RINCÓN, F.; RODRÍGUEZ, I. Z.; SÁNCHEZ, A.; LEÓN, A. & GONZÁLEZ, L. F. The anatomic characteristics of the third head of biceps brachii muscle in a Colombian population. Rev. Chil. Anat., 20(2):197-200, 2002.

SUMMARY: We report the appearance of variations of the biceps brachii muscle and describe their anatomic characteristics in our population. A prospective evaluation was conducted on cadavers at the morgue of the "Nueva Granada" Military University (UMNG) - School of Medicine in Santafe de Bogota, Colombia. Thirty-two arms of 16 cadavers were included. Anatomic description was achieved by measurements of length, width, thickness, insertions, relations, innervating branches and blood supply. A third head for the biceps brachii muscle was found in 6 arms (37.5%, n=16). It appeared most frequently in the right arm (31.25%, n=16) and found bilaterally in 2(12.5%, n=16) cases; arising from the lower third the humeral shaft at 12.82 ± 0.59 cms. from the external humeral condyle and with a total length of 12.9 ± 0.29 cms. These results provide an anatomic description of the characteristics of this variation in the population studied and also is the first report of this accessory head among Colombians.

KEY WORDS: 1. Human Anatomy; 2. Biceps brachii muscle; 3. Accessory head of biceps brachii muscle; 4. Anatomical variations.

INTRODUCTION

Biceps brachii muscle is characteristically described as a two-headed muscle that originates proximally, with a long head at the supraglenoid tubercle and a short head from the coracoid process of the scapula (Gray, 1973). Distally, these two heads join to form a common tendon that inserts into the posterior aspect of the radial tuberosity, mainly contributing to the flexion and supination of the forearm; and with some fine aponeurotic and tendinous fibers into the bicipital aponeurosis.

Testut (1902) has described the biceps brachii muscle as one of the muscles with most frequent anatomic variations. These variations may present as a group of accessory fascicles arising from the coracoid process, pectoralis major tendon (Sargon et al., 1996), proximal head of the humerus, articular capsule of the humerus or from the humerus itself. This last variation is also known as the humeral head of the biceps brachii muscle (HHB). Several authors (Pedraza, 1934; Bergman et al., 1984; Swieter & Carmichael, 1980; Asvat et al., 1993; Sargon et al.; Santo Neto et al., 1998 and Kopuz et al., 1999) have reported the presence of this anomaly with a varying frequency, according to the studied population; Chinese 8%, European white 10%, African Black 12% and Japanese 18%.

The HHB is a thin fascicle, sometimes flattened or voluptuous, that is located below all the normal structures of the biceps brachii muscle. It has its origins, at the humeral shaft, between the corachobrachialis and brachialis muscles, or between the groove of the radial nerve and the brachialis muscle and sometimes, it arises from the anterior aspect of the brachialis (Testut; Pedraza and Kosugi et al, 1992). From here, it descends to join the common distal tendon of the biceps brachii muscle and very rarely joining its muscle body. ]]> Embryological observations by Testut described this variation as a portion of the brachialis muscle separated by the musculocutaneous nerve, in which its distal insertion has been translocated from the ulna to the radius.

This study is aimed to provide a macroscopic description of the third head of the biceps brachii muscle, found in a sample of cadavers of our population, as this variation may become relevant for surgical interventions of the arm, specially, after humeral fractures with subsequent unusual bone displacements (Swieter & Carmichael), unexplained upper arm and/or shoulder pain syndromes (Beattie, 1947 and Warner et al., 1992), and when nerve compression syndromes are sought (Nakatani et al., 1998).

MATERIAL AND METHOD

Sixteen cadavers were dissected at the Morgue of the "Nueva Granada" Military University and Medical School. The Forensic and Legal Institute of Santafe de Bogota donated these cadavers for academic purposes. Cadavers were placed in10% formalin for adequate preservation. Proper consent was achieved from the Department of Morphology and Physiopathology of the Military University and Medical School.

Cadavers were dissected in situ. A longitudinal incision was performed at the anterior aspect of the arm from the level of the acromion to the elbow junction. A perpendicular extension of the incision was achieved bilaterally and in both proximal and distal segments. Careful dissection and separation of skin, sub-cutaneous fat and fascia achieved exposure of the muscular apparatus. Major vessels and anatomic relations were kept intact for comparison analysis.

Length, width and thickness of normal muscles and anatomic variants were considered. Distal insertion level was measured from greater tubercle (GT) to proximal edge of the muscular insertion and compared to GT-lateral epicondyle (LE) length. A ratio was then calculated.

Statistical analysis. All data is presented as mean ± SEM unless otherwise indicated.

RESULTS

A total of 32 arms of 16 subjects were studied. Six arms were found to have a three-headed biceps brachii muscle. The variant was present in 5 males (31.25%, n=16) and 1 female (6.2%, n=16) . It was found in 5 subjects in the right arm (31.25%, n=16) , 3 in the left arm (18.75%, n=16) and 2 bilaterally (12.75%, n=16). All of the specimens were obtained from mestizo subjects (Spanish and Native South-American mixture).

