The implication of repeated versus continuous strain on nerve function in a rat forelimb model

Methylcobalamin in Combination with Early Intervention of Low-Intensity Pulsed Ultrasound Potentiates Nerve Regeneration and Functional Recovery in a Rat Brachial Plexus Injury Model

This study evaluated and compared the functional recovery and histopathological outcomes of treatment involving low-intensity pulsed ultrasound (LIPUS) and methylcobalamin (B12) on brachial plexus injury (BPI) in an experimental rat model. Three days after BPI, the rats were assigned to receive either LIPUS or methylcobalamin alone or in combination consecutively for 12 days. Serial changes in sensory and motor behavioral responses, as well as morphological and immunohistochemical changes for substance P (SP), ionized calcium-binding adapter molecule 1 (iba1), brain-derived neurotrophic factor (BDNF), and S100 were examined 28 days after BPI as the outcome measurements. Early intervention of LIPUS and methylcobalamin, whether alone or in combination, augmented the sensory and motor behavioral recovery as well as modulated SP and iba1 expression in spinal dorsal horns, BDNF, and S100 in the injured nerve. Moreover, the combined therapy with its synergistic effect gave the most beneficial effect in accelerating functional recovery. In view of the effective initiation of early recovery of sensory and motor functions, treatment with LIPUS and methylcobalamin in combination has a potential role in the clinical management of early-phase BPI.

Facet Distraction and Dysphagia: A Prospective Evaluation of This Common Postoperative Issue Following Anterior Cervical Spine Surgery

STUDY DESIGN

Prospective cohort study.

OBJECTIVE

Our primary study was to investigate whether the degree of postoperative facet and disk space distraction following anterior cervical discectomy and fusion (ACDF) affects the rate of postoperative dysphagia.

SUMMARY OF BACKGROUND DATA

Although ACDF is safe and well tolerated, postoperative dysphagia remains a common complication. Intervertebral disk space distraction is necessary in ACDF to visualize the operative field, prepare the endplates for fusion, and facilitate graft insertion. However, the degree of distraction tolerated, before onset of dysphagia, is not well characterized ACDF.

MATERIALS AND METHODS

A prospective cohort study was conducted of 70 patients who underwent ACDF between June 2018 and January 2019. Two independent reviewers measured all preoperative and postoperative radiographs measured for interfacet distraction distance and intervertebral distraction distance, with intrareviewer reproducibility measurements after one month. For multilevel surgery, the level with the greatest distraction was measured. Primary outcomes were numerical dysphagia (0-10), Eating Assessment Tool 10, and Dysphagia Symptom Questionnaire score collected at initial visit and two, six, 12, and 24 weeks postoperatively.

RESULTS

A total of 70 patients were prospectively enrolled, 59 of whom had adequate radiographs. An average of 1.71 (SD: 0.70) levels were included in the ACDF construct. Preoperatively, 13.4% of patients reported symptoms of dysphagia, which subsequently increased in the postoperative period at through 12 weeks postoperatively, before returning to baseline at 24 weeks. Intrareviewer and interreviewer reliability analysis demonstrated strong agreement. There was no relationship between interfacet distraction distance/intervertebral distraction distance and dysphagia prevalence, numerical rating, Eating Assessment Tool 10, or Dysphagia Symptom Questionnaire.

CONCLUSIONS

Patients who had an ACDF have an increased risk of dysphagia in the short term, however, this resolved without intervention by six months. Our data suggests increased facet and intervertebral disk distraction does not influence postoperative dysphagia rates.

LEVEL OF EVIDENCE

3.

Measurement of the median nerve strain within the carpal tunnel using a capacitance-type strain sensor: A cadaver study

BACKGROUND

Direct and quantitative measurement of median nerve strain within the carpal tunnel has been difficult because of the technical limitations associated with conventional devices. We used capacitive sensors (C-stretch), which are thin and flexible, to measure the median nerve strain within the carpal tunnel.

