The anatomy of the neurovascular structures, bones, and ligaments in the shoulder region is complicated [1, 2]. This area is vulnerable to iatrogenic injury during surgery. Numerous studies have reported on the anatomical variations and structural relationships in this region [1-8].

The coracoid process is an important anatomical landmark in shoulder surgery [9]. Surgeons often refer to the coracoid process as the “lighthouse of the shoulder” given its proximity to the brachial plexus and axillary artery and vein and its role in guiding surgical approaches [3]. Moreover, it serves as the site of attachment for the coracobrachialis, short head of the biceps, and pectoralis minor as well as the coracoclavicular, coracoacromial, and coracohumeral ligaments, which provide stability to the shoulder [4]. The neurovascular structures of the area include the axillary nerve, musculocutaneous nerve, lateral cord of the brachial plexus, and axillary artery and its branches, which are located close to the coracoid process. Therefore, shoulder surgery is associated with risk of neurovascular injury [5, 6, 10, 11].

The relationship between the tip of the coracoid process and axillary artery holds significant relevance in shoulder surgery, as do anatomical variations in the axillary artery [4, 10, 12, 13]. Surgical treatment of axillary artery injuries can be difficult, especially when urgent access is needed to control bleeding [14]. The axillary artery is susceptible to damage from penetrating trauma and traumatic shoulder dislocation [15]. The coracoid process is supplied by the second part of the axillary artery [13]. In addition, the distance between the coracoid process and various areas of the axillary artery ranges from 21.10 mm to 52.10 mm [10]. Moreover, LaPrade et al. [12] studied the neurovascular anatomy around the coracoid to identify safe areas for the Latarjet procedure and reported a mean 51.10 mm distance from the tip of the coracoid process to the axillary artery.

However, the anatomical variations and structural relationships in this area remain unclear in the context of arterial supply. Furthermore, the complex arrangement of adjacent vascular structures around the tip of the coracoid process poses a significant challenge for surgeons, who must avoid technical errors that can result in vascular injury [5, 6, 13, 16]. Such injuries may compromise upper limb function or even cause loss of the limb. The most important factor in reducing the risk of vascular injury during surgery involving the coracoid process is a comprehensive knowledge of the anatomical structures in the region [4]. This study aimed to clarify the relationships between the vascular structures around the tip of coracoid process and define a surgical safe zone in the region.

Thirty-six shoulders from 18 embalmed cadavers of known sex and age were examined in the study. The ages ranged from 46 to 86 years. The specimens were obtained from the Department of Anatomy, Faculty of Medicine, Chiang Mai University between November 2022, and May 2023. Institutional ethics committee approval was obtained in accordance with the Declaration of Helsinki of 2013. Before death, all the donors had voluntarily expressed their will to donate their body for anatomical education and study. The specimens exhibited no anatomical variants that could impact the study results. Both shoulders of each cadaver were dissected to expose and study the anatomical structures around the shoulder and coracoid process of the scapula. This study was approved by the Human Research Ethics Committee of the Chulabhorn Research Institute (project code EC034/2565).

Firstly, the arm was placed on the side and the shoulder in neutral rotation, followed by a skin incision from the tip of the coracoid process to the clavicle. This incision was chosen to provide optimal exposure to the relevant structures while minimizing disruption. The dissection was carried out layer by layer, ensuring detailed visualization and documentation of the anatomical relationships.

Secondarily, the surrounding structures were carefully split to expose the tip and base of the coracoid process. Adipose tissue and connective structures were dissected to expose the distal part of the clavicle and the coracoid process. Subsequently, he brachial plexus, axillary artery, and its branches, including the thoracoacromial artery, were carefully exposed without disrupting their spatial relationships. Anatomical variations of the axillary artery branches surrounding the coracoid process were recorded and photographed for each specimen.

For measurements, using a vernier caliper, horizontal distances from the tip of the coracoid process to the branches of the thoracoacromial artery, specifically the acromial, clavicular, deltoid, and pectoral branches, were measured. These measurements were taken with the arm on the side and the shoulder in neutral rotation, ensuring consistency and accuracy. The exact point on the tip of the coracoid process was defined as the most anterior point, approximately 5 mm in diameter (Fig. 1).

Each pedicle underwent extensive dissection, allowing for a detailed exploration from its origin to its termination within the axilla. The measurements recorded included the length and origin of the thoracoacromial artery and its branches, as well as the distance from the tip of the coracoid process to each branch. This detailed approach ensured a comprehensive understanding of the vascular anatomy surrounding the tip of the coracoid process.

A description of the anatomical features of the neurovascular structures surrounding the tip of coracoid process. The calculated means, standard deviations, as well as the ranges of measurements, including the minimum and maximum values is examined.

