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| ORIGINAL ARTICLE |
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| Year : 2023 | Volume
: 22
| Issue : 3 | Page : 359-364 |
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Accessory heads of biceps brachii muscle its embryogenesis and clinical implications: Cadaveric study
Kosuri Kalyan Chakravarthi1, Ankamma Sarvepalli2, Siddaraju Kaadukothanahalli Siddegowda3, Venumadhav Nelluri4
1 Department of Anatomy, Varun Arjun Medical College and Rohilkhand Hospital, Shahjahanpur, Uttar Pradesh, India
2 Department of Anatomy, Konaseema Institute of Medical Sciences and Research Foundation, Amalapuram, Andhra Pradesh, India
3 Department of Anatomy, KMCT Medical College, Kozhikode, Kerala, India
4 Department of Anatomy, Melaka Manipal Medical College, Manipal University, Manipal, Karnataka, India
| Date of Submission | 19-Jun-2022 |
| Date of Decision | 08-Jul-2022 |
| Date of Acceptance | 01-Aug-2022 |
| Date of Web Publication | 4-Jul-2023 |
Correspondence Address:
Kosuri Kalyan Chakravarthi
Department of Anatomy, Varun Arjun Medical College and Rohilkhand Hospital, Banthra, Shahjahanpur - 242 307, Uttar Pradesh
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/aam.aam_93_22
 Abstract | | |
Background: Biceps brachii is an elongated two-headed fusiform muscle of the anterior compartment of the arm which crosses the shoulder as well as the elbow joint. It assists in flexion of the shoulder joint and elbow joint and powerful supinator of the forearm. It also assists in the abduction of the shoulder joint. Accessory heads of biceps brachii muscle not only give additional strength to the joints, at the same time, they may also simulate soft-tissue tumors that can result in neurovascular compression. Aims and Objectives: Accordingly, the aim of this study was designed to evaluate the prevalence of accessory heads of biceps brachii muscle in human cadavers. Materials and Methods: This study was conducted on 107 formalin embalmed human cadavers (male 62 and 45 female), and dissections were performed in accordance with the institutional ethical standards and the Indian Anatomy Act. Results: Out of 107 cadavers, three-headed biceps brachii was noted in 18 cadavers (16.82%) associated with the unusual course of musculocutaneous nerve. Rare and unusual unilateral five-headed biceps brachii was noted in one male cadaver (0.93%). All accessory heads noted in this study were supplied by the separate branches of musculocutaneous nerve except the humeral head of five-headed biceps, which was supplied by the radial nerve. Conclusion: Awareness of these anatomical variations, knowledge is necessary for radiologists, anesthetists, physiotherapists, and orthopedic surgeons to avoid complications during various radiodiagnostic procedures or surgeries of flexor deformities of the upper arm and forearm.
Résumé
Contexte: Le biceps brachial est un muscle allongé fusiforme à deux têtes de la loge antérieure du bras qui traverse l'épaule ainsi que l'articulation du coude. Il aide à la flexion de l'articulation de l'épaule et du coude et supinateur puissant de l'avant-bras. Il aide également à l'abduction de l'articulation de l'épaule. Les têtes accessoires du muscle biceps brachial donnent non seulement une force supplémentaire aux articulations, en même temps, ils peuvent également simuler des tumeurs des tissus mous pouvant entraîner une compression neurovasculaire. Buts et objectifs: En conséquence, le but de ce étude a été conçue pour évaluer la prévalence des têtes accessoires du muscle biceps brachial chez les cadavres humains. Matériels et méthodes: ce étude a été menée sur 107 cadavres humains embaumés au formol (hommes 62 et 45 femmes), et des dissections ont été réalisées dans conformément aux normes éthiques institutionnelles et à la loi sur l'anatomie indienne. Résultats: Sur 107 cadavres, biceps brachial à trois têtes a été notée sur 18 cadavres (16,82 %) associée à l'évolution inhabituelle du nerf musculo-cutané. Unilatérale rare et inhabituelle Un biceps brachial à cinq têtes a été noté sur un cadavre masculin (0,93 %). Toutes les têtes accessoires notées dans cette étude ont été fournies par le branches du nerf musculo-cutané à l'exception de la tête humérale du biceps à cinq têtes, qui était alimentée par le nerf radial. Conclusion: Conscience de ces variations anatomiques, une connaissance est nécessaire aux radiologues, anesthésistes, kinésithérapeutes, et chirurgiens orthopédistes pour éviter les complications lors de diverses procédures de radiodiagnostic ou de chirurgies des déformations des fléchisseurs de la partie supérieure bras et avant-bras.
