Abstract
Background: Distal digital nerve repairs can present unique challenges for hand surgeons due to their sensitive location and ongoing difficulty obtaining soft tissue coverage in this region. Although autografts and nerve conduits have been shown to be of benefit with nerve gaps, they can have morbidities associated with their use. Nerve allografts have become a viable option over the past decade as their use has increased and data are now showing similar outcomes, particularly in short gap segments. Flaps and skin grafts are traditional coverage options for full thickness wounds but can pose challenges with multiple digit involvement, depth of wound, and critical structures exposed. Methods: We present a case where nerve allograft was used for distal digital nerve repair. Due to the distal nature of the nerve repair in the index digit distal to the trifurcation, the distal end of the nerve graft was connected to multiple small nerve ends. Dermal substitute was placed to achieve distal coverage of the affected digits. Results: At 6-month follow-up, the patient demonstrated improved strength, normal sensation, and full return of digital function. Conclusion: Nerve allograft can be used in combination with dermal skin substitute to achieve normal sensation and return of digital function following distal digital nerve injuries.
Keywords: dermal substitute, digital nerve, distal nerve injury, nerve allograft, nerve repair, digits, anatomy, allograft, basic science, composite tissue allotransplantation, nerve reconstruction, nerve, diagnosis, soft tissue reconstruction, trauma
Introduction
Traumatic hand injuries involving the digits happen frequently at home and in the workplace. Involvement with mechanical equipment is usually a common factor.1 In particular, distal digital injuries present difficult challenges due to the branching of small nerves and a scarcity of soft tissue in this area. Traditional approaches to nerve repair include primary repair, nerve conduits, and autografts, all of which aim to restore functional sensibility. Autografts have been the gold standard of treatment but have been complicated by increased operative time, trouble with harvest sites, and donor site comorbidities.2 Nerve conduits promote nerve regeneration by providing a guiding structure to bridge the gap created by a traumatic injury. They can, however, result in an unorganized distribution of nerve fibers as well as a decreased midgraft density when compared to allografts.3 In comparison, nerve allografts have shown promising results for nerve repair. Nerve allografts have demonstrated data showing improved functional and sensory outcomes when compared to nerve conduits.4 They have also shown similar outcomes when compared with autografts for short gap segments without donor site comorbidity.5 In their study of patients receiving processed nerve allograft, Taras et al6 reported an average Quick Disabilities of the Arm, Shoulder, and Hand score of 45 on the first post-operative visit, and no signs of graft rejection or infection. A separate study concluded that decellularized nerve allografts appeared to be well incorporated in the nerve repair site and were capable of returning adequate sensation in nerve defects ranging from 0.5 to 3 cm with no instances of rejection or infection.7
Goals of skin replacement include restoring adequate range of motion, pain reduction, and return of protective sensation. Flaps and skin grafts have been proposed with concomitant improvement in sensation and function, but the potential for donor site morbidity is always present as well as the difficulties presented by coverage in distal fingertip regions.8
Another option is the use dermal substitutes. Integra is a bilayer membrane system for skin replacement consisting of a dermal and epidermal substitute layer. The dermal layer has a defined degradation rate and consists of bovine tendon collagen and glycosaminoglycan with porous fibers. The epidermal layer consists of silicone to control moisture loss from the wound. The substitute converts to the histological appearance of native dermis after placement leading to improved functionality.9 In the following report, we discuss a case of the use of nerve allograft for a distal digital nerve repair and a dermal substitute to restore function and sensation after a distal digital injury in two fingers.
Methods
A 17-year-old male presented with full-thickness open wounds from a table saw to the left index and long digits along the radial contact surfaces of the pinch grip. Portions of the radial digital nerve were missing on both the index and long fingers. The long digit had an open wound with complete full-thickness skin loss of 3 x 1.8 cm2 on the volar radial aspect. The radial digital nerve of the long digit was missing for a length of 1.6 cm and was noted to be at the trifurcation of the nerve. The index digit had skin loss measuring 3.2 x 1.6 cm2 on the radial volar aspect of the digit at the P2 and P3 region. The radial digital nerve of the left index finger was missing with a 2.2-cm gap in zone 1 and zone 2 distal to the trifurcation.
Discussion was held with the patient and his mother regarding different treatment options. The patient did not wish to proceed with autograft because of additional incisions and donor site morbidity. After informed consent, they elected to move forward with allograft reconstruction of the nerves and dermal substitute for wound coverage.
