Influence of reference electrode position on the compound muscle action potential.

OBJECTIVE: When the compound muscle action potential (CMAP) is recorded in motor nerve conduction studies, the reference (E2) electrode can make a significant contribution to the CMAP. This study investigates the E2 recorded signal and its effect on CMAP measurements when E2 electrode is placed at different sites. METHODS: The CMAP was recorded using the active electrode on the muscle belly and 4 different E2 electrodes placed at distal and proximal sites. The signal recorded by each electrode was also measured using a reference electrode on the contralateral limb. Signals were recorded from the abductor pollicis brevis, abductor digiti minimi, tibialis anterior and biceps muscles. RESULTS: The E2 recorded a smaller signal when it was placed near or off the proximal tendon or muscle origin. This affected CMAP latency, duration for tibialis anterior. Contrary to expectation, initial upward deflection was noted for E2 signal. CONCLUSION: A proximal E2 position records a lower volume conducted signal and yields a CMAP that is more representative of the muscle over which the E1 (active) electrode is placed. SIGNIFICANCE: The proposed 'Proximal E2' montage may be better suited to assess pathology.

Effect of fascicle composition on ulnar to musculocutaneous nerve transfer (Oberlin transfer) in neonatal brachial plexus palsy.

OBJECTIVE Neonatal brachial plexus palsy (NBPP) continues to be a problematic occurrence impacting approximately 1.5 per 1000 live births in the United States, with 10%-40% of these infants experiencing permanent disability. These children lose elbow flexion, and one surgical option for recovering it is the Oberlin transfer. Published data support the use of the ulnar nerve fascicle that innervates the flexor carpi ulnaris as the donor nerve in adults, but no analogous published data exist for infants. This study investigated the association of ulnar nerve fascicle choice with functional elbow flexion outcome in NBPP. METHODS The authors conducted a retrospective study of 13 cases in which infants underwent ulnar to musculocutaneous nerve transfer for NBPP at a single institution. They collected data on patient demographics, clinical characteristics, active range of motion (AROM), and intraoperative neuromonitoring (IONM) (using 4 ulnar nerve index muscles). Standard statistical analysis compared pre- and postoperative motor function improvement between specific fascicle transfer (1-2 muscles for either wrist flexion or hand intrinsics) and nonspecific fascicle transfer (> 2 muscles for wrist flexion and hand intrinsics) groups. RESULTS The patients' average age at initial clinic visit was 2.9 months, and their average age at surgical intervention was 7.4 months. All NBPPs were unilateral; the majority of patients were female (61%), were Caucasian (69%), had right-sided NBPP (61%), and had Narakas grade I or II injuries (54%). IONM recordings for the fascicular dissection revealed a donor fascicle with nonspecific innervation in 6 (46%) infants and specific innervation in the remaining 7 (54%) patients. At 6-month follow-up, the AROM improvement in elbow flexion in adduction was 38° in the specific fascicle transfer group versus 36° in the nonspecific fascicle transfer group, with no statistically significant difference (p = 0.93). CONCLUSIONS Both specific and nonspecific fascicle transfers led to functional recovery, but that the composition of the donor fascicle had no impact on early outcomes. In young infants, ulnar nerve fascicular dissection places the ulnar nerve at risk for iatrogenic damage. The data from this study suggest that the use of any motor fascicle, specific or nonspecific, produces similar results and that the Oberlin transfer can be performed with less intrafascicular dissection, less time of surgical exposure, and less potential for donor site morbidity.

Compound Motor Action Potential: Electrophysiological Marker for Muscle Training.

