6 Muscular Case Studies

Chapter Objectives

  • Describe the anatomical variation, population incidence of a range of phenotypes, and Australian and New Zealand context of select examples of the muscular system, including the:
    • biceps brachii
  • Discuss the clinical and/or professional impact of anatomical variation of the muscular system on patients and/or professional settings

Biceps Brachii

Variation Classification: Morphology and Frequency

Description of Anatomy

The biceps brachii is located in the anterior compartment of the brachium, and as its’ name suggests (‘bi’ = two; ‘ceps’ = heads), most commonly consists of two heads. The long and short heads of the biceps brachii attach from the supraglenoid tubercle and coracoid process of the scapula, respectively. The two heads then insert via a common tendon onto the radial tuberosity with an additional medial fascial slip, the bicipital aponeurosis inserting onto the anteromedial muscles of the antebrachium.  

Examples of Phenotypic Variation

The biceps brachii can display supernumerary (accessory) heads with up to seven heads being reported and morphological variations in its attachment sites (both the origin and insertion). Supernumerary heads are most often observed unilaterally. In some cases the biceps brachii demonstrates a third head which most commonly arises from the shaft of the humerus distal to the insertion of the coracobrachialis (frequency variation). It has been hypothesised that supernumerary muscles in the upper limb may be an evolutionary trait, with muscles being more simple and slender in humans compared to primates and the cases of supernumerary heads decreasing over time demonstrating secular trends in incidence of this variation.

Four phenotypes of the biceps brachii are presented in a series of diagrams below. Use the slider tool to move between each phenotype and read the text underneath that describes each phenotype. By dragging the slider tool you can view the transition between each phenotype to clearly see how each phenotype differs from the next.

[Illustrations adapted by L. Gregory  from cadaveric photos in Szewczyk et al., (2022) CC BY-NC 4.0 ]
Four phenotypes of biceps brachii variation.
Figure 6.1: Overview of four phenotypes of biceps brachii variation. A: Single muscle belly; B: Two muscle bellies; C: Inferomedial third muscle head (purple accessory muscle between short and long heads); D: Superior third muscle head (purple muscle head medal to short head). [Illustrations adapted by L. Gregory  from cadaveric photos in Szewczyk et al., (2022) CC BY-NC 4.0 ]


Population Frequencies of Phenotypic Variation of Supernumerary heads

Source Szewczyk et al. (2022) Rodríguez-Niedenführ (2003) Ballesteros et al. (2013) Cucca et al. (2010) Al-Kushi (2013) Kosugi et al. (1992) Nayak et al. (2006)
Population Central European UK Colombia Australia (Western Australia) Saudi Arabia Japan India
Sample size 101 (202 arms)


175 (350 arms)
53 (106 arms)


20 arms


20 (40 arms)


273 (546 arms)




2 heads
64% of cadavers

2.5%* Single muscle belly

29.2%* Two muscle bellies


84.6% of cadavers 80.2%* 80%*

30%* Two bellies

85% 78.8% 97.9%
3 heads
26% of cadavers 13.1% of cadavers

9%* Inferomedial head

1.5%* Superior humeral head

0.3%* Inferolateral head

19.8%* Inferomedial head 20%*

15%* Inferomedial head

5%* Superior humeral head

15%* 21.2% 2.1%
4 heads
6% of cadavers 2.9% of cadavers 0% 0% 0% 0%
5 heads
4% of cadavers 0% 0% 0% 0% 0%

*% of total arms

Australian and New Zealand Context

In 2009, Fogg et al., completed a cadaveric dissection study within an Australian population aimed to describe the morphology of the distal biceps brachii tendon, to inform the common surgical approach used for tendon rupture (endobutton repair). Authors dissected 46 embalmed cadaveric arms (M =16, F = 18) and identified a variable number of distinct tendinous bands of both heads of the biceps brachii enclosed within the tendinous sheath, as opposed to just the typically described two tendinous bands associated with the short and long head of the biceps respectively. The tendinous bands occurred in varying numbers (mean 4.5 ± 2), each with a distinct attachment to the radius from immediately proximal to the radial tuberosity to distal to the radial tuberosity. The exact point of attachment and the distance between each attachment point was highly varied. Identification and description of these bands within the tendinous sheath of the biceps brachii is important, as commonly the endobutton surgical repair utilises stitches that pass through only the margin of the tendon; leaving several tendon bands free to move proximally. Authors suggest that the use of sutures that cross the width of the tendon may improve surgical outcomes (Fogg et al., 2009).

