Structural assessment of rat sciatic nerve following tourniquet compression and vascular manipulation

Morphing electronics enable neuromodulation in growing tissue

Bioelectronics for modulating the nervous system have shown promise in treating neurological diseases^1-3. However, their fixed dimensions cannot accommodate rapid tissue growth^4,5 and may impair development⁶. For infants, children and adolescents, once implanted devices are outgrown, additional surgeries are often needed for device replacement, leading to repeated interventions and complications^6-8. Here, we address this limitation with morphing electronics, which adapt to in vivo nerve tissue growth with minimal mechanical constraint. We design and fabricate multilayered morphing electronics, consisting of viscoplastic electrodes and a strain sensor that eliminate the stress at the interface between the electronics and growing tissue. The ability of morphing electronics to self-heal during implantation surgery allows a reconfigurable and seamless neural interface. During the fastest growth period in rats, morphing electronics caused minimal damage to the rat nerve, which grows 2.4-fold in diameter, and allowed chronic electrical stimulation and monitoring for 2 months without disruption of functional behavior. Morphing electronics offers a path toward growth-adaptive pediatric electronic medicine.

Dexamethasone promotes long-term functional recovery of neuromuscular junction in a murine model of tourniquet-induced ischaemia-reperfusion

AIM

Tourniquet-induced ischaemia and subsequent reperfusion cause serious ischaemia-reperfusion (IR) injury in the neuromuscular junction (NMJ) and skeletal muscle. Here, we investigated whether dexamethasone (Dex) promotes long-term functional recovery of the NMJ and skeletal muscle in tourniquet-induced hindlimb IR.

METHODS

Unilateral hindlimb of C57/BL6 mice was subjected to 3 h of ischaemia following 6 weeks of reperfusion (6-wk IR). Dex treatment began on the day of IR induction and lasted for different periods. Sciatic nerve-stimulated gastrocnemius muscle contraction was detected in situ. Function of the NMJ was measured in situ using electrophysiological recording of the miniature endplate potential (mEPP) and endplate potential (EPP). Western blot was used to detect protein expression of nicotinic acetylcholine receptors (nAChRs) in gastrocnemius muscles.

RESULTS

Gastrocnemius muscle contraction in mice with 6-wk IR was about 60% of normal skeletal muscle contraction recorded in age-matched sham mice. The amplitude of the mEPP and EPP was lower in mice with 6-wk IR, compared to sham mice. Dex treatment for 1 or 3 days did not restore the function of the NMJ and improve gastrocnemius muscle contraction in mice with 6-wk IR. Dex treatment for 1 week exerted a maximum effect on improving the function of the NMJ and skeletal muscle, with the effect of Dex gradually lessening with prolonged Dex treatment. There are no significant differences in protein expression of nAChR-α1 and nAChR-β1 subunits in the gastrocnemius muscle among all groups.

CONCLUSION

Dex promotes repair of the NMJ and subsequently restores skeletal muscle contractile function in tourniquet-induced 6-wk IR.

Palmitoylethanolamide, a neutraceutical, in nerve compression syndromes: efficacy and safety in sciatic pain and carpal tunnel syndrome

Palmitoylethanolamide (PEA) is an endogenous lipid modulator in animals and humans, and has been evaluated since the 1970s as an anti-inflammatory and analgesic drug in more than 30 clinical trials, in a total of ~6,000 patients. PEA is currently available worldwide as a nutraceutical in different formulations, with and without excipients. Here we describe the results of all clinical trials evaluating PEA’s efficacy and safety in nerve compression syndromes: sciatic pain and pain due to carpal tunnel syndrome, and review preclinical evidence in nerve impingement models. Both the pharmacological studies as well as the clinical trials supported PEA’s action as an analgesic compound. In total, eight clinical trials have been published in such entrapment syndromes, and 1,366 patients have been included in these trials. PEA proved to be effective and safe in nerve compression syndromes. In one pivotal, double blind, placebo controlled trial in 636 sciatic pain patients, the number needed to treat to reach 50% pain reduction compared to baseline was 1.5 after 3 weeks of treatment. Furthermore, no drug interactions or troublesome side effects have been described so far. Physicians are not always aware of PEA as a relevant and safe alternative to opioids and co-analgesics in the treatment of neuropathic pain. Especially since the often prescribed co-analgesic pregabaline has been proven to be ineffective in sciatic pain in a double blind enrichment trial, PEA should be considered as a new and safe treatment option for nerve compression syndromes.

