Determining the closest distances from the coracoid base and tip to neurovascular structures in acute high-grade acromioclavicular joint injuries: a cadaveric study

Abstract

Background

High-grade acromioclavicular (AC) joint injuries often require coracoclavicular (CC) stabilization, which increases the risk of neurovascular injury due to coracoid process proximity to vital structures. Previous intact AC joint measurements may have underestimated the surgical risks of high-grade injuries with altered anatomy. Therefore, this study investigated the distance from the coracoid base and tip to the adjacent neurovascular structures in simulated acute high-grade AC joint injuries.

Methods

Eight freshly frozen cadaveric specimens, consisting of four male and four female specimens, were subjected to simulated high-grade AC joint injuries via AC capsule and CC ligament transection and deltotrapezial fascia detachment. Closest distances from the coracoid base and tip to the lateral border of adjacent neurovascular structures were measured in the supine, beach chair, and lateral decubitus positions.

Results

The distance from the coracoid base to the neurovascular structures varied significantly depending on the body position. The supine position provided the greatest distance, reducing the risk of neurovascular injury compared to the beach chair and lateral decubitus positions (p = 0.030 and p < 0.001, respectively). In contrast, the lateral decubitus position had the shortest distance, highlighting an increased risk of neurovascular injury.

Conclusions

This study demonstrates that the supine position provides the safest approach for minimizing neurovascular injury risk during surgical stabilization of high-grade AC joint injuries. These findings contribute to clinical practice by emphasizing the importance of patient positioning to optimize surgical safety and outcomes.

Clinical trial number

Not applicable.

Background

Acromioclavicular (AC) joint injuries are common, particularly among athletes and individuals involved in contact sports or those sustaining direct trauma to the proximal humerus [1, 2]. High-grade AC joint injuries, classified as Rockwood types III-V, often require surgical intervention to restore joint stability and shoulder function [3,4,5]. Coracoclavicular (CC) stabilization is a widely accepted surgical technique for managing these injuries and utilizes methods such as looping around or drilling through the coracoid base for fixation [6,7,8]. However, these procedures carry a significant risk of neurovascular injury because of the close proximity of neurovascular structures, specifically the brachial plexus and axillary vessels, located medially and inferiorly to the coracoid process [8].

The coracoid process of the scapula is integral to shoulder stability and movement due to its diverse muscular and ligamentous attachments. It serves as an important attachment site for muscles such as the pectoralis minor, the coracobrachialis, and the short head of the biceps brachii, which collectively contribute to dynamic shoulder motion and stabilization [9, 10]. In addition, key ligaments, including the coracoacromial ligament, the CC ligaments (comprising the conoid and trapezoid components), the coracohumeral ligament, and the superior transverse scapular ligament, attach to the coracoid base and tip, providing essential structural support and biomechanical integrity. This complex network of attachments highlights the coracoid’s central role in maintaining shoulder mechanics. Furthermore, the development of the coracoid process is intricately linked to its functional demands. As a pivotal element of the shoulder girdle, its morphology and orientation are shaped by the mechanical forces imposed by the attached muscles and ligaments throughout growth and physical activity. A comprehensive understanding of these anatomical and functional relationships is particularly critical in the context of high-grade AC joint injuries. Surgical interventions involving the coracoid must account for and preserve these attachments to ensure the restoration and maintenance of shoulder stability.

Previous anatomical studies [11,12,13] have assessed the distances from the coracoid base and tip to the neurovascular structures in intact AC joints (Fig. 1a). Notably, Paksoy et al. [14] investigated the positions of the clavicle and scapula in AC joint injuries and revealed that scapular displacement, particularly inferior displacement, can occur following such injuries. This displacement may alter the spatial relationship between the coracoid process and adjacent neurovascular structures, which can increase the risk of injury during surgery. Consequently, existing measurements derived from intact AC joint conditions may not accurately reflect the altered anatomy present in acute high-grade injuries; thus, it is essential to assess these distances specifically in high-grade AC joint injuries (Fig. 1b). A comprehensive understanding of these distances is essential for surgeons to mitigate the risk of neurovascular complications during CC stabilization procedures.

