Intraoperative Nerve Identification Research Articles

A longitudinal study of the prevalence of post-surgical inguinodynia and the factors responsible for the development of chronic pain among the patients undergoing open hernioplasty at a tertiary care center

Background: Chronic groin pain (Inguinodynia) is a potential complication following inguinal hernia mesh repair and has a significant impact on the quality of life. The incidence varies among studies ranging between 0% and 62.9%. Aims and Objectives: The present study was conducted with the objectives of estimating the prevalence of post-surgical inguinodynia among the patients undergoing open hernioplasty. The secondary objective was to assess the factors associated with the development of post-surgical inguinodynia. Materials and Methods: A longitudinal study was carried out in a tertiary care center in Bangalore, Karnataka among the hernia patients attending the outpatient department of General Surgery department. A pro forma prepared with expert validation was used to collect details regarding pre-operative characteristics, type of anesthesia, intraoperative findings, and post-operative complications. The pain was assessed by the visual analog scale. Descriptive statistics and Chi-square test were used to identify the risk factors. Results: A total of 112 patients underwent hernioplasty. Out of this, 108 were males and 4 were females. The mean age of the patients was 48±10.8 years. Majority of them (84, 77.7%) presented with indirect inguinal hernia. The prevalence of inguinodynia at 3-month post-hernia surgery was 21.4% (n=24). Patients with significant pre-operative pain had higher chances of developing chronic pain (P=0.000). It was found that post-operative surgical site infection was associated with increased chances of development of chronic pain (P=0.000). Conclusion: Our study found that around one-fifth of the hernia patients had developed chronic post-surgical inguinal pain following open hernioplasty. There was no significant relationship between patients’ characteristics and development of chronic post-operative pain. The presence of pre-operative pain and post-operative infection in the patients was significantly associated with the development of chronic pain. Intraoperative nerve identification and chronic post-operative pain did not have a significant relationship in our study. Most of the patients who developed chronic pain had experienced only mild pain and none of them had severe inguinal pain. From the findings of our study, we would like to recommend that all measures must be taken to prevent and treat post-operative surgical site infection which leads to the development of chronic pain in patients.

The effect of intraoperative nerve identification technique on distally-based dorsal fasciocutaneous flap for thumb and fingertip reconstruction

IntroductionThumb and fingertip resurfacing continues to be a challenge for hand surgeons, as the treatment varies widely. Being donor nerves in the flap for sensory restoration, the dorsal cutaneous nerves in hand have been widely described in the literature. However, their applications in providing anatomical information to sufficiently harvest the longitudinal axis of a robust flap are usually underestimated. This study reports reconstruction of thumb and fingertip defects with the distally based dorsal fasciocutaneous (DDF) flap and explores the effect of intraoperative nerve identification technique on clinical outcomes. HypothesisThe nerve identification technique can contribute considerably to the improvement of flap circulation, with less risk of poor venous return. Materials and methodsA retrospective study was conducted in 89 patients who had thumb or fingertip defects treated with the DDF flap from February 2014 to June 2020. Patients were divided into two groups based on whether intraoperative nerve identification technique was used. Flap survival was evaluated. The follow-up was conducted by using smartphone or by face-to-face visit. Time for complete wound healing, time to return to work, hand performance, the total active motion of the joints and static two-point discrimination of flaps were analyzed. ResultsThe 46 flaps (group A) that underwent intraoperative nerve identification technique had an 8.7% venous congestion rate versus a 27.9% venous congestion rate in the 43 flaps (group B) without using nerve identification technique (p=0.018). The mean follow-up was 11.08 (range 6–26) months. Time for complete wound healing and time to return to work were significantly shorter in group A (p=0.026 and p=0.012). Michigan Hand Outcomes Questionnaire (MHQ) scores were similar between groups. In the face-to-face follow-up, there was no significant difference in the total active motion of the injured fingers and static two-point discrimination between the two groups (p=0.657 and p=0.182). DiscussionThe use of nerve identification technique could decrease the odds of postoperative venous congestion in DDF flap for thumb and fingertip reconstruction, and result in improved outcomes in terms of time for complete wound healing and time to return to work. Level of evidenceIII; retrospective comparative study.

DXM-TransFuse U-net: Dual cross-modal transformer fusion U-net for automated nerve identification.

