The moment arms of the muscles spanning the glenohumeral joint: a systematic review

The moment arm of a muscle represents its leverage or torque‐producing capacity, and is indicative of the role of the muscle in joint actuation. The objective of this study was to undertake a systematic review of the moment arms of the major muscles spanning the glenohumeral joint during abduction, flexion and axial rotation. Moment arm data for the deltoid, pectoralis major, latissimus dorsi, teres major, supraspinatus, infraspinatus, subscapularis and teres minor were reported when measured using the geometric and tendon excursion methods. The anterior and middle sub‐regions of the deltoid had the largest humeral elevator moment arm values of all muscles during coronal‐ and scapular‐plane abduction, as well as during flexion. The pectoralis major, latissimus dorsi and teres major had the largest depressor moment arms, with each of these muscles exhibiting prominent leverage in shoulder adduction, and the latissimus dorsi and teres major also in extension. The rotator cuff muscles had the largest axial rotation moment arms regardless of the axial position of the humerus. The supraspinatus had the most prominent elevator moment arms during early abduction in both the coronal and scapular planes as well as in flexion. This systematic review shows that the rotator cuff muscles function as humeral rotators and weak humeral depressors or elevators, while the three sub‐regions of the deltoid behave as substantial humeral elevators throughout the range of humeral motion. The pectoralis major, latissimus dorsi and teres major are significant shoulder depressors, particularly during abduction. This study provides muscle moment arm data on functionally relevant shoulder movements that are involved in tasks of daily living, including lifting and pushing. The results may be useful in quantifying shoulder muscle function during specific planes of movement, in designing and validating computational models of the shoulder, and in planning surgical procedures such as tendon transfer surgery.     

Semiquantifying of fascicles of the C7 spinal nerve in the upper and lower subscapular nerves innervating the subscapularis and its clinical inference in Erb's palsy

To elucidate anatomic basis of susceptibility for contracture of the subscapularis muscle in Erb's palsy of the brachial plexus, we semiquantitatively studied the spinal nerve origins of the subscapular nerves innervating the subscapularis, with special reference to the contribution of C7 innervation to the subscapularis. Thirty‐three sides of formalin‐fixed upper extremities were dissected to obtain the intact brachial plexus. After immersed in 10% acetic acid for 2 weeks, the upper and lower subscapular nerves innervating the whole subscapularis, were dissected retrogradely to verify their spinal nerve origins. The cross‐sectional area by C7 innervation and that by the upper trunk innervation was calculated respectively to obtain the constituent percentage of different components in the upper and lower subscapular nerves. In the upper subscapular nerve, fascicles of C7 accounted for 0% (interquartile range, 0–1.1%) of cross‐sectional area and those of the upper trunk, 100% (98.9–100%). In the lower subscapular nerve, fascicles of C7 accounted for 40.5% (23.5–47.5%) and those of the upper trunk, 59.5% (52.5–76.5%). In total, 18.6% (13.3–27.3%) of fascicles in the subscapular nerves innervating the subscapularis originated from C7, while 81.4% (72.7–86.7%) of those came from the upper trunk. It is confirmed that innervation of the subscapularis originates from more spinal cord segments than that of infraspinatus and teres minor, and this may be the main reason for which in Erb's palsy, functional recovery of the subscapularis is often faster than that of lateral rotators of the shoulder, resulting in medial rotation contracture of the shoulder. Clin. Anat., 2013. © 2012 Wiley Periodicals, Inc.     