Fig. 1

Left shoulder region of a full-body fresh-frozen cadaver in the supine position. The images depict (a) an intact acromioclavicular (AC) joint and (b) a simulated high-grade AC joint injury. (Black circle: anteromedial aspect of the coracoid base; yellow arrow: distance from the anteromedial border of the coracoid base to the lateral border of the neurovascular structures in the intact AC joint; blue arrow: distance from the anteromedial border of the coracoid base to the lateral border of the neurovascular structures in the simulated high-grade AC joint injury; A: acomion; C: clavicle; CP: coracoid process; and NV: neurovascular structures)

To date, several studies have assessed the safety distances and reported the risk of neurovascular injury associated with procedures involving the coracoid process, such as CC stabilization, the Latarjet procedure, and coracoid decompression. However, no studies have specifically evaluated the distances from the coracoid process to the neurovascular structures in high-grade AC joint injuries. This study aimed to determine the closest distances from the coracoid base and tip to the neurovascular structures in simulated acute high-grade AC joint injuries using full-body fresh-frozen cadaveric specimens. We hypothesized that in acute high-grade AC joint injuries, inferior displacement of the scapula reduces the distance from the coracoid base and tip to the underlying neurovascular structures, thereby increasing the risk of neurovascular injury during surgical intervention.

Methods

The study was conducted in compliance with the principles outlined in the Declaration of Helsinki and received ethical approval from the Faculty of Medicine Ethics Committee of Prince of Songkla University (REC 67-372-11-1) on August 4, 2024. This cadaveric study aimed to simulate acute high-grade AC joint injuries and accurately measure the distance from the coracoid process to adjacent neurovascular structures. Eight full-body fresh-frozen cadaveric specimens (four males and four females; mean age at death: 75 ± 5 years) were obtained from the anatomical donation program of our university. Specimens were carefully screened to ensure the absence of shoulder pathology or prior shoulder surgery. Before dissection, the specimens were thawed at room temperature for 24 h to restore tissue pliability to that observed under in vivo conditions.

Dissection was initiated with each cadaver in the supine position [11]. A curved incision was made from the proximal humerus to the clavicular shaft. The anterior deltoid muscle was detached and reflected laterally, and the pectoralis major muscle was retracted distally from its clavicular origin. The conjoined tendon and pectoralis minor were transected approximately 5 mm from their insertion points and reflected from the coracoid process. This meticulous dissection exposed the neurovascular structures, specifically the axillary nerve, musculocutaneous nerve, lateral cord of the brachial plexus, and axillary artery, while preserving their native anatomical relationships. Maintaining the integrity of these structures is crucial for obtaining accurate measurements.

To simulate high-grade AC joint injury, the AC capsule and CC ligaments were cut at their mid-sections, and the deltotrapezial fascia was detached, to alter the pertinent anatomical relationships. The anteromedial aspects of the coracoid base and tip were precisely identified. To facilitate accurate distance measurements, 2 mm Kirschner wires were inserted into these regions. The distances between each Kirschner wire and the lateral border of the neurovascular structures were measured using a digital Vernier caliper with a precision of 0.01 mm, as illustrated in Fig. 2.