METHODS

We used 12 fresh frozen upper extremity specimens. The transverse carpal ligament was left in situ, and we attached the sensor to the palmar surface of the median nerve to measure the nerve strain at 60 degrees of wrist extension. The sensor measured the median nerve strain at both the carpal tunnel site and the proximal to the carpal tunnel site before and after the carpal tunnel release. The amount of nerve excursion during wrist extension was also measured with the length change of the attached suture by a digital caliper.

FINDINGS

The mean median nerve strain within the carpal tunnel [8.07% (95 %CI:7.17-8.97)] was significantly higher than that proximal to the carpal tunnel [5.21% (95 %CI:4.46-5.97)] at the wrist extension. There was no significant difference of the mean nerve excursion within and proximal to the carpal tunnel. The mean nerve strain and excursion were unaffected by carpal tunnel release.

INTERPRETATION

These results indicated that wrist extension position might lead to increased strain on the median nerve within the carpal tunnel compared with at the proximal to the carpal tunnel. We believe that the current study might provide new information and help us understand the pathogenesis of carpal tunnel syndrome.

Extracellular matrix deformations of the porcine recurrent laryngeal nerve in response to hydrostatic pressure

Damage to the recurrent laryngeal nerve (RLN) caused by supraphysiological compression or tension imposed by adjacent tissue structures, such as the aorta, may contribute to onset of idiopathic unilateral vocal fold paralysis (iUVP) resulting in difficulty speaking, breathing, and swallowing. We previously demonstrated in adolescent pigs that the right RLN epineurium exhibits uniform composition of adipose tissue, with larger quantities along its length within the neck region in contrast to the left RLN that shows greater collagen composition in the thoracic region and greater quantities of adipose tissue in the neck region. In contrast, the epineurium in piglets was primarily composed of collagen tissue that remained uniform along the length of the left and right RLNs. Tensile testing of the left and right RLN in piglets and pigs showed associated differences in strain by RLN side and segment by age. The goal of this study was to investigate how external hydrostatic compression of the RLN affects the nerve's connective tissue and microstructure. RLN segments were harvested from the distal (cervical/neck) regions and proximal (subclavian for the right RLN, thoracic for the left RLN) regions from eight adolescent pigs and nine piglets. RLN segments were isolated and assessed under fluid compression to test hypotheses regarding epineurium composition and response to applied forces. Second harmonic generation (SHG) imaging of epineurial collagen was conducted at 0, 40, and 80 mmHg of compression. The cartesian strain tensor, principal strain (Eps1), and principal direction of the RLN collagen fibers were determined at each pressure step. Significantly larger values of the 1st principal strain occurred in the proximal segments of the pig left RLN when compared to the same segment in piglets (p = 0.001, pig = 0.0287 [IQR = 0.0161 - 0.0428], piglet = 0.0061 [IQR = 0.0033 - 0.0156]). Additionally, the median transverse strain Eyy) for the second pressure increment was larger in the right proximal segment of pigs compared to piglets (p < 0.001, pig = 0.0122 [IQR = 0.0033 - 0.0171], piglet = 0.0013 [IQR = 0.00001 - 0.0028]). Eyy values were significantly larger in the right proximal RLN versus the left proximal RLNs in pigs but not in piglets (p < 0.001). In contrast to piglets, histological analysis of pig RLN demonstrated increased axial alignment of epineurial and endoneurial collagen in response to compressive pressure. These findings support the hypothesis that the biomechanical response of the RLN to compressive pressure changed from being similar to being different between the right and left RLNs during development in the porcine model. Further investigation of these findings associated with age-related onset of idiopathic UVP may illuminate underlying etiologic mechanisms. STATEMENT OF SIGNIFICANCE: Damage to the recurrent laryngeal nerve (RLN) caused by compression imposed by the aorta may contribute to the onset of left-sided idiopathic unilateral vocal fold paralysis resulting in difficulty speaking, breathing, and swallowing. The goal of this study was to investigate how compression affects the connective tissue and microstructure of the RLN. We quantified the pressure induced deformation of the RLN using multiphoton imaging as a function of both location (proximal versus distal) and age (piglets, adolescent pigs). Our results demonstrate that the biomechanical response of the RLN to compression changes in the right versus left RLN throughout development, providing further evidence that the the left RLN is exposed to increasing dynamic loads with age.