Mots-clés: Asymétrie, tumeurs dermoïdes, hypertrophie et lipome, névralgie mandibulaire
Keywords: Asymmetry, dermoid tumors, hypertrophy and lipoma, mandibular neuralgia
How to cite this article:
Chakravarthi KK, Sarvepalli A, Siddegowda SK, Nelluri V. Accessory heads of biceps brachii muscle its embryogenesis and clinical implications: Cadaveric study. Ann Afr Med 2023;22:359-64 |
How to cite this URL:
Chakravarthi KK, Sarvepalli A, Siddegowda SK, Nelluri V. Accessory heads of biceps brachii muscle its embryogenesis and clinical implications: Cadaveric study. Ann Afr Med [serial online] 2023 [cited 2023 Sep 26];22:359-64. Available from: https://www.annalsafrmed.org/text.asp?2023/22/3/359/380169 |
| Introduction | |  |
Biceps brachii is an elongated fusiform muscle that lies on the anterior compartment of the arm and it arises by tendinous heads, short and long. The short head of biceps brachii arises from the tip of the coracoid process, and long heads from the supraglenoid tubercle of the scapula and adjacent glenoid labrum. Distally, both heads of biceps brachii expand into fusiform bellies, about 7 cm above the elbow joint both heads unit to form a common flat tendon and passes through the cubital fossa and is finally inserted into the posterior part of the radial tuberosity. Before insertion, the medial border of the tendon presents a medial fibrous expansion, the bicipital aponeurosis and is attached to the subcutaneous posterior border of the ulna by way of the deep facia of the forearm. It is the only muscle of the anterior compartment of the arm which crosses the shoulder as well as the elbow joint. It is a flexor of the elbow joint and a powerful supinator of the forearm. It assists in the flexion of the shoulder joint and its long head also assists in the lateral rotation of humerus during the abduction of the shoulder from 90° to 120°. Its bicipital aponeurosis pulls the ulna along with the radius during flexion of forearm. The presence of accessory or additional heads of biceps brachii may give additional strength or support to the shoulder and elbow joints, at the same time, they may also simulate soft-tissue tumors that can result in neurovascular compression. Accordingly, the present study was designed to evaluate the accessory heads of biceps brachii and their clinical anatomy.
| Materials and Methods | | |
This study was conducted on 214 upper limbs of 107 formalin embalmed human cadavers (male 62 and 45 female) at Varunarjun Medical College and Rohilkhand Hospital, Uttar Pradesh, Konaseema Institute of Medical Sciences and Research Foundation, Andhra Pradesh, Melaka Manipal Medical College-Manipal University, Karnataka, and KMCT Medical College, Manassery, Calicut, Kerala. Dissections were performed on a body that had been donated for the purpose of medical education and research to the laboratory of anatomy in accordance with the institutional ethical standards and the Indian Anatomy Act. This study was reviewed and approved by the Institutional Ethics Committee (reference number: VAMC-HAREC10 AN Aug 019). Anatomical variations of biceps brachii were observed, and photographs were taken for proper documentation.
| Results | | |
Out of 214 upper limbs of 107 human cadavers (males-62 and females-45), the following unusual anomalous variations of biceps brachii were observed.
Three-headed biceps brachii
Among 107 human cadavers, three-headed biceps brachii was noted in 18 cadavers (16.82%).