PURPOSE: The compound motor action potential (CMAP) represents the summated action potentials of all stimulated motor endplates and potentially reflects muscle hypertrophy and increased muscle contractions. Since electrophysiological biomarkers for high-resistance strength training are lacking, the authors evaluated whether the CMAP of distal and proximal muscles differs between healthy men and women who perform and do not perform high-resistance muscle training. METHODS: Motor neurography was performed with stimulation of the median nerve (recording of abductor pollicis brevis muscle), peroneal nerve (recording of extensor digitorum brevis muscle), femoral nerve (recording of rectus femoris muscle) and musculocutaneous nerve (recording of biceps brachii muscle), and isometric muscle strength, measured with a hand-held dynamometer, were performed on 83 healthy subjects (52 women). RESULTS: Trained women had 25% higher CMAP amplitude in the rectus femoris muscle than untrained women (P < 0.001), whereas CMAP amplitude in the trained male cohort was 25% higher in the biceps (P = 0.005) compared with untrained men. In the trained group, CMAP amplitude in the biceps correlated with isometric muscle strength (R = 0.30; P = 0.046). CONCLUSIONS: The authors' propose the CMAP as an objective neurophysiological parameter for proximal muscle status and training effects in future interventional studies of patients with neuromuscular disorders.

Basal cell carcinoma preferentially arises from stem cells within hair follicle and mechanosensory niches.

Basal cell carcinoma (BCC) is characterized by frequent loss of PTCH1, leading to constitutive activation of the Hedgehog pathway. Although the requirement for Hedgehog in BCC is well established, the identity of disease-initiating cells and the compartments in which they reside remain controversial. By using several inducible Cre drivers to delete Ptch1 in different cell compartments in mice, we show here that multiple hair follicle stem cell populations readily develop BCC-like tumors. In contrast, stem cells within the interfollicular epidermis do not efficiently form tumors. Notably, we observed that innervated Gli1-expressing progenitors within mechanosensory touch dome epithelia are highly tumorigenic. Sensory nerves activate Hedgehog signaling in normal touch domes, while denervation attenuates touch dome-derived tumors. Together, our studies identify varying tumor susceptibilities among different stem cell populations in the skin, highlight touch dome epithelia as "hot spots" for tumor formation, and implicate cutaneous nerves as mediators of tumorigenesis.

Corticomotor excitability of arm muscles modulates according to static position and orientation of the upper limb.

OBJECTIVE: We investigated how multi-joint changes in static upper limb posture impact the corticomotor excitability of the posterior deltoid (PD) and biceps brachii (BIC), and evaluated whether postural variations in excitability related directly to changes in target muscle length. METHODS: The amplitude of individual motor evoked potentials (MEPs) was evaluated in each of thirteen different static postures. Four functional postures were investigated that varied in shoulder and elbow angle, while the forearm was positioned in each of three orientations. Posture-related changes in muscle lengths were assessed using a biomechanical arm model. Additionally, M-waves were evoked in the BIC in each of three forearm orientations to assess the impact of posture on recorded signal characteristics. RESULTS: BIC-MEP amplitudes were altered by shoulder and elbow posture, and demonstrated robust changes according to forearm orientation. Observed changes in BIC-MEP amplitudes exceeded those of the M-waves. PD-MEP amplitudes changed predominantly with shoulder posture, but were not completely independent of influence from forearm orientation. CONCLUSIONS: Results provide evidence that overall corticomotor excitability can be modulated according to multi-joint upper limb posture. SIGNIFICANCE: The ability to alter motor pathway excitability using static limb posture suggests the importance of posture selection during rehabilitation aimed at retraining individual muscle recruitment and/or overall coordination patterns.

Quantitative assessment of the motor-sensory specificity of the motor and primary sensory neurons after the end-to-side neurorrhaphy.

