Prospective clinical study on digital nerve repair with collagen nerve conduits and review of literature

Potentially commercializable nerve guidance conduits for peripheral nerve injury: Past, present, and future

Peripheral nerve injuries are a prevalent global issue that has garnered great concern. Although autografts remain the preferred clinical approach to repair, their efficacy is hampered by factors like donor scarcity. The emergence of nerve guidance conduits as novel tissue engineering tools offers a promising alternative strategy. This review aims to interpret nerve guidance conduits and their commercialization from both clinical and laboratory perspectives. To enhance comprehension of clinical situations, this article provides a comprehensive analysis of the clinical efficacy of nerve conduits approved by the United States Food and Drug Administration. It proposes that the initial six months post-transplantation is a critical window period for evaluating their efficacy. Additionally, this study conducts a systematic discussion on the research progress of laboratory conduits, focusing on biomaterials and add-on strategies as pivotal factors for nerve regeneration, as supported by the literature analysis. The clinical conduit materials and prospective optimal materials are thoroughly discussed. The add-on strategies, together with their distinct obstacles and potentials are deeply analyzed. Based on the above evaluations, the development path and manufacturing strategy for the commercialization of nerve guidance conduits are envisioned. The critical conclusion promoting commercialization is summarized as follows: 1) The optimization of biomaterials is the fundamental means; 2) The phased application of additional strategies is the emphasized direction; 3) The additive manufacturing techniques are the necessary tools. As a result, the findings of this research provide academic and clinical practitioners with valuable insights that may facilitate future commercialization endeavors of nerve guidance conduits.

Non degradation of chitosan and initial degradation of collagen nerve conduits used for protection of nerve coaptations

BACKGROUND

Nerve conduits are either used to bridge nerve gaps of up to 3 cm or to protect nerve coaptations. Biodegradable nerve conduits, which are currently commercially available, include Chitosan or collagen-based ones. As histological aspects of their degradation are highly relevant for the progress of neuronal regeneration, the aim of this study was to report the histopathological signs of such nerve conduits, which were removed during revision surgery.

MATERIALS AND METHODS

Either Chitosan (n = 2) or collagen (n = 2) nerve conduits were implanted after neuroma resection and nerve grafting (n = 2) or traumatic nerve lesion after cut (n = 1) or crush injury (n = 1) in two females and two men, aged between 17 and 57 years. Revision surgery with removal of the nerve conduits was indicated due to persisting neuropathic pain and sensorimotor deficits, limited joint motion, or neurolysis with hardware removal at a median time of 17 months (range: 5.5-48 months). Histopathological analyses of all removed nerve conduits were performed.

RESULTS

A scar neuroma was diagnosed in one out of four patients. Mechanical complication occurred in one patient after nerve conduit implantation bridged over finger joints. Intraoperatively no or only initial signs of degradation of the nerve conduits were observed. Chitosan conduits revealed largely unchanged shape and structure of chitosan, and coating of the conduit by a vascularized fibrous membrane. The latter contained deposits taken up by macrophages, most likely representing dissolved chitosan. Characteristic histopathologic features of the degradation of collagen conduits were a disintegration of the compact collagen into separate fine circular strands, No foreign body reaction was observed in all removed nerve conduits.

CONCLUSIONS

Both Chitosan nerve conduits have not been degraded. The collagen nerve conduits showed a beginning degradation process. Furthermore, wrapping the repaired nerve with a nerve conduit did neither prevent adhesions nor improved nerve gliding. Therefore, biodegradation in time should be particularly addressed in further developments of nerve conduits.

