2395 COPYRIGHT © 2006 BY THE JOURNAL OF BONE AND JOINT SURGERY, INCORPORATED Is THERE A SAFE AREA FOR THE AXILLARY NERVE IN THE DELTOID MUSCLE? A CADAVERIC STUDY BY OZGUR CETIK, MD, MURAD USLU, MD, HALIL IBRAHIM ACAR, MD, AYHAN COMERT, MD, IBRAHIM TEKDEMIR, MD, AND HAKAN CIFT, MD Investigation performed at Department of Orthopaedics and Traumatology, Kirikkale University School of Medicine, Kirikkale, Turkey, and Department ofAnatomy, Ankara University School of Medicine, Ankara, Turkey Background: Several authors have defined a variety of so-called safe zones for deltoid-splitting incisions. The first aim of the present study was to investigate the distance of the axillary nerve from the acromion and its relation to arm length. The second aim was to identify a safe area for the axillary nerve during surgical dissection of the deltoid muscle. Methods: Twenty-four shoulders of embalmed adult cadavers were included in the study. The distance from the anterior edge of the acromion to the course of the axillary nerve was measured and was recorded as the anterior distance. The same measurement from the posterior edge of the acromion to the course of the axillary nerve was made and was re- corded as the posterior distance for each limb. Correlation analysis was performed between the arm iength and the an- terior distance and the posterior distance for each limb. The ratios between arm length and the anterior and posterior distances were calculated for each case and were recorded as an anterior index and a posterior index. Results: The average arm length was 30.40 cm. The average anterior distance was 6.08 cm, and the average poste- rior distance was 4.87 cm. There was a significant correlation between arm length and both anterior distance (r = 0.79, p < 0.001) and posterior distance (r = 0.61, p = 0.001). The axillary nerve was not found to lie at a constant distance from the acromion at every point along its course. The average anterior index was 0.20, and the average posterior index was 0.16. Conclusions: The present study describes a safe area above the axillary nerve that is quadrangular in shape, with the length of the lateral edges being dependent on the individual's arm length. Using this safe area should provide a safe exposure for the axillary nerve during shoulder operations. T he deltoid muscle is frequently split during exposures of the shoulder, and the axillary nerve, which lies un- der this muscle, has a serious risk of injury, which can result in hmitation of shoulder function''^ Many studies have investigated the anatomical course of this nerve, and it has been reported to lie an average of 5 cm distal to the acromion^"'. However, several anatomical studies have demonstrated a very wide range of the "safe zone" for the axillary nerve, ranging from 3 to 7 cm from the acromion""". Various entry points through the deltoid muscle are necessary for different procedures, such as open rotator cuff repair, arthroscopy, intrameduUary fixation, or percutaneous pinning of proximal humeral fractures""""". To perform a safe surgical procedure, the surgeon must know the worst pos- sible anatomical course of the axillary nerve throughout its entire length rather than its distance from a fixed point. The aim of the present study was to investigate whether the distance of the axillary nerve from the acromion varies with arm length and whether a safe area for the axillary nerve during surgical dissection of the deltoid muscle can be defined. Materials and Methods rr^ wenty-four shoulders of adult cadavers that had been em- L balmed in 10% formaldehyde were included in the study. The distance from the anterior edge of the acromion to the lateral humeral condyle was measured and was recorded as the arm length. Dissection was performed through the deltopec- toral groove, and the deltoid muscle was released from the ac- romion. The inner surface of the deltoid muscle was exposed, and the subdeltoid fascia was removed to expose the axillary nerve (Fig. 1). Needles were pierced through the axillary nerve in order to represent its course on the outer surface of deltoid muscle. Then, the deltoid muscle was sutured back in its origi- nal anatomic position, and the course of the axillary nerve was