Nerve Allografts: Current Utility and Future Directions.

Processed nerve allograft is a widely accepted tool for reconstructing peripheral nerve defects. Repair parameters that need to be considered include gap length, nerve diameter, nerve type (motor, sensory, or mixed), and the soft tissue envelope. Although the use of processed nerve allograft must be considered based on each unique clinical scenario, a rough algorithm can be formed based on the available animal and clinical literature. This article critically reviews the current surgical algorithm, defines the role of processed nerve allograft compared with nerve autograft, and discusses how this role may change in the future.

Usability of Nerve Tape: A Novel Sutureless Nerve Coaptation Device.

PURPOSE: Microsuture neurorrhaphy is technically challenging and has inherent drawbacks. This study evaluated the potential of a novel, sutureless nerve coaptation device to improve efficiency and precision. METHODS: Twelve surgeons participated in this study-six attending hand/microsurgeons and six trainees (orthopedic and plastic surgery residents or hand surgery fellows). Twenty-four cadaver arm specimens were used, and nerve repairs were performed at six sites in each specimen-the median and ulnar nerves in the proximal forearm, the median and ulnar nerves in the distal forearm, and the common digital nerves to the second and third web spaces. Each study participant performed nerve repairs at all six injury locations in two different cadaver arms (n = 12 total repairs for each participating surgeon). The nerve repairs were timed, tested for tensile strength, and graded for alignment and technical repair quality. RESULTS: A substantial reduction in time was required to perform repairs with the novel coaptation device (1.6 ± 0.8 minutes) compared with microsuture (7.2 ± 3.6 minutes). Device repairs were judged clinically acceptable (scoring "Excellent" or "Good" by most of the expert panel) in 97% of the repairs; the percentage of suture repairs receiving Excellent/Good scores by most of the expert panel was 69.4% for attending surgeons and 36.1% for trainees. The device repairs exhibited a higher average peak tensile force (7.0 ± 3.6 N) compared with suture repairs (2.6 ± 1.6 N). CONCLUSIONS: Nerve repairs performed with a novel repair device were performed faster and with higher technical precision than those performed using microsutures. Device repairs had substantially greater tensile strength than microsuture repairs. CLINICAL RELEVANCE: The evaluated novel nerve repair device may improve surgical efficiency and nerve repair quality.

Reverse Shoulder Arthroplasty for Irreparable Rotator Cuff Tear After Radial to Axillary End-to-Side Transfer: A Case Report.

CASE: A 60-year-old man sustained a massive irreparable rotator cuff tear and axillary nerve palsy with deltoid dysfunction after an anterior shoulder dislocation. He underwent staged reverse end-to-side radial-to-axillary nerve transfer with return of deltoid function allowing for subsequent reverse shoulder arthroplasty. At 1 year postoperatively, he returned to full activity. CONCLUSION: Irreparable rotator cuff tears complicated by axillary nerve palsy can be effectively treated with a staged approach of nerve transfer followed by reverse shoulder arthroplasty.

A Multicenter Prospective Randomized Comparison of Conduits Versus Decellularized Nerve Allograft for Digital Nerve Repairs.