Case Study on Biceps Brachii: Case of supernumerary head of biceps brachii

A 34 year old male patient presents to the emergency department following a motorcycle accident. Dislocation of the right and left glenohumeral joints and rotator cuff muscle tears are suspected. During assessment of the patient’s MRI of the shoulder, a third head of the right biceps brachii is observed.

QUESTION 1: Would a supernumerary head of the biceps brachii result in any functional advantage to the patient?

QUESTION 2: Why is an accessory head of the biceps brachii sometimes mistaken for a tumour during medical image interpretation?

QUESTION 3: Compare and contrast the anatomy of the anterior muscle compartment of the brachium between humans and primates, and hypothesise why supernumerary heads of the biceps brachii suggest an evolutionary trait. Refer to Oxnard and Franklin (2008) for guidance.

References and Further Reading

Al-Kushi, A.G. (2013) Anatomical study of the third head of biceps brachii muscle and its innervation by median nerve in human dissection. Journal of Clinical Medicine and Research, 5(4), 47-52.
Ballesteros, L. E., Forero, P. L., & Buitrago, E. R. (2014). Evaluation of additional head of biceps brachii: a study with autopsy material. Folia Morphologica, 73(2), 193–198. https://doi.org/10.5603/FM.2014.0028
Cucca, Y. Y., McLay, S. V. B., Okamoto, T., Ecker, J., & McMenamin, P. G. (2010). The biceps brachii muscle and its distal insertion: observations of surgical and evolutionary relevance. Surgical and Radiologic Anatomy (English Ed.), 32(4), 371–375. https://doi.org/10.1007/s00276-009-0575-y
Fogg, Q. A., Hess, B. R., Rodgers, K. G., & Ashwood, N. (2009). Distal biceps brachii tendon anatomy revisited from a surgical perspective. Clinical Anatomy (New York, N.Y.), 22(3), 346–351. https://doi.org/10.1002/ca.20786
KOSUGI, K., SHIBATA, S., & YAMASHITA, H. (1992). SUPERNUMERARY HEAD OF BICEPS BRACHII AND BRANCHING PATTERN OF THE MUSCULOCUTANEUS NERVE IN JAPANESE. Surgical and Radiologic Anatomy (English Ed.), 14(2), 175–185. https://doi.org/10.1007/BF01794898
Nayak, S. R., Prabhu, L. V., & Sivanandan, R. (2006). Third head of biceps brachii: A rare occurrence in the Indian population. Annals of Anatomy, 188(2), 159–161. https://doi.org/10.1016/j.aanat.2005.10.004

Oxnard, C. ., & Franklin, D. (2008). Ghosts of the Past II: Muscles and Fasciae in the Primate Forelimb Domain. Folia Primatologica, 79(6), 441–457. https://doi.org/10.1159/000151357

Rodríguez-Niedenführ, M., Vázquez, T., Choi, D., Parkin, I., & Sañudo, J. R. (2003). Supernumerary humeral heads of the biceps brachii muscle revisited. Clinical Anatomy (New York, N.Y.), 16(3), 197–203. https://doi.org/10.1002/ca.10060

Szewczyk, B., Sanudo, J. R., Podgórski, M., Zielinska, N., Pires, M. B., Aragonés, P., & Olewnik, Ł. (2022). A Proposal for a New Classification of the Supernumerary Heads of the Biceps Brachii Muscle. BioMed Research International, 2022, 1510363–1510369. https://doi.org/10.1155/2022/1510363


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Anatomical Variation: An Australian and New Zealand Context Copyright © 2023 by Queensland University of Technology is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

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