Preparation of Collagen/Hydroxyapatite Composites Using the Alternate Immersion Method and Evaluation of the Cranial Bone-Forming Capability of Composites Complexed with Acidic Gelatin and b-FGF

Bone-substitute materials are essential in dental implantology. We prepared collagen (Col)/hydroxyapatite (Hap)/acidic gelatin (AG)/basic fibroblast growth factor (b-FGF) constructs with enhanced bone-forming capability. The Col/Hap apatite composites were prepared by immersing Col sponges alternately in calcium and phosphate ion solutions five times, for 20 and 60 min, respectively. Then, the sponges were heated to 56 °C for 48 h. Scanning electron microscopy/energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction analyses showed that the Col/Hap composites contained poorly crystalline Hap precipitates on the Col matrix. Col/Hap composite granules were infiltrated by AG, freeze-dried, and immersed in b-FGF solution. The wet quaternary constructs were implanted in rat cranial bone defects for 8 weeks, followed by soft X-ray measurements and histological analysis. Animal studies have shown that the constructs moderately increase bone formation in cranial bone defects. We found that an alternate immersion time of 20 min led to the greatest bone formation (p < 0.05). Constructs placed inside defects slightly extend the preexisting bone from the defect edges and lead to the formation of small island-like bones inside the defect, followed by disappearance of the constructs. The combined use of Col, Hap, AG, and b-FGF might bring about novel bone-forming biomaterials.

Bioengineered nerve conduits and wraps for peripheral nerve repair of the upper limb

BACKGROUND

Traumatic peripheral nerve injury is common and incurs significant cost to individuals and society. Healing following direct nerve repair or repair with autograft is slow and can be incomplete. Several bioengineered nerve wraps or devices have become available as an alternative to direct repair or autologous nerve graft. Nerve wraps attempt to reduce axonal escape across a direct repair site and nerve devices negate the need for a donor site defect, required by an autologous nerve graft. Comparative evidence to guide clinicians in their potential use is lacking. We collated existing evidence to guide the clinical application of currently available nerve wraps and conduits.

OBJECTIVES

To assess and compare the effects and complication rates of licensed bioengineered nerve conduits or wraps for surgical repair of traumatic peripheral nerve injuries of the upper limb. To compare effects and complications against the current gold surgical standard (direct repair or nerve autograft).

SEARCH METHODS

We used standard, extensive Cochrane search methods. The latest search was 26 January 2022. We searched online and, where not accessible, contacted societies' secretariats to review abstracts from the British Surgical Society of the Hand, International Federation of Surgical Societies of the Hand, Federation of European Surgical Societies of the Hand, and the American Society for Peripheral Nerve from October 2007 to October 2018.

SELECTION CRITERIA

We included parallel group randomised controlled trials (RCTs) and quasi-RCTs of nerve repair in the upper limb using a bioengineered wrap or conduit, with at least 12 months of follow-up.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane procedures. Our primary outcomes were 1. muscle strength and 2. sensory recovery at 24 months or more. Our secondary outcomes were 3. British Medical Research Council (BMRC) grading, 4. integrated functional outcome (Rosén Model Instrument (RMI)), 5. touch threshold, 6. two-point discrimination, 7. cold intolerance, 8. impact on daily living measured using the Disability of Arm Shoulder and Hand Patient-Reported Outcome Measure (DASH-PROM), 9. sensory nerve action potential, 10. cost of the device, and 11. adverse events (any and specific serious adverse events (further surgery)). We used GRADE to assess the certainty of the evidence.

