An anatomic study of structure and innervation of the serratus anterior muscle.

BACKGROUND: The structure and function of the serratus anterior muscle are partitioned into three parts. If the morphological characteristics in each part can be demonstrated in more detail, the cause of dysfunction will probably be identifiable more accurately. The purpose of this study was to demonstrate the details of the structure and innervation in each part of the serratus anterior muscle. MATERIALS AND METHODS: This macroscopic anatomic study was conducted using ten sides from five cadavers. The structure and innervation in each part of this muscle were examined. RESULTS: In the superior part, the independent branch was divided from a branch innervating the levator scapulae muscle. In the middle part, the long thoracic nerve descended on one-third of the anterior region between the origin and insertion. In the inferior part, the long thoracic nerve which ramified into many branches and branches from the intercostal nerves were distributed on all sides. CONCLUSION: This study demonstrated that the innervation of the serratus anterior muscle was different in each part. The difference indicates that the superior part has an intimate relation with the levator scapulae muscle while the middle and inferior parts could be the actual serratus anterior muscle. Moreover, the distribution of branches from the intercostal nerves shows that the inferior part has a connection with some trunk elements. Understanding these characteristics of innervation is useful to identify the cause of dysfunction. In addition, we assert that the constant distribution of branches from the intercostal nerves is significant for the morphology.

The anatomical rationale for an upper limb sympathetic blockade: preliminary report.

Stellate ganglion blockade (SGB) has long been considered pivotal in the diagnosis, determination of prognosis and management of chronic regional pain syndrome (CRPS) by sympathectomy. To date a variety of SGB techniques have been described. An inaccurate SGB may mislead clinicians and deny patients a potentially beneficial procedure. In order to obtain a predictable and readily reproducible blockade of the upper limb, a modified anterior technique was evaluated. This modified sympathetic block was performed in 10 adult cadavers (n=19 sides). Toluidine blue solution (10 ml) was injected and, following median sternotomy, the extent of spread of dye was evaluated. In one cadaver a dual block using both the modified and the standard techniques was performed. Proximal spread to the seventh cervical vertebra was noted in all blocks; distal spread extended to the neck of the third rib (n=3), neck of the fourth rib 7 (n=15) and neck of the seventh rib (n=1). Medial spread was greater than lateral spread and extended to the vertebral bodies (vagus nerve was also stained) while lateral spread in all cases "blocked" lower roots of the brachial plexus and was consistently noted beyond the usual location of the nerve of Kuntz. This modified technique demonstrated that the lower cervical ganglia and proximal thoracic sympathetic trunk were consistently stained. It should be noted that the spread was sufficiently lateral to block the nerve of Kuntz. The pitfalls of this technique aside, we suggest that this technique be reserved for therapeutic purposes, particularly when sympathectomy is not possible.

Intraoperative thermographic monitoring during neurogenic thoracic outlet decompressive surgery.

This article reports the use of thermography to monitor 123 plexus decompressions for neurogenic thoracic outlet syndrome. The diagnosis and management of this disease continues to be controversial. Questions about pathologic mechanisms, the extent and frequency of muscular entrapment, scar, and interdigitations, as well as their relative contributions, remain. Thermographic visualization of the operated extremity allowed us to map and correlate thermal changes with specific surgical manipulations, as well as to analyze the tissues resected to better answer these questions. Initial thermal abnormalities indicating, usually, ulnar entrapments or irritation, normalized sequentially as discrete entrapments were resected. Thermographic monitoring continues to provide surgically useful information in one third of operations.

Effect of altered flow on the pattern of permeability around rabbit aortic branches.

Uptake of circulating macromolecules by the aortic wall is greater downstream than upstream of branch sites in immature rabbits, but the opposite pattern is seen at later ages. The mature pattern is nitric oxide dependent; we tested whether it is also flow dependent. Intercostal arteries of anesthetized rabbits were occluded, sham operated, or left alone. Uptake of rhodamine-labeled albumin was assessed by quantitative fluorescence microscopy of the sections through the aorta. In mature animals, uptake was higher upstream than downstream of the control and sham-operated branches, but the pattern was reversed at occluded branches. In young animals, uptake was not significantly different between regions upstream and downstream of control, sham-operated, or occluded branches. The absence of the normal immature pattern may reflect an influence of anesthesia and will assist in the elucidation of mechanisms underlying this pattern. The data for mature animals provide the first direct evidence that flow determines permeability near arterial branches and may account for the inverse spatial correlation between shear stress and disease prevalence at branches of adult human arteries.

Bifid ribs observed in the third and the fourth ribs.

Three cases of bifid ribs were found in two cadavers during routine dissections at the Iwate Medical University School of Dentistry. All of the cases were found in the third or the fourth rib. The distal parts of the osseous rib bifurcated with an angle of 60 degrees and both of the branches had their own costal cartilage. The costal cartilage fused again to form the trunk which was connected to the sternum. The space between the two branches was filled with presumably normal intercostal muscles. Blood supply was maintained by a small branch from the interthoracic artery to the upper branches. However, the intercostal nerves did not branch toward the upper branch but only ran along the lower margins of the lower branches of the bifid ribs.