The details of our axillary artery branch observations are presented in Table 1. The data is based on a sample of 36 shoulders (18 cadavers). The thoracoacromial artery was observed in 97.22% (35/36) of all specimens. It was found in male specimens (13 right, 12 left). It was found in female specimens (5 on both right and left sides). This high prevalence suggests that the thoracoacromial artery is a consistent anatomical feature across the population studied. The acromial branch was observed in 13 out of 36 shoulders (36.11% of cases). Interestingly, it was only observed in male specimens (6 right, 7 left). No acromial branches were observed in female specimens in this study. The clavicular branch was observed in 16 out of 36 shoulders (44.44% of cases). Similar to the acromial branch, it was only observed in male specimens, with an equal distribution of 8 on each side. No clavicular branches were observed in female specimens. The deltoid branch was observed in 19 out of 36 shoulders (52.78% of cases). It was found exclusively in male specimens, with a slight predominance on the right side (10 right, 9 left). No deltoid branches were observed in female specimens.

The pectoral branch was the second most common branch after the thoracoacromial artery, present in 21 out of 36 shoulders (58.33% of cases). It was only observed in male specimens, with 11 on the right side and 10 on the left. No pectoral branches were observed in female specimens.

These findings suggest a marked difference in the anatomical variations of the axillary artery between males and females in our study population. While the thoracoacromial artery showed similar distribution across sexes, the acromial, clavicular, deltoid, and pectoral branches were exclusively observed in male specimens.

The mean distance (mean±SD) between the tip of the coracoid process and the thoracoacromial artery was 31.89±15.43 mm (range, 9.23–49.66 mm). The mean distance between the tip of the coracoid process and the acromial branch was 11.02±3.15 mm (range, 9.32–13.90 mm). The mean distance between the tip of the coracoid process and the clavicular branch was 23.76±6.69 mm (range, 20.56–25.95 mm; Table 2).

The variations and dimensions of the six branches of the axillary artery are presented in Table 3. The mean length of the thoracoacromial artery was 2.66±0.62 mm (range, 1.66–4.43 mm). Twenty-seven of the 35 the thoracoacromial arteries arose from the second part of the axillary artery (77.14%); the others arose from the first part of the artery. The mean length of the acromial branch was 1.10±0.28 mm (range, 0.53–1.53 mm). Twelve of the 13 acromial branches arose from the thoracoacromial artery (92.30%); the remaining one arose from the second part of the axillary artery. Interestingly, six acromial branches ran superiorly and anastomosed with the suprascapular artery, which originates from the thyrocervical trunk. The mean distance between these six and the distal end of the clavicle was 20.00±11.41 mm (range, 12.17–59.27 mm). The mean small clavicular branch diameter was 1.11±0.72 mm (range, 0.40–1.84 mm). Fourteen of 16 small clavicular branches arose from the thoracoacromial artery (87.50%); the remaining two arose from the second part of the axillary artery (12.50%; Fig. 2).

The mean length of the deltoid branch was 1.48±0.50 mm (range, 0.80–2.68 mm). Seventeen of the 19 deltoid branches arose from the thoracoacromial artery (89.47%) and two arose from the second part of the axillary artery. The mean diameter of the pectoral branches was 1.59±0.49 mm (range, 0.83–2.76 mm). Nineteen of the 21 pectoral branches arose from the thoracoacromial artery (90.48%) and two arose from the second part of the axillary artery (Fig. 3). Branch diameter data are presented in Table 3.

A deltoclavicular trunk was found in one of the 35 thoracoacromial arteries (2.86%; Fig. 4A); deltoacromial and clavipectoral trunks were found in nine (25.71%) and four (11.43%), respectively (Fig. 4B).

The observed variations in axillary artery branching patterns, particularly the sex-based differences, contribute significantly to our understanding of shoulder region anatomy. The high prevalence of the thoracoacromial artery (97.22%) aligns with previous studies. Huelke [17] reported its presence in 92% of cases, while Geddes et al. [18] found it in all specimens. This consistency suggests the thoracoacromial artery’s reliability as an anatomical landmark for surgical procedures.

However, our findings of sex-based differences in other branches are remarkable. The presence of acromial, clavicular, deltoid, and pectoral branches in male specimens contrasts with some previous reports. Nyemb et al. [19] found the acromial branch in 54.17% of specimens without noting sex-specific differences. Similarly, Park et al. [20] reported a consistent presence of the pectoral branch across their study population.

The acromial branch was observed in 36.11% of our specimens, exclusively in males. This is lower than the 54.17% reported by Nyemb et al. [19], but higher than the 13% reported by Reid and Taylor [21]. The clavicular branch, found in 44.44% of our specimens (all male), shows a higher prevalence than typically reported in the literature, where it’s often described as a variable branch.