Anatomy and quantitation of the subscapular nerves

Information regarding branches of the brachial plexus can be of utility to the surgeon for neurotization procedures following injury. Sixty-two adult cadaveric upper extremities were dissected and the subscapular nerves identified and measured. The upper subscapular nerve originated from the posterior cord in 97% of the cases and in 3% of the cases directly from the axillary nerve. The upper subscapular nerve originated as a single nerve in 90.3% of the cases, as two independent nerve trunks in 8% of the cases and as three independent nerve trunks in 1.6% of the cases. The thoracodorsal nerve originated from the posterior cord in 98.5% of the cases and in 1.5% of the cases directly from the proximal segment of the radial nerve. The thoracodorsal nerve always originated as a single nerve from the brachial plexus. The lower subscapular nerve originated from the posterior cord in 79% of the cases and in 21% of the cases directly from the proximal segment of the axillary nerve. The lower subscapular nerve originated as a single nerve in 93.6% of the cases and as two independent nerve trunks in 6.4% of the cases. The mean length of the lower subscapular nerve from its origin until it provided its branch into the subscapularis muscle was 3.5 cm and the mean distance from this branch until its termination into the teres major muscle was 6 cm. The mean diameter of this nerve was 1.9 mm. The mean length of the upper subscapular nerve from its origin to its termination into the subscapularis muscle was 5 cm and the mean diameter of the nerve was 2.3 mm. The mean length of the thoracodorsal nerve from its origin to its termination into the latissimus dorsi muscle was 13.7 cm. The mean diameter of this nerve was 2.6 mm. Our hopes are that these data will prove useful to the surgeon in surgical planning for potential neurotization procedures of the brachial plexus.     

Moment arms of the muscles crossing the anatomical shoulder

The objective of the present study was to determine the instantaneous moment arms of 18 major muscle sub-regions crossing the glenohumeral joint during coronal-plane abduction and sagittal-plane flexion. Muscle moment-arm data for sub-regions of the shoulder musculature during humeral elevation are currently not available. The tendon-excursion method was used to measure instantaneous muscle moment arms in eight entire upper-extremity cadaver specimens. Significant differences in moment arms were reported across sub-regions of the deltoid, pectoralis major, latissimus dorsi, subscapularis, infraspinatus and supraspinatus (P < 0.01). The most effective abductors were the middle and anterior deltoid, whereas the most effective adductors were the teres major, middle and inferior latissimus dorsi (lumbar vertebrae and iliac crest fibers, respectively), and middle and inferior pectoralis major (sternal and lower-costal fibers, respectively). In flexion, the superior pectoralis major (clavicular fibers), anterior and posterior supraspinatus, and anterior deltoid were the most effective flexors, whereas the teres major and posterior deltoid had the largest extensor moment arms. Division of multi-pennate shoulder muscles of broad origins into sub-regions highlighted distinct functional differences across those sub-regions. Most significantly, we found that the superior sub-region of the pectoralis major had the capacity to exert substantial torque in flexion, whereas the middle and inferior sub-regions tended to behave as a stabilizer and extensor, respectively. Knowledge of moment arm differences between muscle sub-regions may assist in identifying the functional effects of muscle sub-region tears, assist surgeons in planning tendon reconstructive surgery, and aid in the development and validation of biomechanical computer models used in implant design.     

Musculotopic organization of the motor neurons supplying forelimb and shoulder girdle muscles in the mouse

We identified the motor neurons (MNs) supplying the shoulder girdle and forelimb muscles in the C57BL/6J mouse spinal cord using Fluoro-Gold retrograde tracer injections. In spinal cord transverse sections from C2 to T2, we observed two MN columns (medial and lateral) both with ventral and dorsal subdivisions. The dorsolateral column consisted of the biceps brachii, forearm extensors, forearm flexors, and hand MNs, and the ventrolateral column consisted of the latissimus dorsi, trapezius, teres major, deltoid, and triceps MNs. The supraspinatus muscle MNs were located in the dorsomedial column, and pectoralis major and serratus anterior MNs were located in the ventromedial columns. MNs of the dorsolateral column innervated the biceps brachii in mid-C4 to mid-C7, forearm extensors in caudal C4 to mid-T1, forearm flexors in rostral C5 to mid-T1, and hand muscles in mid-C8 to mid-T2 segments. The MNs innervating the trapezius were located in mid-C2 to mid-C4, triceps brachii in mid-C6 to rostral T1, deltoid in rostral C4 to mid-C6, teres major in rostral C5 to mid-C8, and latissimus dorsi in mid-C5 to caudal C8. In addition, MNs innervating the supraspinatus were located from rostral C4 to caudal C8, pectoralis major in mid-C6 to mid-T2, and serratus anterior in rostral C5 to caudal C7/rostral C8 segments. While the musculotopic pattern of MN groups was very similar to that documented for other species, we found differences in the position and cranio-caudal extent of some MN pools compared with previous reports. The identification of mouse forelimb MNs can serve as an anatomical reference for studying degenerative MN diseases, spinal cord injury, and developmental gene expression.     

