THE ANATOMICAL RECORD 232:316-317 (1992) Position of the Axillary Nerve in the Deltoid Muscle ROOPA R. KULKARNI, ASHALATA N. NANDEDKAR, AND V.R. MYSOREKAR Department of Anatomy, M.S. Ramaiah Medical College, Bangalore (R.R.K., V.R.M.), and Department of Anatomy, Armed Forces Medical College, Pune (A.N.N.), India ABSTRACT The relationship of the anterior branch of the axillary nerve to the deltoid muscle was studied on both sides in 66 adult cadavers. The nerve runs a course on the deep surface of the deltoid muscle about 2.2 cm above the midpoint on the vertical plane of the muscle. Intramuscular injection into the deltoid muscle is still a common practice. In such a procedure, a knowledge of the precise position of the axillary (circumflex) nerve gains importance because a n accidental injection into this nerve could cause undesirable side effects. Textbook descriptions of the axillary nerve are vague. According to Johnston and Whillis (1946), the axillary nerve crosses the humerus about 2 cm above the midpoint of a line joining the tip of the acromion to the insertion of the deltoid muscle. Gardner et al. (1975) indicate the level of the axillary nerve by a horizontal plane through the middle of the deltoid. Basmajian (1978) states that the axillary nerve's position can be indicated on the skin surface by a horizontal line drawn 5 cm below the angle of the acromion. Hollinshead (1982) notes that the nerve lies only about 1.5-2 below the acromion. According to Ellis (1983), the axillary nerve is related closely to the surgical neck of the humerus, a hand's breadth below the acromion process. MATERIALS AND METHODS Nineteen male and seven female adult cadavers from the M.S. Ramaiah Medical College, Bangalore, and 24 male and 16 female adult cadavers from the Armed Forces Medical College, Pune, were studied. The procedure followed was identical in all the cadavers. The skin and fascia over both deltoid muscles in each cadaver were reflected. The origin and insertion of the deltoid muscle were defined. The total length of the deltoid muscle across its convexity was measured by a thread from the angle of the acromion to the lowest part of the insertion, and it was read on a scale graduated in millimeters. The midpoint on the vertical plane of the deltoid muscle was marked and a transverse incision across the muscle was made at this level. The two flaps of the muscle were reflected, and i t was found that in all cases the anterior branch of the axillary nerve was in the upper flap. The precise position of this branch from the margin of the upper flap was measured and read on the scale. The pooled data from the two colleges were statistically analyzed. Table 1. Mean position of the anterior branch of the axillary nerve' Limb R L 'Z = Mean distance above the centre of the deltoid muscle in cm 2.37 2.41 SE 0.07 0.07 n 66 66 0.396: P > 0.05. follows a normal distribution, the 99% confidence interval for the mean distance of the nerve from the midpoint on the vertical plane of the deltoid muscle lies between 2.2-2.6 cm. When the data for the two sexes were separately analyzed statistically, there was no difference found on both of the sides, in the position of the nerve from the midpoint, on the vertical plane of the deltoid muscle. A regression equation was drawn to give the precise position of the anterior branch of the axillary nerve when the length of the deltoid muscle was known. The equation was Y = 0.19 X - 0.81 where X is the total length of the deltoid muscle and Y is the position of the nerve from the midpoint of the muscle. DISCUSSION Since the origin and insertion of the deltoid muscle can be precisely defined in a living individual, our findings in the cadaver can be extrapolated to those in the living. Various textbooks have given the position of the axillary nerve as coursing from the midpoint of the deltoid muscle to a point 1.5" below the angle of the acromion. From our findings, it is clear that this nerve is 2.2-2.6 cm above the midpoint on the vertical plane of the muscle. Our findings substantiate only the description of the axillary nerve given by Johnston and Whillis (1946). ACKNOWLEDGMENTS RESULTS We are grateful to Shri. N.S. Narasimha Murthy, assistant professor of statistics, Department of Com- Table 1gives the data for the position of the anterior branch of the axillary nerve in the two limbs, irrespective of sex. The mean position of the anterior branch of the axillary nerve is the same for the right and left limbs. Assuming t h a t the mean position of the axillary nerve Received April 10, 1991; accepted July 31, 1991. Address reprint requests to Dr. V.R. Mysorekar, Dept. of Anatomy, M.S. Ramaiah Medical College, Gokula Extension Post, Bangalore 560 054, India. 0 1992 WILEY-LISS, INC AXILLARY NERVE munity Medicine, M.S. Ramaiah Medical College, Bangalore, for statistical analysis of the data. LITERATURE CITED Basmajian, J.V. 1978 Grant’s Method of Anatomy, 9th ed. S. Chand & Co., New Delhi, pp. 95-96. 317 Ellis, H. 1983 Clinical Anatomy, 7th ed. Blackwell, Oxford, p. 200. Gardner, E., D.J. Gray, and R. ORahilly 1975 Anatomy, 4th ed. W.B. Saunders, Philadelphia, p. 114. Hollinshead, W.H. 1982 Anatomy for Surgeons, 3rd ed., Vol. 3. Harper & Row, Philadelphia, p. 336. Johnston, T.B., and J. Whillis 1946 Gray’s Anatomy, 29th ed. Longmans Green, London, p. 1497.