The deltoid branch, present in 52.78% of our specimens (all male), and the pectoral branch, found in 58.33% (all male), show lower prevalence than reported by Geddes et al. [18], who found these branches consistently present. This discrepancy highlights the potential for significant anatomical variations.

These differences could be attributed to several factors. Biau et al. [22] emphasized the importance of sample size in accounting for individual variations. Our relatively small sample, particularly of female specimens, may have influenced these observations. Additionally, Ramdass et al. [23] noted significant differences in arterial patterns among different ethnic groups, suggesting population-specific variations.

The potential clinical implications of these findings are significant. Bonczar et al. [24] highlighted the importance of thorough knowledge of thoracoacromial artery variations for procedures such as breast reconstruction and coracoid transfer. Our observed sex-based differences, if confirmed in larger studies, could necessitate sex-specific considerations in surgical planning and technique.

The slight predominance of branches on the right side in male specimens, though minimal, is an interesting observation that warrants further investigation. LaPrade et al. [12] discussed the importance of understanding neurovascular anatomy variations for safe execution of shoulder procedures like the Latarjet technique.

This study found considerable variability of the thoracoacromial artery in the region of the coracoid process. In addition, the mean distance between the deltoid branch and the coracoid process tip was 40.51 mm, which is greater than in previous reports. This branch provides the blood supply to the deltoid muscle, potentially impacting surgical technique in shoulder operations and postoperative rehabilitation. Understanding these anatomical differences is essential to minimize the risk of intraoperative complications.

The coracoid process is frequently used as a landmark in open and arthroscopic shoulder operations. During anterior shoulder surgery, various neurovascular structures located adjacent to the coracoid process are potentially at risk [5, 6, 10].

We examined the anatomical relationships of neurovascular structures surrounding the coracoid process in the context of shoulder surgery, with the arm placed at the side and the shoulder in neutral rotation, as in previous anatomical studies [5, 6, 25]. Moreover, we focused on the branches of the axillary artery, which is closely associated with the coracoid process and clavicle when employing an anterior approach.

In a cadaver study conducted by Khundkar and Giele [4], the blood supply to the coracoid process arose from the second part of the axillary artery behind the pectoralis minor in every case. In our study, the thoracoacromial artery also originated from the second part of the axillary artery in most specimens.

Numerous studies have identified a wide range of anatomical variations in the branching of the thoracoacromial artery [13, 17, 18, 24-26]. This trunk is an important branch that plays a significant role in providing extensive collateral circulation [16]. The thoracoacromial artery gives rise to three major branches, the pectoral, clavicular, and deltoid arteries [18]. The acromial branch may also be considered a main branch. The thoracoacromial artery originates along the medial margin of the pectoralis minor and gives rise to the deltoid and pectoral branches, which are constant, as well as two small and inconstant branches, the acromial and clavicular branches [19, 24, 27]. We specifically examined the relationships of the thoracoacromial artery branches with the coracoid process and clavicle because of the critical role these branches play in supplying the integumentary structures on the superior aspect of the anterior thoracic wall [28]. However, we did not measure the distance between the pectoral branch and the tip of coracoid process, despite its perceived clinical relevance.

Tom et al. [6] studied 27 shoulders and reported that the shortest distance from the axillary artery to the tip of the coracoid process was less than 40 mm. Bonczar et al. [24] reported this distance as 33.55 mm. Khundkar and Giele [4] reported that the second part of the axillary artery supplies the anterior 20 mm to 30 mm of the coracoid process. Stone et al. [10] noted that the distance between the coracoid process and various areas of the axillary artery ranged from 21.10 mm to 52.10 mm. Furthermore, LaPrade et al. [12] reported a mean coracoid–axillary artery distance of 51.10 mm. In our study, the distance from the thoracoacromial artery to the tip of the coracoid process was 31.89 mm, which closely aligns with the results of previous studies.

The thoracoacromial artery exhibited a mean length of 2.66±0.62 mm, with a range from 1.66 mm to 4.43 mm (Table 3). This is consistent with previous studies, confirming the reliability of the thoracoacromial artery as an anatomical landmark for shoulder surgeries.

We observed two variable branches, acromial and clavicular, which are generally smaller perforators than the deltoid and pectoral branches. These branches, when they occur, show a greater propensity for anatomical variations compared with the more consistent pectoral and deltoid branches [19, 21].

For the acromial branch, we observed a mean length of 1.10±0.28 mm, ranging from 0.53 mm to 1.53 mm. from the tip of the coracoid process. This finding is slightly lower than the 54.17% prevalence reported by Nyemb et al. [28], but it aligns with the variability observed across different studies. Hamel et al. [13] reported that the coracoid process is related to the acromial branch of the thoracoacromial artery and the second part of the axillary artery.