Case – I: In five middle-aged female cadavers, a three-headed left biceps brachii muscle with the unusual course of musculocutaneous nerve was noted. The third head was originated from the anteromedial surface of the humerus just below the insertion of coracobrachialis muscle. Distally, the third head expands into the fusiform belly, about 1 cm above the elbow joined third head joined the other two heads to form a common flat tendon and passes through the cubital fossa and is finally inserted into the posterior part of the radial tuberosity. The third head was innervated by a separate branch of the musculocutaneous nerve [Figure 1]a and [Figure 1]b. | Figure 1: (a and b) Showing a third head of biceps brachii muscle in the left flexor compartment of arm. Blue arrow – third head of biceps brachii; Red arrow – Musculocutaneous nerve piercing third head of biceps; Orchid color arrow – Biceps tendon; Red color circle – Brachialis muscle
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Case – II: In ten male cadavers in the left arm and in one male cadaver in the right arm, three-headed biceps brachii muscle with the unusual course of musculocutaneous nerve was noted. All left side three-headed biceps were originated from the anteromedial surface of the humerus just below the insertion of coracobrachialis muscle except one which originated from the brachialis muscle. Distally, the third head expanded into a long fusiform belly, about 1 cm above the elbow merged with the other two heads to form a common flat tendon and passes through the cubital fossa, and finally inserted into the posterior part of the radial tuberosity. All third heads noted were innervated by a separate branch from the musculocutaneous nerve [Figure 2]a, [Figure 2]b and [Figure 3]a, [Figure 3]b. | Figure 2: (a and b) Showing a third head of biceps brachii muscle in the left (a) and right (a) flexor compartment of arm. Blue arrow – third head of biceps brachii; Green color arrow – short head of biceps; Red arrow – long head of biceps; Orchid color arrow – Biceps tendon
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 | Figure 3: (a and b) Showing a third head of biceps brachii muscle in the left flexor compartment of arm with unusual course of musculocutaneous nerve. Blue arrow – third head of biceps brachii; Green colour arrow – short head of biceps; Red arrow – long head of biceps; Orchid colour arrow – Biceps tendon; Black arrow musculocutaneous nerve
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Case – III: In two middle-aged male cadavers, bilateral three-headed biceps brachii muscle with the unusual course of musculocutaneous nerve was noted. The third head on both sides was originated from the superomedial and superior lateral surface of humerus above the brachialis muscle. Distally, the third head expands into fusiform belly, about 1 cm above the elbow merged with the other two heads to form a common flat tendon and passes through the cubital fossa and is finally inserted into the posterior part of the radial tuberosity. Musculocutaneous nerve was sandwiched between the third head and fusiform muscle belli formed by fused other two heads. Third head on both sides is innervated by a separate branch from the musculocutaneous nerve [Figure 4]a, [Figure 4]b, and [Figure 5]a, [Figure 5]b. | Figure 4: (a and b) Showing a third head of biceps brachii muscle in the left flexor compartment of arm with unusual course of musculocutaneous nerve. Blue arrow – third head of biceps brachii; Red arrow – fusiform muscle belli formed by fused long and short head of biceps; Orchid color arrow – Biceps tendon; Green color arrow musculocutaneous nerve; Yellow color arrow Median nerve
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 | Figure 5: (a and b) Showing a third head of biceps brachii muscle in the left flexor compartment of arm. Blue arrow – third head of biceps brachii; Green color arrow musculocutaneous nerve; Red color arrow Median nerve
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Five-headed biceps brachii
Among 107 human cadavers, the third head of biceps brachii was noted in 1 cadaver (0.9%).
Case – IV: In the left upper limb of a middle-aged male cadaver, a five-headed biceps brachii muscle was noted. Long and short heads of biceps were observed to be normal and third fleshy head originated from the deltoid tubercle and anterolateral surface of the humerus below the insertion of deltoid muscle. Fourth accessory tendinous head (coracoid head) originated from the coracoid prosses of the scapula along with short head, when traced distally, it separated from the short head and form a thick elongated tendon and inserted to the anterior limb of deltoid tuberosity of the shaft of the humerus opposite to the insertion of coracobrachialis muscle. Long and slender fifth accessory tendinous head (capsular head) originated from the fibrous capsule of the shoulder joint, and in the upper part, blended with the short head by a thin tendinous sheath. Distally, the third head expanded into a long fusiform belly, about 1 cm above the elbow merged with the muscle belli formed by fused the other three heads of biceps to form a common flat tendon and passes through the cubital fossa and finally inserted into the posterior part of the radial tuberosity. Out of five heads, four heads were innervated by a separate branch from the musculocutaneous nerve and humeral head from the radial nerve [Figure 6]a and [Figure 6]b. | Figure 6: (a and b) Showing a five head of biceps brachii muscle in the left flexor compartment of arm with unusual course of musculocutaneous and radial nerve. Orchid color arrow – short head of biceps; Aqua color arrow – long head of biceps; Blue arrow – third head of biceps brachii; Red color arrow – Fourth head of biceps; Grenn color arrow – Fifth head of biceps brachii; Black color arrow – Biceps tendon; Yellow color arrow musculocutaneous nerve; Yellow color circle – Radial nerve branch to third head of biceps
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| Discussion | | |
Anomalous or accessory muscles or tendons in the upper limb are quite common and may lead to confusion during surgical procedures which result in errors in both diagnosis and treatment. Hypertrophy of brachii biceps is commonly seen in the case of a professional bodybuilder any accessory or aberrant musculature of biceps may stimulate ganglion or soft-tissue tumors or if in proximity to a nerve, it may cause pressure neuritis. Identification of these variations is important in defining the anatomical features for clinical diagnosis and surgical procedures.
