INCIDENCE OF THE THIRD AND FOURTH HEAD OF THE BICEPS BRACHII MUSCLE IN CAUCASIAN RACE – A STUDY AND REVIEW OF LITERATURE

Address for Correspondence: Dr. Sushil Kumar, Assistant Professor, Anatomy division, Department of radiology, Weill Cornell Medicine, New York. E-Mail: sushilbhu2001@yahoo.co.in Anatomic variations in the heads of biceps brachii are not uncommon. It varies from one head to seven heads but two heads (long and short) are considered normal. In this study, 56 arms from 28 cadavers were studied for third and fourth heads in the anatomy laboratory of Weill Cornell Medicine. We observed supernumerary heads in 5 cadavers (8.92%), out of which three heads were seen in 4 cadavers (7.14%) and four heads in only one cadaver (1.78%). Clinically, these kinds of anomalies are important because supernumerary heads could compress neighboring blood vessels and nerves.


INTRODUCTION
upper limb with the most frequent anatomic variations [3,4]. Incidence varies in different races [4]. The aim of this study was to assess the incidence of the third and fourth head of the biceps brachii muscle in Caucasian cadavers in the united states and compare it with other ethnic groups.
The biceps brachii is one of the muscles of the anterior compartment of the arm, which derives its name from its two proximally attached parts or heads. The long head arises from the supraglenoid tubercle and adjoining part of the glenoid labrum of the scapula. The short head arises from the apex of the coracoid process together with and to the lateral side of the coracobrachialis. The two heads join together and form a common tendon laterally, which inserts on the posterior aspect of the radial tuberosity and medially it forms bicipital aponeurosis, which blends with the deep fascia of the forearm. The musculocutaneous nerve, a branch of the lateral cord of the brachial plexus, innervates it [1,2]. Several authors have described the biceps brachii muscle as one of the muscles in the 28 dissected cadavers, 12 males and 16 females were used for this study. Fifty-six upper limbs (28 right and 28 left) were observed for additional heads of the biceps brachii muscle on already dissected cadavers at the Anatomy laboratory of Weill Cornell Medicine. Incidences of classical as well as additional heads were noted. Appropriate photographs were taken.

RESULTS
Among the 56 upper extremities studied, one male and one female cadaver had third head bilaterally. In one male cadaver four heads of biceps brachii was seen on the right side. The third head of the biceps brachii in all cases was arising from the anteromedial aspect of the lower part of the humeral shaft between the insertion of the coracobrachialis muscle and the origin of brachialis muscle. It inserted in the belly of the short head of the biceps brachii from the inferomedial aspect. The fourth head was present in one of the male cadaver. It was arising from the medial aspect of the greater tubercle of the humerus and blended with the long head of the biceps brachii from lateral side. Both the third and fourth heads of the biceps brachii were much slender and shorter than the other two heads. The nerve supplies of these two heads were also from the musculocutaneous nerve just like short head and long head.

DISCUSSION
heads -long head that originates from the supraglenoid tubercle and a short head, which originates from the coracoid process of the scapula. Sometimes the supernumerary head is found as a third head or rarely fourth head. Heads up to seven has also been reported [3]. There is geographic and gender variations in the incidence of supernumerary heads. Gray's anatomy reported the incidence of the third head in 10% of cases [5]. Biceps brachii with three heads is found in 8% of Chinese, 10% of white Europeans, 18% of Japanese, 20.5% of South African blacks, 8.3% of South African white, 15% of Turkish and 37.5% of Colombians [6][7][8][9][10][11][12]. Incidence of variations on biceps brachii is more in males compare to females [4,9,13,14]. However, there is no specific functional explanation for these findings in terms of geographic or gender differences [4]. Incidences of four heads are rare. Nakatani etal in 1998 reported this anomaly bilaterally. [15] Vazquez et al. in 2003 reported it unilaterally [16]. In 2008, Soubhgya et al reported one rare variation in which there was 4 th head in both biceps and triceps brachii muscle [17]. In our study, we observed 5 limbs out of 56 limbs (8.92%) having supernumerary heads. Out of these we found three heads in 4 limbs (7.14%) and 4 th head in one limb (1.78%). Third head was present bilaterally in one male and one female cadaver. 4 th head was present in male cadaver on the right side. Left limb of this cadaver had normal two heads. In my study, incidence of supernumerary head is very close to the observation made by Aswat in South African white population [4]. Origins of the supernumerary heads are variable. According to the Gray's anatomy, third head arises from the superomedial part of the brachialis and is attached to the bicipital aponerosis and the medial side of the tendon of insertion [5]. According to Kosugi there are various sources of the origins of the additional heads, which are from humerus, medial intermuscular septum, tendon of pectoralis major or the deltoid and even from articular capsule or from the crest of the greater tubercle [10]. Kumar et al reported the presence of third head in 3.33% cases bilaterally [11]. In our study we also observed the bilateral presence of the third head. Kopuz  reported the origin of third head from the anterior surface of the humerus just distal to the insertion of coracocobrachialis just like our study [12]. Nakatani et al reported origin of 4 th head from the crest of the greater tubercle of the humerus. In our study we also found fourth head coming from the crest of the greater tubercle of the humerus. Developmentally third head is considered as detached part of the brachialis muscle [3]. Morphologically, third head is considered as the long head of coracobrachialis as it commonly originates from the point of insertion of coracobrachialis [4].

REFERENCES
The presence of additional heads of the biceps brachii may confuse surgeons during surgery or radiologist while interpreting radiographs of the arm. Additional heads may compress the underlying nerves and produce symptoms of nerve compression or they may compress the underlying blood vessels and compromise the blood supply of the forearm and hand.