Anatomy of the lateral intermuscular septum of the arm and its relationships to the radial nerve and its proximal branches. Laboratory investigation

OBJECT

Other than very simple descriptions of the existence of the lateral intermuscular septum (LIS), the literature offers almost nothing about its detailed anatomy, relationships to the radial nerve, and proximal branches. To further elucidate its morphological characteristics, the present cadaveric study was performed.

METHODS

The lateral arm was bilaterally dissected from 25 adult fixed cadavers (50 sides). Specifically, a detailed evaluation of the LIS was made, and this structure's attachments and relationships to the radial nerve were analyzed and measured.

RESULTS

In addition to the previously described muscles arising from the LIS, the authors identified the extensor carpi radialis brevis muscles as partially arising from this structure. The deep and posterior portion of the deltoid tendon was confluent with the superior aspect of the LIS. The mean thickness of the LIS was 1.0 mm. Distally, the LIS attached strongly to the lateral epicondyle of the humerus and became confluent with the annular ligament encircling the head of the radius. The distal attachment of the LIS was confluent with the capsule of the elbow joint. All radial nerves traveled through a defect (mean diameter 1 cm) in the LIS. With traction on the nerve from proximal and distal to this defect, there was free excursion. In 85% of the specimens, however, the posterior antebrachial cutaneous nerve traveled through a tunnel within the LIS and pierced the septum at a mean of 5 cm proximal to the lateral epicondyle. The lower lateral brachial cutaneous nerve proximally pierced the LIS near its origin, occurring a mean of 3.2 cm distal to the LIS's origin from the humerus.

CONCLUSIONS

To the authors' knowledge, the details regarding the LIS and its relationships to the radial nerve have not been reported. Such information may be of use to surgeons who operate in this region, for example, during neural repair or entrapment procedures.

Regional anatomic structures of the elbow that may potentially compress the ulnar nerve

HYPOTHESIS

Traumatic injuries to the ulnar nerve at the elbow are a frequent problem as it is vulnerable to stretching and compression with motion of the upper limb. The aim of the present study was to explore the course of the ulnar nerve at the elbow and forearm and to determine possible anatomical structures that may cause compression of this structure.

MATERIALS AND METHODS

We examined 12 upper limbs from cadavers. The length of any fibrous bands, and if present, their distance to the medial epicondyle was recorded.

RESULTS

On 5 sides a fibrous band originating from the medial intermuscular septum was observed to cross over the ulnar nerve. The average length of the fibrous band was 5.7 cm, and it attached to the medial epicondyle. The mean length of the ulnar nerve as it coursed in the cubital tunnel was 3.8 cm. In 4 of the cases, the ulnar nerve was covered by muscle fibers originating from the flexor digitorum superficialis and extending to the flexor carpi ulnaris. On 5 sides we observed fibrous thickenings, and on 8 sides vascular structures were found crossing over the ulnar nerve.

DISCUSSION

The cubital tunnel is the most common site of compression of the ulnar nerve. Numerous surgical procedures are recommended for cubital tunnel syndrome. Simple decompression is used most commonly. Although surgical procedures are reported to provide efficient pain relief and functional recovery, residual or recurrent symptoms have been reported. Reasons for such recurrences may be more proximal or distal compression of the ulnar nerve as seen in our study.

CONCLUSION

Knowledge of possible compression sites of the ulnar nerve is important to the surgeon so that complications are avoided and postoperative recurrence is decreased.

LEVEL OF EVIDENCE

Basic science study.

