Rare origin of the third head of biceps brachii muscle, its clinical significance, review on incidence and clinical application

Abstract

The anatomical variations of the biceps brachii muscle are well-known and well-documented. Awareness of these variations is necessary  to avoid complications during radio diagnostic procedures or surgeries in the arm. The biceps brachii muscle is one of the most variable  muscles in the human body, in terms of the number and morphology of its heads. Thus, the anatomical variations and gross innervations  pattern of the biceps brachii muscle were studied in the present work by using 62 arms from 31 adult cadavers. Among 62  studied arms, 26 arms (41.9%) were males, and 36 arms (58.1%) were females. During the study, the third head was found in seven out of  62 arms (11.3%). It was found that four out of 26 studied male biceps muscles (15.4%) revealed third heads while three out of 36 studied  female biceps muscles (8.3%) revealed third heads. Also, third head prevalence among male subjects was found to be nearly doubled  than those of female subjects. It was found that three out of 31 left-sided biceps muscles (9.3%) included third heads while four out of 31  rightsided biceps muscles (12.9%) included third heads. So, the third head prevalence on the right side was found to be higher than that  of the left side. Bilateral third heads were found in two out of 31 cadavers (6.4%) and three out of 31 studied cadavers (9.6%) had  unilateral third heads. There were three types of variations encountered in the origin of the third head. They could be categorized as (1)  infero-medial humeral origin was found in five arms (71.4%), (2) infero-lateral humeral origin was found in one arm (14.3%), (3) coracoid  origin was found in one arm (14.3%). The third head originated from the coracoid process of scapula together with the short head of biceps brachii was a rare variant found by Macalister in 1875. In the present study, it was found in one out of seven third heads (14.3%).  Based on the current literature review, it was the first time to find this rare origin of the third head since the day of the Macalister.  Understanding of such variations is helpful in preoperative diagnosis and surgery of the upper limb.