Accurate nerve identification is critical during surgical procedures to prevent damage to nerve tissues. Nerve injury can cause long-term adverse effects for patients, as well as financial overburden. Birefringence imaging is a noninvasive technique derived from polarized images that have successfully identified nerves that can assist during intraoperative surgery. Furthermore, birefringence images can be processed under 20ms with a GPGPU implementation, making it a viable image modality option for real-time processing. In this study, we first comprehensively investigate the usage of birefringence images combined with deep learning, which can automatically detect nerves with gains upwards of 14% over its color image-based (RGB) counterparts on the F2 score. Additionally, we develop a deep learning network framework using the U-Net architecture with a Transformer based fusion module at the bottleneck that leverages both birefringence and RGB modalities. The dual-modality framework achieves 76.12 on the F2 score, a gain of 19.6 % over single-modality networks using only RGB images. By leveraging and extracting the feature maps of each modality independently and using each modality's information for cross-modal interactions, we aim to provide a solution that would further increase the effectiveness of imaging systems for enabling noninvasive intraoperative nerve identification.

COMPARISON OF RECURRENT LARYNGEAL NERVE (RLN) PALSY WITH AND WITHOUT INTRAOPERATIVE NERVE IDENTIFICATION DURING THYROIDECTOMY – A CROSS-SECTIONAL STUDY FROM A TERTIARY LEVEL HOSPITAL IN PESHAWAR

Background:Recurrent laryngeal nerve (RLN) palsy is one of the most common and feared complications of thyroid surgeries. These may be transient or permanent and occur unilaterally or bilaterally, in case of which fatal airway obstruction is possible.
 Objectives:To compare the incidence of RLN palsy with and without intraoperative nerve identification during thyroidectomy.
 Materials and Methods: This is a descriptive cross-sectional study spanning over 9 months during the period July 2020 to March 2021. A pool of 70 patients was included in the study comprising of 18 males and 52 females. Data on demographic, clinical and postoperative variables were compared in relation to RLN palsy.
 Results:The overall incidence of RLN palsy in the study pool was 7.1%. The rate of RLN palsy was 3.51% in the 81.42% cases where intraoperative nerve identification was done and 13.04% incidence was found the remaining 32.86% cases where the nerve was not identified. The incidence of RLN palsy was 14.82% in ages above 45 years, 11.11% in male, 14.29% after total thyroidectomy and 40% with follicular carcinoma.
 Conclusion:Intraoperative nerve identification is an essential step in any thyroid surgery and has proven beneficial in reducing the incidence of RLN palsy.
 
 

Improvement of nerve imaging speed with coherent anti-Stokes Raman scattering rigid endoscope using deep-learning noise reduction

A coherent anti-Stokes Raman scattering (CARS) rigid endoscope was developed to visualize peripheral nerves without labeling for nerve-sparing endoscopic surgery. The developed CARS endoscope had a problem with low imaging speed, i.e. low imaging rate. In this study, we demonstrate that noise reduction with deep learning boosts the nerve imaging speed with CARS endoscopy. We employ fine-tuning and ensemble learning and compare deep learning models with three different architectures. In the fine-tuning strategy, deep learning models are pre-trained with CARS microscopy nerve images and retrained with CARS endoscopy nerve images to compensate for the small dataset of CARS endoscopy images. We propose using the equivalent imaging rate (EIR) as a new evaluation metric for quantitatively and directly assessing the imaging rate improvement by deep learning models. The highest EIR of the deep learning model was 7.0 images/min, which was 5 times higher than that of the raw endoscopic image of 1.4 images/min. We believe that the improvement of the nerve imaging speed will open up the possibility of reducing postoperative dysfunction by intraoperative nerve identification.

A study on the recurrent laryngeal nerve injuries in thyroid surgeries at PESIMSR, Kuppam

Background: Thyroid surgeries are routinely performed by general surgeons all over India. Although the incidence of recurrent laryngeal nerve (RLN) injury is uncommon, it still carries a significant impact on patient’s quality of life post operatively. Hence this study was done to identify and discuss incidence and various factors involved in RLN injury.Methods: This is a prospective observational study carried out at a rural health care setup at PES Institute of Medical Sciences and Research (PESIMSR), Kuppam. A total of 60 patients who qualified the inclusion and exclusion criteria were studied from December 2016 to June 2018. All the patient data including relevant history, clinical findings, intra operative findings and post-operative follow up were recorded and the results were tabulated. Institutional ethics committee clearance was obtained before the start of the study.Results: Out of 60 patients 51 were females and 9 were males. 30 patients had unilateral involvement and the other 30 patients had bilateral involvement of thyroid lobes on clinical and ultrasound examination. On fine needle aspiration cytology (FNAC), 57 were benign, 2 were malignant and 1 was Hashimoto’s thyroiditis. Surgeries were done according to standard protocol. Intra operatively RLN was identified in 56 patients. In 3 of them there was a structural anomaly. Postoperative hoarseness of voice was seen in 8 patients, however long term vocal cord palsy was seen in 3 patients.Conclusions: This study shows the importance of intra-operative nerve identification, incidence of RLN injury and role of postoperative rehabilitation.