Defining the macroscopic and microscopic findings of experimental focal brain ischemia in rats from a forensic scientist's point of view

Approximately 10% of all deaths in the world occur as a result of stroke. Determination of the time schedule of the pathologic events in a stroke patient is invaluable for a forensic specialist. The aim of this study was to define the schedule of the macroscopic and microscopic changes that occurred in a rat model of permanent focal ischemia for providing useful clues for the evaluation of stroke patients. Male Wistar rats weighing 250 to 350 g were used in this study. Permanent focal brain ischemia was applied by the suture occlusion method. The animals were divided into 7 experimental groups (n = 6) with time schedules including 1.5, 3, 6, 12, 24, 72 hours, and the sham. Brains were harvested at the end of the determined time schedule. Lesions in the frontoparietal cortex were evaluated macroscopically first and later hematoxylin eosin stained sections from the infarct core were investigated microscopically. Macroscopically, enlargement of the ipsilateral hemisphere was mild at 6 hour, apparent at 12 and 24 hours, and mild again at 72 hours. Microscopically, ischemic changes were apparent even at 1.5 hour. Red neurons and infiltration of the parenchyma with neutrophil leukocytes were observed at 12 hours. Pannecrosis and massive leukocyte infiltration were observed at 72 hours. Macroscopic and microscopic findings obtained from a rat model may provide clues for determination of the time-dependent changes due to brain ischemia in human subjects. Finally, the benefits of determination of time course of pathologic changes in the brain for forensic scientists were discussed.

Anatomy of the reflected ligament of the inguinal region

BACKGROUND

There is a paucity in the literature regarding the reflected ligament. Therefore, the present study was performed in order to further elucidate this anatomy.

MATERIAL AND METHODS

Eighteen formalin-fixed adult cadavers (35 sides) underwent dissection of the medial inguinal region. The reflected ligament was observed for and when identified, its dimensions were measured.

RESULTS

83% of sides were found to have a reflected ligament. These were identified in 16 male and 13 female bodies. The size and shape for the reflected ligaments were variable but overall, triangular in nature. In general, the reflected ligament was found to extend from the lacunar and medial inguinal ligaments and extended obliquely toward the midline at an approximate 45 degrees angle to insert near the linea alba. Two ligaments (6.9 %) were identified that interdigitated with the contralateral reflected ligament. The medial and lateral lengths of the ligament had a mean measurement of 2.28 and 2.58 cm. The base of the reflected ligament had a mean of 2.52 cm and the height of this ligament was found to have a mean of 2.56 cm. The mean area of the reflected ligament was calculated as 2.93 cm(2). There was no statistically significant difference between right or left sides or between genders.

CONCLUSIONS

The reflected ligament was identified in the majority of our specimens and this structure usually contributed to the formation of the posteromedial wall of the external inguinal ring. Therefore, this fact should be included in future descriptions of this ligament.

Arcuate line of the rectus sheath: clinical approach

The rectus sheath has been extensively described in gross anatomic studies but there is very little information available regarding the arcuate line (AL). The aim of the present study therefore was to explore and delineate the morphology, topography and morphometry of the arcuate line and provide a comprehensive picture of its anatomy across a broad range of specimens. The AL was present in all specimens examined. In addition, the AL was found to be located at a mean of 70.2% (67.3-75.2%) of the distance between the pubic symphysis and the umbilicus, and at 33.9% (30.2-35.4%) of the distance between the pubic symphysis and the xiphoid process. This location was found to be at a mean of 2.1 +/- 2.3 cm superior to the level of the anterior superior iliac spines. Furthermore, there were three distinct types of AL morphology. In type I (65%), the fibers of the posterior rectus sheath (PRS) gradually disappeared over the transversalis fascia, creating an incomplete demarcation of the actual location of the AL. In type II (25%) the termination of the fibers of the PRS was acutely demarcated over the transversalis fascia, creating a clear border with the AL. In type III (10%) the fibers of the PRS created a double and thickened aponeurotic line. In these cases a double AL was observed. Better preoperative knowledge of the location of the AL may, in some cases, help preoperative planning to facilitate primary fascial repair, which can then be supported with on-lay mesh, depending on the clinical situation.

Morphologic variation of the diaphragmatic crura: a correlation with pathologic processes of the esophageal hiatus?