In all, 1 to 2 mm in diameter allografts were selected to match the native nerve size in the digits. The allograft was positioned between ends of the nerve segments followed by a nerve connector over each anastomosis (Figure 1). Due to the distal nature of the nerve repair in the index digit distal to the trifurcation, the distal end of the nerve graft was connected to multiple small nerve ends.
Figure 1.
Digit injury with nerve in place.
Note. Allograft reconstruction of the left index and long digital radial nerves.
Due to multiple digits involved and difficulty gaining distal coverage of the fingers, we elected to place dermal substitute (Figure 2). For the long and index digit, we placed a piece of bilayer meshed integra directly over the nerve repair and wound which measured 3 x 1.8 cm2 and 3.2 x 1.6 cm2 in each digit, respectively. Xeroform bolsters were placed over the integra followed by a light compression wrap.
Figure 2.
Dermal substitute in place on digits.
Note. Placement of Integra dermal substitute over the grafted nerve in the left index and long digits.
The index digit was stabilized across the distal interphalangeal joint for 3 weeks with a pin and the silicone layer of the integra was removed from both digits at 3 weeks post-op and allowed to heal by secondary intention rather than grafting. The wounds were fully healed at 5 weeks.
Results
The patient was compliant with follow-up and attended rehabilitation therapy. Six months after follow-up, the patient reported improvements in strength and return of full range of motion. The patient subjectively reported normal sensation, and objective data in the form of a Semmes-Weinstein score of 2.83 correlated with these results (Figure 3). The 2-point discrimination was also normal. The patient presented with normal range of motion at his 6-month follow-up.
Figure 3.
Six-month post-injury.
Note. Healed wounds in index and long digit.
Discussions
Among the myriad of approaches to surgical reconstruction of nerves, autograft has long been the benchmark against which all other methods and materials are measured. Morbidities associated with the use of autograft call for further exploration of effective alternatives. In the case we present, it is evident that allograft placement is a viable replacement in cases of traumatic injury to digital nerves as it mitigates the unorganized distribution of nerve fibers found in nerve conduits as well as donor site morbidities found with autografts.3 Return of sensation was especially important in this case as the mechanism of injury caused deficits on the pinch surfaces of the radial aspects of his index and long fingers. Our use of nerve allografts for distal digital nerve gap repairs offers the hand surgeon another option for the restoration of normal sensation and function if there are concerns of donor site morbidity associated with the use of conduits or autografts.
Traditional options for dermal replacement include skin grafts and flaps taken from the patient’s own tissue. While these are used extensively for many injuries, the distal nature of the injuries and the multiple digits involved precluded these options. In this case, we used a dermal substitute to cover and protect the underlying subdermal structures including the nerve allograft. The porosity of this material allows it to better approximate the physiological function of the skin originally covering the wound, resulting in a more complete return to normal functionality as well as superior esthetic outcomes.
Conclusion
This case indicates that dermal skin substitute can be considered as an alternative to autograft and skin flaps in pursuit of increased functionality and reduced donor site morbidity. For these reasons, dermal skin substitute is beginning to find utility in complex hand reconstruction in cases with exposed structures resulting from trauma.10 Advances in surgical and technical approaches, as well as the use of appropriate tools and products can help allow a greater range of options in patient care following traumatic injuries.
Acknowledgments
The authors would like to thank Nancy Swinford, CCRC, Clinical Research Coordinator Texas Tech, and Joash Suryavanshi, BA, Texas Tech Health Sciences Center, School of Medicine.
Footnotes
Ethical Approval: This study was approved by our institutional review board.
Statement of Human and Animal Rights: This article does not contain any studies with human or animal subjects.
Statement of Informed Consent: This is a case report, and no informed consent is applicable given that no identifying information was used.
Declaration of Conflicting Interests: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding: The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This case report was internally funded by Texas Tech University Health Sciences Center Department of Orthopedic Surgery. We gratefully recognize the Shannon Holloway Chair in Orthopedic Surgery for their support of this department. The primary author and surgeon does not directly receive monetary compensation from any vendors. Texas Tech University Department of Orthopedics does receive some funding and grant awards to participate in the nationwide RANGER nerve allograft trial as well as investigating uses of AVIVE (human umbilical membrane) sponsored by Axogen.
ORCID iD: Desirae McKee 
https://orcid.org/0000-0002-2646-399X
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