The Management of Persistent and Recurrent Cubital Tunnel Syndrome

Cubital tunnel syndrome (CuTS) is the second most common compressive neuropathy in the upper extremity. There are considerable diagnostic and therapeutic challenges associated with treating patients after a failed primary procedure for CuTS. Distinguishing cases of recurrence versus persistence and identifying concomitant pathology can guide treatment. Conditions that mimic CuTS must be carefully ruled out and coexisting dysfunction of the medial antebrachial cutaneous nerve needs to be addressed. Results of revision procedures are not as reliable as primary procedures for CuTS; however, improvements in pain and paresthesias are noted in approximately 75% of patients. Nerve wraps represent a promising adjuvant treatment option, but long-term outcome data are lacking. External neurolysis and anterior transposition after failed CuTS procedures are supported by case series; multicenter, prospective randomized trials are needed to guide treatment further and improve outcomes.

Effect of Oscillation on Perineal Pressure in Cyclists: Implications for Micro-Trauma

BACKGROUND

Genital numbness and erectile dysfunction in cyclists may result from repeated perineal impacts on the bicycle saddle (micro-trauma) that occur during routine cycling.

AIM

To evaluate the relationship between oscillation forces and perineal pressures among cyclists in a simulated laboratory setting.

METHODS

Participants were fit to a study bicycle to ensure all cyclists had the same torso angle (60 ± 1 degree) and maximum knee angle (150 ± 1 degree). A lever system was used to generate oscillation events of 3 progressively increasing magnitudes. Perineal pressure was continuously measured using a pressure sensor on the bicycle saddle. This process was carried out in each of the following conditions: (1) stationary (not pedaling) with the standard seatpost, (2) pedaling with standard seatpost, (3) stationary with seatpost shock absorber, and (4) pedaling with seatpost shock absorber.

OUTCOMES

We compared perineal pressure changes during oscillation events in the stationary and pedaling states, with and without the seatpost shock absorber.

RESULTS

A total of 39 individuals were recruited (29 men and 10 women). As the amount of oscillation increased from an average of 0.7g (acceleration due to Earth's gravity) to 1.3g, the perineal pressure increased from 10.3% over baseline to 19.4% over baseline. There was a strong linear relationship between the amount of oscillation and increase in pressure (r² = 0.8, P < .001). A seatpost shock absorber decreased the impact of oscillation by 53% in the stationary condition. Men and women absorbed the majority of shock in areas corresponding to pelvic bony landmarks.

CONCLUSION

This study represents one of the first characterizations of cycling-associated perineal micro-trauma in a laboratory setting. We found a strong linear relationship between oscillation magnitude and perineal pressure during cycling, which was mitigated by a seatpost shock absorber. The use of shock absorption in bicycle design may reduce perineal micro-trauma and potentially improve cycling-associated perineal numbness and erectile dysfunction. Sanford T, Gadzinski AJ, Gaither T, et al. Effect of Oscillation on Perineal Pressure in Cyclists: Implications for Micro-Trauma. Sex Med 2018;6:239-247.

Novel Anti-Adhesive CMC-PE Hydrogel Significantly Enhanced Morphological and Physiological Recovery after Surgical Decompression in an Animal Model of Entrapment Neuropathy

We developed a novel hydrogel derived from sodium carboxymethylcellulose (CMC) in which phosphatidylethanolamine (PE) was introduced into the carboxyl groups of CMC to prevent perineural adhesions. This hydrogel has previously shown excellent anti-adhesive effects even after aggressive internal neurolysis in a rat model. Here, we confirmed the effects of the hydrogel on morphological and physiological recovery after nerve decompression. We prepared a rat model of chronic sciatic nerve compression using silicone tubing. Morphological and physiological recovery was confirmed at one, two, and three months after nerve decompression by assessing motor conduction velocity (MCV), the wet weight of the tibialis anterior muscle and morphometric evaluations of nerves. Electrophysiology showed significantly quicker recovery in the CMC-PE group than in the control group (24.0 ± 3.1 vs. 21.0± 2.1 m/s (p < 0.05) at one months and MCV continued to be significantly faster thereafter. Wet muscle weight at one month significantly differed between the CMC-PE (BW) and control groups (0.148 ± 0.020 vs. 0.108 ± 0.019%BW). The mean wet muscle weight was constantly higher in the CMC-PE group than in the control group throughout the experimental period. The axon area at one month was twice as large in the CMC-PE group compared with the control group (24.1 ± 17.3 vs. 12.3 ± 9 μm²) due to the higher ratio of axons with a larger diameter. Although the trend continued throughout the experimental period, the difference decreased after two months and was not statistically significant at three months. Although anti-adhesives can reduce adhesion after nerve injury, their effects on morphological and physiological recovery after surgical decompression of chronic entrapment neuropathy have not been investigated in detail. The present study showed that the new anti-adhesive CMC-PE gel can accelerate morphological and physiological recovery of nerves after decompression surgery.