The contributions of muscle fibers from the right and left diaphragmatic crura to the formation of the esophageal hiatus have been documented in several studies, none coming to a complete consensus on the number of anatomic variations or the prevalence of these variations in the human population. These variations may play a role in the pathogenicity of specific diseases that involve the esophageal hiatus, such as hiatal hernias. We examined a total of two hundred adult cadavers during 2000-2007. The variations in the diaphragmatic crura, particularly their muscular contributions to the formation of the esophageal hiatus, were grossly examined and revealed a bilateral occurrence of diaphragmatic crura in all 200 specimens. The results of the various morphological patterns of circumferential muscle fibers forming the esophageal hiatus were classified into six groups. The most common type (Type I, 45%) formed the esophageal hiatus from muscular contributions arising solely from the right crus. In Type II (20%) the esophageal hiatus was formed by muscular contributions from the right and left crura. In Type III (15%), the right and left muscular contributions arose from the right crus with an additional band from the left crus. Type IV (10%) showed that the right and left muscular contributions arose from the right crus, with two additional (anterior and posterior) bands arising from the left crus. Type V (5%) demonstrated the contributions arising solely from the left crus. In Type VI (5%) the right and left contributions originated from the left crus with two additional bands, one from the right crus and one from the left crus. These variations may play a role in the pathogenicity of specific diseases that involve the esophageal hiatus such as hiatal hernia, gastroesophageal reflux disease and Dunbar's syndrome.

Lateral lakes of Trolard: anatomy, quantitation, and surgical landmarks. Laboratory investigation

OBJECT

There is scant and conflicting information in the literature regarding the lateral lacunae, or lateral lakes of Trolard. As these venous structures can be encountered surgically, this study aimed at further elucidating their anatomy, identifying surgical landmarks, and associated quantitation.

METHODS

Thirty-five adult cadavers were dissected of lateral lacunae. Following quantitation of the lacunae, these structures were measured, as were the distances from them to the coronal and sagittal sutures.

RESULTS

A mean of 1.9 lacunae were identified on the right sides and 1.4 lacunae on the left sides. Although there tended to be slightly more lacunae on the right sides, this difference did not reach statistical significance (p > 0.05). The average lengths of the lacunae were 3.2 and 2.0 cm for the right and left sides, respectively. The mean widths of these venous lakes were 1.5 cm for the right sides and 0.8 cm for the left sides. Lacunae were variably positioned but tended to cluster near the vertex of the skull. None were identified posterior to the lambdoid sutures, and only 5 were found to lie anterior to the coronal suture, with 4 of these located on right sides (p < 0.05). When lacunae were identified anterior to the coronal suture, they were generally 5-6 cm from this structure. The majority of lacunae could be identified between the coronal and lambdoid sutures and within 3 cm of the midline.

CONCLUSIONS

Although the situation varies, lateral lacunae are concentrated posterior to the coronal suture and anterior to the lambdoid sutures. They are most often found within 3 cm of the sagittal suture. These previously unreported data could be useful to the neurosurgeon in planning surgical procedures that traverse the calvaria.

Costanzo Varolio (Constantius Varolius 1543-1575) and the Pons Varolli

COSTANZO VAROLIO (CONSTANTIUS Varolius) (1543-1575) was born in Bologna and died in Rome. This professor of anatomy and papal physician was the first to examine the brain from its base up, in contrast with previous dissections of this organ performed from the top down. Varolio was the first to describe many structures, including the pons, which is still known today as the pons Varolli. Varolio was a pupil to the well-known anatomist Aranzio, who was in turn a pupil of Vesalius. Our current understanding of the nervous system is based on the early anatomic descriptions and depictions by such individuals as Varolio.

Contributions of the fourth spinal nerve to the brachial plexus without prefixation

Object

The intradural contributions of the C-4 nerve rootlets have not been previously evaluated for their connections to the brachial plexus. The authors undertook a cadaveric study to evaluate the C-4 contributions to the upper trunk of the brachial plexus.

Methods

The posterior cervical triangles from 60 adult cadavers were dissected. All specimens that were found to have extradural C-4 contributions to the upper trunk of the brachial plexus were excluded from further study. In specimens found to have no extradural C-4 contributions to the brachial plexus a C1–T1 laminectomy was performed. Observations were made of any neural communications between adjacent spinal rootlets, specifically between C-4 and C-5.

