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The Anterior Trunk Of The Axillary Nerve: Surgical Anatomy And Guidelines. A Fresh, Cadavers Study

Eran Maman*,**, Guy Morag*,**, Oleg Safir*, Mony Benifla*, Gavriel Mozes**, Erin Boynton*

* Department of Orthopedics, Mt. Sinai Hospital, 600 University Avenue, Suite 476D, Toronto, Ontario, Canada M5G 1X5 

**Department of Orthopedics “ B”, Tel-Aviv Sourasky Medical Center and the Sackler Faculty of Medicine, Tel-Aviv University, Tel-Aviv, Israel

Address for Correspondence:  

Eran Maman, MD,
Department of Orthopedics“ B”,
Tel-Aviv Sourasky Medical Center, Tel-Aviv, Israel 62439.
97236973920, Fax: 9723694546 



Background: Injury to the axillary nerve has devastating results. Variations in the distance between the acromial edge and axillary nerve range from 20-70 mm. The purpose of this study was to anatomically analyze the relations between the anterior trunk of the axillary nerve and the acromion in order to provide guidelines for minimizing intraoperative iatrogenic neural injury.

Methods: The distances between the axillary nerve and the posterolateral, midlateral , and anterolateral edges of the acromion were measured in 60 cadaveric shoulders (30 fresh cadavers). The correlations between these measurements to the weight, height and sex of the cadavers were statistically analyzed.

Results: The distances between the axillary nerve and all three acromial anatomic landmarks significantly correlated with the cadaver’s height (p<0.001) The axillary nerve was found as close as 30-35 mm distal to the acromion in cadavers shorter than 170 cm, (5.7”), whereas the minimal distance between the acromion and axillary nerve was 45-49 mm in cadavers taller than 170 cm.

Interpretation: We recommend using the height of the patients as an index for determining the relations between the axillary nerve and the acromion. We defined a general safety zone for patients shorter and those taller than 170 cm. We believe that using these guidelines can minimize iatrogenic injuries to the axillary nerve better than the commonly used 5‑cm safety zone when performing a deltoid split.

This study quantifies the relative risk of injury to the axillary nerve during shoulder surgery based on the patient’s height and provides guidelines in avoiding such injury

J.Orthopaedics 2008;5(2)e7


Iatrogenic nerve injury is one of the most dreaded complications of any surgery, and on potential site is axillary’s nerve injury associated with deltoid muscle surgery, be it arthroscopic or open. Injury to the anterior trunk of the axillary nerve leads to devastating loss of shoulder flexion strength. 1.
The exact location of the nerve varies, and few cadaveric studies have examined the variability of the axillary nerve and its course in the deltoid muscle. 2,3,4,5,6,7,8,9
The axillary nerve has been described as being located about 5-7 cm vertically from the lateral edge of the acromion, and even less as the nerve curves upwards. 2,10,11,12,13 Some studies demonstrated that the distance from the lateral edge of the acromion to the axillary nerve (A-A distance) might be as much as 2-3.1 cm shorter 2,7. These conflicting data complicate the estimation of a safety zone for incisions around the deltoid muscle.
There have been several attempts to correlate the axillary nerve’s location to the patient’s surface anatomy. A study by Vathana et al. showed that the length of the acromion was not useful nor did the length of the arm correlate with the distance of the axillary nerve from the acromion, the latter finding in disagreement with an earlier study by Burkhead et al. 3,7 However, a recent study by Cetik et al. demonstrated a significant correlation between arm length and A-A distance.13 Several authors correlated the sex of the cadaver with the A-A distance. 7,14 Others have tried to measure the distance from the acromioclavicular joint and the proximal humerus to the nerve. 6,14 Thus, the current guidelines for estimating the location of the axillary nerve in different locations along the deltoid muscle are either not clear cut or not easy to perform.
The “Bone Bank”, receives its organs (bones, tendons etc) from relatively young donors that have been found to be suitable tissue donors for re-implantation. The cretaria for tissue donation includes no known pathology or previous surgery to the donated site.
The team performing the harvesting procedure includes senior orthopedic surgeons who have a special interest in shoulder surgery. Having the rare opportunity to examine the anatomy of a large amount of fresh cadaveric shoulders of relatively young organ donors with complete medical history we conduct a study that will provide guide lines for surgeons in shoulder surgery.
We hypothesized that there is a correlation between the height of the patients and the distance of the axillary nerve from the acromion. We suspected some positive correlation of this distance to the patient’s body mass index (BMI) and sex as well. Our purposes were to confirm the results of previous studies regarding the axillary nerve location and course, and provide reliable, practical surface anatomy guidelines in order to help reduce iatrogenic injury to the nerve around the deltoid muscle. To that end, we examined a group of fresh, relatively young, cadavers of individuals who had not undergone any previous relevant surgeries to the shoulder. These measurements were later correlated to the patients’ selected physical attributes.