PURPOSE: While there are advantages and disadvantages to both processed nerve allografts (PNA) and conduits, a large, well-controlled prospective study is needed to compare the efficacy and to delineate how each of these repair tools can be best applied to digital nerve injuries. We hypothesized that PNA digital nerve repairs would achieve superior functional recovery for longer length gaps compared with conduit-based repairs. METHODS: Patients (aged 18-69 years) presenting with suspected acute or subacute (less than 24 weeks old) digital nerve injuries were recruited to prticipate at 20 medical centers across the United States. After stratification to short (5-14 mm) and long (15-25 mm) gap subgroups, the patients were randomized (1:1) to repair with either a commercially available PNA or collagen conduit. Baseline and outcomes assessments were obtained either before or immediately after surgery and planned at 3-, 6-, 9-, and 12-months after surgery. All assessors and patients were blinded to the treatment arm. RESULTS: In total, 220 patients were enrolled, and 183 patients completed an acceptable last evaluable visit (at least 6 months and not more than 15 months postrepair). At last follow-up, for the short gap repair groups, average static two-point discrimination was 7.3 ± 2.8 mm for PNA and 7.5 ± 3.1 mm for conduit repairs. For the long gap group, average static two-point discrimination was significantly lower at 6.1 ± 3.3 mm for PNA compared with 7.5 ± 2.4 mm for conduit repairs. Normal sensation (American Society for Surgery of the Hand scale) was achieved in 40% of PNA long gap repairs, which was significantly more than the 18% observed in long conduit patients. Long gap conduits had more clinical failures (lack of protective sensation) than short gap conduits. CONCLUSIONS: Although supporting similar levels of nerve regeneration for short gap length digital nerve repairs, PNA was clinically superior to conduits for long gap reconstructions. TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic I.

Prophylactic Common Peroneal Nerve Release for Total Arthroplasty of the Valgus Knee: Surgical Technique and Early Outcomes.

Background: Common peroneal nerve (CPN) palsy after primary total knee arthroplasty represents a relatively rare but serious complication. Recently, there has been a growing interest in prophylactic CPN decompression in high-risk patients with significant combined valgus and flexion deformity. This study aimed to examine outcomes at our institution in those undergoing prophylactic CPN decompression at the time of total knee arthroplasty. Methods: A retrospective evaluation of a single-institution experience with selected patients at high risk for CPN palsy who underwent prophylactic nerve decompression through a separate incision at the time total knee arthroplasty was performed between July 1, 2018 and December 31, 2022. Patient demographics as well as perioperative and intraoperative clinical and radiographic measurements were collected and analyzed. Results: A total of 14 patients (15 knees) met our inclusion criteria. The mean preoperative femorotibial angle was 18.6° of valgus (range 13°-22°). The mean preoperative flexion contracture was 4.3° (range 0°-25°). The patients with flexion contractures preoperatively had a mean combined valgus/flexion contracture deformity of 28.8° (range 23°-38°) . There was preservation of nerve function in all knees. No knees required subsequent operative intervention within 90 days of surgery. Conclusions: Early experience with prophylactic CPN release in our high-risk population demonstrates preservation of nerve function in all patients and is reasonable to consider in patients with a large preoperative combined valgus/flexion deformity. Further studies with larger sample sizes would be beneficial in verification of the results with this technique, as well as determining an angular deformity threshold for which CPN release should be considered.

Surgical Treatment of Symptomatic End-Neuroma With a New Bioresorbable Copolyester Nerve Capping Device: A Multicenter Prospective Cohort Study.

BACKGROUND: Neuroma-induced neuropathic pain is associated with loss of function and reduced quality of life. No consistently effective standard-of-care treatment has been defined. Neurocap, a bioresorbable nerve capping device, has been designed to isolate the nerve stump from surrounding tissues to reduce development of symptomatic end-neuromas. METHODS: Patients with peripheral symptomatic end-neuromas were included in a prospective, multicenter, single-arm design. Data were collected presurgery up till 24 months postsurgery. Eligible patients with neuromas were identified based on blocks using anesthetic. Intervention included surgical excision and capping of the transected proximal nerve end with the Neurocap. Main outcome measures were pain, function, recurrence of symptomatic neuroma, use of analgesics, and adverse events. RESULTS: In total, 73 patients with 50 upper-extremity and 23 lower-extremity end-neuromas were enrolled. End-neuromas were predominately located in the digits and lower leg. Statistical power of the study outcomes was preserved by 46 of 73 patients completing 24-month follow-up. The mean VAS-Pain score at baseline was 70.2 ± 17.8 (scale 0-100) and decreased significantly to 31 ± 32.5 (P < 0.001). Function significantly improved over time. The recurrence rate of confirmed symptomatic neuroma was low (2 of 98 capped nerves). Adverse event rate was low and included pain and infection; there were no unexpected device-related adverse events. Most patients reported lower use of nonsteroidal anti-inflammatory drugs, opioids, and antineuropathic medications at last follow-up compared with baseline. CONCLUSIONS: End-neuroma treatment with excision and capping resulted in long-term significant reduction in reported pain, disability, and analgesic medication use. Adverse event rate was low.