Results

Nine (15%) of the 60 sides were found to have extradural C-4 contributions to the upper trunk of the brachial plexus. These sides were excluded from further study. No specimen was found to have a postfixed brachial plexus. Of the remaining 51 sides, 11 (21.6%) were found to have intradural neural connections between C-4 and C-5 dorsal rootlets and 1 (1.96%) had a connection between the ventral roots of C-4 and C-5. Communications between these 2 adjacent dorsal cervical cord levels were of 3 types. Type I was a vertical communication between the more horizontally traveling dorsal roots. Type II was a forked communication between adjacent C-4 and C-5 dorsal rootlets. The Type III designation was applied to connections between ventral rootlets. Although communications were slightly more frequent on left sides, this did not reach statistical significance.

Conclusions

In ~ 20% of normally composed brachial plexuses (those with extradural contributions from only C5–T1) we found intradural C4–5 neural connections. Such variations may lead to misinterpretation of spinal levels in pathological conditions of the spinal axis and should be considered in surgical procedures of this region, such as rhizotomy.

Ibn al-Nafis (1210–1288): The First Description of the Pulmonary Circulation

Ibn al-Nafis (1210–1288) was an Arab physician who contributed much to the advancement of medical knowledge and science in the 13th century. He was involved in jurisprudence, politics, and anatomical studies as well. Although a prominent ophthalmologist by training, today he is most recognized for his discovery of the lesser or pulmonary circulation. His was the first work to contradict the accepted teachings of Galen, which had existed since the 2nd century AD. His description included the observation that the wall of the septum is not porous either grossly or macroscopically as was believed by earlier scholars. Therefore, blood from the venous circulation had to be directed through the pulmonary artery (“venous artery”) through the lungs to be “mixed with air” and drained back to the left side of the heart through the pulmonary vein (“arterial vein”). This discovery would lead to a change in the historical observations that the pulmonary circulation was discovered by European scientists in the 16th century and lead many to wonder if these scientists had access to Ibn al-Nafis’ translated works. Ibn al-Nafis was devout to his work and to his religion, contributing much to the body of knowledge in anatomy and medicine as well as being a prominent and exceptional physician.

Ibn al-Nafis (1210-1288): the first description of the pulmonary circulation

Ibn al-Nafis (1210-1288) was an Arab physician who contributed much to the advancement of medical knowledge and science in the 13th century. He was involved in jurisprudence, politics, and anatomical studies as well. Although a prominent ophthalmologist by training, today he is most recognized for his discovery of the lesser or pulmonary circulation. His was the first work to contradict the accepted teachings of Galen, which had existed since the 2nd century AD. His description included the observation that the wall of the septum is not porous either grossly or macroscopically as was believed by earlier scholars. Therefore, blood from the venous circulation had to be directed through the pulmonary artery ("venous artery") through the lungs to be "mixed with air" and drained back to the left side of the heart through the pulmonary vein ("arterial vein"). This discovery would lead to a change in the historical observations that the pulmonary circulation was discovered by European scientists in the 16th century and lead many to wonder if these scientists had access to Ibn al-Nafis' translated works. Ibn al-Nafis was devout to his work and to his religion, contributing much to the body of knowledge in anatomy and medicine as well as being a prominent and exceptional physician.

The intriguing history of the human calvaria: sinister and religious

INTRODUCTION

A review of the ancient world finds multiple documentations describing the use of the human calvaria as a drinking implement.

TERMINOLOGY

This term, which is frequently and incorrectly called the "calvarium," has a unique history among multiple cultures of the world. For example, the purported site of Jesus' crucifixion "Calvary" is derived from this term calvaria. The present report explores the derivation, misuse, and history of the human calvaria.