Material and Methods :
After obtaining the Institutional Review Board approval, 62 fresh shoulders from 31 cadavers were traced for our study. 2 shoulders were not suitable (one sustained a fracture to the proximal humerus and the other was status post a previous surgery). The remained 60 shoulders (mean age 45.37 years, median 50.5 range 15-74, 17 males) had no previous known pathology or surgery.
Dissection was performed while observing several rules to minimize the chances of bias and to unify the results: the deltoid muscle was always attached to the bone on both sides and it was reflected backward only to the point of measurement (i.e. moving the point of reference of the nerve with the acromion and humerus). The measurements were done with the arm in about 30º abduction and in neutral rotation.
On dissection the skin was removed until full exposure of the entire anterolateral deltoid muscle was achieved, followed by delto-pectoral splitting. The anterior deltoid was sharply released from its origin at the acromion while retracting the muscle laterally and posteriorly. When reaching to the anterolateral tip of the acromion The distance from the inferior anterolateral tip vertically to the superior border of the anterior branch of the axillary nerve was measured (Figure 1) with a plastic ruler commonly available in the operating theatre (Securline, Surgical Skin Marker, San Fernando, CA). further release of the deltoid posteriorly was done until the middle acromion was exposed and the same on the other end of the muscle on the humeral attachment. A second measurement was taken from the inferior edge of the mid lateral acromion vertically to the axillary nerve. (Figure 2) Completing the deltoid release until the posterolateral acromion and the posterior attachment to the humerus, a third measurement was taken from the posterolateral corner of the acromion vertically to the axillary nerve. (Figure 3)


Figure 1:  Axillary nerve measurement from the inferior anterolateral tip of the acromion vertically to the superior border of the anterior branch of the nerve


Figure 2:  Axillary nerve measurement from the inferior edge of the mid‑lateral acromion vertically to the anterior branch of the nerve



Figure 3:  Axillary nerve measurement from the inferior anterolateral tip of the acromion vertically to the superior border of the nerve


Three senior orthopaedic surgeons were involved in the dissections and measurements (E.M, G.M., O.S.)

We correlated these measurements with the age, sex, side (right or left shoulder), height, weight (which we obtained from the medical records) and BMI (weight/height2).

Statistical analyses of height, weight and BMI were done by univariate logistic regression analysis, with the dependent variable being average A‑A distance of greater or less than 5 cm. The distance of 5 cm served as a point of comparison since it was the median distance of our study population. The level of statistical significance was set at p<0.05.  The cadavers were divided between the ones that were ≤170 cm tall and those that were >170 cm tall, and Pearson's chi-square and Fisher's Exact Tests were used with confidence interval (CI) OF 95% for comparisons between the two groups.

Results :

The vertical A-A distance at three measurement sites of the same cadaver were no different between the right and the left shoulders (p=0.59). The median A-A distance was 50 mm, the mean distance was 50.3 mm and the range was 30.0–70.0 mm. The distance was <40 mm in only four shoulders of two cadavers (164 and 170 cm tall) for which the respective measurements were 35-38 mm in the posterior tip of acromion and mid‑acromion and 30-33 mm in relation to the anterolateral tip of the acromion.