GT-LE length was 28.48 ± 1.38 cms. There was just one common proximal insertion at the antero-medial and lower third aspect of the humerus at 12.82 ± 0.59 cms, between the brachialis and coracobrachialis muscles, where it extended to join the common tendon, that inserts into the radial tuberosity and bicipital aponeurosis. The length of the muscle body of the fascicle was 12.90 ± 0.29 cms. ]]> Table I. Anatomic characteristics of the third head of biceps brachii muscle in a Colombian population.

Measures	Cm ± SEM
GT-LE	28.48 ± 1.39
Insertion-LE	12.82 ± 0.59
Biceps brachii common tendon	6.05 ± 0.28
HHB body (HHB)	12.9 ± 0.29
HHB total length (TL)	18.95 ± 0.47
Ratio HHB TL/EHT-LE	0.68 ± 0.05
HHB Thickness	0.45 ± 0.05
HHB Width	]]> 1.48 ± 0.03

Blood supply was assured by small branches from the brachial artery in all of the cases. The musculocutaneous nerve supplied the innervation with a short filament entering at the superior third and anterior aspect, just after perforating the coracobrachialis muscle. Venous drainage was found to be through the brachial vein.

The fascicle was in relationship, anteriorly to the musculocutaneous nerve, long and short head of biceps brachii muscle, posteriorly to the brachialis muscle and humerus, laterally to the long head of the biceps brachii muscle (Fig. 1), medially to the median nerve, humeral artery, vein and lymphatic vessels.

Fig. 1.Antero-medial compartment of the arm showing the normal anatomy of the Biceps brachii muscle, with its long head (B1), short head (B2), and third-head (B3) extending proximally from the lower third of the humeral shaft and joining distally the common tendon of the biceps brachii; brachialis (BA) and coracobrachialis (CB) being perforated by the musculocutaneus nerve (Mcn).

DISCUSSION

Gray has reported the incidence of this variation as much as 10% in his studies, this agrees with the observations of Bergman et al. in white Europeans. The percentage of this among other ethnic groups varies substantially from 8% to 18%. Asvat et al. reported an incidence of 21.5% in his study group for blacks, 8.3% for whites, and correlated it to the results by Greig et al. (1952). It seems that the incidence varies among ethnic groups and therefore should be reported accordingly. It is not known yet, whether or not, this means a specific functional adaptation of populations characterized for continuous moderate physical activity. Kopuz et al. attributes the appearance of this variant to evolutionary and/or racial trends. Embryological observations (Testut) may support this hypothesis as the translocation of the insertion of some of the fibers of the brachialis to the common tendon of the biceps brachii muscle may enhance primarily supination and secondary flexion of the forearm, and also could be an explanation of the high incidence of the third-head of the biceps in right arms, as much as 31.25% (n=16) in this report. The present data, however, was not correlated to this last variable, as the functional information of the individuals was either unknown and/or kept confidential by the Forensic and Legal institute of Bogota, and is based on general statistics, but it has been addressed by Kosugi et al. as well. Santo-Neto et al. reports an incidence of 9% among blacks significantly lower than the reported incidence for whites in his series, but there is no clear definition in regards to the white population included and/or if it was mixed with mestizos. Khaledpour (1985), also contradicts Santo-Neto's results by comparing his series to the results of other authors, he concludes that the third head of the biceps is rare in whites and relatively high among blacks. Male cadavers were found to have the variant in 31.2% (n=16) of the cases in this study. Several authors have demonstrated that males are affected predominantly (Asvat et al. and Bergman et al.).

In this series the proximal insertion of the variant fascicle was at the level of the humeral shaft, between the coracobrachialis and brachialis muscles, in all of the cases, as reported by others (Asvat et al.). The innervation and vascularization relied on the normal structures of the ventral aspect of the arm, mainly the musculocutaneous nerve and brachial artery. This agrees with normal embryologic development of the related dermatomes and myotomes and also has been reported in other series before (Testut; Gray, 1973; and Asvat et al.).

The relevance of all these observations in the clinical scenario is related to some physiopathologic considerations, not yet reported in the literature for the variant described herein.Warner et al., described an accessory head of the biceps brachii muscle originating at the level of the lesser tuberosity of the humerus, running parallel to the short head of the biceps brachii muscle, that had to be dissected for proper visualization of the underlying articular capsule, during a standard arthrotomy with T-plasty capsulorrhaphy, in a case of chronic shoulder dislocation. Similarly, Nakatani et al., describes a case of a Japanese male with bilateral four headed biceps brachii muscle, in which the left third head gave off a muscle slip into the posterior fascia of the pronator teres, forming a tunnel, the median nerve and the brachial artery passed through this tunnel where they appeared compressible.

Therefore, surgeons, orthopedic surgeons and medical community in general should be knowledgeable of this anatomic variant when dealing with some of the clinical syndromes mentioned previously; this study provides a description of the anatomic characteristics of the third head of the biceps brachii muscle also known as the humeral head of the biceps brachii muscle in Colombians, and previous hypothesis considering its origin may be supported by the observations presented in this report. ]]> AKNOWLEDGMENTS

The authors wish to thank Mr. Casimiro Cañon, Curator of the Morgue of the "Nueva Granada" Military University (UMNG) and School of Medicine, for his active cooperation in the dissection of the specimens.