Evaluation of collimated polarized light imaging for real-time intraoperative selective nerve identification in the human hand.

Intraoperative peripheral nerve lesions are common complications due to misidentification and limitations of surgical nerve identification. This study validates a real-time non-invasive intraoperative method of nerve identification. Long working distance collimated polarized light imaging (CPLi) was used to identify peripheral radial nerve branches in a human cadaver hand by their nerve specific anisotropic optical reflection. Seven ex situ and six in situ samples were examined for nerves, resulting after histological validation, in a 100% positive correct score (CPLi) versus 77% (surgeon). Nerves were visible during a clinical in vivo observation using CPLi. Therefore CPLi is a promising technique for intraoperative nerve identification.

Laminin targeting of a peripheral nerve-highlighting peptide enables degenerated nerve visualization

Target-blind activity-based screening of molecular libraries is often used to develop first-generation compounds, but subsequent target identification is rate-limiting to developing improved agents with higher specific affinity and lower off-target binding. A fluorescently labeled nerve-binding peptide, NP41, selected by phage display, highlights peripheral nerves in vivo. Nerve highlighting has the potential to improve surgical outcomes by facilitating intraoperative nerve identification, reducing accidental nerve transection, and facilitating repair of damaged nerves. To enable screening of molecular target-specific molecules for higher nerve contrast and to identify potential toxicities, NP41's binding target was sought. Laminin-421 and -211 were identified by proximity-based labeling using singlet oxygen and by an adapted version of TRICEPS-based ligand-receptor capture to identify glycoprotein receptors via ligand cross-linking. In proximity labeling, photooxidation of a ligand-conjugated singlet oxygen generator is coupled to chemical labeling of locally oxidized residues. Photooxidation of methylene blue-NP41-bound nerves, followed by biotin hydrazide labeling and purification, resulted in light-induced enrichment of laminin subunits α4 and α2, nidogen 1, and decorin (FDR-adjusted P value < 10-7) and minor enrichment of laminin-γ1 and collagens I and VI. Glycoprotein receptor capture also identified laminin-α4 and -γ1. Laminins colocalized with NP41 within nerve sheath, particularly perineurium, where laminin-421 is predominant. Binding assays with phage expressing NP41 confirmed binding to purified laminin-421, laminin-211, and laminin-α4. Affinity for these extracellular matrix proteins explains the striking ability of NP41 to highlight degenerated nerve "ghosts" months posttransection that are invisible to the unaided eye but retain hollow laminin-rich tubular structures.

Improved facial nerve identification during parotidectomy with fluorescently labeled peptide.

Additional intraoperative guidance could reduce the risk of iatrogenic injury during parotid gland cancer surgery. We evaluated the intraoperative use of fluorescently labeled nerve binding peptide NP41 to aid facial nerve identification and preservation during parotidectomy in an orthotopic model of murine parotid gland cancer. We also quantified the accuracy of intraoperative nerve detection for surface and buried nerves in the head and neck with NP41 versus white light (WL) alone. Twenty-eight mice underwent parotid gland cancer surgeries with additional fluorescence (FL) guidance versus WL reflectance (WLR) alone. Eight mice were used for additional nerve-imaging experiments. Twenty-eight parotid tumor-bearing mice underwent parotidectomy. Eight mice underwent imaging of both sides of the face after skin removal. Postoperative assessment of facial nerve function measured by automated whisker tracking were compared between FL guidance (n = 13) versus WL alone (n=15). In eight mice, nerve to surrounding tissue contrast was measured under FL versus WLR for all nerve branches detectable in the field of view. Postoperative facial nerve function after parotid gland cancer surgery tended to be better with additional FL guidance. Fluorescent labeling significantly improved nerve to surrounding tissue contrast for both large and smaller buried nerve branches compared to WLR visualization and improved detection sensitivity and specificity. NP41 FL imaging significantly aids the intraoperative identification of nerve braches otherwise nearly invisible to the naked eye. Its application in a murine model of parotid gland cancer surgery tended to improve functional preservation of the facial nerve. NA Laryngoscope, 126:2711-2717, 2016.