Fig. 2

Left shoulder region of a full-body fresh-frozen cadaver in the supine position. The images depict distances from the anteromedial aspect of the coracoid base and the coracoid tip to the lateral border of neurovascular structures in a simulated high-grade acromioclavicular (AC) joint injury. (Black circle: anteromedial aspect of the coracoid base; green circle: anteromedial aspect of the coracoid tip; blue arrow: distance from the anteromedial border of the coracoid base to the lateral border of the neurovascular structures; yellow arrow: distance from the anteromedial border of the coracoid tip to the lateral border of the neurovascular structures; A: acomion; C: clavicle; CP: coracoid process; and NV: neurovascular structures)

Each cadaver was evaluated in supine, beach chair, and lateral decubitus positions, in a randomized sequence. After measurements were taken in each position, the cadaver was repositioned in the supine position, with the arm maintained in adduction to ensure consistency across assessments. To minimize potential measurement bias, each distance was measured three times by an experienced orthopedist and anatomist. The mean values of these measurements were calculated and used in the analyses.

All procedures adhered to ethical guidelines, and the experimental protocol was approved by the Research and Development Office of Faculty of Medicine of Prince of Songkla University (Institutional Review Board number 67-372-11-1). The cadavers were donated for scientific research with prior consent, and anonymity and ethical compliance were ensured throughout the study.

Data analysis was performed using R software with the “epicalc” package (version 3.4.3; R Foundation for Statistical Computing, Vienna, Austria). Paired t-tests were used to compare the measured distances from the anteromedial aspects of the coracoid base and tip to the lateral border of the neurovascular structures at each position. Statistical significance was set at p < 0.05.

Results

The closest distances from the anteromedial border of the coracoid base and tip to the lateral margin of the neurovascular structures across the three positions are summarized in Fig. 3. These distances were significantly influenced by the cadaver positioning (p < 0.05). Specifically, the supine position exhibited the greatest distance from the neurovascular structures, whereas the lateral decubitus position showed the shortest distance. Tables 1 and 2 summarize the closest distances from the anteromedial border of the coracoid base and tip to the lateral margin of the neurovascular structures across the three cadaver positions, stratified by sex. Although female specimens showed shorter distances from both the coracoid base and tip to the neurovascular structures compared to male specimens, these differences were not statistically significant. Both interobserver and intraobserver reliability scores exceeded 0.9 for all measurements, indicating high measurement consistency.

Fig. 3

The closest distances from the anteromedial aspect of the coracoid base and tip to the lateral border of the neurovascular structure in various positions. (mm: millimeter)

Table 1 Mean distances (± SD) from the coracoid base to neurovascular structures across different patient positions by sex (mm: millimeter)

Table 2 Mean distances (± SD) from the coracoid tip to neurovascular structures across different patient positions by sex (mm: millimeter)

Discussion

Our findings indicate that the supine position represents the safest posture for CC stabilization, whereas the lateral decubitus position is associated with the highest risk of neurovascular injury. Patient positioning considerably influenced the distances between the coracoid base and tip and the lateral border of the neurovascular structures. These positional variations underscore the importance of selecting an optimal surgical position to minimize the risk of iatrogenic damage during CC stabilization.

Surgical realignment of the AC joint is the preferred treatment for acute high-grade AC joint injuries [15, 16]. However, CC stabilization procedures that involve looping or drilling of the coracoid base pose a remarkable risk of iatrogenic neurovascular injury due to the proximity of neurovascular structures. Previous studies have determined the distances between the coracoid process and these structures; however, the measurements were conducted on specimens with intact AC joints [11,12,13, 17]. For instance, Lo et al. [12] reported that the lateral cord of the brachial plexus and the axillary nerve are approximately 28.5 mm and 29.3 mm from the coracoid tip and base, respectively, which suggests a relatively safe margin during coracoid surgeries. Similarly, Chuaychoosakoon et al. [11] found that the shortest distances occurred in the beach chair position, particularly with arm abduction, thereby increasing the risk of neurovascular injury. Knudsen et al. [17] highlighted that the axillary and musculocutaneous nerves lie closer to the coracoid tip than was previously documented, thus emphasizing the need for a meticulous surgical approach. Furthermore, Pan et al. [13] used radiographs to evaluate the distances between the musculocutaneous nerve and the coracoid process. They reported that shoulder positioning markedly affected neurovascular distance, although their cadaveric model lacked full soft-tissue tension, which may have influenced anatomical relationships.

