microparticle application at weeks 2 and 3. One week after UBM application the patient was referred for physical therapy. As expected, at 2 weeks postoperatively lack of sensation to light touch persisted in the index, middle, ring, and small fingers owing to transected and recently repaired proper digital nerves. Although motor control of the flexor digitorum superficialis and flexor digitorum profundus remained intact, finger movement was not appreciable (Figure 4). At 4 weeks postoperatively, the patient had no significant change in sensation to the fingers; however, a positive Tinel sign was noted over the proximal digital nerves at the MCP joint crease. Overall sensation to the palmar region was improved, and the patient had 30° to 40° of wrist flexion and extension.

At 6 weeks postoperatively, near complete closure of the palmar wound was achieved, with no evidence of infection or necrosis (Figure 5). Although there was some difficulty with differential gliding and stiffness of the second MCP joint, the patient was able to touch the tips of his index and middle fingers to his thumb and showed significant improvement in range of motion (ROM). He exhibited 40° to 50° of active wrist flexion and extension and had intact sensation in the radial nerve distribution. At 9 weeks, ROM and strength continued to improve, and the patient was able to hold objects (Figure 6). 

At 3 months postoperatively, all wounds were closed except for a small, clean, superficial wound in the palm (Figure 7). The patient had improved strength with an advancing Tinel sign at and distal to the proximal interphalangeal (PIP) joints. At that time, measurements showed improved total active ROM of 105° for the index finger, 95° for the middle finger, 105° for the ring finger, and 80° for the small finger. 

At 5 months, all wounds were completely healed, and sensation had returned in the small and index fingers. The patient exhibited continued improvement in grip strength and sensation, with the Tinel sign present at the tips of all fingers. At that time, the patient was able to pass functional requirements and was deemed able to return to work. 

At 6 months, the patient returned to full duty manual construction work and reported continued improvement in function. He had sensation near the tip of the small finger as well as to the distal interphalangeal (DIP) joint of the remaining affected digits. Motion was improved in both the MCP and PIP joints, and the patient could make a tighter fist.

At 1-year follow-up, wounds were completely healed, with limited scarring. The patient exhibited 15° to 20° of flexion contracture at the PIP joints, consistent with expectations for repair of complex zone 2 flexor tendon lacerations.^15,16 All fingers were vascularly intact. Sensation was intact to the median, radial, and ulnar nerve distributions proximal to the DIP joint in the index, middle, and ring fingers, which was indicative of progressing regeneration (Figure 8). The patient also reported serial improvement in grip strength. At the time of this writing, nerve regeneration was expected to continue until the patient achieved intact sensation to the tips of all fingers of his right hand. 

As expected, some scar contracture occurred in the small and long digits, and a release procedure was discussed with the patient. Given that he had returned to full work and activity without pain or functional deficits, the patient elected to forgo contracture release at that time.

The palm of the hand is unique in that the epithelial basement membrane is tethered subcutaneously to the palmar fascia, allowing for resistance to shear forces as well as maximum mobility of tendinous structures in the deep fascia. Given this phenomenon, wound coverage must be as free from scar tissue and contracture as possible, ensuring a near anatomic end result for maximum function. Typically, these deficits are treated with free flaps and rotational flaps, each of which has strengths and weaknesses.

As previously mentioned, flaps address some goals of reconstruction, such as improved durability and early mobilization. However, donor site morbidity is chief among the complications associated with this method, and the graft does not accurately approximate the structure and sensory function of palmar tissue. Cho et al¹⁷ outlined one of the more innovative methods of volar tissue repair using a second toe plantar free flap to provide histologic equivalency. Although this method showed promising results compared with conventional donor tissue, 2 of 12 patients in that study demonstrated no significant sensory recovery. While recent case reports have described resurfacing of large palmar defects using novel methods such as medial plantar artery flaps and free intercostal artery perforator flaps, direct comparisons are difficult because the cause of injury and defect size are highly variable.^18-20 Time to healing of 6 to 16 months has been reported and is often determined by the extent of the initial soft tissue defect.^18-21

Acellular dermal matrix was developed by LifeCell and was first used in 1992 to treat burn injuries. Since then, the utility of ADM has grown to include treatment of a variety of soft tissue deficits ranging from periodontal plastic surgery to dermal regeneration in the upper extremity.²² HuMend (Omnia Health), AlloDerm (LifeCell), Puros Dermis (Zimmer Biomet), FlexHD (MTF Biologics), DermaMatrix (Synthes), AlloMax (CR Bard), and SurgiMend (Integra LifeSciences) are among the products offered by companies currently producing ADM.²³ These regenerative templates use a decellularized ECM as a structural scaffold for the regrowth of native cells. 