Digital Nerve Injury: Assessment and Treatment.

Undertreated digital nerve injuries may result in sensory deficits and pain. Early recognition and treatment will optimize outcomes, and providers should maintain a high index of suspicion when assessing patients with open wounds. Acute, sharp lacerations may be amenable to direct repair while avulsion injuries or delayed repairs require adequate resection and bridging with nerve autograft, processed nerve allograft, or conduits. Conduits are most appropriate for gaps less than 15 mm, and processed nerve allografts have demonstrated reliable outcomes across longer gaps.

In Vivo Efficacy of a Novel, Sutureless Coaptation Device for Repairing Peripheral Nerve Defects.

Although microsuture neurorrhaphy is the accepted clinical standard treatment for severed peripheral nerves, this technique requires microsurgical proficiency and still often fails to provide adequate nerve approximation for effective regeneration. Entubulation utilizing commercially available conduits may enhance the technical quality of the nerve coaptation and potentially provide a proregenerative microenvironment, but still requires precise suture placement. We developed a sutureless nerve coaptation device, Nerve Tape®, that utilizes Nitinol microhooks embedded within a porcine small intestinal submucosa backing. These tiny microhooks engage the outer epineurium of the nerve, while the backing wraps the coaptation to provide a stable, entubulated repair. In this study, we examine the impact of Nerve Tape on nerve tissue and axonal regeneration, compared with repairs performed with commercially available conduit-assisted or microsuture-only repairs. Eighteen male New Zealand white rabbits underwent a tibial nerve transection, immediately repaired with (1) Nerve Tape, (2) conduit plus anchoring sutures, or (3) four 9-0 nylon epineurial microsutures. At 16 weeks postinjury, the nerves were re-exposed to test sensory and motor nerve conduction, measure target muscle weight and girth, and perform nerve tissue histology. Nerve conduction velocities in the Nerve Tape group were significantly better than both the microsuture and conduit groups, while nerve compound action potential amplitudes in the Nerve Tape group were significantly better than the conduit group only. Gross morphology, muscle characteristics, and axon histomorphometry were not statistically different between the three repair groups. In the rabbit tibial nerve repair model, Nerve Tape offers similar regeneration efficacy compared with conduit-assisted and microsuture-only repairs, suggesting minimal impact of microhooks on nerve tissue.

Biomechanical Testing of a Novel Device for Sutureless Nerve Repair.

Suboptimal nerve end alignment achieved with conventional nerve repair techniques may contribute to poor clinical outcomes. In this study, we introduce Nerve Tape®, a novel nerve repair device that integrates flexible columns of Nitinol microhooks within a biologic backing to entubulate, align, and secure approximated nerve ends. This study compares the repair strength of Nerve Tape with that of conventional microsuture repairs. Thirty small (2 mm) and 30 large (7 mm) diameter human cadaveric nerves were transected and repaired utilizing Nerve Tape or appropriate microsuture technique. Biomechanical testing was performed using a horizontal tensile tester. The repaired nerves were loaded until failure at a distraction rate of 40 mm/min, and the maximum failure load was determined. In the small nerve groups, the load-to-failure for Nerve Tape repairs (2.33 ± 0.66 N) was significantly higher than for suture repairs (1.22 ± 0.52 N; p < 0.05). In the large nerve groups, no significant difference in load-to-failure was found between Nerve Tape (7.45 ± 2.66 N) and suture repairs (5.82 ± 1.59 N: p = 0.12). Suture repairs tended to fail by rupture, whereas Nerve Tape failures resulted from microhook pullout. Nerve Tape is a novel nerve coaptation device that provides mechanical repair strength equal or greater to clinically relevant microsuture repairs.

