Rare muscular variations identified in a single cadaveric upper limb: a four-headed biceps brachii and muscular elevator of the latissimus dorsi tendon

Supernumerary or accessory heads of the biceps brachii are persistent muscular structures which can vary in number and location in the arm. Variations in other arm muscles, such as the coracobrachialis, can accompany supernumerary biceps brachii musculature in the upper limb. In this case report, we describe two rare muscular variants in a single adult male: a four-headed biceps brachii and the muscular elevator of the latissimus dorsi tendon. Additionally, accessory muscles of the brachialis and flexor digiti minimi brevis were identified in the upper limb. To our knowledge, the muscular variants identified here are considered rare, and their co-occurrence in a single upper limb has not been described previously. Also, a four-headed biceps brachii consisting of both the infero-medial and infero-lateral humeral heads has not been described previously to our knowledge. We postulate that the simultaneous appearance of several muscular variations may indicate a signaling disruption in embryogenesis during muscle patterning of the ventral limb bud. Knowledge of variant musculature in the arm is important for surgeons and clinicians as these muscles and their aberrant innervation patterns can complicate surgical procedures and may compress arteries and nerves producing upper limb pain and paresthesia. The clinical, functional and embryological implications of the upper limb variants are discussed.     

Anomalies of the biceps muscle of the arm

The author studied the biceps brachii muscle with respect to the incidence of accessory heads (Caput accessorium) and compared the data obtained with those in different human races. Dissection of 552 human arms in Teheran and Mainz, revealed the presence of 2 biceps brachii muscles with accessory heads one of a right arm with one accessory head, the other on a left arm with two accessory heads. From data in the literature it is concluded that in the white race the incidence of accessory heads of the biceps brachii m. is relatively rare, high in the yellow race and intermediate in negroes.     

Unusual variation of a third head of the biceps brachii muscle

A human cadaver was studied which presented a biceps brachii with three heads of origin in the left arm. The third or humeral head presented an unique area of insertion into the bicipital aponeurosis (lacertus fibrosus).     

On the incidence of third head of biceps brachii in Turkish neonates and adults.

The occurrence of a third head of the biceps brachii has been reported in several articles. The aim of this study is to determine on the incidence of the third head of biceps brachii in Turkish neonates and adults, and to compare it with other studies. Also the functional and phylogenetic importance of the third head was described here. The third head was studied in 160 arms of 60 (45 males, 15 females) neonatal and 20 (13 males, 7 females) adult cadavers and was found in 24 (15%) specimens. It had the three different origins and frequently arose from the anterior surface of the humerus and distal to the insertion of the coracobrachialis muscle. In all cases, the third head inserted into the conjoined tendon of biceps brachii and received its nerve supply from the musculocutaneous nerve. In our study the rate of the third head was different than those for most other published series and that the difference are possibly caused by evolutionary and/or racial trends in different studied populations. We believe that the third head of biceps brachii muscle is not a relatively rare variant. The knowledge of such variations may become significant in preoperative diagnosis and during surgery.     

Relationship between the tendon of the long head of the biceps brachii muscle and the glenoid labrum

For many authors, the insertion of the long head of the biceps brachii muscle is exclusively or mainly located on the supraglenoid tubercle. The aim of this work was to study the insertion of the long head of the biceps brachii at macroscopic and microscopic examinations. 31 shoulders of macerated cadavers of both sex (age range: 52-92 years) were dissected by a posterior approach in order to study the glenoid labrum and the origin of the long head of the biceps brachii muscle. At macroscopic examination two types of the proximal part of the long head of the biceps brachii were demonstrated: a flattened shape in 84% of the cases and a hemicylindrical shape in 16% of the cases. Four types of origin were demonstrated at dissection: in 64.5% of the cases the tendon inserted mainly on the postero-superior part of the labrum, in 19.4% of the cases the tendon inserted both on the postero-superior and postero-anterior labrum, in 6.4% of the cases it inserted only on the supraglenoid tubercle and in three cases the tendon inserted on the intertubercular groove. The histologic examination performed on 6 superior part of the bicipitolabral complex have all shown that the tendinous fibers blended with the glenoid labrum. The examination performed on an complete labrum demonstrated tendinous fibers within the glenoid labrum up to the junction between the postero-superior and postero-inferior part of the labrum.     