MAIN RESULTS

Five studies involving 213 participants and 257 nerve injuries reconstructed with wraps or conduits (129 participants) or standard repair (128 participants) met the inclusion criteria. Of those in the standard repair group, 119 nerve injuries were managed with direct epineurial repair, and nine autologous nerve grafts were performed. One study excluded the outcome data for the repair using an autologous nerve graft from their analysis, as it was the only autologous nerve graft in the study, so data were available for 127 standard repairs. There was variation in the functional outcome measures reported and the time postoperatively at which they were recorded. Mean sensory recovery, assessed with BMRC sensory grading (range S0 to S4, higher score considered better) was 0.03 points higher in the device group (range 0.43 lower to 0.49 higher; 1 RCT, 28 participants; very low-certainty evidence) than in the standard repair group (mean 2.75 points), which suggested little or no difference between the groups, but the evidence is very uncertain. There may be little or no difference at 24 months in mean touch thresholds between standard repair (0.81) and repair using devices, which was 0.01 higher but this evidence is also very uncertain (95% confidence interval (CI) 0.06 lower to 0.08 higher; 1 trial, 32 participants; very low-certainty evidence). Data were not available to assess BMRC motor grading at 24 months or more. Repair using bioengineered devices may not improve integrated functional outcome scores at 24 months more than standard techniques, as assessed by the Rosén Model Instrument (RMI; range 0 to 3, higher scores better); the CIs allow for both no important difference and a better outcome with standard repair (mean RMI 1.875), compared to the device group (0.17 lower, 95% CI 0.38 lower to 0.05 higher; P = 0.13; 2 trials, 60 participants; low-certainty evidence). Data from one study suggested that the five-year postoperative outcome of RMI may be slightly improved after repair using a device (mean difference (MD) 0.23, 95% CI 0.07 to 0.38; 1 trial, 28 participants; low-certainty evidence). No studies measured impact on daily living using DASH-PROM. The proportion of people with adverse events may be greater with nerve wraps or conduits than with standard techniques, but the evidence is very uncertain (risk ratio (RR) 7.15, 95% CI 1.74 to 29.42; 5 RCTs, 213 participants; very low-certainty evidence). This corresponds to 10 adverse events per 1000 people in the standard repair group and 68 per 1000 (95% CI 17 to 280) in the device group. The use of nerve repair devices may be associated with a greater need for revision surgery but this evidence is also very uncertain (12/129 device repairs required revision surgery (removal) versus 0/127 standard repairs; RR 7.61, 95% CI 1.48 to 39.02; 5 RCTs, 256 nerve repairs; very low-certainty evidence).

AUTHORS' CONCLUSIONS

Based on the available evidence, this review does not support use of currently available nerve repair devices over standard repair. There is significant heterogeneity in participants, injury pattern, repair timing, and outcome measures and their timing across studies of nerve repair using bioengineered devices, which make comparisons unreliable. Studies were generally small and at high or unclear risk of bias. These factors render the overall certainty of evidence for any outcome low or very low. The data reviewed here provide some evidence that more people may experience adverse events with use of currently available bioengineered devices than with standard repair techniques, and the need for revision surgery may also be greater. The evidence for sensory recovery is very uncertain and there are no data for muscle strength at 24 months (our primary outcome measures). We need further trials, adhering to a minimum standard of outcome reporting (with at least 12 months' follow-up, including integrated sensorimotor evaluation and patient-reported outcomes) to provide high-certainty evidence and facilitate more detailed analysis of effectiveness of emerging, increasingly sophisticated, bioengineered repair devices.

Long-term sensibility outcomes of secondary digital nerve reconstruction with sural nerve autografts: a retrospective study

Background

Recovery of sensibility after digital nerve injury is crucial for restoring normal hand function. We evaluated long-term outcomes of digital nerve reconstruction with autografts.

Methods

This retrospective study included patients who underwent secondary reconstruction of digital nerves with nerve autografting. Recovery of sensibility was evaluated based on the following: patient self-assessment, two-point discrimination (2PD), and a total sensation score (sum of proprioception, temperature sensation, and sharp/dull discrimination). Mixed models regression was used to study predictors of sensibility outcomes. The predictors analyzed were age, sex, smoking status, number of fingers involved in a patient (as a measure of injury severity), time to reconstruction, and time to follow-up.

Results

In 61 patients, 174 digital nerves in 126 fingers were reconstructed after an average of 33.1 weeks from injury. The mean follow-up was 6.4 years from reconstruction. The mean graft length was 3.6 cm. Self-rated sensibility in the affected area was very good in 13% of patients, good in 33%, satisfactory in 40%, and poor in 24%. 2PD at 6 mm was present in 17% of patients, at 10 mm in 12%, and at 15 mm in 18% (mean 2PD was 10.8). Proprioception was preserved in 107 (85%) fingers, sensation of temperature was preserved in 99 (75%) of fingers, and sharp/dull discrimination in 88 (70%) fingers. Time from injury to reconstruction was the only significant predictor of the total sensation score.

Conclusion

Our data indicate that earlier reconstruction is associated with a favorable outcome.