Outcomes of Darrach and Sauvé-Kapandji Procedures: A Systematic Review.

BACKGROUND: To review the available literature on Darrach and Sauvé-Kapandji (SK) procedures and perform a systematic review to identify differences in clinical outcomes. We hypothesized that SK would have a higher complication rate without significant clinical benefit. METHODS: A literature search was conducted using PubMed, EMBASE, Cochrane Library, and SCOPUS (from inception to January 2020) to identify studies evaluating outcomes of Darrach and SK procedures. Primary outcome measures included the Quick Disabilities of the Arm, Shoulder, and Hand (QuickDASH) score, range of motion, grip strength, complications, and overall satisfaction. RESULTS: A total of 103 articles were identified and screened, and of these, 44 full-text articles were used for data extraction and qualitative analysis. Outcomes were similar for QuickDASH scores, grip strength, and range of motion, as was overall satisfaction. Specifically, satisfaction rates for stabilized SK and Darrach procedures in patients without rheumatoid arthritis were comparable at 70.2% and 72.6%, respectively. Average QuickDASH scores were similar (21 for Darrach and 29 for SK). Mechanical symptoms due to stump instability occur with either procedure but were higher with the Darrach procedure (12.5% compared with 6.8%). The SK had more surgery-related complications such as nonunions (2.3%), symptomatic hardware, and reoperations (6.8% compared with 3.2%). CONCLUSIONS: Both Darrach and SK procedures provide comparable satisfaction rates regardless of the underlying pathology. Improvement in range of motion, strength, and overall function is similar for both procedures; however, the reoperation rate is higher with SK.

Follistatin Protein Enhances Satellite Cell Counts in Reinnervated Muscle.

Background Muscle recovery following peripheral nerve repair is sup-optimal. Follistatin (FST), a potent muscle stimulant, enhances muscle size and satellite cell counts following reinnervation when administered as recombinant FST DNA via viral vectors. Local administration of recombinant FST protein, if effective, would be more clinically translatable but has yet to be investigated following muscle reinnervation. Objective The aim of this study is to assess the effect of direct delivery of recombinant FST protein on muscle recovery following muscle reinnervation. Materials and Methods In total, 72 Sprague-Dawley rats underwent temporary (3 or 6 months) denervation or sham denervation. After reinnervation, rats received FST protein (isoform FS-288) or sham treatment via a subcutaneous osmotic pump delivery system. Outcome measures included muscle force, muscle histomorphology, and FST protein quantification. Results Follistatin treatment resulted in smaller muscles after 3 months denervation ( p = 0.019) and reduced force after 3 months sham denervation ( p < 0.001). Conversely, after 6 months of denervation, FST treatment trended toward increased force output ( p = 0.066). Follistatin increased satellite cell counts after denervation ( p < 0.001) but reduced satellite cell counts after sham denervation ( p = 0.037). Conclusion Follistatin had mixed effects on muscle weight and force. Direct FST protein delivery enhanced satellite cell counts following reinnervation. The positive effect on the satellite cell population is intriguing and warrants further investigation.

Reverse End-to-Side (Supercharging) Nerve Transfer: Conceptualization, Validation, and Translation.

Partial nerve recovery either after expectant observation following an injury in-continuity or after nerve repair is not an uncommon occurrence. Historically, treatment strategies in these situations-late repair, revision repair, or acceptance of a mediocre result-were unsatisfying. The reverse end-to-side, or supercharging, nerve transfer was conceived to offer a more palatable option. Partially validated primarily through small animal research, supercharging has been rapidly translated to clinical practice. Many have extended the indications beyond the original intent, though the final place of this technique in the peripheral nerve surgeon's armamentarium is still yet to be determined.

Evaluation of the Induced Membrane for Neurotrophic Factors.