Role of the long head of the biceps brachii muscle in axial humeral rotation control

This anatomical and biomechanical study focuses on the specific influence of the long head of biceps brachii muscle in controlling axial humeral rotation. The tendon of the long head of the biceps brachii (biceps tendon) is shown to either facilitate or restrict axial humeral rotation. Its effect on axial humeral rotation is strongly related to firstly the amount of biceps tendon load, secondly glenohumeral scapular plane elevation, and thirdly the rotatory position of the humerus. At 0° glenohumeral elevation, biceps tendon load caused an increase of internal humeral rotation, from 0° at 2.25 N biceps tendon load to 23° at 82.25 N. Under 45° glenohumeral elevation, biceps tendon load can restrict and facilitate as well internal and external axial humeral rotation, increasing the rotatory range of motion. Above 45° glenohumeral elevation biceps tendon load restricts internal and external axial humeral rotation, increasing actively joint stability by increasing torsional rigidity. These findings on the function of the biceps tendon could have consequences for the clinical interpretation. In the elevated arm position, extreme rotation loads the long head of the biceps tendon and may turn out to biceps or bicepslabrum complex injuries.     

Morphological study of the communication between the musculocutaneous and median nerves

We investigated the incidence of each pattern of the communications between the musculocutaneous and median nerves and discussed its morphological significance. The communications between both nerves were seen in 188 (41.5%) of 453 specimens. They were classified into five regular patterns according to their directions and formations. The incidence of the communication was significantly higher in those with excessive heads of biceps brachii than in those without them (p < 0.05). As a result, we established a classification of the regular pattern of the communications and revealed that the musculocutaneous and median nerves had the possibility of forming plexuses in the humeral area. The musculocutaneous nerves are regarded as the bundles that arise from the median nerve with the lateral cutaneous nerve of forearm and the branches to the biceps brachii and brachialis muscles.     

Two bellies of the coracobrachialis muscle associated with a third head of the biceps brachii muscle.

Reports that describe the abnormalities and complexities of the anatomy of the arm are important with regard to surgical approaches. This case study reports a combined abnormal form of the coracobrachialis and biceps brachii muscles of the left arm of an adult male cadaver that was detected during the educational gross anatomy dissections of embalmed cadavers. The coracobrachialis muscle demonstrated two bellies which formed shortly inferior to its origin from the coracoid process of the scapula. One belly inserted into the middle of the antero-medial surface of the humerus, whereas the other belly inserted into the medial head of the triceps brachii muscle. The musculocutaneous nerve passed between the two bellies, giving a separate branch to each. We suggest that the two bellies of the coracobrachialis muscle may represent the incompletely fused short heads of the ancestral muscle. The biceps brachii muscle showed a third head, which originated mainly from the antero-medial surface of the humerus and partially from an aponeurosis belonging to the medial head of the triceps brachii muscle. These observations were confined to the left upper limb and were not accompanied by any other abnormality.     

An unusual origin for the accessory head of biceps brachii muscle

During the superficial dissection of the pectoral region and the arm, an abnormal biceps brachii muscle was observed unilaterally. This muscle had three heads. Whereas the short and long heads had their normal origin, the accessory head originated from the anterior surface of the distal part of the pectoralis major muscle, which formed the anterior axillary fold. To our knowledge, this variation has not been previously described. Innervation and vascular supply of this accessory head was from the musculocutaneous nerve and the brachial artery, respectively. © 1996 Wiley-Liss, Inc.     

Supernumerary head of biceps brachii and branching pattern of the musculocutaneus nerve in Japanese

Summary Out of 546 upper limbs (273 cadavers), supernumerary heads of the biceps brachii were found in 75 limbs (13.7%) of 58 cadavers (21.3%). The form, origin, and insertion of the supernumerary heads, and branching pattern of the musculocutaneus nerve were studied. In addition, the dimensions of the heads were measured. In many cases, the supernumerary head arose from the humerus, between the insertion of the coracobrachialis and the upper part of the origin of the brachialis, and/or from the medial intermuscular septum. In a few cases, a supernumerary head arose from the tendon of the pectoralis major or the deltoid, or from the articular capsule, or from the crest of the greater tubercle. The supernumerary heads typically joined the common belly, or the aponeurosis of the biceps brachii. Some heads joined the belly of the long head or that of the short head. In the examination of the branching pattern of the musculocutaneus nerve, communication between the musculocutaneus nerve and the median nerve was found in 43 out of the 75 limbs (57.3%). The communicating branch ran from the musculocutaneus nerve to the median nerve in 24, from the median nerve to the musculocutaneus nerve in 12, in both directions in 5, or in another type of pattern in 2 out of 43 limbs. Sometimes a branch of the musculocutaneus nerve ran around a supernumerary head and then fused with the present trunk. The presence of a supernumerary head seemed to affect the course and branching of the musculocutaneus nerve.