Human and xenograft ECM have been shown to trigger neovascularization and modulate in vitro cell growth patterns.²⁴ Human ECM has been associated with positive outcomes for various soft tissue reconstruction procedures, including diabetic ulcerations, traumatic and battle wounds, failed free flap procedures, and deep partial-thickness burns.^25-28 Extracellular matrix provides the much-needed scaffolding for reepithelialization via chemotaxis of non-senescent progenitor cells further supported with blood vessel formation to bolster the healing process at the site of injury. 

Urinary bladder matrix is a porcine ECM scaffold that has recently been used to facilitate remodeling of site-appropriate tissue.²⁹ Although UBM is decellularized, multiple growth factors maintained within an epithelial basement membrane make this scaffolding uniquely amenable to regeneration of native tissue with minimal scarring. Retained growth factors include vascular endothelial growth factor, fibroblast growth factor, epithelial growth factor, transforming growth factor-β, keratinocyte growth factor, hepatocyte growth factor, platelet-derived growth factor, and bone morphogenetic proteins.³⁰ The structure of intact basement membrane provides a stable substrate to regulate the layered proliferation, making it desirable for sustaining noninvasive growth of epithelial cells.^31,32 In turn, new epithelial cells serve to protect underlying tissue and stimulate nerve cell growth and fibroblast migration, as well as minimize wound contraction.²⁴

Infection following open wounds of the hand has been reported in the literature.³³ Delayed treatment of mutilating hand injuries is associated with infection and secondary loss of tissues resulting from exposure and desiccation.³⁴ However, UBM has intrinsic antimicrobial properties that help sterilize open wounds³⁵; the patient discussed in this case report was found to be free from infection at the 1-year follow-up visit. Degradation of the ECM present in UBM is thought to create peptide fragments with antimicrobial activity.³⁵ The UBM is ultimately absorbed and incorporated to the injury bed, minimizing the need for further postoperative wound care and the chance of infection.^13,36

Urinary bladder matrices can be divided into two broad categories—sheet UBM and micronized UBM. In the case reported herein, both were used to allow maximum regeneration while maintaining flexible coverage. Sheet UBM often is applied over more shallow tissue defects, while micronized UBM is injected into the deficit and covered with a layer of lubricant to prevent dehydration.³⁷

Micronized UBM may be favorable for deep deficits involving exposure of multiple tissue layers and organ systems. Owing to its increased surface area, micronized UBM comes in contact with more exposed tissue in complex injuries with multiple levels of depth.³⁸ More research is needed to directly compare micronized and sheet UBM in the treatment of severe defects.

In traumatic injuries of the hand with associated neurovascular compromise, the patient is at risk of a lack of revascularization as well as partial or complete amputation of the affected hand. After undergoing multiple revascularization procedures and the placement of ECM, the patient in this case retained motor and sensory function of his injured extremity, with continued improvement in functional outcomes. 

Patient satisfaction with aesthetics is a critical component of addressing soft tissue injuries. The patient discussed herein presented with minimal scarring and excellent aesthetic results following applications of human ECM on a mangled hand. The patient was satisfied with the results of the procedure and at the time of this writing remained content with the functional and aesthetic results. 

The present report is necessarily limited by the anecdotal nature of case reports. Severe palmar defects such as the one described herein are relatively rare, however, and prospective studies of this injury pattern with a large sample size may be untenable. Although the particulars of each clinical scenario vary, this case provides valuable data showing that UBM may be an effective treatment modality for definitive coverage of the palmar surface of the hand because it provides an initial scaffolding to facilitate native tissue regeneration and minimal scarring.

Traumatic wounds to the hand present a complex challenge to the reconstructive surgeon, with available techniques using either different biologic templates for final coverage via skin grafting or technically demanding, resource-heavy flaps for definitive coverage. Application of UBM for definitive coverage of the hand has yet to be reported in the literature; however, use of UBM has shown promise in the lower extremity, with burn contracture excision, and in one forearm wound with exposed muscle and tendon complicated by soft tissue infection.^2,14 Given the typical complications associated with a palmar defect of the size sustained by this patient and the success of this case, it is reasonable to conclude that UBM played a major role in achieving the final outcome of this particular patient.

The authors would like to thank Nancy Swinford, CCRC, Clinical Research Coordinator, Texas Tech University Health Sciences Center, for her assistance. 

Authors: Cy Daneshfar, MD; Joash Suryavanshi, BA; Hillary Powers Wall, BA; Cameron Cox, BA; and Brendan MacKay, MD

Affiliation: Department of Orthopaedic Surgery, Texas Tech University Health Sciences Center, Lubbock, TX

Correspondence: Brendan MacKay, MD, 3601 4th Street, Mail Stop 9436, Department of Orthopaedic Surgery, Texas Tech University Health Sciences Center, Lubbock, TX 79430-9436; brendan.j.mackay@ttuhsc.edu

Disclosure: Although not directly related to this article, the authors disclose that Brendan MacKay, MD, is a paid teacher for TriMed; teacher, consultant, and researcher support from AxoGen; and consultant for Baxter/Synovis and GLG. The authors disclose no financial or other conflicts of interest.