PURPOSE: Despite gaining popularity as a bridge for small and moderate nerve gaps, an acellular nerve allograft (ANA) lacks many of the neurotrophic characteristics of a nerve autograft. Pseudomembranes induced to form around temporary skeletal spacers are rich in growth factors. Induced membranes may have beneficial neurotrophic factors which could support ANA. METHODS: Twenty-two male Sprague-Dawley rats underwent resection of 2 cm of the sciatic nerve. A silicone rod was inset in the defect of 11 experimental rats, and marking sutures only were placed in the nerve stumps of the remaining 11 control rats. After allowing 4 weeks for tissue maturation, tissue samples harvested from the induced membrane (experimental group) and the tissue bed (control group) were analyzed using Luminex multiplex assay to quantify differences in detectable levels of the following neurotrophic factors: nerve growth factor, glial-derived nerve factor, vascular endothelial growth factor, and transforming growth factor ß (TGF-ß) 1, 2, and 3, interleukin-1ß, and monocyte chemoattractant protein 1. RESULTS: No difference was detected between the control and experimental groups in levels of vascular endothelial growth factor. Higher levels of TGF-ß1, TGF-ß2, TGF-ß3, glial-derived nerve factor, nerve growth factor, monocyte chemoattractant protein 1, and interleukin-1ß were detected in the experimental group. CONCLUSIONS: In the setting of peripheral nerve injury, an induced membrane has higher levels of several neurotrophic factors that may support nerve regeneration compared to wound bed cicatrix. CLINICAL RELEVANCE: This investigation provides impetus for further study examining the utility of using a staged induced membrane technique in conjunction with delayed nerve grafting in reconstruction of some peripheral nerve defects.

Comparison of Nylon Suture Versus 2 Fibrin Glue Products for Delayed Nerve Coaptation in an Animal Model.

PURPOSE: To compare 2 different, commercially available fibrin glue products with nylon suture with regard to repair strength, muscle function, and axon regeneration after delayed nerve repair in an animal model. METHODS: A total of 120 Lewis rats underwent transection of the sciatic nerve. On day 3 after transection, the nerves were reexposed. A primary repair was performed on 40 rats from each group using nylon suture, Tisseel fibrin glue, or Evicel fibrin glue. On days 0, 3, and 7 after repair, 10 rats from each group underwent burst strength testing. Seventy days after repair, 10 rats from each group underwent functional muscle testing and histomorphic analysis of the nerve, with the contralateral limb serving as the control. RESULTS: There was no significant difference in burst strength among the groups on days 0 and 3. On day 7, the burst strength of the Evicel and nylon suture groups was significantly greater than that of the Tisseel group. There were 5 total coaptation failures in both fibrin glue groups and none in the suture group. Seventy days after repair, tetanic muscle strength, muscle mass, axon inner diameter, and g-ratio were equivalent among all groups. Axon counts were equivalent between the nylon suture and Evicel groups, although in the nylon group axon counts were higher than for the Tisseel group. CONCLUSIONS: In an animal model with a 3-day delay in nerve repair, although dehiscences occurred, when the initial repair held, fibrin glue was not inferior to nylon suture with regard to repair strength and muscle recovery. CLINICAL RELEVANCE: Historical concerns regarding spontaneous fibrin glue-based nerve repair dehiscences are well-founded. However, when coaptation is maintained, commercially available fibrin glues support nerve regeneration.

Extensor Tendon Injuries in the Athlete.

An athlete's hands are susceptible to a variety of acute and cumulative traumas depending on their chosen sport. Depending on the timing of the injury, the immediate requirements of the athlete, and future aspirations, treatment strategies may need individual customization. This article offers a brief review of the anatomy and complex function of the extensor mechanism, discusses the etiologies of various extensor injuries, and outlines the multiple treatment options and expected outcomes.

Implantation of Acellular Nerve Allograft Using Nerve Connectors.