Effects of the adducted or abducted position of the arm on the course of the musculocutaneous nerve during anterior approaches to the shoulder

Nerve injury is a common complication during anterior shoulder surgery. The purpose of the study was to evaluate the musculocutaneous nerve (MN) anatomically and to clarify the relationship of the MN to the glenoid labrum and coracoid process in different arm positions. The study was carried out on 40 shoulders of 20 adult cadavers fixed in 10% formaldehyde. The minimum distance of the MN at the entrance point of the nerve into the coracobrachialis to the anteromedial aspect of the coracoid tip and the distance between the MN and the top, middle, and inferior points of the glenoid labrum were measured. All measurements were performed with a digital caliper while the arm was in a neutral position, 45 degrees and 90 degrees of abduction, 90 degrees of abduction-internal rotation and 90 degrees of abduction-external rotation to evaluate whether arm position effects the results statistically or not. The results demonstrated that the position of the arm significantly changes the distance between the coracoid process (CP) and the MN or its cord. The change in distance between the glenoid labrum and the MN or its cord was also statistically significant. The distance between the CP and MN was greatest when the arm was abducted to 45 degrees (mean 3.4 cm) and least when the arm was positioned to 90 degrees of abduction-internal rotation (mean 2.0 cm). While the distance between the MN and the coracoid process was least at 90 degrees of abduction and internal rotation, the distance between the MN and glenoid labrum was lest with 90 degrees of abduction and external rotation. The distance between the glenoid labrum and MN was greatest with 45 degrees of abduction. The results of this study might be of use in avoiding the MN especially during Bristlow operations and certain rotator cuff procedures. Transferring the coracoid process during Bristow operations or placing arthroscopic portals when the arm is abducted to 45 degrees appears to be the safest position in terms of MN injury. Based on our results, when the arm needs to be abducted to 90 degrees during operation, externally rotating it may decrease the tension on the brachial plexus thus increasing the distance between the MN and the portals or retractors.

An anatomic investigation of the serratus posterior superior and serratus posterior inferior muscles

In classical anatomy textbooks the serratus posterior superior muscle was said to elevate the superior four ribs, thus increasing the AP diameter of the thorax and raising the sternum. However, electromyographic and other studies do not support its role in respiration. In order to help resolve this controversy and provide some insight into their possible functionality, the present study aimed at examining the morphology, topography and morphometry of serratus posterior superior and inferior muscles in both normal specimens and those derived from patients with a history of chronic obstructive pulmonary disorder (COPD). These muscles were examined in 50 human cadavers with an age range of 58-82 years. In 18 of the cadavers their histories revealed that they were suffering from COPD. There was no significant difference between right and left sides, race, gender and age and positive COPD history in regard to dimensions and nerves supply of serratus posterior superior and inferior muscles (P > 0.05). Based upon our findings that no morphometric differences exist between the of serratus posterior superior and inferior muscles of COPD patients versus controls, we are suggesting that no respiratory function be attributed to either of the serratus posterior superior and inferior muscles.

The velum interpositum revisited and redefined

INTRODUCTION

Descriptions of the velum interpositum (VI) are typically brief and lacking detail in most neuroanatomical and neurosurgical texts. As this structure may be involved clinically or encountered surgically, the present study seemed warranted.

MATERIALS AND METHODS

Twenty-adult (10 male and 10 female) formalin fixed and fresh cadaveric brains underwent a detailed dissection of the VI via an interhemispheric transcollosal approach. Observations were made of the attachment sites and continuation of the VI. Measurements were made of its length and width at its anterior, midportion, and posterior parts.

RESULTS

The VI extended laterally over the thalami to become continuous with the choroid plexus of the lateral ventricles. At a point along the thalami where the choroid plexus was found, the VI became "tacked" down and thus continuous with the choroid plexus subependymally. No specimen exhibited a separate choroid plexus of the third ventricle. In each, the choroid plexus of the lateral and third ventricles were the same tissue layer, all arising from the VI. This structure was adherent to but not fused to the deep surface of the fornix. The VI was also not fused to the pineal gland or habenula commissure but simply covered these structures. This membrane was confluent with the pia/arachnoid over the cerebellum and from the inferior surface of the parietal/occipital lobes and extended laterally into the choroid fissure.