Interventions in the disturbances in the motor and sensory environment

Treatment of peripheral nervous system (PNS) pathology presents intervention challenges to every therapist. Many of the current and future interventions will be directed at restoring the normal anatomy, function, and biomechanical properties of the PNS, restoring normal neural physiology and ultimately patient function and quality of life. Present interventions use mechanical (movement) or electrical procedures to affect various properties of the peripheral nerve. The purpose of this article was to apply basic science to clinical practice. The pathology and accompanying structural and biomechanical changes in the PNS will be presented in three specific areas commonly encountered in the clinic: nerve injury and laceration; compression neuropathies; and neuropathic pain and neural tension dysfunction. The intent is to address possible interventions exploring the clinical reasoning process that combines basic science and evidence-based best practice. The current lack of literature to support any one intervention requires a strong foundation and understanding of the PNSs' structure and function to refine current and develop new intervention strategies. Current evidence will be presented and linked with future considerations for intervention and research. During this interlude of development and refinement, best practice will rely on sound clinical reasoning skills that incorporate basic science to achieve a successful outcome when treating these challenging patients.

Laxity of the ulnar nerve during elbow flexion and extension

PURPOSE

To evaluate the dynamic anatomy of the ulnar nerve at the elbow.

METHODS

We studied 11 fresh cadavers. We placed metal clips on the ulnar nerve at three locations: at the medial epicondyle (point A), 3 cm proximal to the epicondyle (point B), and 14 cm proximal to the epicondyle (point C). The distances from the medial epicondyle to points A, B, and C on the ulnar nerve and between each pair of points were measured in full elbow extension and flexion.

RESULTS

With full elbow flexion, there was no movement of the ulnar nerve at point A (adjacent to the medial epicondyle). Point A and the adjacent distal ulnar nerve moved as a unit with the forearm around the medial epicondyle. Proximal to the cubital tunnel, there was significant ulnar nerve excursion (P < .01) at points B (0.7 ± 0.3 cm) and C (0.2 ± 0.2 cm). There was differential excursion of the ulnar nerve at points B and C relative to the medial epicondyle. The distances between the markers revealed that the nerve did not stretch to account for the discrepant distances of the 3 points, but a slack region of the nerve proximal to the medial epicondyle was taken up with flexion. Release of the intermuscular septum and the canal of Struthers did not influence movement of the nerve.

CONCLUSIONS

With elbow flexion, the ulnar nerve did not move appreciably in the distal-proximal direction directly at the cubital tunnel, but maximal excursion was in the fatty region proximal to the elbow. This slack region of the nerve was taken up during flexion, whereas only 2 mm of motion occurred through the canal of Struthers. The slack region might predispose to subluxation of the nerve. Conversely, decreased laxity might result in increased traction of the nerve, contributing to cubital tunnel syndrome.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic II.

Mechanically evoked sensory and motor responses to dynamic compression of the ulnar nerve

Mechanical deformation of a peripheral nerve can evoke action potentials in sensory and motor axons. The generation of these impulses with brief stimuli (<0.5 s) and their relationship to the deformation conditions have not been systematically studied in human subjects. Controlled compression stimuli over a range of amplitudes, durations, and loading rates were delivered to the ulnar nerve at the medial epicondyle in awake human subjects. Compound muscle action potentials were recorded from the first dorsal interosseous muscle. Subjects rated the magnitude of evoked paresthesias. Mechanically evoked motor and sensory responses varied linearly with the magnitude (P < 0.001) and rate of deformation (P < 0.01), but not the duration, and occurred only during the compression phase. Cutaneous axons had lower mechanical thresholds than motor axons. We relate these findings to the viscoelastic properties of peripheral nerves and differences in biophysical properties of cutaneous and motor axons.