We sought to evaluate the motor-sensory specificity of the motor and primary sensory neurons after the end-to-side neurorrhaphy. We divided 90 rats into three groups: (1) end-to-side neurorrhaphy using the ulnar nerve as donor nerve and the musculocutaneous nerve as recipient nerve; (2) normal control; and (3) transected nerve with the stumps buried. At 5 months, we monitored the grooming test, the electromyographic recordings, the histologic changes in the nerve, and quantitatively evaluated motoneurons and dorsal root ganglion (DRG) neurons following their retrograde labeling by Fluoro-Gold (Sigma, St. Louis, MO) applied to the musculocutaneous nerve and its biceps brachii branch. Grooming and electrophysiological investigations recovered successfully in the end-to-side group. The implanted musculocutaneous nerve contained varying but satisfactory numbers of axons. In the end-to-side group, the proportion of motoneurons for the biceps brachii branch of musculocutaneous nerve was very similar to the musculocutaneous nerve sections proximal to this branch (17.3% ± 2.7% and 21.7% ± 3.7%, respectively), but it did not correspond with the proportion of the biceps brachii branch of musculocutaneous nerve in the normal group (28.3% ± 3.5%). The present study confirms that limited but functional reinnervation can occur after the end-to-side neurorrhaphy, and the motor-sensory specificity is not important.

Neural progenitor cells generate motoneuron-like cells to form functional connections with target muscles after transplantation into the musculocutaneous nerve.

Neural progenitor cells (NPCs) are suggested to be a valuable source of cell transplant in treatment of various neurological diseases because of their distinct attributes. They can be expanded and induced to differentiate in vitro. However, it remains uncertain whether in vitro expanded NPCs have the capacity to give rise to functional motoneurons after transplantation in vivo. Here, we showed that in vitro expanded NPCs, when transplanted into the musculocutaneous nerve, generated motoneuron-like cells that exhibited typical morphology with large cell bodies, expressed specific molecules, and extended axons to form functional connections with the target muscle. In contrast, transplanted NPCs failed to yield motoneurons in the injured ventral horn of the spinal cord. The results of the study demonstrate that NPCs have the potential to generate functional motoneurons in an appropriate environment. The distinct differentiating fate of NPCs in the musculocutaneous nerve and the injured ventral horn suggests the importance and necessity of modifying the host microenvironment in use of NPCs for cell replacement therapies for motoneuron diseases.

[Diagnosis of patients with thoracic outlet syndrome (TOS) using physiological measures of the medial antebrachial cutaneous nerve].

The diagnosis of thoracic outlet syndrome (TOS) remains difficult; therefore, reliable and objective tests are required. We examined the process to diagnose TOS, and assessed the validity of measuring the medial antebrachial cutaneous nerve (MAC), also the ulnar nerve (UN) as a diagnostic tool. Between 2008 and 2011, 86 sides in 73 patients admitted to our hospital for the treatment of TOS were analyzed. In the process for the diagnosis as TOS, the narrow parts of the subclavian artery that was compressed by the anterior scalene muscle were confirmed with a three-dimensional CT angiography. All patients were taken a brachial plexus anesthesiological block to aim at both for diagnosis and treatment of TOS. For the diagnosis of TOS, measurements of latency (LT) and sensory nerve action potential (SNAP) of MAC and UN were analyzed between the TOS side and the non-TOS side and separated into traumatic type or disputed type. In our research, the LT of MAC and UN did not differ much between the TOS side and the non-TOS side; however, the amplitude of SNAP of MAC and UN were lower on the TOS side, especially in traumatic TOS. We concluded that comparison of the amplitude of SNAP of MAC on the injured or non-injured side was comparatively helpful for the diagnosis of TOS.

Enhancement of musculocutaneous nerve reinnervation after vascular endothelial growth factor (VEGF) gene therapy.