SUMMARY: Reportamos variaciones anatómicas del músculo bíceps braquial en la población colombiana. El estudio fue realizado en 32 miembros superiores de 16 cadáveres provenientes del Servicio de Tanatología de "Nueva Granada" Universidad Militar (UMNG) - Escuela de Medicina, Santafe de Bogota, Colombia. Efectuamos la descripción anatómica y medimos el largo, ancho, espesor, determinándose además sus inserciones y relaciones, inervación e irrigación de los músculos. La tercera cabeza para el músculo bíceps braquial fue encontrada en 6 cadáveres (37.5%). Su presencia era más frecuente en el miembro superior derecho (31.25%); su presencia fue bilateral en 2 casos (12.5%); se originó del tercio inferior del húmero a 12.82 ± 0.59 cm del epicóndilo lateral y con un largo total de 12.9 ± 0.29 cm. Estos resultados, además de aportar una descripción anatómica de esta variación, es el primer relato de la presencia de la tercera cabeza del músculo bíceps braquial, en la población colombiana.

KEY WORDS: 1. Anatomía Humana; 2. Músculo bíceps braquial; 3. Tercera cabeza del músculo bíceps braquial; 4. Variación anatómica.

REFERENCES

Asvat, E.; Candler, P. & Sarmiento, E. High incidence of the third head of biceps brachii in South African populations. J. Anat., 182:101-4, 1993.         [  ]

Beattie, P. H. Description of bilateral coracobrachialis brevis muscle, with a note on its significance. Anat Rec., 97, 123, 1947.         [  ]

Bergman, R. A.; Thompson, S. A. & Aifi, A. K. Catalogue of human variation. Munich, Urban and Schwartzenberg, 1984. pp 27-30.         [  ]

Gray, H. Anatomy of the Human Body. 29th. American ed. Philadelphia, Lea and Febiger, 1973. pp 488-99.         [  ]

Greig, H. W.; Anson, B.J. & Budinger, J. M. Variations in the form and attachment of the biceps brachii muscle. Quarterly Bulletin, Northwestern University Medical School, 2:241-4, 1952.         [  ]

Khaledpour, C. Anomalies of the biceps muscle of the arm. Anat Anz., 158(1):79-85, 1985.         [  ]

Kopuz, C.; Sancack, B. & Ozbenli, S. On the incidence of the third head of biceps brachii in Turkish neonates and adults. Acta Anat Nippon, 74(3):301-5, 1999.         [  ]

Kosugi, K.; Shibata, S. &Yamashita, H. Supernumerary head of biceps brachii and branching pattern of the musculocutaneous nerve in Japanese. Surg. Rad. Anat. (14)2:175-85, 1992.         [  ]

Nakatani, T.; Tanaka, S. & Mizukami, S.Bilateral four-headed biceps brachii muscles: the median nerve and brachial artery passing through a tunnel formed by a muscle slip from the accessory head. Clin. Anat., 11(3):209-12, 1998.         [  ]

Pedraza, M. H. Principales anomalías musculares observadas en los anfiteatros de la Facultad. Revista de la Facultad de Medicina de la Universidad Nacional 3(2):75, 1934.         [  ]

Santo Neto, H.; Camilli, J. A.; Andrade, J. C.; Meciano, F.J. & Marques, M. J. On the incidence of the biceps brachii third head in Brazilian white and blacks. Anat. Anz., 180(1):69-71, 1998.         [  ]

Sargon, M. F.; Tuncali, D. & Celik, H. H. An unusual origin for the accessory head of biceps brachii muscle. Clin Anat., 9(3):160-2, 1996.         [  ]

Swieter, M. G. & Carmichael, S. W. Bilateral three-headed biceps brachii muscles. Anat. Anz., 148(4):346-9, 1980.         [  ]

Testut, L. Tratado de Anatomía Humana. Barcelona, Salvat, 1902. p 1022         [  ]

Warner, J. P.; Palleta, G. A. & Warren, R. F. Accessory Head of the Biceps brachii, Case report demonstrating clinical relevance. Clin. Ortho. Res., 280:179-81, 1992.         [  ]

Correspondence:
Dr. Fred Rincon, MD
Research Scholar, Division of Vascular Surgery
10 Washington Drive Apt. A
Little Falls, NJ 07424 - USA

Fredrincon@hotmail.com

Recibido : 26-03-2002
Aceptado: 28-05-2002 

Department of Morphology & Physiopathology, Section of Anatomy, "Nueva Granada" Military University (UMNG) and School of Medicine, Santafe de Bogotá, Colombia. ]]> 1993 182 101-4 1947 97 1984 27-30 1973 29 488-99 1952 2 241-4 1985 158 1 1 79-85 1999 74 3 3 301-5 1992 2 14 14 175-85 1998 11 3 3 209-12 1934 3 2 2 1998 180 1 1 69-71 1996 9 3 3 160-2 1980 148 4 4 346-9 1902 1992 280 179-81