Visualizing Oxazine 4 nerve-specific fluorescence ex vivo in frozen tissue sections.

Nerve damage plagues surgical outcomes and remains a major burden for patients, surgeons, and the healthcare system. Fluorescence image-guided surgery using nerve specific small molecule fluorophores offers a solution to diminish surgical nerve damage through improved intraoperative nerve identification and visualization. Oxazine 4 has shown superior nerve specificity in initial testing in vivo, while exhibiting a red shifted excitation and emission spectra compared to other nerve-specific fluorophores. However, Oxazine 4 does not exhibit near-infrared (NIR) excitation and emission, which would be ideal to improve penetration depth and nerve signal to background ratios for in vivo imaging. Successful development of a NIR nerve-specific fluorophore will require understanding of the molecular target of fluorophore nerve specificity. While previous small molecule nerve-specific fluorophores have demonstrated excellent ex vivo nerve specificity, Oxazine 4 ex vivo nerve specific fluorescence has been difficult to visualize. In the present study, we examined each step of the ex vivo fluorescence microscopy sample preparation procedure to discover how in vivo nerve-specific fluorescence is changed during ex vivo tissue sample preparation. Through step-by-step examination we found that Oxazine 4 fluorescence was significantly diminished by washing and mounting tissue sections for microscopy. A method to preserve Oxazine 4 nerve specific fluorescence ex vivo was determined, which can be utilized for visualization by fluorescence microscopy.

Long-term follow-up after mesh removal and selective neurectomy for persistent inguinal postherniorrhaphy pain

Persistent inguinal pain, influencing daily activities, is seen in about 5 % of patients following inguinal herniorrhaphy. Surgical treatment of patients with persistent postherniorrhaphy pain has been associated with pain relief and improvement in functional status. However, the detailed long-term outcome effects remain to be clarified. The aim of this study was to determine the long-term effects of mesh removal and selective neurectomy in patients with persistent postherniorrhaphy pain after previous open repair. The study consecutively included 54 inguinal postherniorrhaphy pain patients treated with mesh removal and aimed neurectomy. Patients completed questionnaires evaluating pain intensity with a numerical rating scale (NRS) and pain-related functional impairment preoperatively, and, 3, 6, 12, 24, and 36 months postoperatively. Endpoints were changes in pain intensity and functional ability when comparing preoperative and postoperative assessments. Pain intensities (average, maximum, and during activity) were significantly lower at all time points during follow-up compared to preoperative values (p < 0.01 for all) with a reduction in median (IQR) average pain intensity from 6.0 (5.0-7.0) preoperatively to 3.0 (1.0-5.5) at 36-month follow-up. There was no association between positive pain outcome and intraoperative nerve identification (p = 0.47). The number of patients who reported a long-term negative effect of the operation (≥ 25 % increase in average pain intensity at 36-month follow-up) was 1 of 8. The functional ability was improved at 3 months after the operation (p < 0.01), but the improvement was not statistically significant in the follow-up period. Preoperative signs of depression, anxiety, and catastrophizing had no influence on outcome. Mesh removal and attempted neurectomy may provide long-lasting analgesic effects in most patients and with a small proportion being worse, without relation to pain history and operative findings. Detailed multicenter collaboration is required to define preoperative diagnostics and the indication for mesh removal and neurectomy, the exact surgical procedure (type of neurectomy) and with detailed follow-up.