Pathophysiology and Etiology of Nerve Injury Following Peripheral Nerve Blockade

This review synthesizes anatomical, anesthetic, surgical, and patient factors that may contribute to neurologic complications associated with peripheral nerve blockade. Peripheral nerves have anatomical features unique to a given location that may influence risk of injury. Peripheral nerve blockade-related peripheral nerve injury (PNI) is most severe with intrafascicular injection. Surgery and its associated requirements such as positioning and tourniquet have specific risks. Patients with preexisting neuropathy may be at an increased risk of postoperative neurologic dysfunction. Distinguishing potential causes of PNI require clinical assessment and investigation; a definitive diagnosis, however, is not always possible. Fortunately, most postoperative neurologic dysfunction appears to resolve with time, and the incidence of serious long-term nerve injury directly attributable to peripheral nerve blockade is relatively uncommon. Nonetheless, despite the use of ultrasound guidance, the risk of block-related PNI remains unchanged.

WHAT'S NEW

Since the 2008 Practice Advisory, new information has been published, furthering our understanding of the microanatomy of peripheral nerves, mechanisms of peripheral nerve injection injury, toxicity of local anesthetics, the etiology of and monitoring methods, and technologies that may decrease the risk of nerve block-related peripheral nerve injury.

Tourniquet cuff pressure and nerve injury in knee arthroplasty in a bloodless field: a neurophysiological study

BACKGROUND AND PURPOSE

Tourniquet-related nerve injuries remain a concern in orthopedic surgery. The cuff pressures used today are generally lower, and therefore a decreasing incidence of peripheral nerve injuries might also be expected. However, there have been few neurophysiological studies describing the outcome after bloodless field surgery. We describe the results of neurophysiological examinations and report the incidence of nerve injuries after total knee arthroplasty (TKA) in a bloodless field.

PATIENTS AND METHODS

This study was part of a prospective, randomized controlled clinical trial in patients scheduled for TKA in a bloodless field. 20 consecutive patients were enrolled. Electroneurography (ENeG) and quantitative sensory testing (QST) of thermal thresholds were performed on day 3. These tests were repeated 2 months after surgery when electromyography (EMG) with a concentric-needle electrode was also performed.

RESULTS

The mean tourniquet cuff pressure was 237 (SD 33) mmHg. Electromyographic signs of denervation were found in 1 patient, who also had the highest cuff pressure in the study population (294 mmHg). The sensory nerve response amplitudes were lower in the operated leg on day 3; otherwise, the neurophysiological examinations showed no differences between the legs.

INTERPRETATION

When low tourniquet cuff pressures are used the risk of nerve injury is minor.

Cuff width increases the serum biochemical markers of tourniquet-induced skeletal muscle ischemia in rabbits

Tourniquet application is a widely accepted adjuvant technique in extremity surgery. The purpose of this prospective, randomized trial was to evaluate the effect of cuff width on skeletal muscle ischemia-reperfusion injury. A 2- or 4-cm wide curved tourniquet cuff was applied around the midthigh of 36 New Zealand White rabbits and inflated to a pressure of 200 or 400 mm Hg for 2 hours: group A=2 cm to 200 mm Hg; group B=2 cm to 400 mm Hg; group C=4 cm to 200 mm Hg; group D=4 cm to 400 mm Hg. Blood levels of potassium, lactic acid, urea, lactic dehydrogenase, and creatinine phosphokinase MM isoenzyme (CPK-MM) were measured as basic indicators for limb ischemia before tourniquet inflation and 1, 5, and 30 minutes after cuff release.Potassium values did not differ among the 4 groups. Lactic acid and urea concentrations were always higher in the 400 mm Hg groups (B and D) (P<.001). However, cuff width did not affect their levels (P>.16). Lactic dehydrogenase and CPK-MM values were also greater in the 400 mm Hg groups at all times (P<.001). Further subgroup analysis of 200 mm Hg pressure groups showed higher lactic dehydrogenase (P<.02) but not CPK-MM (P>.9) concentrations in group C than in group A during the 30-minute period. At 400 mm Hg, lactic dehydrogenase and CPK-MM values were higher in group D compared with group B only 30 minutes after cuff deflation (P<.001). Broad tourniquets are associated with significantly greater and prolonged elevation of serum biochemical markers of inducible skeletal muscle ischemia-reperfusion injury compared with narrow ones. This difference is more prominent when a wide cuff is inflated to a high pressure.

A correlative electrophysiologic study of nerve fiber involvement in carpal tunnel syndrome using current perception thresholds

OBJECTIVE

To relate clinical severity of idiopathic carpal tunnel syndrome (CTS) to current perception threshold (CPT).

METHODS

Subjects were 51 patients with CTS (involving 51 hands), and 50 healthy control subjects (50 hands). Involved hands were grouped into three clinical grades (mild, moderate, severe). Using a neurometer (Neurotron, Baltimore, MD), we investigated the relationship between clinical grade and CPT abnormalities.

RESULTS

In the mild CTS group, most hands showed CPT abnormalities only at 2000 Hz stimulation. The moderate group included a higher percentage of hands showing abnormalities at both 2000 and 250 Hz stimulation increased. The severe group included the highest percentage of hands with abnormal values at all frequencies tested.