Lines of action and stabilizing potential of the shoulder musculature

The objective of the present study was to measure the lines of action of 18 major muscles and muscle sub‐regions crossing the glenohumeral joint of the human shoulder, and to compute the potential contribution of these muscles to joint shear and compression during scapular‐plane abduction and sagittal‐plane flexion. The stabilizing potential of a muscle was found by assessing its contribution to superior/inferior and anterior/posterior joint shear in the scapular and transverse planes, respectively. A muscle with stabilizing potential was oriented to apply more compression than shear at the glenohumeral joint, whereas a muscle with destabilizing potential was oriented to apply more shear. Significant differences in lines of action and stabilizing capacities were measured across sub‐regions of the deltoid and rotator cuff in both planes of elevation (P < 0.05), and substantial differences were observed in the pectoralis major and latissimus dorsi. The results showed that, during abduction and flexion, the rotator cuff muscle sub‐regions were more favourably aligned to stabilize the glenohumeral joint in the transverse plane than in the scapular plane and that, overall, the anterior supraspinatus was most favourably oriented to apply glenohumeral joint compression. The superior pectoralis major and inferior latissimus dorsi were the chief potential scapular‐plane destabilizers, demonstrating the most significant capacity to impart superior and inferior shear to the glenohumeral joint, respectively. The middle and anterior deltoid were also significant potential contributors to superior shear, opposing the combined destabilizing inferior shear potential of the latissimus dorsi and inferior subscapularis. As potential stabilizers, the posterior deltoid and subscapularis had posteriorly‐directed muscle lines of action, whereas the teres minor and infraspinatus had anteriorly‐directed lines of action. Knowledge of the lines of action and stabilizing potential of individual sub‐regions of the shoulder musculature may assist clinicians in identifying muscle‐related joint instabilities, assist surgeons in planning tendon reconstructive surgery, aid in the development of rehabilitation procedures designed to improve joint stability, and facilitate development and validation of biomechanical computer models of the shoulder complex.     

Nerve fiber analysis on the so-called accessory subscapularis muscle and its morphological significance

A rare muscular anomaly, so-called accessory subscapularis muscle, was found in the left axillary fossa of a 95-year-old male cadaver during a student dissection practise. The muscle arose near the lateral margin of the scapula from the surface of the subscapularis muscle and ran upward to fuse with the capsule of the shoulder joint via a tendon. It measured 1.0 cm in width, 7.0 cm in length and 1.5 mm in thickness, and was separated from the underlying subscapularis muscle by the axillary and inferior subscapular nerves. Macroscopically, the anomalous muscle received its nerve supply from a branch arising from the lower root of the radial nerve near the origin of the thoracodorsal nerve and entered the muscle from its ventral surface. Nerve fiber analysis showed that the supplying nerve originated from fibers of the dorsal element of C7 immediately cranial to the thoracodorsal nerve. These findings indicate that the present anomalous muscle might be close to the formation of the latissimus dorsi muscle in its derivation rather than the subscapularis muscle.     

Innervation of the levator scapulae, the serratus anterior, and the rhomboideus in crab-eating macaques and its morphological significance

The origin, course and distribution of the nerves supplying the levator scapulae, the serratus anterior, and the rhomboideus were carefully examined in four body-halves of crab-eating macaques. The levator scapulae arises from all the cervical vertebrae and is continuous with the serratus anterior, which arises from the upper ten ribs. The rhomboideus originates not only from the dorsal midline but also from the occipital bone. 6 segmental nerves from C3 to C8 innervate the 3 muscles: C3, C4, C5, and C6 innervate the levator scapulae; C6, C7, and C8 the serratus anterior; and C3, C4, C5, and C6 the rhomboideus. Each segmental nerve of supply originates as one or 2 branches from the dorsal surface of the corresponding root of the cervico-brachial plexus and runs dorso-caudally to enter the muscles. After supplying them, 6 or 7 branches pierce the levator scapulae and serratus anterior to reach the deep surface of the rhomboideus which they innervate. The upper segmental nerve tends to be distributed to the upper part of the muscle it innervates, while the lower segmental nerve is distributed to the lower part. According to the relationships between nerves and muscles, these 3 muscles may be regarded as the most medial of the dorsal musculature which is connected to the pectoral girdle and limb, as they are in man. It may surmised that the occipital portion of the rhomboideus and the caudal portion of the levator scapulae in crab-eating macapues correspond to the cranial portions of the levator scapulae and serratus anterior, respectively, in man.     