Response of the inspiratory intercostal [correction of intercoastal] muscles to increased inertial loads.

To test the hypothesis that the external intercostals and levator costae constitute an inspiratory reserve system, we have examined the response of these muscles to increased inertial loads. Weights were t hus attached sequentially to the ribs in ten lightly anesthetized, spontaneously breathing dogs. As weights were attached, the ribs were progressively displaced caudally at end-expiration, so that the external intercostal muscles were lengthened. In addition, the cranial motion of the ribs during inspiration was gradually reduced, the inspiratory shortening of external intercostal disappeared, and the external intercostal and levator costae inspiratory EMG activities increased. The parasternal intercostal inspiratory activity, however, remained unchanged. Studies also showed that: (1) the increases in external intercostal activity appeared with the first loaded breath and disappeared as soon as the load was removed; (2) these increases were related to the suppression of the inspiratory muscle shortening, rather than to the increase in precontraction muscle length or to vagal inputs; and (3) denervation of the external intercostal caused inspiratory muscle lengthening but had little effect on the inspiratory motion of the ribs. These observations thus indicate that increased inertial loads on the ribs trigger reflexes, possibly spindle reflexes, which cause selective increases in external intercostal and levator costae inspiratory EMG activities. In that sense, the present findings are consistent with the idea that these two muscles constitute an inspiratory reserve system. However, it appears that the major effect of these increased activities is simply to prevent the muscles from lengthening during inspiration.

Surgical anatomy of the phrenic nerve and internal mammary artery.

Dissection of the thoracic inlet was performed on 22 cadavers to determine the relationship of the phrenic nerve to the internal mammary artery as it passes from lateral to medial behind the first rib. On the left the nerve was found to cross superior to the artery and then medial to it in 14 of 22 specimens; on the right this was found in ten of 22 specimens. In all other specimens, it crossed inferior to the internal mammary artery. These findings demonstrate that there is no constant relationship between these structures, and emphasize the need for caution when dissecting the internal mammary artery at or above the level of the first rib.

Effects of intercostal nerve resection on the longitudinal rib growth in the growing rabbit.

Two, three, or four intercostal nerves with their vasoconstrictive sympathetic fibers were resected on the right side of 15 growing rabbits. Animals submitted to sham operations and intact animals formed two control groups. A scintigraphic study with 99mTc-methylene diphosphonate, performed on the test group 2 months after the resection, showed a significantly greater uptake of the isotope on the right than on the left costochondral junctions (p less than 0.05). Three months later the difference was still larger. There was no such significant difference in the rabbits of the two reference groups. In the rabbits of both these groups, the right and left ribs of each pair were almost equal in length. Of the denervated ribs of the rabbits composing the test group, the right ribs increased in length to a greater extent than the corresponding left ribs. The difference was statistically significant (p less than 0.05). As a consequence of this left-right difference in length, mild thoracic scoliosis convex to the left developed 2 months after the resection. The total weight and volume of the denervated right ribs increased significantly more than those of the corresponding control left ribs (p less than 0.05), but their mineral content per unit of weight or volume showed no significant difference.

Respiratory responses to external resistive loads during vagal blockade in awake dogs.

The present study examined the possibility that mechanoreceptors in the chest wall structures (rib cage and diaphragm) contribute to the increase in the neuromuscular drive to breathe (occlusion pressure) when the load on the respiratory muscles is increased in conscious animals and humans. Studies were carried out in 4 awake dogs in which external resistive loads (12 cmH2O/L/s) were applied during inspiration to increase the load on the respiratory muscles. Loads were applied via a tracheostomy during complete vagal blockade performed by cooling exteriorized cervical vagal loops. The ventilatory and occlusion pressure responses to the load were compared over the same range of chemical drive by applying loads during CO2 rebreathing. During vagal blockade, inspiratory resistive loads had no consistent effect on the duration of inspiration or expiration and decreased the ventilatory response to hypercapnia by decreasing average inspiratory flow rate. In all animals, however, inspiratory loading increased the occlusion pressure (P100) response to hypercapnia. The P100 at PCO2 = 55 mmHg increased during flow loading in all 4 animals, and the slope of the change in P100 produced for a given change in PCO2 (delta P100/delta PCO2) increased in 3 of the 4. Flow loading had no effect on end-expiratory lung volume at rest and did not influence the decrease in lung volume observed during hypercapnia. The present study indicated that the neuromuscular drive to breathe, as assessed from the occlusion pressure, is increased in conscious animals subjected to ventilatory loads during vagal blockade.(ABSTRACT TRUNCATED AT 250 WORDS)