Upper limb neural tension testing and mobilization. Fact, fiction, and a practical approach

The use of upper limb neural tension testing (ULNTT) and neural mobilization by physical and occupational therapists has become common in clinical practice. The purpose of this article is to discuss the basic science and the research that supports or refutes the efficacy of these techniques. There is sufficient biomechanical evidence that the peripheral nerve under tension undergoes strain and glides within its interfacing tissue. Evidence supports that ULNTT causes strain within the peripheral nervous system however; it is also evident that ULNTT places strain on other multisegmental tissues. Clinical investigation has examined intrarater reliability and has begun to define the parameters of a positive test but there is lack of randomized controlled studies. There is limited evidence reporting favorable outcomes when using neural mobilization to treat specific patient populations, and the appropriate parameters of dosage (i.e., duration, frequency, and amplitude) remain to be confirmed. Clinical application of these techniques must be applied in a practical manner that relies on continual clinical reasoning. The clinician should integrate basic science and experimental evidence as we work to achieve a sufficient level of confidence in the development of evidence-based practice.

Pathomechanics of peripheral nerve loading. Evidence in carpal tunnel syndrome

Peripheral nerve injury is a common occurrence, with carpal tunnel syndrome (CTS) receiving the most attention. Nerve dysfunction associated with compression syndromes results from an interruption or localized interference of microvascular function due to structural changes in the nerves or surrounding tissues. This article reviews the physiologic, pathophysiologic, and histologic effects of compressing peripheral nerves in animal models, and then examines the evidence for similar processes in humans using CTS as a model.

An experimental model of peripheral nerve adhesion in rabbits

We studied the effects of peripheral nerve adhesion in a rabbit sciatic nerve model. After nerve exposure, its adventitial layer was sutured with 8-0 nylon to the nerve bed, which had been cauterised to promote adhesion. Nerve kinematics, electrophysiology, blood flow and histology were assessed. Rabbits in which Fontana's bands were visible as normal through the epineurium, classified as a nonadhesion group (group I), lacked intraneural fibrosis. In this group, nerve conduction and nerve blood flow were well maintained. Rabbits in which Fontana's bands could not be seen were classified as the adhesion group (group II). This group was classified into two levels pathologically; thickening of epineurium and perineurium was observed but no endoneurial fibrosis (group IIa), and endoneurial fibrosis (Wallerian degeneration, myelin sheath thinning and fibrosis between nerve fibers) was noted (group IIb). Compound muscle action potentials (CMAP) were reduced in amplitude and blood flow was significantly decreased at adhesion sites in group IIb. In conclusion, adhesion of peripheral nerve to surrounding tissues results in fibrosis in the nerve that contributes to peripheral nerve dysfunction.

Work-related musculoskeletal disorders of the hand and wrist: epidemiology, pathophysiology, and sensorimotor changes

The purpose of this commentary is to present recent epidemiological findings regarding work-related musculoskeletal disorders (WMSDs) of the hand and wrist, and to summarize experimental evidence of underlying tissue pathophysiology and sensorimotor changes in WMSDs. Sixty-five percent of the 333 800 newly reported cases of occupational illness in 2001 were attributed to repeated trauma. WMSDs of the hand and wrist are associated with the longest absences from work and are, therefore, associated with greater lost productivity and wages than those of other anatomical regions. Selected epidemiological studies of hand/wrist WMSDs published since 1998 are reviewed and summarized. Results from selected animal studies concerning underlying tissue pathophysiology in response to repetitive movement or tissue loading are reviewed and summarized. To the extent possible, corroborating evidence in human studies for various tissue pathomechanisms suggested in animal models is presented. Repetitive, hand-intensive movements, alone or in combination with other physical, nonphysical, and nonoccupational risk factors, contribute to the development of hand/wrist WMSDs. Possible pathophysiological mechanisms of tissue injury include inflammation followed by repair and/or fibrotic scarring, peripheral nerve injury, and central nervous system reorganization. Clinicians should consider all of these pathomechanisms when examining and treating patients with hand/wrist WMSDs.