Nyemb et al. [28] reported an acromial branch in 13 of 24 cadaver specimens (54.17%). The same prevalence rate in our study was 36.11%, which is relatively similar. Although the acromial branch is relatively small, including it in the dissection range for the perforator flap of the deltoid branch can enhance its dimensions and potentially reduce the rate of necrosis [28]. Therefore, it is important for surgeons to consider the anatomical variations of the acromial branch when performing any anterior approach to the shoulder.

Moreover, the distance from the acromial branch to the clavicle was 20 mm in our study. In a study by Park et al. [20], all the branches of the thoracoacromial artery ran laterally 20 mm to 30 mm below the clavicle.

Mean small clavicular branch diameter was 1.11±0.72 mm, ranging from 0.40 mm to 1.84 mm. This variation further emphasizes the importance of considering these anatomical differences during shoulder surgery, particularly in male patients. This branch arose from the thoracoacromial artery in 14 of 16 cases (87.50%) and from the second part of the axillary artery in the remaining two. Reid and Taylor [21] reported that the clavicular branch is one of the most variable branches of the axillary artery. The surface landmarks on the ventral margin of the flap are crucial. It is believed that these branches can be safely used as pedicles for flaps [27].

The deltoid branch presented with a mean length of 1.48±0.50 mm, ranging from 0.80 mm to 2.68 mm, while the pectoral branch had a mean length of 1.59±0.49 mm, with a range from 0.83 mm to 2.76 mm. These measurements are critical in understanding the vascular supply to the shoulder region, which can influence surgical planning and technique.

Embryological development of the axillary artery is rooted in the vascular plexus of the upper limb bud and prone to variations [29]. These anomalies are influenced by genetic factors, abnormal molecular signals, and blood flow dynamics and can lead to unusual branching patterns. Variations in the branches of the axillary artery, which is essential for upper limb vascularization, are clinically significant in shoulder surgery and arterial catheterization procedures [30]. Surgeons must be aware of these variations to prevent complications.

In the axillary region, critical anatomical structures and their inter-relationships are identified using various landmarks to ensure safe operations [27]. The coracoid process serves a dual role: it functions as a critical surgical landmark and is actively involved in various surgical procedures [5, 6, 10, 11]. These procedures include coracoid osteotomy and transfer in the Latarjet technique and subcoracoid decompression for treating subcoracoid impingement syndrome [25].

Anatomical variations in the branches of the axillary artery, particularly in the vicinity of the coracoid process, are of significant importance in orthopedic practice, particularly in clavicle fracture surgery [31, 32]. It is vital for orthopedic surgeons to comprehend these variations to effectively plan and execute surgical procedures and minimize complications. Distal clavicle fractures represent a common shoulder joint injury [31]. Currently, there is no consensus regarding treatment, as each technique presents its own set of advantages and disadvantages; however, coracoclavicular stabilization is widely favored owing to its simplicity and provision of reliable stability.

The thoracoacromial artery is widely variable in its branching. Surgeons must be aware of these variations when planning surgery involving the clavicle and coracoid process to avoid unintentional vascular injuries.

A recent adaptation of arthroscopically assisted anterior shoulder stabilization that involves a 2 to 5 cm incision near the coracoid process has effectively enhanced a previously established open surgery technique, achieving impressive success rates in excess of 90% [33]. Therefore, the findings of this study are important for orthopedic surgeons, as they emphasize the effectiveness of this approach in obviating the need for operating within 5 cm of the coracoid process, which reduces the risk of severe intraoperative bleeding.

This cadaver study has several limitations. The primary limitations include its relatively small sample size and demographic homogeneity, which restrict the generalizability of findings. The use of absolute measurements rather than proportional ratios limits cross-population comparisons. As a single-institution study, results may not fully represent broader anatomical variations. Additionally, future research should aim to significantly increase the sample size, ideally to at least 50 cadavers, to accumulate more comprehensive data and enhance the statistical power of the findings. Despite these limitations, this research provides valuable insights into axillary artery branching patterns, while emphasizing the need for more extensive investigations to further elucidate the complex anatomical variations in this critical area of surgical anatomy.

In conclusion, knowledge of the relevant neurovascular structures around the coracoid process is important for surgeons performing shoulder surgery. Variations in the number of vessels across different branches can have technical implications. The relatively large number of variations in the thoracoacromial artery highlight their significance in surgical planning. Based on the anatomical data collected, particularly the measurements of the thoracoacromial artery and its branches, we propose a surgical safe zone for shoulder procedures involving the acromion and coracoid process. Our findings suggest that the region between 30 mm to 40 mm from the tip of the coracoid process, where the thoracoacromial artery is located, provides a relatively low risk of vascular injury. The acromial and clavicular branches, which exhibit considerable variability, are also most commonly positioned at distances that allow safe dissection in this area. These findings guide surgeons in minimizing the risk of neurovascular complications during procedures such as coracoclavicular stabilization and subcoracoid decompression.