How close is the axillary nerve to the inferior glenoid? A magnetic resonance study of normal and arthritic shoulders.

INTRODUCTION: Axillary nerve injury is a major complication of shoulder surgery during glenoid exposure. The aim of this study was to measure the mean distance between the inferior glenoid and the axillary nerve in healthy shoulders and then to compare this distance between osteoarthritic and rotator cuff deficient glenohumeral joints. METHODS: The magnetic resonance images of 50 patients with normal glenohumeral joints were reviewed. The infra-glenoid tubercle was determined as a fixed point and the distance to the axillary nerve was measured. Two separate assessors measured on the same sagittal sections. With a study power of 80%, the sample needed in each comparison group was 28 patients. Measurements were then performed on scans in patients with osteoarthritis and cuff tear arthropathy. The mean distance was compared between groups. RESULTS: The mean distance between the infra-glenoid tubercle and axillary nerve was 12mm (standard deviation, SD, 5.6mm) in normal shoulders, 10.6mm (SD 5.4mm) in shoulders with osteoarthritis and 9.7mm (SD 3.7mm) in those with cuff tear arthropathy. For this sample size of 50 patients with a confidence interval of 95%, the mean range is 12mm (95% CI 10.4-13.6). A comparison between normal shoulder and osteoarthritis showed a p-value of 0.3, and between normal and cuff tear arthropathy a p-value of 0.06. This was not statistically significant. CONCLUSIONS: The axillary nerve lies on average 12mm from the infra-glenoid tubercle. The presence of inferior osteophytes in glenohumeral osteoarthritis and the proximal migration of humeral head in cuff tear arthropathy does not seem to alter the course of the nerve significantly in relation to the inferior glenoid tubercle.

The position of the upper limb during shoulder arthroscopy does not affect the distance between axillary nerve and glenoid.

PURPOSE: The segment of the axillary nerve (AxN) near the glenoid rim is at risk of iatrogenic lesion during arthroscopic procedures. We hypothesize that the distance between the AxN and the glenoid rim is not modified by the patient's positioning. The primary objective was to compare the position of the AxN with the inferior glenoid rim in lateral decubitus or in beach chair and positions of the upper limb. METHODS: Sixteen shoulders were dissected in beach chair position with the shoulder in neutral rotation. Needle one was placed in the axillary nerve where it was the closest with the inferior glenoid rim. In lateral decubitus with traction and 70° of abduction needle two was placed in the AxN at the closest with the inferior glenoid rim. The glenoid rim was marked with a needle at 6 o'clock. In beach chair position, the distance between needle one and the glenoid needle was measured for six positions. In lateral decubitus, measures were done for two positions of abduction. In lateral decubitus with 70° of abduction, the distance between needle two and the glenoid needle was also measured. RESULTS: The mean distance between AxN and the inferior glenoid rim was 14.4 mm in reference position in beach chair. The results showed the absence of difference between the positions during surgery except for lateral decubitus with 70° of abduction. CONCLUSION: Our study showed that the position of the shoulder during arthroscopic procedures cannot take away the AxN from the inferior glenoid rim. LEVEL OF EVIDENCE: Level IV-basic science study.

Distal suprascapular nerve block-do it yourself: cadaveric feasibility study.

BACKGROUND: A bone landmark-based approach (LBA) to the distal suprascapular nerve (dSSN) block is an attractive "low-tech" method available to physicians with no advanced training in regional anesthesia or ultrasound guidance. The primary aim of this study was to validate the feasibility of an LBA to blockade of the dSSN by orthopedic surgeons using anatomic analysis. The secondary aim was to describe the anatomic features of the sensory branches of the dSSN. MATERIALS AND METHODS: An LBA was performed in 15 cadaver shoulders by an orthopedic resident. Then, 10 mL of methylene blue-infused 0.75% ropivacaine was injected around the dSSN; 2.5mL of red latex solution was also injected to identify the position of the needle tip. The division and distribution of the sensory branches that originate from the suprascapular nerve were described. RESULTS: The median distance between the dSSN and the site of injection was 1.5 cm (0-4.5 cm). The most common injection site was at the proximal third of the scapular neck (n = 8). Fifteen dSSNs were stained proximal to the origin of the most proximal sensory branch. All 15 dSSNs gave off 3 sensory branches that innervated the posterior glenohumeral capsule, the subacromial bursa, and the coracoclavicular and acromioclavicular ligaments. CONCLUSIONS: An LBA for anesthetic blockade of the dSSN by an orthopedic surgeon is a simple, reliable, and accurate method. Injection close to the suprascapular notch is recommended to involve the dSSN proximally and its 3 sensory branches.

Morphological study of the inferior transverse scapular ligament.

The suprascapular nerve can be compressed by the inferior transverse scapular ligament (ITSL), also known as the spinoglenoid ligament, and this entrapment results in dysfunction of the external rotation of the upper arm owing to isolated weakness of the infraspinatus muscle. The morphology of the ITSL has not been adequately characterized. The aim of this study was to clarify the morphological characteristics of the ITSL. In total, 110 shoulders from 72 cadavers were dissected in this study. The ITSL was present in 73 (66.4%) of the 110 specimens, and comprised membrane in 40 (36.4%), ligament in 25 (22.7%), and both membrane and ligament in eight (7.3%). This structure could be classified into three types on the basis of its shape: band-like (33.6%, type I), triangular (15.5%, type II), or irregular (17.3%, type III). In the spinoglenoid notch, the suprascapular nerve was always close to the lateral margin of the scapular spine. The length of the ligament between its origin and insertion sites ranged from 8.7 to 23.4 mm at its superior margin and from 8.9 to 17.5 mm at its inferior margin. The ligament width and thickness at its midportion ranged from 1.6 to 10.0 mm and from 0.1 to 1.2 mm, respectively. The results of this study improve understanding of the ITSL and will be helpful for successful diagnoses and treatments for selective suprascapular nerve entrapment.