BACKGROUND: Vascular endothelial growth factor (VEGF) is not only a potent angiogenic factor but it also promotes axonal outgrowth and proliferation of Schwann cells. The aim of the present study was to quantitatively assess reinnervation of musculocutaneous nerve (MCN) stumps using motor and primary sensory neurons after plasmid phVEGF transfection and end-to-end (ETE) or end-to-side (ETS) neurorrhaphy. The distal stump of rat transected MCN, was transfected with plasmid phVEGF, plasmid alone or treated with vehiculum and reinnervated following ETE or ETS neurorrhaphy for 2 months. The number of motor and dorsal root ganglia neurons reinnervating the MCN stump was estimated following their retrograde labeling with Fluoro-Ruby and Fluoro-Emerald. Reinnervation of the MCN stumps was assessed based on density, diameter and myelin sheath thickness of regenerated axons, grooming test and the wet weight index of the biceps brachii muscles. RESULTS: Immunohistochemical detection under the same conditions revealed increased VEGF in the Schwann cells of the MCN stumps transfected with the plasmid phVEGF, as opposed to control stumps transfected with only the plasmid or treated with vehiculum. The MCN stumps transfected with the plasmid phVEGF were reinnervated by moderately higher numbers of motor and sensory neurons after ETE neurorrhaphy compared with control stumps. However, morphometric quality of myelinated axons, grooming test and the wet weight index were significantly better in the MCN plasmid phVEGF transfected stumps. The ETS neurorrhaphy of the MCN plasmid phVEGF transfected stumps in comparison with control stumps resulted in significant elevation of motor and sensory neurons that reinnervated the MCN. Especially noteworthy was the increased numbers of neurons that sent out collateral sprouts into the MCN stumps. Similarly to ETE neurorrhaphy, phVEGF transfection resulted in significantly higher morphometric quality of myelinated axons, behavioral test and the wet weight index of the biceps brachii muscles. CONCLUSION: Our results showed that plasmid phVEGF transfection of MCN stumps could induce an increase in VEGF protein in Schwann cells, which resulted in higher quality axon reinnervation after both ETE and ETS neurorrhaphy. This was also associated with a better wet weight biceps brachii muscle index and functional tests than in control rats.

Functional motor nerve regeneration without motor-sensory specificity following end-to-side neurorrhaphy: an experimental study.

PURPOSE: To evaluate the quality of regenerating myelinated axons and motor-sensory specificity in an end-to-side nerve repair model. METHODS: We divided 20 rats into 3 groups: (1) end-to-side neurorrhaphy using the ulnar nerve as donor nerve and the musculocutaneous nerve as recipient nerve; (2) normal control; and (3) transected nerve with the stumps buried. At 5 months, we monitored the grooming test, the electrophysiological response, and the histologic changes in nerve and muscle. RESULTS: Grooming recovered successfully, and electrophysiological investigations revealed that the target muscles had been reinnervated in the end-to-side group. The mean wet weight of the reinnervated biceps brachii muscle was 72% of the normal muscle, and the mean muscle fiber cross-sectional area of the reinnervated muscle was similar to the normal muscle. The implanted musculocutaneous nerve contained varying but satisfactory numbers of axons (end-to-side group: 596 ± 348 vs normal group: 1,340 ± 241). Acetylcholinesterase staining revealed a similar percentage of myelinated fibers in the musculocutaneous nerve (39%) and the biceps brachii branch of the musculocutaneous nerve (38%) in the end-to-side group. This was similar to the number of myelinated fibers in the donor ulnar nerve (37%). CONCLUSIONS: The present study confirms that limited but functional reinnervation can occur on the basis of collateral sprouting of intact axons from the ulnar nerve. The motor-sensory specificity is not important.

Skin temperature measured by infrared thermography after specific ultrasound-guided blocking of the musculocutaneous, radial, ulnar, and median nerves in the upper extremity.

BACKGROUND: Sympathetic block causes vasodilatation and increases in skin temperature (T(s)). However, the T(s) response after specific nerve blocking is unknown. In this study, we hypothesized that T(s) would increase after specific blocking of the nerve innervating that area. METHODS: Forty-six patients undergoing hand surgery were included. We performed ultrasound-guided, specific nerve blocking of either the musculocutaneous, radial, ulnar, or median nerve in each patient and analysed T(s) in the forearm and hand at 2 min intervals in the following 22 min by the use of infrared thermography. Areas of interest corresponding to the cutaneous innervation area of each of the four nerves were defined and the mean T(s) in each area was analysed. RESULTS: Specific blocking of the ulnar and median nerves caused a substantial increase in mean (sd) T(s) in the areas innervated by these nerves [5.2 (3.2)°C and 5.1 (2.5)°C, respectively; both P<0.0001]. The increase was even larger at the fingertips. Median nerve blocking also increased T(s) in the area of the hand innervated by the radial nerve (P<0.0001). However, T(s) did not increase in any area after either musculocutaneous or radial nerve blocking. CONCLUSIONS: Specific blocking of the ulnar and median nerve causes substantial increases in T(s) in specific areas of the hand. In contrast, the specific blocking of the musculocutaneous or radial nerve does not increase T(s). Further studies are needed to clarify if these findings can be used to objectively evaluate brachial plexus block success.