The observed differences in neurovascular distances between male and female specimens further highlight anatomical variability with potential implications for surgical planning. Female specimens exhibited shorter distances from the coracoid base and tip to neurovascular structures compared to males, though these differences were not statistically significant. These variations are likely attributable to differences in skeletal dimensions, muscle mass, and soft tissue characteristics between sexes. Importantly, the shorter distances observed in females could elevate the risk of neurovascular injury during coracoid-related procedures, particularly in the management of high-grade AC joint injuries. These findings emphasize the need for individualized surgical planning that accounts for patient-specific anatomical characteristics to optimize safety and outcomes.

The findings of this study have significant clinical implications for the surgical management of high-grade AC joint injuries, particularly in minimizing the risk of iatrogenic neurovascular injury during CC stabilization. For open CC stabilization, the supine position demonstrated the greatest safety margin, with the longest distances between the coracoid base and tip and adjacent neurovascular structures, making it the preferred posture for such procedures. For arthroscopic CC stabilization, the beach chair position is recommended as it balances accessibility and safety. In contrast, the lateral decubitus position, while commonly used in arthroscopic procedures for its improved visualization, poses the highest risk of injury due to the shortest distances observed between the coracoid process and neurovascular structures, such as the axillary artery and brachial plexus. These findings underscore the critical importance of patient positioning in optimizing surgical safety and emphasize the need for meticulous planning, particularly when employing the lateral decubitus position, to mitigate potential complications. Moreover, the results extend beyond CC stabilization to other procedures involving the coracoid process, such as coracoplasty for enhancing the subcoracoid space during subscapularis tendon repair or subacromial decompression. In these cases, caution is crucial to avoid extending the shaver tip beyond the coracoid base, which is located at distances of 34 ± 4.7 mm, 31 ± 7.6 mm, and 26.6 ± 8.2 mm in the supine, beach chair, and lateral decubitus positions, respectively. These measurements underscore the proximity of neurovascular structures medially to the coracoid process and reinforce the necessity of precise surgical techniques to minimize the risk of injury.

The risk of neurovascular injury and fractures, such as coracoid or clavicle fractures, is a significant concern in CC stabilization. Coracoid or clavicle fractures occur in approximately 20% of cases and are influenced by factors such as osteoporosis, large bone drill holes, multiple clavicle drill holes, and poor drilling techniques [18]. To mitigate this risk, surgeons should carefully select patients, ensure an adequate view of the coracoid base, and use smaller-diameter tunnels on the clavicle and/or coracoid, or consider a single-tunnel technique. Alternatively, the use of a hook plate is an effective option, particularly in cases of combined AC joint injuries and coracoid fractures or in instances of iatrogenic coracoid base fractures [19]. This study retrospectively analyzed 18 patients with coracoid process fractures combined with AC joint dislocations treated using clavicular hook plate fixation. The findings demonstrated that fixation of the AC joint alone often achieves indirect reduction of coracoid fractures, yielding satisfactory functional and radiological outcomes. This highlights the importance of accurate diagnosis and tailored surgical techniques to enhance shoulder stability and biomechanics.

This study has some limitations that should be noted when interpreting our findings. First, the sample size was limited to eight cadavers, which may affect the generalizability of the results. Additionally, cadaveric models cannot fully replicate in vivo conditions, especially with respect to muscle tone and vascular pulsation, which may influence the anatomical relationships evaluated in this study.

Conclusions

The supine position conferred the lowest risk of iatrogenic neurovascular injury during CC stabilization for acute high-grade AC joint injuries. Conversely, the lateral decubitus position was associated with the highest risk of neurovascular complications. These findings highlight the critical importance of patient positioning in surgical planning and execution and emphasize the need for surgeons to carefully consider anatomical alterations to minimize the potential for neurovascular injury during CC stabilization.