CONCLUSIONS

CPT showed abnormalities appear progressively from 'higher to lower' frequency stimulations relative to the increasing severity of CTS.

SIGNIFICANCE

Sensory nerve fiber dysfunction apparently begins in larger fibers, extending stepwise to smaller fibers as the clinical grade of CTS progresses.

Tourniquet compression: a non-invasive method to enhance nerve regeneration in nerve grafts

One hindlimb of a rat was subjected to tourniquet compression (150, 200 and 300 mmHg; 2 h). After 6 days a 10 mm sciatic or tibial nerve graft from the compressed limb was sutured to bridge a 3-4 mm gap in the sciatic nerve of the non-compressed limb. The distances of regenerating sensory axons were measured 6 days post surgery (tibial grafts, 8 days). Compression at 200 and 300 mmHg led to significantly longer regeneration distances than those seen in controls. Incorporation of BrdU and expression of p75 receptor by non-neuronal cells (Schwann cells) in sciatic nerves 6 days after compression (150 and 300 mmHg; 2 h) was also increased as a sign of Schwann cell activation. Tourniquet compression may be used as a non-invasive method to enhance nerve regeneration in nerve grafts.

Nerve regeneration enhancement by tourniquet

The use of tourniquet compression as a non-invasive method to enhance axonal regeneration was assessed in the rat sciatic nerve. One hind limb of the rat was subjected to compression by a tourniquet set at 300 mmHg for 30 or 120 min followed by bilateral test crush lesions performed either directly or after a conditioning interval of 3 or 6 days, with the non-compressed side serving as a control. Axonal regeneration distances were evaluated after 3 days by the pinch reflex test. We found that compression caused an increased outgrowth length of sensory axons compared to the controls. The effect was most obvious after 120 min of compression with a conditioning interval of 6 days. Tourniquet compression has a conditioning lesion effect on peripheral nerve and may enhance nerve regeneration.

Effects of tourniquet compression on neuromuscular function

Neuromuscular function in New Zealand White rabbits was evaluated after thigh tourniquet compression in the directly compressed quadriceps muscles and the distal tibialis anterior by measuring isometric contractile function after supramaximal stimulation of the motor nerve. Tourniquet compression resulted in markedly decreased force production beneath and distal to the tourniquet. Two days after compression, maximal quadriceps force production was decreased to 46% of control values with 125 mm Hg compression and 21% of control values after 350 mm Hg compression. Maximum tibialis anterior force production declined to 70% of control values after 125 mm Hg thigh compression and 24% of control values after 350 mm Hg thigh compression. Functional deficits were greater in the directly compressed quadriceps muscles, but the quadriceps and tibialis anterior had significantly increased impairment when the tourniquet inflation pressure was increased from 125 mm Hg to 350 mm Hg. Three weeks after compression, quadriceps function had returned to 94% of control value after 125 mm Hg compression and 83% after 350 mm Hg. Tibialis anterior function returned to 88% of control values after 125 mm Hg thigh compression and 83% after 350 mm Hg. Clinically, the use of lower inflation pressures may minimize the complications of tourniquet use and enhance postoperative recovery.

Effects of tourniquet use in anterior cruciate ligament reconstruction

Although tourniquets are used commonly during anterior cruciate ligament (ACL) surgery, little data are available regarding their effects on postoperative function. This retrospective study evaluated 94 patients who had an arthroscopically assisted, autogenous bone-patellar ligament-bone ACL reconstruction between 1988 and 1991 at the San Diego Kaiser Hospital. A tourniquet was used in 48 patients (T+ group). No tourniquet was used in 46 patients (T- group). The surgical and postoperative protocols were identical for the two groups. There were no bleeding complications. There was no significant difference in anesthesia time between the two groups. This study has shown that ACL surgery can be performed expeditiously without a pneumatic tourniquet. Quadriceps strength recovery after surgery was less in the T+ group at 12 weeks after surgery, but there was no significant difference between the groups 52 weeks after surgery. Difference in thigh girth was greater in T+ group 6 and 12 weeks after surgery, but there was no significant difference between the groups 52 weeks after surgery.

Peripheral nerve elongation by laser Doppler flowmetry controlled expansion: functional and neurophysiological aspects

A new method for elongation of peripheral nerves with preservation of function is presented. Nerve blood flow during experimental nerve expansion of rabbit sciatic nerve is controlled by laser Doppler flowmetry in order to avoid nerve ischemia. Using this method, nerve function in relation to gait remained intact in 72.5% of the animals and recovered within 3 weeks in the others. Disturbances in toe-spread reflex recovered completely in all animals after 3 weeks. Significant nerve elongation up to 40% is possible with preservation of function when nerve blood flow is controlled by laser Doppler flowmetry.

