Published online December 27th, 2010 © http://www.ijav.org
Case Report
International Journal of Anatomical Variations (2010) 3: 214–215
Introduction
Biceps brachii, as the name suggests is characteristically a two-headed muscle of flexor compartment of arm. However, supernumerary heads of biceps brachii are frequent of which three heads of biceps brachii is the most commonly reported variation. Such variations can cause unusual bone displacement after a fracture [1]. Neurovascular symptoms have been reported due to compression of median nerve while passing below the fibromuscular canal caused by the supernumerary heads of biceps brachii [2].
Case Report
During routine undergraduate dissection of the upper limb of a 45–55 year old adult male cadaver, an unilateral supernumerary head of biceps brachii was found in the right arm.
The third head was a flat muscular belly which originated from the upper and medial part of brachialis. It lay lateral to the brachial artery and median nerve. Then it got inserted into the conjoint muscle belly of biceps brachii on its medial side and not its tendon. It was supplied by a branch from musculocutaneous nerve. Communication between musculocutaneous nerve and median nerve was noted proximal to the third head of biceps brachii. The musculocutaneous nerve did not pierce the coracobrachialis. Coracobrachialis was Akhilandeswari BALASUBRAMANIAN
Department of Anatomy, Bangalore Medical College and Research Institute, Bangalore, INDIA.
Dr. Akhilandeswari Balasubramanian, MD Assistant Professor
Department of Anatomy
Bangalore Medical College and Research Institute Bangalore, INDIA.
+91 80 26492048 akhilandeswarib@gmail.com
Received June 21st, 2010; accepted December 20th, 2010
ABSTRACT
The biceps brachii muscle and the musculocutaneous nerve of arm are frequent in their variations. A third head of biceps brachii was noted unilaterally during routine anatomy dissection. Variation in musculocutaneous nerve was also seen on the same arm. The evolutionary and functional basis of such variations are discussed. Such variations become relevant during surgical intervention of the arm, especially after humeral fracture with
subsequent unusual bone displacements. © IJAV. 2010; 3: 214–215.
Key words [accessory head] [third head] [supernumerary head of biceps brachii] eISSN 1308-4038
Supernumerary head of biceps brachii
supplied by a branch from medial root of median nerve. The musculocutaneous nerve gave a branch to biceps brachii and brachialis from a common point. The nerve to biceps brachii gave a branch to the conjoint belly of biceps brachii and then continued down to pierce the third head of biceps and supplying it. Further down, this branch continued as lateral cutaneous nerve of forearm. Discussion
In man, the frequency of third head of biceps brachii varied according to the population studied and three distinct origins of the third head have been reported [3]. Most common, was from the medial shaft of humerus in common with and distal to the insertion of coracobrachialis.
Next frequent, was from medial aspect of humerus adjacent of origin of brachialis.
Least common was a dual fascial origin from lateral aspect of short head of biceps brachii and from medial aspect of deltoid and its insertion area [1].
The muscle descends to join the common distal tendon of biceps brachii and very rarely joined its muscle belly [4]. In the present case, the third or the supernumerary head arose from upper and medial part of brachialis and inserted into the conjoint muscle belly. It was supplied by a branch of the nerve to biceps brachii from musculocutaneous nerve. As it lay lateral to brachial artery and median nerve it did not form a tunnel or *Presented at Annual Meeting of North States Chapter of Anatomical Society of India at M.
215 Supernumerary head of biceps brachii
Figure 1. The photograph shows the third head of biceps brachii in relation to the conjoint tendon. (1: third head of biceps brachii; 2:
musculocutaneous nerve; 3: median nerve; 4: branch to brachialis; 5:
lateral cutaneous nerve of forearm)
1 2
3 4
5
compress them. The development of the third head may have influenced the variant musculocutaneous nerve, as in this case where, the musculocutaneous nerve did not pierce the coracobrachialis [5].
Such a third head of biceps brachii would allow flexion of elbow joint irrespective of the position of the shoulder
joint. It may also enhance the strength of elbow flexion [2].
In cases where the brachial artery or median nerve ran under the third muscle slip, neurovascular symptoms can be produced due to compression by the muscle slip. Accessory heads gain importance in plastic surgery as they would be expandable and of more value in flap surgery than the two main heads. If a nerve or artery pierces the accessory head then it can cause difficulty during elevation or transferral of the flap [6].
These accessory heads become relevant during surgical intervention of the arm, especially after humeral fracture with subsequent unusual bone displacements.
Explanation according to the evolutionary point of view:
The third head of biceps brachii in humans is probably derived from muscles of anterior compartment of arm as implied by its innervation. In human, where long head of coracobrachialis is absent, the third head of biceps brachii which arises in continuity with the insertion of coracobrachialis may represent a remnant of long head of coracobrachialis the ancestral hominoid condition [1]. It is yet to be proven, whether the accessory head is a specific functional adaptation of population who show continuous, moderate physical activity. Several authors found that males had the variation predominantly and that the incidence was higher in the right arm.
Embryological studies by Testut, described the variation as a portion of brachialis muscle where its distal insertion has been translocated from ulna to the radius. This supports the hypothesis of functional adaptation [4].
Figure 2. The photograph shows the third head of biceps brachii innervated by the branch from musculocutaneous nerve. (1: third head
of biceps brachii; 2: musculocutaneous nerve branch supplying the
third head of biceps brachii; 3: median nerve; 4: branch to brachialis; 5: lateral cutaneous nerve of forearm)
1 2
3
4 5
References
[1] Asvat R, Candler P, Sarmiento EE. High incidence of the third head of biceps brachii in South African populations. J Anat. 1993; 182: 101–104.
[2] Nayak S, Samuel VP, Somayaji N. Concurrent variations of median nerve, musculocutaneous nerve and biceps brachii muscle. Neuroanatomy. 2006; 5: 30–32.
[3] Bergman RA, Thompson SA, Afifi AK, Saadeh FA. Compendium of Human Anatomic Variation. Munich, Urban and Schwarzenberg. 1988; 27–30.
[4] Rincon F, Rodriguez ZI, Sanchez A, Leon A, Gonzalez LF. The anatomic characteristics of the third head of biceps brachii in a Colombian population. Rev Chil Anat. 2002; 20; 197–200.
[5] Abu-Hijleh MF. Three headed biceps brachii muscle associated with duplicated musculocutaneous nerve.
Clin Anat. 2005; 18: 376–379.