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Chef surnuméraire du biceps brachial et organisation du nerf musculo-cutané chez les japonais

Résumé A partir de l'étude de 546 membres supérieurs (273 cadavres) nous avons trouvé 75 cas (chez 58 cadavres) de chef surnuméraire de muscle biceps brachial (21.3%). Nous en avons étudié la forme, le trajet, la taille et les insertions ainsi que l'organisation des divisions du nerf musculo-cutané. Dans de nombreux cas le chef surnuméraire provient soit de l'humérus où il s'insère entre le m. coraco-brachial et la partie proximale du muscle brachial soit/et du septum intermusculaire médial. Dans quelques cas un chef surnuméraire a été observé à partir du tendon du m. grand pectoral ou du m. deltoïde ou encore de la capsule articulaire, voire du tubercule majeur. II rejoint habituellement le chef commun du m. biceps brachial ou son aponévrose. Parfois la jonction se fait sur l'un ou l'autre des deux corps musculaire. L'étude du n. musculo-cutané montre une anastomose avec le nerf médian dans 43 des 75 membres concernés (57.3%). Cette branche anastomotique va du n. musculo-cutané au nerf médian dans 24 cas et du n. médian au n. musculo-cutané dans 12 cas, elle va dans les deux directions dans 5 cas; dans les 2 cas restant le modèle d'anastomose est variable. Parfois une branche du n. musculo-cutané entoure le chef surnuméraire et fusionne ensuite avec le tronc du nerf. La présence d'un chef surnuméraire semble donc modifier le trajet et les connexions du nerf musculo-cutané.

     

俯卧撑中前臂旋转对上肢肌肉电活动的影响

目的 分析俯卧撑中前臂旋转对上肢肌肉电活动的影响。方法 采集十个对象在前臂内旋90°（IR90）,中立位（NEU）和外旋90°（ER90）三个支撑位下肱三头肌长头和侧头、三角肌前部和中部、胸大肌和肱二头肌的肌电信号,计算肌电信号的均方根值,并作归一化处理,运用单因素方差分析法比较不同支撑位下肌电信号的差异。同时对一个周期内肌电信号进行包络线分析。结果 从IR90到ER90,肱三头肌长头信号无显著变化,肱三头肌侧头和三角肌中部信号逐渐减小,而三角肌前部、胸大肌和肱二头肌则逐渐增大。另外,包络分析结果显示了三种不同类型的肌电信号曲线。结论 不同前臂转动支撑位对肌肉活性产生影响,而对各肌肉的影响程度和方式并不相同。     

The course and variations of the branches of the musculocutaneous nerve in human fetuses

The course and branches of the musculocutaneous nerve (MCN) were dissected in 140 human fetal arms. The MCN entered the superior, middle, and inferior part of coracobrachialis in 43%, 37%, and 17% of arms, respectively, and the remaining 3% did not pierce coracobrachialis. The motor branches to biceps were classified as follows: Type 1 (83.6%): a single branch that bifurcated to supply the two heads of biceps; Type 2 (14.3%): two separate branches each innervating one head of biceps; Type 3 (2.1%): a single branch that bifurcated to supply each head of biceps plus an additional branch that innervated the distal part of biceps. The motor branches to brachialis were classified as follows: Type 1 (93.6%): a single branch to brachialis; Type 2 (6.4%): a single branch that bifurcated into two branches both supplying brachialis. Communications between the MCN and the median nerve (MN) were observed in 10% of specimens, of which three types (A, B, C) could be identified depending on their origin and union. In the most frequently observed type (B, 50% of cases) the communicating branch arose from the proximal part of the MCN and joined the MN in the middle or distal part of arm. The data presented here will be of use to surgeons, especially pediatric surgeons who undertake surgical procedures in the axilla and arm. Clin. Anat. 22:337–345, 2009. © 2008 Wiley‐Liss, Inc.     