EMG study of the pectoralis major (sternal portion), teres major, latissimus dorsi and deltoid medial muscles in volleyball players

The pectoralis major (sternal portion), teres major, latissimus dorsi and deltoid medial muscles has been studied through in the electromyography in 8 male individuals, who practice volleyball, youth category, (age between 15 and 17 (average 16.25), right-handed, involved in volleyball for about one year. The objective was to analyze the potential of action of these muscles engaged in the volleyball movements: service, spike, pass, set and blocking with and without ball. The work was developed in the laboratory of Electromyography and Biomechanics of Posture (Physical Education Faculty - State University of Campinas - UNICAMP). To caption the muscles action potential, surface electrodes were set with conductive gel and fixed on the skin, in the center of the muscles. It was used an electromyography Lynx with 6 channels. The apparatus calibration was 3000 microV; 1199.760 Hz. The sequential experiments without ball were performed for 10 seconds, and the sequential experiments with ball in 12 seconds. RESULTS: None of the muscles presented significative difference (p > 0,05) when compared to the sequential movements executed with and without ball. When compared to the sequential movements executed without ball, the only muscles that presented significative differences (p < 0,05) were: pectoralis major / deltoid and latissimus dorsi / deltoid, for another hand when in the comparative of the movements with ball, all muscles when compared to the latissimus dorsi, presented a significance difference (p < 0,05). It is interesting to observe, that the general average and the standard deviation of the deltoid muscle (medial portion), teres major, and latis-simus dorsi were higher in the sequential movements executed without ball.     

A rare variation of posterior cord brachial plexus branching coexisting with the intercalated ectopic muscle

During a dissection of the brachial plexus we found a rare variation of left posterior cord branching coexisting with an unusual intercalated ectopic muscle. This muscle originated from the shoulder joint capsule at the lesser tubercle on insertion of the subscapularis then pierced between the brachial plexus, enclosed by two roots of the radial nerve, and inserted into the upper part of the latissimus dorsi muscle. The variant posterior cord divided into two roots; a thin lateral and thick medial root. The lateral root gave off the thoracodorsal nerve that penetrated and also innervated the ectopic muscle. The medial root gave off five nerve branches; two upper subscapular, one lower subscapular, one axillary and one terminal branch. A terminal branch fused with the lateral root to form a loop enclosing the ectopic muscle then continued as the radial nerve. This type of variation may be useful to interpret unexplained clinical signs and symptoms and provided additional knowledge to surgeons who perform brachial plexus surgery.     

冻结肩三维运动表面肌电信号特征分析

目的 通过肩周肌肉手法治疗前、后积分肌电值差异,探讨肩周肌肉功能变化。方法选取冻结肩患者7例,利用AMT-8肌电仪对手法治疗前、后肌肉肌电值进行采集,将数据用MATLAB软件进行分析,求积分肌电值。用Stata11.0软件统计。结果①外展时三角肌、冈下肌治疗前、后积分肌电值差异有统计学意义(P＜0.05),肱二头肌、肱...     

Spinal root origins and innervations of the suprascapular nerve

The suprascapular nerve branches provide efferent innervation to the supraspinatus and infraspinatus muscles as well as sensory innervation to the shoulder joint. This study was carried out to verify the spinal root origins and innervations of the suprascapular nerve. Fifty samples of the suprascapular nerve taken from 37 adult Korean cadavers were used in this study. The suprascapular nerve was found to comprise the ventral rami of the C5 and C6 in 76.0% of the fifty samples; C4, C5, and C6 nerves in 18.0%; and C5 nerve in only 6.0%. The C5 nerve was consistently shown to be the largest in mean diameter and was found to be a major contributor of nerve fibers leading to the suprascapular nerve. This study shows that the main spinal component of the suprascapular nerve is C5 nerve. In most cases, the rate of the involvement of the C4 and C6 nerves (18.0 and 94.0%, respectively) with the suprascapular nerve was less than that of C5 nerve. C4 and C5 nerves were shown to contribute nerve fibers to the supraspinatus and infraspinatus muscles and to both shoulder joints, whereas C6 nerve displayed variable patterns of innervation.     