Modification of tubular chitosan-based peripheral nerve implants: applications for simple or more complex approaches

Surgical treatment of peripheral nerve injuries is still a major challenge in human clinic. Up to now, none of the well-developed microsurgical treatment options is able to guarantee a complete restoration of nerve function. This restriction is also effective for novel clinically approved artificial nerve guides. In this review, we compare surgical repair techniques primarily for digital nerve injuries reported with relatively high prevalence to be valuable attempts in clinical digital nerve repair and point out their advantages and shortcomings. We furthermore discuss the use of artificial nerve grafts with a focus on chitosan-based nerve guides, for which our own studies contributed to their approval for clinical use. In the second part of this review, very recent future perspectives for the enhancement of tubular (commonly hollow) nerve guides are discussed in terms of their clinical translatability and ability to form three-dimensional constructs that biomimick the natural nerve structure. This includes materials that have already shown their beneficial potential in in vivo studies like fibrous intraluminal guidance structures, hydrogels, growth factors, and approaches of cell transplantation. Additionally, we highlight upcoming future perspectives comprising co-application of stem cell secretome. From our overview, we conclude that already simple attempts are highly effective to increase the regeneration supporting properties of nerve guides in experimental studies. But for bringing nerve repair with bioartificial nerve grafts to the next level, e.g. repair of defects > 3 cm in human patients, more complex intraluminal guidance structures such as innovatively manufactured hydrogels and likely supplementation of stem cells or their secretome for therapeutic purposes may represent promising future perspectives.

Sensory Outcomes in Digital Nerve Repair Techniques: An Updated Meta-analysis and Systematic Review

Background: Injuries to digital nerves are common with trauma to the hand, often requiring surgery. Surgical management of these injuries can be performed using several techniques: direct repair (neurorrhaphy), autograft, allograft, and conduit repair. In light of increasing the availability and use of various digital nerve repair techniques, a new systematic review and meta-analysis was undertaken to comparatively review the available evidence to determine any differences in outcomes to better guide treatment in cases with digital nerve gaps. Methods: Current literature on sensory outcomes of various digital nerve repair techniques was reviewed using static 2-point discrimination (S2PD), moving 2-point discrimination (M2PD), Semmes-Weinstein monofilament testing (SWMF), and complication rates as outcomes of interest. After inclusion and exclusion criteria were applied, 15 articles were reviewed and 625 nerve repairs were analyzed. Results: The average gap length for allograft repair, autograft repair, and conduit repair was 15.4, 24.7, and 13.4 mm, respectively. For S2PD outcomes, autograft repair was statistically superior to all other forms of repair. Allograft trended higher than neurorrhaphy and conduit repair, but results were not statistically significant. For SWMF outcomes, autograft repair was statistically superior to conduit repair and neurorrhaphy; it was statistically comparable with allograft repair. Allograft performed statistically superior to conduit repair relative to M2PD. Conclusions: Based on the current updated meta-analysis using newer data and techniques, we found that all available techniques have reasonable outcomes. Yet when managing a digital nerve injury with a gap, thereby excluding direct neurorrhaphy, both autograft and allograft performed comparably and were superior to conduit repair.

Anatomical Considerations to Optimize Sensory Recovery in Breast Neurotization with Allograft

Background:

Breast numbness is a recognized problem following mastectomy and subsequent reconstruction. Contemporary literature acknowledges the positive role of breast neurotization, but it is characterized by a variety of technical approaches and substantial heterogeneity with respect to the degree of recovered sensibility that remains suboptimal in comparison with other sensory nerve reconstructions. This study’s purpose was to provide an anatomical basis for observed inconsistencies and therein provide a principle that can be used to develop a technical approach that will optimize sensory recovery.

Methods:

Anatomical dissections on 6 fresh cadavers, that is, 12 hemi-abdominal flaps and 12 hemi-chest dissections, were performed. The technical aspects of harvesting the abdominal flap with a nerve target, that is, inclusion of a sensory nerve branch only, recipient nerves in the chest, and the applications of allograft for acquired nerve gap reconstruction were investigated.

Results:

Abdominal flaps that include sensory-only intercostal nerve 10–12 segments and identification of recipient chest wall intercostal nerves 2–4 could be consistently performed. The dissection and extraction of the donor sensory nerve target allowed preservation of the motor rectus innervation. The acquired nerve gap was easily bridged by an interposing allograft, allowing free arch of rotation for flap inset, suitable for either single or dual neurotization.