Three-headed biceps brachii
Anatomically, biceps brachii is a two-headed muscle in the flexor compartment of the arm. The third head of biceps also called as humeral head is the most frequent anatomical variation, arises from the interval between the insertion of coracobrachialis and the origin of brachialis from the anterior surface of middle of the shaft of the humerus. The incidence of a third head of the biceps brachii muscle and a race-dependent comparison variation are described in [Table 1].[1],[2],[3],[4],[5],[6],[7],[8],[9] In the present study, the incidence of a third head of the biceps brachii was noted at 16.82% similar to the percentage reported by Avadhani and Chakravarthi[8] in the Indian population. Parthasarathy and Sowmya (2.08%)[10] and Anil Kumar and Ravitheja (7.50%)[11] reported that bilateral tricipital anatomical variation was found more in males than females. The present study (1.87%) also showed a male preponderance of tricipital anatomical variation. | Table 1: The incidence of a third head of the biceps brachii muscle and a race-dependent comparison variation
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Five-headed biceps brachii
Toomsan et al. reported five-headed biceps brachii muscle in the right arm of a 67-year-old Thai female cadaver, in which the third head originated from the coracoid process of the scapula, fourth and the fifth heads (humeral heads) from the humeral shaft between the insertion of the coracobrachialis and the origin of the brachialis muscles.[12] Je et al. reported in a 43-year-old Korean male cadaver a very rare five-headed biceps brachii muscle, in which supernumerary head was originated from the pectoralis major muscle, and additional two accessory heads (humeral heads) were originated from the anterior surface of humerus.[13] The present study also showed a very rare unusual five-headed biceps brachii muscle in a middle-aged Indian male cadaver. The shoulder joint capsular origin of the third head blended with the short head of the biceps was reported in the literature.[14],[15] Similar capsular head was also seen as a fifth head in the present study of rare five-headed biceps brachii muscle. Such capsular head anatomical variations should keep in mind during the surgeries for dislocated shoulder, for adequate exposure of the joint through the deltopectoral incision. The fourth head took origin from the coracoid process of the scapula, distally it forms tendinous insertion to the anterior limb of deltoid tuberosity and few fleshy fibers continued with the third head (humeral head), such anatomical variation of five-headed biceps made this study more unique.
Biomechanics of additional heads of biceps brachii
The skeleton muscles of upper limb take an important part of movements at the joints of upper limb. Anomalous musculature or accessory muscles may interfere with the biomechanics of the joint. The third head is the most common anatomical variation, unlike the long and short heads of biceps brachii, the third head (humeral head) only crosses the elbow joint and may enhance the strength of pronation of the forearm and flexion of the forearm irrespective of the position of the shoulder joint. The fourth head is being comparatively rare anatomical variation, thick bulky tendentious insertion of the fourth head of five-headed biceps to the anterior limb of deltoid tuberosity noted in this study may add the flexion and medial rotation of humerus at the shoulder joint. Even though the coracobrachialis and fourth head of five-headed biceps took same origin from the coracoid process of scapula, the insertion was totally in the opposite direction, the former muscle to the medial border and later to the deltoid tuberosity. These two muscles were innervated by separate branches from the musculocutaneous nerve. Hypertrophy or muscle tear or tendon tear or any spasmodic contraction of the accessory fourth head will definitely interfere with the action of coracobrachialis or biomechanics of the shoulder joint. The rarest fifth head originated from the fibrous capsule of the shoulder in the present study may enhance the strength of the shoulder and elbow flexion and forearm supination. Injury or overuse of such additional heads may lead to the tear of additional heads, which may confuse a surgeon during operations and may be confused with pathological conditions such as tumors.
Accessory heads of biceps brachii in relation to musculocutaneous nerve
Musculocutaneous nerve is an infraclavicular branch of lateral cord of brachial plexus of upper limb and conveys the fibers from C5, C6, and C7 roots. In the axilla initially, it accompanies the lateral side of the third part of the axillary artery and it pierces the coracobrachialis muscle near its point of insertion. In the lower part of the arm, it passes down between biceps brachii and brachialis muscle. It innervates the coracobrachialis, long and short head of biceps brachii, and medial major part of brachialis muscle. Just below the elbow, it pierces the deep facia lateral to the tendon of biceps brachii and extends further downwards as lateral cutaneous nerve of the forearm to supply the sensory innervation skin of the anterolateral aspect of the forearm as far distally as the base of the thenar eminence. For the superficial surgeries of forearm, such as arteriovenous fistula surgery, or for pain treatment of minor trauma or surgery or supplement to incomplete brachial plexus block, local esthetic is injected along the lateral side of the biceps tendon to block the lateral cutaneous nerve of forearm (cutaneous branch of musculocutaneous nerve). In the present study, the lateral cutaneous nerve of forearm running on the medial side of biceps tendon [Figure 1]a, [Figure 2]b, [Figure 2]b, [Figure 3]b and [Figure 5]a was observed in 14 cadaveric specimens (14.95%) associated with accessory heads of biceps. Such comprehensive knowledge of anatomical variations will be important for anesthetists, radiologists, surgeons, and traumatologists can increase the success of diagnostic evaluation and surgical approaches to the region. Additional heads of biceps brachii muscle with anatomical variation in the course of musculocutaneous nerve have been reported in the literature. In the present study also unusual course of musculocutaneous nerve at different levels of the arm was noted, such as in the middle of the arm, it pierces the humeral head of biceps [Figure 1]b, in the lower part, it was sandwiched between humeral head of biceps and biceps muscle (formed by fused long head and short head) [Figure 5]a and [Figure 5]b. Such an unusual course of musculocutaneous nerve can create a potential site of compression and leads to pain, paresthesia, numbness over the lateral aspect of the forearm, and weakened flexion of shoulder and elbow. Hence, anatomical knowledge of the variant morphology of biceps brachii in relation to the musculocutaneous nerve would provide a clinical strategy for diagnosis and effective management of the upper limb diseases and minimize the neurovascular injury.