腋窝入路桡神经肱三头肌支转位移植修复腋神经的应用解剖

背景：上臂后上切口入路肱三头肌肌支转位移植修复腋神经牵拉三角肌时易损伤腋神经后支及锁骨上臂丛,探查和联合其他神经转位时需变更体位。 目的：分析腋窝入路桡神经肱三头肌支转位移植修复腋神经的可行性。 方法：取常规甲醛固定成人上肢标本10具20侧,于标本平卧,上肢外展外旋位,腋窝入路,对腋窝处神经血管进行显微解剖。测量腋神经起始处至分支处距离及其分支起始处的横径,肱三头肌各肌支起始处横径,各肌支由入肌点向近端进行无损伤分离长度。 结果与结论：腋神经肩胛下肌下缘分成前后两支,前支横径平均为2.5(1.6~3.4) mm。桡神经肱三头肌长头支,起点处横径为2.2(1.4-2.8) mm。桡神经与腋神经距离平均为18.2(10.2~30.0) mm。腋神经前支与桡神经肱三头肌支横径相似,距离短。表明腋窝入路可暴露和辨别腋神经前后分支,桡神经肱三头肌支在背阔肌腱表面水平靠近腋神经,可选择任一肌支转位移植修复腋神经。      

A rare human variation: the relationship of the axillary and inferior subscapular nerves to an accessory subscapularis muscle

A case of bilateral occurrence of a variant subscapularis muscle is reported. The superior lateral aspect of each subscapularis muscle presented a small accessory muscle with an accompanying tendon that inserted into the lesser tubercle of the humerus along with the primary tendon of the subscapularis muscle. Each accessory subscapularis muscle was separated from the primary subscapularis muscle by the axillary and inferior subscapular nerves. No branches of the axillary or inferior subscapular nerves supplied the primary subscapularis muscle or the accessory muscle while the nerves passed through the myotendinous tunnel. The relationship of the nerves with the variant subscapularis muscles has clinical significance with regard to entrapment neuropathy.     

A rare human variation: The relationship of the axillary and inferior subscapular nerves to an acessory subscapularis muscle

A case of bilateral occurrence of a variant subscapularis muscle is reported. The superior lateral aspect of each subscapularis muscle presented a small accessory muscle with an accompanying tendon that inserted into the lesser tubercle of the humerus along with the primary tendon of the subscapularis muscle. Each accessory subscapularis muscle was separated from the primary subscapularis muscle by the axillary and inferior subscapular nerves. No branches of the axillary or inferior subscapular nerves supplied the primary subscapularis muscle or the accessory muscle while the nerves passed through the myotendinous tunnel. The relationship of the nerves with the variant subscapularis muscles has clinical significance with regard to entrapment neuropathy.     

Bilateral absence of the quadrangular space of the axilla]

In the 1988 student course on gross anatomy dissection of cadavers at Iwate Medical University School of Medicine, two cases of the absence of the quadrangular space of the axilla were found bilaterally in a 92-year-old female who had died of heart failure. The cases were investigated anatomically. The tendons of insertion of the latissimus dorsi and the teres major muscles and the tendon of origin of the long head of the triceps brachii muscle were united, forming a conjoint tendon that attached to the infraglenoid tubercle of the scapula and the lower part of the anatomical neck of the humerus adhering to the articular capsule of the shoulder joint. The subscapularis muscle was normal except that a muscular bundle arose from the conjoint tendon and inserted to the lesser tubercle of the humerus and the crest continuing down from the tubercle. A part of the conjoint tendon was covered by the insertion of the subscapularis muscle, and there was no space between the conjoint tendon and the insertion of the subscapularis muscle. The teres major muscle was poorly developed, but the area of origin was rather wide and arose from both the dorsal and costal surfaces of the scapula. The anatomical features of the latissimus dorsi and the long head of the triceps brachii muscles were normal except for the insertion of the former and the origin of the latter. The triangular space of the axilla was found to be surrounded by the conjoint tendon, teres major muscle, and the lateral border of the scapula covered by the subscapularis and the teres minor muscles.(ABSTRACT TRUNCATED AT 250 WORDS)     