背阔肌腱下滑囊炎的应用解剖研究

目的    为临床诊治背阔肌腱下滑囊炎提供应用解剖学基础。  方法　20侧成人肩关节标本（右11侧、左9侧），对背阔肌腱下滑囊及与其邻近易误诊的解剖结构进行观测。  结果　背阔肌腱下滑囊位于肱骨结节嵴间沟底、肱骨小结节嵴、大圆肌附着部与背阔肌腱止点之间。肱骨结节间沟可分为肱骨大、小结节间沟和大、小结节嵴间沟，确定该滑囊的上下位置，即从肱骨小结节最高点至背阔肌腱下滑囊上端距离为（27.43±4.71）mm，可以确定该滑囊的上下位置，背阔肌腱下滑囊的内外位置关系，从肱二头肌长头腱内侧缘距背阔肌腱下滑囊中点为（8.12±1.23）mm，可以确定该滑囊的内外位置关系。背阔肌腱下滑囊的相关数据，在肱骨结节嵴间沟上、下高度为（36.5±4.79）mm，中点宽度为（8.62±1.83）mm。背阔肌腱下滑囊周围易发生炎症的有肱二头肌长头腱滑液鞘、大圆肌腱下滑囊、喙突下滑囊、胸大肌骨管等。  结论　本研究为背阔肌腱下滑囊的诊疗提供了形态学依据。     

Innervation of biceps brachii and brachialis: Anatomical and surgical approach

This study describes the anatomy of the musculocutaneous nerve (MCN) in the middle and lower thirds of the arm, with special reference to the motor branches to the biceps and brachialis muscles, given their importance in certain clinical, particularly surgical, procedures. In each dissection (46 upper limbs) we recorded the course of the MCN and its variations, and the number, type of distribution pattern and length of the motor branches to the biceps brachii and brachialis muscles. We also recorded the position at which those branches arose from the MCN trunk. We found three branching patterns for biceps brachii: 1) one branch (60.5%); 2) two branches, one for each biceps head (27.9%); and 3) two branches, one for the two biceps heads and one for the common belly (11.6%). The mean distance between the acromion and the motor branches to biceps brachii was 133.8 mm, 45.3% of the acromion-lateral epicondyle distance. The mean length of those branches was 31.2 mm. We found two branching patterns for brachialis: 1) one branch (72.1%); and 2) two branches (27.9%). These motor nerves to brachialis arose from the MCN at a mean distance of 185.3 mm, 61.5% of the acromion-lateral epicondyle distance, and their average length was 33.0 mm. The data were expressed as the percentage of the distance between the acromion and the lateral epicondyle of the humerus, to make their clinical use easy and to avoid errors caused by anthropometric differences.     

肱二头肌额外头的形态学观察及其应用解剖

目的为肱二头肌短头转位治疗肩锁关节脱位手术入路提供解剖学基础。方法观察52具成人尸体(104侧)的肱二头肌额外头的形态、神经支配和动脉供应。结果52具尸体中14具有肱二头肌额外头,出现率为26.9%±1.6%,其中1具为双侧性。15侧肱二头肌额外头均由肌皮神经支配。由肱动脉分支供血。结论本地区人群中,肱二头肌额外头的出现率为26.9%,根据其起止点可分为4种类型。肱二头肌额外头的存在原因可从种系发生与个体发生两方面来解释。在肱骨骨折时考虑是否有肱二头肌额外头的存在来进行生物力学分析,取肱二头短头转位治疗肩锁关节脱位手术入路时应注意肱二头肌额外头的动脉分支。     

Differential activation of regions within the biceps brachii muscle during fatigue

Aim: To examine the occurrence of repeated differential activation between the heads of the biceps brachii muscle and its relation to fatigue prevention during a submaximal contraction. Methods: Thirty‐nine subjects carried out an isometric contraction of elbow flexion at 25% of maximal voluntary contraction (MVC) until exhaustion. A grid of 13 by 10 electrodes was used to record surface electromyographic signals from both heads of the biceps brachii. The root‐mean‐square of signals recorded from electrodes located medially and laterally was used to analyse activation differences. Differential activation was defined as periods of 33% different activation level between the two heads of the biceps brachii muscle. Results: Differential muscle activation was demonstrated in 30 of 33 subjects with appropriate data quality. The frequency of differential activation increased from 4.9 to 6.6 min^?1 at the end of the contractions with no change in duration of the differential activations (about 1.4 s). Moreover, the frequency of differential activation was, in general, negatively correlated with time to exhaustion. Conclusion: The observed differential activation between the heads of the biceps brachii can be explained by an uneven distribution of synaptic input to the motor neurone pool. The findings of this study indicate that differential activation of regions within a muscle does not prevent fatigue at a contraction level of 25% of MVC.     