Helicoid end-to-side and oblique attachment technique in repair of the musculocutaneous nerve injury with the phrenic nerve as a donor: an experimental study in rats.

The purpose of this study was to identify if a modified end-to-side repair can achieve equal results of nerve regeneration compared to an end-to-end repair using donor phrenic nerves in repair of the musculocutaneous nerve and also pulmonary protection. Eighteen rats were divided into three groups of six each comparing two nerve graft techniques: helicoid end-to-side plus distal oblique repair vs. traditional end-to-end repair, using a donor phrenic nerve. The saphenous nerve was used as a graft between the phrenic nerve and the musculocutaneous nerve. The third group was used as control; the musculocutaneous nerve was transected without any repair. Three months postoperatively, electrophysiology, tetanic force, moist muscle weight, histology, nerve fiber counting, and chest X-ray were evaluated. All results have shown that this modified end-to-side repair was superior to the end-to-end repair. The former did not compromise the diaphragm function, but the latter showed an elevation of the diaphragm. Little recovery was seen in the third group. The conclusion is that this modified end-to-side repair can replace the traditional end-to-end repair using donor phrenic nerves with better results of nerve regeneration without diaphragm compromise.

Concurrent variations of median and musculocutaneous nerves and their clinical correlation--a cadaveric study.

Variations of median nerve, musculocutaneous nerve and their communicating branches are of interest for anatomists and surgeons. These variations may be vulnerable to damage in surgical procedures. We examined median nerve and musculocutaneous nerve concurrently in 58 cadavers, i.e. 116 superior extremities, and found median nerve innervating muscle of the anterior compartment of arm in the absence of musculocutaneous nerve in 11.2% superior extremities, splitting of median nerve in the arm into median nerve proper and musculocutaneous nerve in 5.12% superior extremities, and communication between median and musculocutaneous nerves in 20.7% superior extremities. Knowledge of such anatomical variations is helpful for surgeons treating neoplasm or repairing trauma.

The efficacy of end-to-end and end-to-side nerve repair (neurorrhaphy) in the rat brachial plexus.

Proximal nerve injury often requires nerve transfer to restore function. Here we evaluated the efficacy of end-to-end and end-to-side neurorrhaphy of rat musculocutaneous nerve, the recipient, to ulnar nerve, the donor. The donor was transected for end-to-end, while an epineurial window was exposed for end-to-side neurorrhaphy. Retrograde tracing showed that 70% donor motor and sensory neurons grew into the recipient 3 months following end-to-end neurorrhaphy compared to 40-50% at 6 months following end-to-side neurorrhaphy. In end-to-end neurorrhaphy, regenerating axons appeared as thick fibers which regained diameters comparable to those of controls in 3-4 months. However, end-to-side neurorrhaphy induced slow sprouting fibers of mostly thin collaterals that barely approached control diameters by 6 months. The motor end plates regained their control density at 4 months following end-to-end but remained low 6 months following end-to-side neurorrhaphy. The short-latency compound muscle action potential, typical of that of control, was readily restored following end-to-end neurorrhaphy. End-to-side neurorrhaphy had low amplitude and wide-ranging latency at 4 months and failed to regain control sizes by 6 months. Grooming test recovered successfully at 3 and 6 months following end-to-end and end-to-side neurorrhaphy, respectively, suggesting that powerful muscle was not required. In short, both neurorrhaphies resulted in functional recovery but end-to-end neurorrhaphy was quicker and better, albeit at the expense of donor function. End-to-side neurorrhaphy supplemented with factors to overcome the slow collateral sprouting and weak motor recovery may warrant further exploration.