Microanatomical study on the functional origin and direction of the thoracodorsal nerve from the trunks of brachial plexus

Ipsilateral C7 nerve root transfer or neurotization has been used for the repair of brachial plexus avulsions. In this procedure, the ipsilateral C7 nerve root is used as a donor nerve and is implanted into the damaged nerve of the brachial plexus in order to reinnervate distal muscles. However, this procedure may result in unintended injury to the thoracodorsal nerve, which receives motor fascicles form the cervical nerves of C6, C7, and C8, but mainly from C7. Damage to the thoracodorsal nerve ultimately results in weakness or paralysis of the latissimus dorsi muscle, which it innervates. In the present study, 20 adult cadaveric brachial plexus specimens and 3 fresh specimens were dissected using microscopy. The origin and direction of motor fascicles from the three trunks of the brachial plexus to the thoracodorsal nerve were investigated. Motor fiber counts of C7 and the thoracodorsal nerve were also performed. Several observations can be made: (1) The origin of the thoracodorsal nerve can be divided into three types: Type A, the thoracodorsal nerve originated from the superior and middle trunks; Type B, the thoracodorsal nerve originated from the inferior and middle trunks; and Type C, the thoracodorsal nerve originated from all three trunks. (2) More than 52% of the motor fibers in the thoracodorsal nerve originated in the C7 nerve root. (3) Motor fascicles from C7 to the thoracodorsal nerve were mostly localized in the posterior-internal part of C7 at the trunk-division boundary. In conclusion, we suggest that: (1) Because of variation in the origin of the thoracodorsal nerve, electromyography should be routinely performed intraoperatively during C7 nerve root transfer to determine the origin type and avoid thoracodorsal fascicle injury. (2) Preservation of the posterior-internal part of C7 (selective C7 transfer) can protect thoracodorsal nerve fascicles from damage and prevent postoperative dysfunction of the latissimus dorsi muscle.     

A comprehensive analysis of muscle recruitment patterns during shoulder flexion: an electromyographic study

Although flexion is a common component of the routine clinical assessment of the shoulder the muscle recruitment patterns during this movement are not clearly understood making valid interpretation of potential muscle dysfunction problematic. The purpose of this study was to comprehensively examine shoulder muscle activity during flexion in order to compare the activity levels and recruitment patterns of shoulder flexor, scapular lateral rotator and rotator cuff muscles. Electromyographic (EMG) data were recorded from 12 shoulder muscles sites in 15 volunteers. Flexion was performed in standing in the sagittal plane at no load, 20%, and 60% of each subject's maximum load. EMG data were normalized to maximum values obtained during maximum voluntary contractions. Results indicated that anterior deltoid, pectoralis major, supraspinatus, infraspinatus, serratus anterior, upper, and lower trapezius were activated at similar moderate levels. However, subscapularis was activated at low levels and significantly lower than supraspinatus and infraspinatus. Similar activity patterns across time were demonstrated in the muscles that produce flexion torque, laterally rotate the scapula, as well as supraspinatus and infraspinatus, and did not change as flexion load increased. The onset of activity in supraspinatus and anterior deltoid occurred at the same time and prior to movement of the limb at all loads with infraspinatus activity also occurring prior to movement onset at the medium and high load conditions only. Posterior rotator cuff muscles appear to be counterbalancing anterior translational forces produced during flexion and it would appear that supraspinatus is one of the muscles that consistently "initiates" flexion.     

The deep axillary artery

An aberrant axillary artery running deep to the brachial plexus during its course was observed. The brachial plexus in this case was formed by the fourth cervical nerve to the first thoracic nerve and the radial nerve received a small nerve bundle (accessory radial nerve root) from the posterior aspect of the lower trunk. The axillary artery passed between the lateral and the medial cords of the brachial plexus, the same as for an ordinary axillary artery. In addition, it passed between their posterior divisions, forming the posterior cord, and further ran between the radial nerve root and the accessory radial nerve root from deep to superficial. This axillary artery was recognized as the deep axillary artery, the same as the axillary artery we have reported previously. It was thought that the branches to the subscapularis and serratus anterior muscles, nutrient branch to the radial nerve root and the subscapular artery played important roles in its formation.