Accessory heads of biceps brachii in relation to median nerve
Median nerve is a mixed nerve arises from the lateral and medial cords of brachial plexus and innervates most of the flexor muscles of forearm and five intrinsic muscles of hand (three thenar muscles and first and second lumbrical). Potential sites of compression of the median nerve reported in the literature are, in the carpal tunnel due to the presence of anomalous lumbricals[16] or additional tendons in the carpal tunnel arising from the flexor compartment,[17],[18] between the two heads of pronator teres muscle or any anomalous variations or aberrant slips at pronator teres muscle,[19],[20] anomalous Gantzer's muscle in the middle of forearm[21] may lead to entrapment neuropathy of the medial nerve. The median nerve in the middle of arm, opposite the insertion of coracobrachialis, it crosses the brachial artery from lateral to medial and runs along the medial side of the brachial artery. Tendinous insertion of third head and fifth head origin in the middle of the arm of five-headed biceps noted in this study was very close to the median nerve, where the nerve crosses the brachial artery from lateral to medial. Hypertrophy or spasmodic contraction of such accessory heads of biceps brachii in relation to the median nerve may cause peripheral neuropathy of median nerve. The occurrence of five-headed biceps brachii is a very rare condition, its presence definitely will increase the volume of the flexor compartment of the arm, can result in compartment syndrome arm, and leads to neurovascular compression. Such neuromuscular variations noted in the present study are not cited in the modern medical literature and are clinically important because symptoms of median nerve compression arising from similar variations are often confused with more common causes such as trauma, tumors, tendon tear, and pronator teres syndrome.
Embryogenesis
Skeletal musculature of upper limb is derived from the mesodermal somites that migrated in to the developing limb bud during the 5th week of development. At first, the mesodermal somites arranged along the preaxial and postaxial borders in the later stage of development, regroup into flexor muscles ventrally and extensor muscles dorsally. The most common additional head of biceps is humeral head (third head of biceps) takes origin from the anterolateral or anteromedial surface of the humerus below the insertion of coracobrachialis or deltoid muscle or anterior to the brachialis muscle. If the humeral takes origin from the deltoid tubercle or lateral border of humerus, its lateral part will be innervated by the radial nerve branch [Figure 6]. Such anomalous humeral head might be due to results of reduplication of hybrid muscle brachialis muscle (medial part is innervated by the musculocutaneous nerve and lateral part by radial nerve). Such neuromuscular variations may also influence the abnormal formation or splitting of vasculature of upper limb. Coracoid and capsular accessory heads of biceps might be the result reduplication of coracobrachialis and long head of biceps brachii muscle. In 50% of third heads (humeral heads) noted in the study were connected to the coracobrachialis by a round tendon on their deep surface [Figure 1]a, [Figure 2]b and [Figure 6]b. This unusual tendinous connection might be the result of incomplete splitting or abnormal mixing of mesodermal somites during intrauterine development of musculature of upper limb. Such reduplication or abnormal splitting of mesodermal somites arise primarily due to genetic composition or an inheritance carried over from ancient origins or persistence of an embryonic condition.
| Conclusion | | |
As per modern review of medical literature, anatomical variation of three-headed and five-headed accessory heads of biceps brachii muscle its nerve supply with an unusual course of musculocutaneous nerve has not been documented yet. Awareness of these variations is necessary to avoid complications during radiodiagnostic procedures or surgeries in the arm, antebrachial, and hand during various surgical procedures.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1]
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