CONCLUSIONS

To our knowledge, the extent of the VI as described herein has not been reported earlier. The supratentorial choroid plexus is simply a vascular extension of the VI. There is no separate choroid plexus of the third ventricle as often described. Clear planes exist between the VI and surrounding structures such as the pineal gland. Such data may be useful to neurosurgeons who operate in this region and to clinicians who interpret imaging in the area of the VI.

Popliteal artery aneurysms: a review

Popliteal artery aneurysms (PAAs) are the most common form of peripheral arterial aneurysms. The popliteal artery is the continuation of the femoral artery and represents the major source of blood to the leg. Thrombus formation as a result of PAA may reduce blood flow, leading to limb-threatening ischemia and potential limb amputation. Popliteal artery aneurysms are predominantly seen in males (95-99% of cases), presumably owing to their predisposition for arteriosclerosis, which is also a major factor for PAA predisposition. Additionally, it is not uncommon to see an abdominal aortic aneurysm associated with a PAA (30-50% of cases) or bilateral presentation of PAA (approximately 50% of cases). A consequence of a PAA and thrombus located in the popliteal fossa is an inflammatory reaction, potentially involving adjacent structures in the fossa. This may present clinically as pain in the leg and/or edema. Treatment of PAA involves either a conservative management protocol or a more aggressive intervention such as surgery. Proponents of conservative management will regulate the diameter of the aneurysm by ultrasound, while those in favor of surgical intervention will repair the aneurysm through a number of open surgical methods or by endovascular stent grafting. This review summarizes the historical points related to PAA and analyzes the pertinent anatomical implications, clinical findings and treatment methods for PAA.

Anatomy and potential clinical significance of the vastoadductor membrane

Few reports are found in the extant medical literature regarding the vastoadductor membrane. This membrane effectively creates a subcompartment within the subsartorial canal. The lower limbs of 16 embalmed adult cadavers were dissected to identify the vastoadductor membrane and note its measurements. A vastoadductor membrane was identified in all specimens and was derived from the medial intermuscular septum. This membrane connected the medial edge of the vastus medialis muscle to the lateral edge of the adductor magnus muscle. Membranes were all wider proximally and narrowed distally. The mean length of this structure was 7.6 cm. The mean width of the vastoadductor membrane at its proximal, midportion, and distal parts was 2.2, 1.7, and 0.5 cm, respectively. The mean distance from the anterior superior iliac spine to the proximal border of the vastoadductor membrane was 28 cm. The mean distance from the distal border of the membrane to the adductor tubercle was 10 cm. Seventy-five percent of specimens exhibited a fenestrated vastoadductor membrane. Branches of the saphenous nerve to the skin of the medial thigh pierced the vastoadductor membrane in 31% of specimens. Two specimens demonstrated branches derived from the branch of the obturator nerve that pierced this membrane en route to the skin of the medial thigh. Perforating venous branches from the great saphenous vein were identified in 22% of specimens. As compression of the femoral artery at the adductor hiatus is a well-recognized entity, the clinician may also try to explore potential compression of this vessel more proximally by an overlying vastoadductor membrane. The authors would also hypothesize that due to the interconnection between the adductor magnus and vastus medialis by the vastoadductor membrane that a potential synergy exists between the functions of these two muscles.