Background: Nerve connectors are short nerve conduits used to approximate nerve ends. Acellular nerve allografts are viable alternatives when direct repair is not possible but do not produce exudate essential for fibrin clot formation. We hypothesize that acellular nerve allograft implanted using nerve connectors must have end-to-end contact with the in situ nerve stumps to support nerve regeneration. Methods: Sixty Sprague Dawley rats underwent a 14-mm unilateral tibial nerve injury and subsequent repair using various combinations of acellular nerve grafts and nerve connectors. Proximal repairs for all groups utilized direct contact with the nerve stump within connector. Variations in distal repair methods (allograft length, nerve gap, and connector length) defined our 4 groups-group A: 14 mm allograft, no distal gap, and distal connector; group B: 11.5 mm allograft, 2.5 mm distal gap, and distal connector; group C: 9 mm allograft, 5 mm distal gap, and distal connector; group D: 14 mm allograft, no distal gap, and no distal connector. At 3 months post-repair, function and histomorphology were assessed. Results: Developed muscle force was significantly lower in group C (0.073 ± 0.077 N) compared with the other 3 groups (group A = 0.529 ± 0.312 N, group B = 0.461 ± 0.462 N, and group D = 0.409 ± 0.327 N). Axon counts were significantly lower in group C (2121 ± 389) compared with group A (6401 ± 855), group B (4710 ± 755), and group D (4450 ± 126). There was no statistically significant difference in G-ratios (myelination) between groups (P > .05). Conclusion: Nerve regeneration was significantly impaired as the gap distance between the distal end of the allograft and the distal nerve stump increased to 5 mm.

Side-to-side supercharging nerve allograft enhances neurotrophic potential.

INTRODUCTION: Critical limitations of processed acellular nerve allograft (PNA) are linked to Schwann cell function. Side-to-side bridge grafting may enhance PNA neurotrophic potential. METHODS: Sprague-Dawley rats underwent tibial nerve transection and immediate repair with 20-mm PNA (n = 33) or isograft (ISO; n = 9) or 40-mm PNA (n = 33) or ISO (n = 9). Processed acellular nerve allograft groups received zero, one, or three side-to-side bridge grafts between the peroneal nerve and graft. Muscle weight, force generation, and nerve histomorphology were tested 20 weeks after repair. Selected animals underwent neuron back labeling with fluorescent dyes. RESULTS: Inner axon diameters, g-ratios, and axon counts were smaller in the distal vs proximal aspect of each graft (P < .05). Schwann cell counts were greater, with a lower proportion of senescent cells for groups with bridges (P < .05). Retrograde labeling demonstrated that 6.6% to 17.7% of reinnervating neurons were from the peroneal pool. DISCUSSION: Bridge grafting positively influenced muscle recovery and Schwann cell counts and senescence after long PNA nerve reconstruction.

Viral vector delivery of follistatin enhances recovery of reinnervated muscle.

INTRODUCTION: Poor recovery following nerve repair is due to progressive temporal loss of muscle function. Follistatin (FS), a glycoprotein with anabolic properties, may enhance muscle recovery following reinnervation. METHODS: Seventy-two male Sprague-Dawley rats underwent temporary (3 or 6 month) denervation or sham denervation. After reinnervation, rats were administered adeno-associated viral vectors expressing FS deoxyribonucleic acid (isoform FS-317) injected into the target muscle or sham treatment. Final assessment included muscle function testing, muscle histomorphology, nerve histomorphology, and FS protein quantification. RESULTS: FS improved muscle mass and type IIB muscle fiber size, and increased G-ratios and mean axon diameter in the 6-month temporary denervation group (P < .05). Elevated FS protein levels were detected in treated muscle (P < .05). FS increased satellite cell counts following temporary denervation and repair (P < .05). DISCUSSION: FS treatment had anabolic, neurotrophic, and satellite cell stimulatory effects when administered following prolonged (6-month) temporary denervation and repair.

The Use of a Lumbrical Muscle Flap for Treatment of Chronic Tenocutaneous Fistula.

Tenocutaneous fistulas after trauma or open release of the A1 pulley provide a unique reconstructive challenge. We describe the use of a lumbrical muscle turnover flap as a novel technique for managing these wounds and present its successful use in a patient with a tenocutaneous fistula after A1 pulley release of the middle finger. This flap provides a simple, local reconstructive option in patients with an array of palmar wounds that have failed conservative management.