Intraoperative nerve identification and chronic postherniorrhaphy pain

First of all, we thank Drs. Chen and Amid [1] for their very thoughtful comments and update on the role of intraoperative nerve identification during groin hernia repair and the risk of development of chronic pain. We agree with all their comments, except that our conclusions in the abstract does not ‘‘conclude that nerve identification does not decrease rates of pain in routine practice’’ as quoted, but rather that ‘‘although intraoperative inguinal nerve identification should be aimed at, other factors may contribute to the risk of nerve damage and persistent pain after open groin hernia repair’’ [2]. This conclusion supports the comments by Chen and Amid [1], despite that we in the present study were not able to demonstrate any influence of nerve identification on signs of nerve damage or on development of persistent pain. The discussion on identification of the ‘‘genitofemoral nerve’’ (which we entirely agree should be named ‘‘genital branch’’) is to some extent semantic as we agree that routine direct identification should not be done, but only if necessary for the herniotomy per se. This may explain our low identification rate of the genital branch (21.3 %) which, interestingly, is within the same range as reported from a recent hernia specialist publication on persistent pain problems, with an identification rate of 26.5 % [3]. Also, we agree that the use of heavy-weight mesh may have contributed to the pain problems, but when the study was conducted there was little conclusive evidence for differences between mesh type and persistent pain. In summary, the valuable comment by Drs. Chen and Amid provides a sound balance on this important (but also difficult) topic of persistent postherniorrhaphy pain compared to our rather negative findings [1]. We entirely support their conclusion that surgical technique is a crucial component to reduce this disturbing problem.

Erratum to: Questioning the favorable influence of nerve identification during open inguinal herniorrhaphy is misleading and may increase the risk of surgeons’ liability

It was with great interest that we read the manuscript ‘‘Does nerve identification during open inguinal herniorrhaphy reduce the risk of persistent pain?’’ The question is both a worthy and challenging one and remains one of the most important issues in inguinal hernia repair. This study’s main aim was to correlate intraoperative nerve identification with the risk of nerve damage at 6 months assessed both subjectively and objectively. The authors are to be commended for their work and sound methodology including the use of quantitative sensory testing to help provide some measure of objective data to a complex condition that has primarily been subjectively defined. They report that in their prospective series of 244 patients, despite a high rate of nerve identification, there are still significant signs of nerve damage postoperatively and a risk of persistent pain. Thirty-nine patients (16.0 %) had substantial pain-related functional impairment at 6-month follow-up. They conclude that ‘‘intraoperative nerve identification had no influence on sensory loss in the groin, persistent pain or improvement in functional ability 6 months after surgery.’’ While the data and conclusions presented are accurate in the context of this series, there are several confounding variables and their conclusions regarding intraoperative nerve identification are not necessarily consistent with current evidence and recommendations for best available practice. The main conclusion that chronic pain and nerve injury persist despite a high rate of nerve identification is limited by a low rate of identification of the genital branch of the genitofemoral nerve. Failure to reliably identify anything less than all three nerves renders the findings inconclusive at best, and it would be misleading to conclude that nerve identification does not decrease rates of pain in routine practice. In order to draw a conclusion that contradicts the best available evidence, the design and data of the study must be supportive. The reported 16 % rate of persistent pain with proper nerve identification is higher than that reported in the literature [1, 2]. This may be a function of the time point measured, definitions used, low rates of identification of the genital nerve, the use of heavyweight mesh, or improper nerve handling. These variables illustrate the challenges faced by all investigators seeking to define best available technique and practice with regard to the prevention of chronic pain. It is well known to hernia surgeons that chronic pain has a multifactorial etiology and may develop after hernia operations despite careful handling of nerves and meticulous surgical technique [1, 3–5]. In 2008, the International Consensus Conference was held in Rome with a working group of nine hernia experts and an audience of 200 participants—a group well known to both the authors of this manuscript and the reviewers. This was a culmination of a yearlong review of the best available evidence-based literature with a goal to reach a consensus on several issues related to the prevention and management of chronic pain. While not every answer could be reached with consensus, the issue of nerve identification was well established [1]. Two published studies reporting the results of the role of the identification of all three inguinal nerves (2,305 cases all together) with a long follow-up period (ranging from 1 to 5 years) concluded that identification and preservation D. C. Chen (&) P. K. Amid Division of General Surgery, Lichtenstein Amid Hernia Clinic at UCLA, David Geffen School of Medicine at UCLA, 1304 15th Street, Suite 213, Santa Monica, CA 90404, USA e-mail: dcchen@mednet.ucla.edu

Does nerve identification during open inguinal herniorrhaphy reduce the risk of nerve damage and persistent pain?