The A-A distance differed according to the location of the measurements. The mean A-A distance for the three points of measurements (the posterior tip, the mid‑acromion and the anterolateral tip) was 51.7, 50.8, and 48.5 mm, respectively (Table 1). There was a significant difference between the anterolateral measurements and those of the two others sites (p<0.001), but there was no significant difference between the measurements at the midlateral and the posterior sites.

Table 1. The vertical distance of the axillary nerve from the inferior acromion at three measurement sites.

Vertical distance (acromion-axillary n.) in mm

Heights cm

anterior (mean)

anterior (range)

middle (mean)

middle (range)

posterior  (mean)

posterior  (range)

≤170 (n=28)







>170 (n=32)











Discussion :

Although the popularity of arthroscopic procedures is rising, the role of open or mini open procedures around the shoulder is still major. Procedures such as reverse total shoulder prosthesis, mini open rotator cuff repair, resurfacing arthroplasty or fracture fixation are commonly performed through a deltoid split.. in these procedures shoulder surgeons need to estimate the location of the axillary nerve in order to avoid iatrogenic injury. Anatomical variations are relevant whether the procedures are arthroscopic or open. Guidelines for estimating the location of the axillary nerve in different individuals will lower the risk for iatrogenic injury during these procedures.
The course of the axillary nerve runs along the deep surface of the deltoid muscle and is parallel to the acromion. It curves upward closer to the acromion as it progress anteriorly. The nerve is commonly described as being located 5-7 cm distal to the acromion, but it might be as close as 2-3.1 cm. 10,11,12,5,13,2,7 Past measurements were carried out using various anatomical landmarks. Bono et al. described the distance of the axillary nerve in relation to the proximal humerus and found it to be an average of 6.1 cm.6 Brayan et al. measured the distance starting from a 5 cm vertical incision (deltoid split) to the axillary nerve: the average A A distance was 5.9 cm for a posterior incision and 5.65 cm for an anterolateral incision. More disturbing was the fact that the deltoid split actually crossed the axillary nerve in 7 anterior and 4 anterolateral incisions.5
According to Kamineni et al.’s measurements, the average distance of the axillary nerve was 5.7 cm (range 3.5–7.0 cm) in relation to the tip of the acromial process along the lateral aspect of the arm, and 5.1 cm (range 3.5–8.5 cm) along the anterior aspect.12 Thus, while the literature can provide reliable information on surface anatomy, variations such as these in describing the course of the nerve emphasize the need for reliable guidelines for conducting surgery at this site.
Vathana et al. 3 attempted to correlate locations of the axillary nerve and patient’s relevant physical data, such as the length of the arm and of the acromion, and Burkhead et al. suggested guidelines to help predict the location of the axillary nerve. The latter authors found a gender based difference in the distance from the acromion to the nerve as well as in the length of the arm. They concluded a deltoid split of no more than 2.5-3.75 cm from the acromion is safe for males and 2.5 cm for females, and that shorter deltoid splitting is safe when the arm is abducted. 3,7 Recently the correlation of the distance from the acromion to the nerve and the length of the arm has been further established by Cetik et al. they found a significant correlation between arm length and both anterior and posterior distances.13
Nassar et al. 14 proposed an axillary nerve index based on the distance of the nerve from the acromioclavicular joint to the length of the deltoid. This calculation requires the drawing of a line from the anterior border of the clavicle and acromion laterally over the deltoid, locating the deltoid tuberosity, and multiplying the derived value by 0.48 for males and 0.41 for females. The result of this equation is an estimation of the distance of the axillary nerve from the acromioclavicular joint. Although accurate, this method requires identifying the deltoid tuberosity, which may sometimes be difficult (e.g., obesity, edema, and change in arm length post trauma). Moreover, this index refers to incisions planned along this line only and might not be accurate for more posterior ones.14
We sought to provide guidelines that would be practical, user friendly and reliable while, at the same time, not limiting the surgeon to a too narrow safety zone. We tried to provide uniformity in the measurements and have them reflect operating conditions as much as possible (e.g., the arm in adduction or no more than 30 degrees of abduction and natural rotation). Another confounding factor, contracture of the muscle after detachment from the bone, was avoided by measuring the distance when the muscle was still attached to the bone on its ends. Finally, we bore in mind that positioning the arm in abduction or rotation and previous trauma to the arm may change the length of the muscle/bone and that these factors will affect the measurements.
Our data support the findings of previous anatomical investigations on the distance of the axillary nerve from the acromion that show a great variety in the A-A distance (30-70 mm). 10,11,12,5,2,7,13. In 60 shoulders of the 30 cadavers we studied (51.7%), the distance was <50 mm from the anterolateral corner of the acromion, <50 mm in 14/60 (23.3%) from the midlateral acromion and <50 mm in 11/60 (18.3%) from the posterolateral acromion. In only 4 shoulders (6.66%) was the distance <40 mm.
The A-A distance shortens as we move anteriorly. We demonstrated a significantly shorter distance on the more anterior measurements compared to the others measurements (p<0.001), a finding that can be explained by the nerve curving upward, by the fact that our measurements were done from the inferior edge of the acromion where it curves downward (type II/III) or has anterior osteophytes, or both.
The A-A distance changed significantly with height (p<0.001). The ≤170 cm cadavers had an A-A distance ranging between 30-55 mm while the ones taller than 170 cm had a range of 45-70 mm. In order to find the “safety zone” (calculated from the inferolateral acromial edge to the axillary nerve) in which the chances for iatrogenic injury to the axillary nerve will be far less likely; we examined the smallest measurements for each group. The safety zone can be as small as 30 mm anteriorly or 35 mm mid laterally and posteriorly in the shorter group, while the axillary nerve can be expected to be as close as 45 49 mm in the taller group. We further subdivided the taller cadavers into one group 171-180 cm in height and another group >180 cm in height and found no significance difference between them.
Unlike others who showed gender differences as being significant, the A-A distance between our female and male cadavers was of borderline significance(p=0.063). Thus, the two factors of height and location defined the largest safety zone at the posterolateral deltoid on an individual >170 cm and the smallest safety zone on the anterolateral deltoid of shorter ones.
The small number of shoulders is a limitation of our study. Greater numbers of shoulders from different cadavers might have allowed us to arrive at more precise guidelines. Although we tried to avoid bias by applying strict rules in the way dissection was carried as well positioning and taking measurements, the fact that the measurements were taken by more than one surgeon might create interoberver bias. All measurements were taken from the undersurface of the acromion, which contributes to shorter and safer measured distances; however, they do not faithfully reproduce the surgeon’s measurement from the top aspect of the acromion intraoperatively.


