Intramuscular Neural Distribution of Rhomboid Muscles: Evaluation for Botulinum Toxin Injection Using Modified Sihler’s Method

This study describes the nerve entry point and intramuscular nerve branching of the rhomboid major and minor, providing essential information for improved performance of botulinum toxin injections and electromyography. A modified Sihler method was performed on the rhomboid major and minor muscles (10 specimens each). The nerve entry point and intramuscular arborization areas were identified in terms of the spinous processes and medial and lateral angles of the scapula. The nerve entry point for both the rhomboid major and minor was found in the middle muscular area between levels C7 and T1. The intramuscular neural distribution for the rhomboid minor had the largest arborization patterns in the medial and lateral sections between levels C7 and T1. The rhomboid major muscle had the largest arborization area in the middle section between levels T1 and T5. In conclusion, botulinum neurotoxin injection and electromyography should be administered in the medial and lateral sections of C7−T1 for the rhomboid minor and the middle section of T1−T7 for the rhomboid major. Injections in the middle section of C7−T1 should also be avoided to prevent mechanical injury to the nerve trunk. Clinicians can administer safe and effective treatments with botulinum toxin injections and other types of injections by following the methods in our study.

Changes in neuromuscular structure and functions of human colon during ageing are region-dependent

ObjectiveTo determine if human colonic neuromuscular functions decline with increasing age.DesignLooking for non-specific changes in neuromuscular function, a standard burst of electrical field stimulation (EFS) was used to evoke neuronally mediated (cholinergic/nitrergic) contractions/relaxations in ex vivomuscle strips of human ascending and descending colon, aged 35–91 years (macroscopically normal tissue; 239 patients undergoing cancer resection). Then, to understand mechanisms of change, numbers and phenotype of myenteric neurons (30 306 neurons stained with different markers), densities of intramuscular nerve fibres (51 patients in total) and pathways involved in functional changes were systematically investigated (by immunohistochemistry and use of pharmacological tools) in elderly (≥70 years) and adult (35–60 years) groups.ResultsWith increasing age, EFS was more likely to evoke muscle relaxation in ascending colon instead of contraction (linear regression: n=109, slope 0.49%±0.21%/year, 95% CI), generally uninfluenced by comorbidity or use of medications. Similar changes were absent in descending colon. In the elderly, overall numbers of myenteric and neuronal nitric oxide synthase-immunoreactive neurons and intramuscular nerve densities were unchanged in ascending and descending colon, compared with adults. In elderly ascending, not descending, colon numbers of cell bodies exhibiting choline acetyltransferase immunoreactivity increased compared with adults (5.0±0.6 vs 2.4±0.3 neurons/mm myenteric plexus, p=0.04). Cholinergically mediated contractions were smaller in elderly ascending colon compared with adults (2.1±0.4 and 4.1±1.1 g-tension/g-tissue during EFS; n=25/14; p=0.04); there were no changes in nitrergic function or in ability of the muscle to contract/relax. Similar changes were absent in descending colon.ConclusionIn ascending not descending colon, ageing impairs cholinergic function.

Immunohistochemical Detection of Motor Endplates in the Long-Term Denervated Muscle

Background We have demonstrated that the native motor zone (NMZ) within a muscle is an ideal target for performing nerve-muscle-endplate band grafting (NMEG) to restore motor function of a denervated muscle. This study was designed to determine spatiotemporal alterations of the myofibers, motor endplates (MEPs), and axons in the NMZ of long-term denervated muscles for exploring if NMEG-NMZ technique would have the potential for delayed reinnervation. Methods Sternomastoid (SM) muscles of adult female Sprague-Dawley rats (n = 21) were experimentally denervated and denervation-induced changes in muscle weight, myofiber size, MEPs, and intramuscular nerve axons were evaluated histomorphometrically and immunohistochemically at the end of 3, 6, and 9 months after denervation. The values obtained from the ipsilateral normal side served as control. Results The denervated SM muscles exhibited a progressive reduction in muscle weight (38%, 31%, and 19% of the control) and fiber diameter (52%, 40%, and 28% of the control) for 3-, 6-, and 9-month denervation, respectively. The denervated MEPs were still detectable even 9 months after denervation. The mean number of the denervated MEPs was 79%, 65%, and 43% of the control in the 3-, 6-, and 9-month denervated SM, respectively. Degenerated axons in the denervated muscles became fragmented. Conclusions Persistence of MEPs in the long-term denervated SM suggests that some surgeries targeting the MEPs such as NMEG-NMZ technique should be effective for delayed reinnervation. However, more work is needed to develop strategies for preservation of muscle mass and MEPs after denervation.