Effects of reperfusion intervals on skeletal muscle injury beneath and distal to a pneumatic tourniquet

To date there have been no experimental studies specifically directed at effects of reperfusion intervals on skeletal muscle injury beneath the tourniquet. 99mTechnetium pyrophosphate (Tc 99) incorporation and correlative histology were used to assess injury 2 days after tourniquet application in muscles beneath (thigh) and distal (leg) to the cuff. Tourniquets were applied to rabbit hindlimbs for a total of either 2 or 4 hours. In the 4-hour series, tourniquet compression (either 125 mm Hg or 350 mm Hg cuff inflation pressure) was either continuous or interrupted by 10-minute reperfusion intervals after 2 hours or after every hour of cuff inflation. In the 2-hour series, tourniquet compression (350 mm Hg) was either continuous or interrupted by 10-minute reperfusion intervals after 2 hours or after every hour of cuff inflation. In the 2-hour series, tourniquet compression (350 mm Hg) was either continuous or interrupted by a 10-minute reperfusion interval after 1 hour. Pyrophosphate incorporation (Tc 99 uptake) was significantly greater in the thigh region than in the leg region in all of the 4-hour tourniquet groups. Tc 99 uptake was significantly reduced by reperfusion after each hour of cuff inflation. With 350 mm Hg tourniquet pressure, a reperfusion interval after 2 hours of cuff inflation tended to exacerbate tourniquet compression injury. Reperfusion intervals did not significantly affect Tc 99 uptake in the leg region of these groups. With a 2-hour tourniquet time, Tc 99 uptake in the thigh was significantly decreased by reperfusion after 1 hour of cuff inflation. Previous clinical recommendations, based on serum creatine phosphokinase abnormalities after experimental tourniquet ischemia, probably reflected tourniquet compression injury. Hourly reperfusion limits skeletal muscle injury during extended periods of tourniquet use.

Muscle injury induced beneath and distal to a pneumatic tourniquet: a quantitative animal study of effects of tourniquet pressure and duration

Previous recommendations regarding the "safe" period of tourniquet hemostasis were based largely on studies of ischemia distal to the tourniquet. This study quantitatively analyzed skeletal muscle injury induced beneath and distal to a pneumatic tourniquet applied to the hindlimbs of rabbits for 1, 2, or 4 hours with a cuff inflation pressure of 125, 200, or 350 mm Hg. Technetium Tc 99m pyrophosphate incorporation after systemic injection (Tc 99 uptake) and correlative histology were used to evaluate tissue damage 2 days after tourniquet application. Compared with the contralateral control limbs, compression and ischemia induced statistically significant increases in Tc 99 uptake in the thigh and leg regions of all groups. Pyrophosphate incorporation was significantly greater in the thigh region than in the leg region after 2 hours of compression in the 200 and 350 mm Hg pressure groups and following 4 hours of compression in all pressure groups. Focal and regional fiber necrosis and degeneration were observed in thigh muscles after 2 hours of tourniquet compression. Two hours of continuous tourniquet application at clinically relevant cuff inflation pressures induced significant skeletal muscle necrosis beneath the tourniquet. Use of the lowest possible inflation pressure for a limited duration should minimize the degree of tissue injury caused by tourniquet application.

Nerve function and structure beneath and distal to a pneumatic tourniquet applied to rabbit hindlimbs

Neurophysiologic and neuropathologic changes were studied in rabbit hindlimbs after 2 hours of pneumatic tourniquet application with either 350 mmHg (n = 18) or 1,000 mmHg (n = 6) cuff inflation pressure. The toe spread reflex was decreased in 66% and absent in 33% of limbs 2 days after 350 mmHg compression, and was absent in all limbs after 1,000 mmHg compression. Compound motor action potential amplitudes (CMAPs), recorded from the abductor hallucis muscle, were significantly decreased with sciatic nerve stimulation 1 hour after 350 mmHg compression. CMAPs returned to baseline values one and two days later, however nerve conduction velocity (NCV) was still significantly decreased in the compressed sciatic nerves of these groups. In contrast, complete nerve conduction block, localized beneath the cuff's distal border, was observed two days after 1,000 mmHg compression, and NCV was still significantly decreased distal to the tourniquet zone. Using light and electron microscopy, scattered axonal degeneration, mild myelin damage, and normal nodes of Ranvier were observed two days after 350 mmHg tourniquet compression. Severe fiber damage and nodal obliteration were noted after 1,000 mmHg tourniquet compression. Although nodal invagination is probably not a significant pathogenic mechanism at clinically relevant tourniquet pressures and durations, functional abnormalities were induced by 2 hour, 350 mmHg tourniquet compression. Such changes probably correlate with clinical electromyographic abnormalities and delayed post-operative recovery following 'routine' extremity surgery using pneumatic tourniquets.