The novelty of our study is by providing new and applicable guidelines for avoiding axillary nerve injury during shoulder surgery. According to the results of the present study, the common expectation of the axillary nerve being located around 50 mm from the lateral edge of the acromion will be correct in about half of the cases. There is a significant correlation between the patient’s height and the vertical distance measured in all examined sites. The shorter the patient and the more anterior the deltoid incision, the shorter will be the distance of the axillary nerve to the acromion.


  • Height ≤170 cm (5.7”): the safety zone might be as short as 30 mm anteriorly or 35 mm midlateral and posterior.

  • Height >170 cm (5.7”): the axillary nerve can be expected to be as close as 45 mm vertically from the anterolateral acromion and 49 mm from mid‑lateral and posterolateral acromion. In some of these patients the nerve may lie as far as 70 mm from the inferior acromion. (Our measurements were in relation to the inferior acromion: since they will be taken from the superior edge intraoperatively, the surgeon can add the width of the acromion to the safety zone.)


Reference : 

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  13. Cetik O. Uslu M. Acar HI. Comert A. Tekdemir I. Cift H. Is there a safe area for the axillary nerve in the deltoid muscle? A cadaveric study. J.Bone Joint Surg.Am. 2006; 88: 2395-9.

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This is a peer reviewed paper 

Please cite as : Eran Maman : The Anterior Trunk Of The Axillary Nerve: Surgical Anatomy And Guidelines. A Fresh, Cadavers Study

J.Orthopaedics 2008;5(2)e7





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