Evaluation of anatomic landmarks for axillary nerve block in the quadrilateral space

Axillary nerve block (ANB) was recently introduced along with suprascapular nerve block as an alternative to inter-scalene brachial plexus block for post-operative pain control. However, the methods for performing ANB are variable. We studied the relationship between surface anatomy and the location of the axillary nerve in the quadrilateral space to ensure a technically safe and simple ANB.

Eighty-eight shoulders were included. All measurements were performed with the subjects seated and the shoulders in a neutral position. We located the posterior circumflex humeral artery (PCHA) using a vascular Doppler system and named this point 'AN'. We used this point to locate the axillary nerve, since this nerve is generally present with the PCHA in the quadrilateral space. We then examined the relationship between surface anatomic landmarks and AN. The depth of the medial side of the humerus at the AN (AN depth), which is at the lateral border of the quadrilateral space, was measured using ultrasonography.

AN was located on the line between the posterolateral corner of the acromion (Ac) and the axillary fold (Axf) (Ac-Axf) in 77% of shoulders. The ratio of the distance from Ac to AN (Ac-AN) to Ac-Axf in all shoulders was 0.6 [standard deviation (SD), 0.1]. AN depth was 4.0 (SD, 0.5) cm in men and 3.6 (SD, 0.4) cm in women.

Knowledge of the relationship between surface anatomy and AN, as well as estimated AN depth may aid in locating the axillary nerve in the quadrilateral space.