Nerve conduction studies of the axillary, musculocutaneous and radial nerves in elite ice hockey players.

AIM: The peripheral nerves of the upper extremity are exposed to acute and chronic mechanical injuries in ice hockey players, because of the high repetition of motions, high muscular forces and extreme shoulder positions. This study was performed to evaluate the effect of ice hockey playing on the axillary, musculocutaneous and radial nerves crossing the upper arm region. METHODS: The ice hockey group consisted of 20 first-division male ice hockey players and the control group consisted of 20 non-active males. The neurophysiological study consisted of motor nerve conduction latency of the axillary, musculocutaneous and radial nerves. RESULTS: The values of distal motor latency (DML) of the axillary, radial and musculocutaneous nerves were significantly prolonged in the ice hockey players compared with the controls. Ice hockey can repetitively stress the upper extremity during shooting, because of forceful throwing to move the puck from the stick blade to the opponent's net. The mechanism of prolonged DML in the axillary nerve may both tract and compress as the axillary nerve stretches across the humerus during movement. From this study it emerged that using the biceps and coracobrachialis muscles can create notable muscle compartment pressure on the musculocutaneus nerve. The significant differences detected in the neurophysiologic study of the musculocutaneous nerve between the ice hockey players and controls may reflect the fact that the forces acting on the shoulder and the elbow during ice hockey matches can effectively influence DML. CONCLUSIONS: The authors suggest two plausible causes for prolonged radial nerve DML: direct compression by the hypertrophied triceps muscle and stretching of the arm. The study suggests it is likely that a combination of skeletal muscle hypertrophy and excessive biomechanical demands on neurological structures during ice hockey matches may be a major etiologic factor in compression of the axillary, musculocutaneous and radial nerves.

Cortical brain mapping of peripheral nerves using functional magnetic resonance imaging in a rodent model.

The regions of the body have cortical and subcortical representation in proportion to their degree of innervation. The rat forepaw has been studied extensively in recent years using functional magnetic resonance imaging (fMRI), typically by stimulation using electrodes directly inserted into the skin of the forepaw. Here we stimulate the nerve directly using surgically implanted electrodes. A major distinction is that stimulation of the skin of the forepaw is mostly sensory, whereas direct nerve stimulation reveals not only the sensory system but also deep brain structures associated with motor activity. In this article, we seek to define both the motor and sensory cortical and subcortical representations associated with the four major nerves of the rodent upper extremity. We electrically stimulated each nerve (median, ulnar, radial, and musculocutaneous) during fMRI acquisition using a 9.4-T Bruker scanner (Bruker BioSpin, Billerica, MA). A current level of 0.5 to 1.0 mA and a frequency of 5 Hz were used while keeping the duration constant. A distinct pattern of cortical activation was found for each nerve that can be correlated with known sensorimotor afferent and efferent pathways to the rat forepaw. This direct nerve stimulation rat model can provide insight into peripheral nerve injury.

Medial antebrachial cutaneous nerve measurements to diagnose neurogenic thoracic outlet syndrome.