Motor nerve lengths of twenty-seven muscles in upper extremity

The purpose of this study is to determine the lengths of motor nerves in the upper extremity. Motor nerves of 27 muscles in 10 cadavers (16 extremities) were dissected from their roots at the level of intervertebral foramen to the entry point of the nerves to the corresponding muscles. Distance between acromion and the lateral epicondyle of the humerus was also measured in all cadavers. Nerve length of the coracobrachialis muscle was the shortest (18.26 ± 1.64 cm), while the longest was the nerve of the extensor indicis (59.51 ± 4.80 cm). The biceps brachii, the extensor digitorum communis, and the brachialis muscles showed highest coefficient of variation that makes these nerve lengths of muscles inconsistent about their lengths. This study also offers quotients using division of the lengths of each nerve to acromion-the lateral epicondyle distance. Knowledge of the nerve lengths in the upper extremity may provide a better understanding the reinnervation sequence and the recovery time in the multilevel injuries such as brachial plexus lesions. Quotients may be used to estimate average lengths of nerves of upper extremity in infants and children. Moreover, reliability of the biceps brachii as a determinant factor for surgery in obstetrical brachial plexus lesions should be reconsidered due to its highest variation coefficient.     

Patterns of motor branching of the musculocutaneous nerve in human fetuses and clinical significance

The purpose of this morphologic study is to investigate the course and the branching pattern of motor branches of musculocutaneous nerve (MCN) in human fetuses. Twenty upper limbs (10 right, 10 left) of spontaneously aborted formalin-fixed fetuses were dissected under a stereomicroscope to determine motor branches for the biceps brachii and brachialis and the communicating branches between the MCN and median nerve (MN). The MCN entered the proximal and middle part of coracobrachialis in 13/20 and 5/20 of arms, respectively, and the remaining 2/20 did not pierce coracobrachialis. The communication between MCN and MN was observed in 5/20 of the arms and detected only in the distal part of the coracobrachialis. The most frequently observed innervation is the type wherein a single branch to biceps brachii, which bifurcated for supplying the short and long heads (12/20). For the innervation of brachialis, the most frequent type was a single branch from the main trunk of the MCN (15/20). During the dissections, the distance between the acromion and the emerging point of the motor branches was measured. The mean distance between the acromion and the emerging point of the all motor branches for biceps brachii in all types of specimens was 33.8 ± 6.1% of acromion-lateral epicondyle length and for brachialis was 50.6 ± 11.5% of acromion-lateral epicondyle length. The data of the MCN variations in the human fetus may be useful for the clinicians and pediatric surgery.     

Accessory muscles in the lower part of the anterior compartment of the arm that may entrap neurovascular elements

The aim of this study was to evaluate the incidence of abnormal muscular bands of the anterior compartment of the arm that may compress the median, the ulnar, and the medial antebrachial cutaneous nerve as well as the brachial artery and vein, thus causing entrapment at and above the elbow. A total of 56 adult cadavers were studied during routine dissections that occurred in our laboratory. In the 112 upper limbs studied, we found three variant muscles of the flexor compartment of the arm (2.68%) entrapping nerves and vessels. The first muscle was emerging from the tendon of long head of biceps brachii and coracobrachialis muscle insertion. The second muscle inserted partially into the belly of biceps brachii and should be considered as a supernumenary head of biceps brachii. The third muscle, in fact, represents an accessory fascicle of the brachialis muscle that is an embryonic remnant of that muscle. A number of structures cross anterior to the median, ulnar, and medial antebrachial cutaneous nerve as well as the brachial artery and vein. Compression of nerves and vessels may be caused by additional muscular bundles that pass anterior to these structures. These additional muscular bundles arise either from the brachialis, coracobrachialis, or biceps brachii muscle. Such variations have clinical implications and should be considered in patients, with a high median or ulnar or medial antebrachial cutaneous nerve paralysis with symptoms of lower brachial artery or brachial vein compression.