Acute changes in the axonal cytoskeleton after mild stretching of the rat brachial plexus

We have developed an animal model to investigate acute changes in the axonal cytoskeleton caused by a mild stretching of the peripheral nerve in the upper limbs of rats. Rat forelimbs were continuously stretched at 2 N for 1 h. Thereafter, a part of the brachial plexus and median nerve were harvested and processed for electron microscopic analysis. The total number of microtubules in the brachial plexus decreased to 55% of that of the control animals (p<0.05) without change in the number of neurofilaments. No significant changes in microtubules or neurofilaments were observed in the median nerve. By Western blotting analysis, the amount of tau protein in the stretch group significantly decreased in the brachial plexus but not in the median nerve. However, no significant changes in the amount of tubulin protein were observed in either the brachial plexus or median nerve. These results suggest that the microtubules were depolymerized by stretching of the brachial plexus and that the depolymerization may have been mediated by the decrease in the tau protein.

Strain in the median and ulnar nerves during upper-extremity positioning

The purpose of this study was to quantify the strain of the median nerve and the ulnar nerve throughout upper-extremity positioning sequences used by clinicians to evaluate nerve dysfunction. A microstrain gauge was used to quantify strain and digital calipers were used to assess nerve excursion in 4, fresh, intact cadavers. Data analysis of noncontinuous motion trials showed that the median nerve tension test caused a maximum summative strain in the median nerve at the carpal tunnel of 7.6%, with the largest increase in strain during elbow extension (3.5%). Components of the median nerve tension test decreased strain in the ulnar nerve at the cubital tunnel. The ulnar-nerve tension test caused a maximum summative strain in the ulnar nerve of 2.1%, with the largest increase in strain during shoulder abduction (0.9%). Some components of the ulnar-nerve tension test decreased strain in the median nerve. These cadaver findings lend support to the use of upper-extremity positioning sequences in the clinic to induce nerve strain during evaluation of nerve dysfunction.

Pathophysiology of nerve compression

Both ischemic and mechanical factors are involved in the development of compression neuropathy. Experimental studies suggest a dose response curve such that the greater the duration and amount of pressure, the more significant is neural dysfunction. With changes of axonal injury, significant neurologic dysfunction would be anticipated; however, the vast majority of patients with CTS present with symptoms in association with electrophysiologic findings of demyelination (prolonged latency). Frequently, the prolongation in latency is minimal and some patients may even present with normal electrodiagnostic studies, still complaining of significant symptomatology. This would support the concept that in the majority of patients with CTS, the symptoms relate to problems with the connective tissue "container" of the nerve rather than pathology of the nerve fiber itself. This would be in keeping with the histopathologic findings of fibrosis, with thickening of the external epineurium and perineurium. These changes would interfere with blood flow as the vessels pass through the epineurium and perineurium and produce dynamic ischemia to the nerve fibers. As well, this fibrosis would decrease the excursion of the nerve fibers, resulting in traction, and prevent the nerve fibers themselves from going through a full range of movement without traction and decreased gliding. The importance of neural gliding and movement of the nerve in the extremity has been recently emphasized in the clinical management of patients with multilevel nerve compression. Clinical maneuvers that put the nerve on stretch will provoke patients' symptoms and have been used to diagnose specific compression neuropathies (neural tension test). Similarly, physical therapy modalities to stretch the nerves and restore neural gliding are frequently successful in relieving patients' symptoms [33]. This physical therapy approach is based on the premise that the connective tissue "container" of the nerve is tight and short and needs to be mobilized. This is in keeping with the histopathologic findings of increased connective tissue at the perineurial and epineurial levels. A greater understanding of the pathophysiology of compression neuropathy will have immediate impact on our management of this problem and likely result in emphasis on conservative management and physical therapy rather than surgical intervention.