A reliable objective test is still needed to confirm the diagnosis of neurogenic thoracic outlet syndrome (NTOS). Over the past 20 years, it has been suggested that responses to medial antebrachial cutaneous nerve (MAC) and C8 nerve root stimulation could be used for this purpose. Herein, we explore this thesis. A clinical diagnosis of NTOS was established in 41 patients, all of whom underwent surgical decompression. Preoperatively, all patients were studied with MAC sensory neural action potential (SNAP) determinations and C8 nerve root stimulation. Controls were 19 asymptomatic, healthy volunteers. MAC sensory latency on 79 control sides was 1.5-2.4 msec, while latency in 41 symptomatic patients ranged 2.2-2.8 msec. Latency of 2.5 or greater was noted in 30 patients (specificity 99%, sensitivity 73%), confirming a diagnosis of NTOS, while the remaining 11 (27%) fell into the borderline zone of 2.2-2.4 msec. The latency difference between right and left sides in controls was 0-0.2 msec in 17 (89%), while in NTOS patients 31 had a difference of 0.3 msec or more (sensitivity 89%, specificity 63%). Amplitudes of 10 muV or more occurred in 77 of 79 control sides, whereas the amplitude was under 10 muV in 28 patients (specificity 97%, sensitivity 68%). Amplitude ratios between right and left sides in controls were 1.7 or less. Ratios of 2.0 or more were measured in 25 patients (specificity 100%, sensitivity 61%). Using the four diagnostic criteria (latency over 2.4 msec, latency difference between sides of 0.3 or more, amplitude under 10 muV, and amplitude ratios of 2.0 or more), 40 of the 41 patients had at least one of the four diagnostic criteria, 23 patients (56%) had three or four positive criteria, and 12 (29%) had two. C8 nerve root stimulation responses were below normal (56 M/sec) in 54%. MAC measurement is a fairly reliable technique for confirming the diagnosis of NTOS. Latency determination appeared to be a slightly more consistent measurement in this study, but amplitude and C8 nerve root stimulation were also helpful. A combination of these techniques seems to be the most reliable approach.

Quantitative characterization of regenerating axons after end-to-side and end-to-end coaptation in a rat brachial plexus model: a retrograde tracer study.

The efficacy of end-to-side repair as a method of nerve reconstruction has been questioned, and most studies that characterize the mode of re-innervation are marred by inappropriate experimental design and lack quantitative analysis. This makes characterization of re-innervating neurons confusing and consequently controversy remains as to the extent and source of reinnervating axons. In an experimental brachial plexus rat model, we transected the musculocutaneous nerve, labeled its neuron pool with Fast-Blue and joined the distal stump to the side of the intact ulnar nerve, or to the proximal stump of the divided ulnar nerve, to characterize neurons that reinnervate the recipient nerve. Tetramethyl-rhodamine dextran (TMRD) or fluoro-gold was used to map the reinnervating motor and sensory neurons at 12 weeks post-transection. No neurons originally labeled from musculocutaneous nerve were subsequently labeled with TMRD or fluoro-gold, showing that this original neuron pool does not contribute to re-innervation of the distal musculocutaneous nerve, but that reinnervation occurs solely by ulnar nerve motor and sensory axons. In the end-to-side group, 16.4% of the motor and 7% of the sensory donor ulnar nerve neurons re-innervated the musculocutaneous nerve exclusively, and a further 10% motor and 11.6% sensory innervated the musculocutaneous nerve by collateral sprouting of their axons. This compared to re-innervation by 62.6% of motor and 70.4% of ulnar nerve sensory neurons in the positive control that underwent end-to-end repair. Our results confirm the concept of collateral sprouting and support the use of end-to-side repair.

The optimal motor response for infraclavicular brachial plexus block.

BACKGROUND: In this prospective study we compared the success of the infraclavicular brachial plexus block using double-stimulation in regard to the second nerve response elicited with neurostimulation. METHODS: Six-hundred-twenty-eight patients undergoing emergency upper limb surgery using infraclavicular brachial plexus block were included in this study. The musculocutaneous nerve was initially blocked and the groups were then evaluated according to the second nerve located, which was radial in 54%, median in 35%, and ulnar in 11% of patients. Blocks were performed using lidocaine 1.5% with 1/400,000 epinephrine 40 mL in all cases. The block was assessed every 5 min for 30 min after completion of the block. RESULTS: The success rate was 96% for the radial response group, 89% for the median response group, and 90% for the ulnar response group (P < 0.05). Time to perform the block and the onset time were not significantly different among groups. No serious complications were observed. CONCLUSION: We conclude that having initially located and blocked the musculocutaneous nerve, subsequent injection on a radial response resulted in a slightly more reliable success rate than injection with an ulnar or median response.