Conclusions:

We provide a likely anatomical explanation for suboptimal sensory recovery after deep inferior epigastric perforator (DIEP) flap breast neurotization, as mixed intercostal autograft is prohibitive to maximal sensory recovery. Breast neurotization with allograft that bridges sensory donor intercostal nerves to sensory recipient intercostal nerves should anatomically optimize restoration of breast sensibility.

An Optimized Collagen-Fibrin Blend Engineered Neural Tissue Promotes Peripheral Nerve Repair

Tissue engineering approaches in nerve regeneration often aim to improve results by bridging nerve defects with conduits that mimic key features of the nerve autograft. One such approach uses Schwann cell self-alignment and stabilization within collagen gels to generate engineered neural tissue (EngNT). In this study, we investigated whether a novel blend of fibrin and collagen could be used to form EngNT, as before EngNT design a beneficial effect of fibrin on Schwann cell proliferation was observed. A range of blend formulations was tested in terms of mechanical behavior (gel formation, stabilization, swelling, tensile strength, and stiffness), and lead formulations were assessed in vitro. A 90% collagen 10% fibrin blend was found to promote SCL4.1/F7 Schwann cell viability and supported the formation of aligned EngNT, which enhanced neurite outgrowth in vitro (NG108 cells) compared to formulations with higher and lower fibrin content. Initial in vivo tests in an 8 mm rat sciatic nerve model using rolled collagen-fibrin EngNT rods revealed a significantly enhanced axonal count in the midsection of the repair, as well as in the distal part of the nerve after 4 weeks. This optimized collagen-fibrin blend therefore provides a novel way to improve the capacity of EngNT to promote regeneration following peripheral nerve injury.

Nerve Repair with Nerve Conduits: Problems, Solutions, and Future Directions

Nerve conduits are becoming increasingly popular for the repair of peripheral nerve injuries. Their ease of application and lack of donor site morbidity make them an attractive option for nerve repair in many situations. Today, there are many different conduits to choose in different sizes and materials, giving the reconstructive surgeon many options for any given clinical problem. However, to properly utilize these unique reconstructive tools, the peripheral nerve surgeon must be familiar not only with their standard indications but also with their functional limitations. In this review, the authors identify the common applications of nerve conduits, expected results, and shortcomings of current techniques. Furthermore, future directions for nerve conduit use are identified.

Nerve wrap after end-to-end and tension-free neurorrhaphy attenuates neuropathic pain: A prospective study based on cohorts of digit replantation

The repair of injured peripheral nerve is still challenging for surgeons. The end-to-end and tension-free neurorrhaphy is the current gold standard for reconstruction after complete nerve transection without significant defect. The main objective of this study neurorrhaphy in digit replantation affects the sensory recovery and neuropathic pain in replanted digit. Total 101 patients who received replantation of single completely amputated digit were included for analysis in this study. In group I (n = 49), the digital nerves were repaired with end-to-end and tension-free neurorrhaphy and then wrapped into a tendon-derived collagen nerve conduit. In group II (n = 52), the digital nerves were repaired with end-to-end and tension-free neurorrhaphy only. The static two-point discrimination (s2PD) was performed to evaluate sensory recovery. Visual analog scale (VAS) scores of pain at rest and with exertion were measured respectively. The s2PD tests at three and six months after surgery did not show any significant difference between the two groups. The VAS scores at rest and with exertion of group I were significantly reduced compared with those of group II at three and six months after surgery. Thus, we concluded that nerve wrap into a collagen conduit after end-to-end and tension-free neurorrhaphy could attenuate neuropathic pain after digit replantation but have no benefit for sensory recovery.

Stem cell therapy for nerve injury

Peripheral nerve injury has remained a substantial clinical complication with no satisfactory treatment options. Despite the great development in the field of microsurgery, some severe types of neural injuries cannot be treated without causing tension to the injured nerve. Thus, current studies have focused on the new approaches for the treatment of peripheral nerve injuries. Stem cells with the ability to differentiate into a variety of cell types have brought a new perspective to this matter. In this review, we will discuss the use of three main sources of mesenchymal stem cells in the treatment of peripheral nerve injuries.