Surgical anatomy of the external branch of the superior laryngeal nerve

Palsy of the external branch of the superior laryngeal nerve (EBSLN) during thyroid surgery is an important complication reported with varying frequency. This study was carried out to investigate the relationship between the EBSLN, the upper part of the thyroid gland and the inferior constrictor muscle of the pharynx (IC), and also to define consistent landmarks for identifying and preserving the EBSLN. Forty neck halves of 20 cadavers were dissected. Measurements were obtained between the crossing point of the EBSLN with the superior thyroid artery (STA) and the upper pole of the thyroid gland, the point where EBSLN penetrates the IC and the inferior thyroid tubercle, and the middle point of the oblique line of the thyroid cartilage, and the EBSLN. In 22.5%, the EBSLN crossed the STA more than 1 cm above the upper pole of the thyroid gland (Type I of Cernea et al. [1992a] Head Neck 14:380-383). In 60%, the EBSLN crossed the STA less than 1 cm above the upper pole of the thyroid gland (Type IIa of Cernea et al. [1992a] Head Neck 14:380-383). In 17.5%, the EBSLN crossed the STA under the upper pole of the thyroid gland (Type IIb of Cernea et al. [1992a], Head Neck 14:380-383). In 22.5%, the full course of the nerve was superficial to the IC (Type 1 of Friedman et al. [2002] Arch Otolaryngol Head Neck Surg 128:296-303). In 67.5%, the nerve penetrated the IC (Type 2 of Friedman et al. [2002] Arch Otolaryngol Head Neck Surg 128:296-303). In 10%, the nerve could not be identified at the lateral side of the IC (Type 3 of Friedman et al. [2002] Arch Otolaryngol Head Neck Surg 128:296-303). In conclusion, it is possible to identify the nerve superficial to the IC in 90% of specimens on average. Knowledge of the relationship between the EBSLN, IC, inferior thyroid tubercle, oblique line of the thyroid cartilage and the sternothyroid muscle will be useful for the surgeon in avoiding unexpected complications.

The anatomic branch pattern of the axillary nerve

The purpose of this study is to determine the surgical anatomy and innervation pattern of the branches of the axillary nerve and discuss the clinical importance of the presented findings. We dissected 30 shoulders in 15 fixed adult cadavers under a microscope through anterior and posterior approaches. The axillary nerve was examined in 2 segments in relation to the underlying subscapularis muscle. The axillary nerve gave off no branches in the first segment in 85% of cases. When the posterior approach was used, the axillary nerve and its branches were observed to be in a triangular-shaped area. The mean distance from the posterolateral corner of the acromion to the axillary nerve and its branches was 7.8 cm. In all cases, the posterior branch of the axillary nerve gave off its first muscular branch to innervate the teres minor. The joint branch of the axillary nerve was observed to branch out in 3 different patterns. The acromial and clavicular parts of the deltoid muscle were observed to be innervated from the anterior branch of the axillary nerve in all cases. The posterior part of the deltoid muscle was observed to be innervated in 3 different patterns. The posterior part of the deltoid was innervated from the branch or branches coming only from the posterior branch in 70% of cases, from the anterior and posterior branches in 26.7% of cases, and from the anterior branch in 3.3% of cases. The findings of this study are useful for identifying each of the branches of the axillary nerve and have implications for surgeries related with selective innervation.

The anatomic relationships of the axillary nerve and surgical landmarks for its localization from the anterior aspect of the shoulder

The axillary nerve has long been known to be one of the nerves vulnerable to damage during shoulder arthroscopic and open surgical procedures. The relationship of the axillary nerve to the shoulder capsule and the subscapularis muscle has not been well defined in orthopedic literature. This descriptive anatomical study aimed to present the course and the relations of the axillary nerve with neighboring neurovascular structures and the shoulder capsule and to define anatomical landmarks and regions that can be used practically in anterior surgical approaches to the shoulder region. To investigate the course of the axillary nerve and its relationship with neighboring structures, 30 shoulders of 15 fixed adult cadavers were dissected under the microscope through an anterior approach. A triangle-shaped anatomic area containing the axillary neurovascular bundle was defined. The closest distance between the axillary nerve and the anteromedial aspect of the coracoid tip and the glenoid labrum was measured as 3.7 cm and 1.1 cm on average, respectively. The distance between the anteromedial aspect of the coracoid tip and the point where the nerve passes through the medial edge of the subscapularis was measured as 2.5 cm on average. The results of this study demonstrate the anatomic pattern and the course of the axillary nerve and its relations with the shoulder capsule. Knowing the exact localization of the axillary nerve under the guidance of the defined anatomic triangle may provide a safer surgery.