Nerve identification during open inguinal hernia herniorrhaphy has been suggested as one of the factors that may reduce the risk of development of persistent postherniorrhaphy pain. In this prospective study, we evaluated whether intraoperative inguinal nerve identification influenced the risk of development of persistent postherniorrhaphy pain, sensory dysfunction in the groin and functional ability score after open hernia repair. A total of 244 men with a primary inguinal hernia underwent open Lichtenstein repair in a high-volume hernia surgery centre, where information on inguinal nerve identification was registered during operation. Before the operation and 6 months postoperatively, functional pain-related impairment was assessed with Activities Assessment Scale and pain intensity scores with Numeric Rating Scale (NRS 0-10). Quantitative sensory testing in the groin was performed before operation and 6 months postoperatively, in order to investigate intraoperative inguinal nerve damage. The intraoperative nerve identification rates for the iliohypogastric, ilioinguinal and genitofemoral nerves were 94.7, 97.5 and 21.3 %, respectively. Thirty-nine patients (16.0 %) had substantial pain-related functional impairment at 6 months follow-up. There was no difference in risk of development of substantial pain-related functional impairment in patients with identification compared with non-identification of the iliohypogastric nerve (P = 1.0), the ilioinguinal nerve (P = 0.59), the genitofemoral nerve (P = 0.40) or all nerves (P = 0.52). There were no differences in regard to sensory loss in the groin area or in regard to improvement in functional outcome following surgery, between patients with and without nerve identification. Although intraoperative inguinal nerve identification should be aimed at, other factors may contribute to the risk of nerve damage and persistent pain after open groin hernia repair.

甲状腺手術時における反回神経の術中モニター

One of the major complications of thyroid surgery is damage to the recurrent laryngeal nerve (RLN). This injury can be avoided by intraoperative nerve identification. A technique is described for electromyographic monitoring of the RLN during thyroidectomy. The RLN was electrically stimulated with a hand-held bipolar stimulator, delivering a voltage of 1 to 7 V. Hooked-wire electrodes were placed in the thyroarytenoid muscles through the cricothyroid membrane. Laryngeal evoked responses were readily recognized by a EMG waveform. No responses were evoked by stimulation of tissue 1 or 2 mm adjacent to the RLN. This procedure can be used to confirm the presence of the RLN during the course of the operation.

Identification of the external branch of the superior laryngeal nerve (EBSLN) in large goiters

Background: Intraoperative injury to the external branch of the superior laryngeal nerve (EBSLN) can result in significant postoperative voice problems. This injury can be avoided by intraoperative nerve identification. The EBSLN has a close anatomic relationship with the superior thyroid pedicle. According to a previous anatomic classification, the type 2b nerve, which crosses the vessels below the superior thyroid pole and is considered high risk, is found in 14% to 20% of persons with normal or slightly enlarged thyroid glands. Objective: To analyze the frequency of this type 2b nerve in a population with large goiters and to compare it with the previously mentioned proportions. Design: Nonrandomized prospective study. Patients and Methods: During a 15-month period, patients with large uninodular or multinodular goiters were entered in the study. The EBSLN was searched with the help of a nerve stimulator and the type was annotated. If the patient had to be submitted to a bilateral thyroidectomy, each superior thyroid pole, with the correspondent nerve, was considered as a separate unit. Results: Nine patients, all women, underwent surgery. The average size of the goiters was 10.9 cm x 7.3 cm x 5.0 cm, and the average weight of the specimens was 431 g. There were four bilateral procedures, totalling 13 nerves analyzed. Seven (54%) were type 2b. Conclusion: The frequency of the type 2b EBSLN is considerably higher in large goiters. This finding suggests that it is even more advisable to try to positively identify the nerve in these situations, in order to prevent its injury, which is permanent and troublesome for voice professionals.

Intraoperative Nerve Fascicle Identification Using Choline Acetyltransferase

One reason for failure of nerve recovery after suture or nerve grafting is the inappropriate matching of motor and sensory fibers. Methods used in attempting to solve this problem have either been unprecise, too time consuming, or unpleasant to the patient. Both experimentally and on cadaver samples, the level of choline acetylase activity is eight times higher in motor nerve fascicles than in sensory fascicles. In experimentally cut nerves, the ChAC activity remained high even after a period of 45 days. Thus it was possible to identify both ends of the motor and sensory fascicles in fresh injuries, and the proximal parts in old injuries. We have since used this method of intraoperative nerve identification in three patients. It has proved to be a rapid (70-80 minutes), viable technique for the immediate differentiation between proximal parts of motor and sensory nerve fascicles in cases of old nerve injuries. In contrast to our animal studies we found that the ChAC activity in the distal segment was still different for the various fascicles five months after transection. Presumably the present need for distal exploration to identify the "target organ" can be avoided.