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.     

An accessory muscle of the shank

An accessory bilateral crural muscle is shown which has not yet been described. The muscle arises like the peronaeus quartus muscle at the proximal third of the flexor surface of the fibula and the interosseous membrane. The tendon runs medially to the tendon of the flexor hallucis longus muscle underneath the flexor retinaculum. On the left side, it is divided in 2 parts. The insertion lies medially to the anterior tubercle of the calcaneus. There is no phylogenetic explanation for such an accessory muscle.     

A Case of the Bilateral Duplicate Palmaris Longus Muscles Coupled with the Palmaris Profundus Muscle

The palmaris longus muscle is one of the most variable muscles in human anatomy. During a routine anatomical dissection for medical students at Tottori University, we found duplicate palmaris longus muscles in the bilateral forearms together with the palmaris profundus muscle in the right forearm. The bilateral aberrant palmaris longus muscles were observed at the ulnar side of the palmaris longus muscle and their distal tendons were attached to the flexor retinaculum. The palmaris profundus muscle found in the right forearm was located at the radial side of the flexor digitorum superficialis muscle. The proximal tendon was originated from the anterior surface in the middle of the radius, while the distal tendon coursed radial to the median nerve through the carpal tunnel, finally inserting into the distal part of the flexor retinaculum. Both the palmaris longus and aberrant palmaris longus muscles were innervated by the median nerve. The palmaris profundus muscle was presumably supplied by the median nerve.     

Dual innervation of the brachialis muscle

A study of the innervation of the brachialis muscle was carried out on 45 male and 31 female Thai cadavers between the ages of 15 and 92 years (mean = 59 years). The dissections revealed that all brachialis muscles received innervation from the musculocutaneous nerve and that 81.6% were also innervated by a branch from the radial nerve. Among the brachialis muscles with a dual nerve supply, two patterns of branching from the radial nerve were observed: in one pattern the branch to the brachialis had a descending course (58%) and in the other pattern the nerve ascended or recurred (42%) to innervate the muscle. The radial nerve branch penetrated the inferolateral part of the brachialis muscle in 83% of cases (103/124) and its middle third in 17% of specimens (21/124). The basis for the dual innervation may result from fusion of two different embryonic muscular primordia: the ventral (flexor) and the dorsal (extensor) muscle masses. In contrast to a brachialis muscle innervated by the musculocutaneous nerve only, a muscle with dual innervation may be spared significant denervation by an anterior approach to the humerus through a longitudinally bisected muscle. In a dually innervated muscle, however, separation of the brachialis and brachioradialis muscles during surgery may put the radial nerve branch to the brachialis at risk.     

Anomalous muscle belly to the index finger.

An unusual variation of flexor digitorum superficialis was observed during the cadaver dissection. The flexor digitorum superficialis (FDS) had a normal origin and insertion, except to the index finger, where a muscle belly replaced the tendon of FDS. The unusual muscle belly originated as a continuation of FDS tendon in the carpal tunnel and inserted normally into the middle phalanx. A branch of the median nerve innervated the anomalous muscle belly. The anomalous muscle belly described here should be considered in the aetiology of carpal tunnel syndrome.     

Anomalous flexor of the little finger

We report an anomalous palmar muscle belly of the flexor digitorum superficialis muscle (FDS) in the right hand of an 80-year-old female cadaver. The muscle originated from the center of the volar surface of the flexor retinaculum and inserted onto the palmar aspect of the base of the middle phalanx of the little finger. Its tendon of insertion divided into two bands, a pattern typical of the FDS tendon, between which the tendon of flexor digitorum profundus muscle to the little finger passed. The tendon of the usual antebrachial FDS to the little finger was absent. The anomalous muscle belly was innervated by a branch from the median nerve.     

正中神经返支卡压及易损伤部位的解剖学基础

目的：探讨腕管综合征术后大鱼际功能恢复不良的原因与返支易损伤部位。方法：对20侧成人新鲜上肢标本进行显微解剖，观测正中神经返支走行中存在的卡压因素以及易损伤部位。结果：(1)拇短屈肌浅头尺侧存在腱弓及腱纤维束结构，对正中神经返支形成卡压；(2)住屈肌支持带远侧返支与掌腱膜关系密切，在此部位掌腱膜可对返支形成卡压或术中易误伤返支；(3)走行中返支与拇长屈肌腱和示指屈肌腱存在交叉走行关系。结论：(1)返支走行中存在易卡压因素，治疗腕管综合征时应常规探查松解返支；(2)涉及拇长屈肌腱，示指屈肌腱和掌腱膜手术时，应注意防止损伤返支。     

Epifascial accessory palmaris longus muscle

In hand reconstructive surgery the palmaris longus muscle is one of the most utilized donor site for tendon reconstruction procedures. However, its anatomic position is variable and anatomic variations may be responsible for median nerve compression. We report the case of a 40-year-old, right-handed woman, who presented with numbness and paresthesias in the palm and in the flexor aspect of the first, second, and third fingers of her right hand for the preceding 5 months, coinciding with increase of office work (typing). The clinical examination and radiological investigations (ultrasound and magnetic resonance) revealed a subcutaneous mass (15 mm x 2.3 mm x 6 cm), with a lenticular shape and definite edges at the level of the volar aspect of the distal third of the forearm. The fine-needle aspiration biopsy revealed the presence of striated muscle fibers. During surgery, a muscle belly was found in the epifascial plane. This muscle originated from subcutaneous septa in the middle forearm and inserted on to the superficial palmar aponeurosis with fine short tendon fibers. Exposure of the antebrachial fascia did not reveal any area of weakness or muscle herniation. The palmaris longus tendon, flexor digitorum superficialis tendons, and flexor carpi radialis tendon showed usual topography under the antebrachial fascia. The accessory muscle was excised and histology revealed unremarkable striated muscle fibers, limited by a thin connective sheath. The presence of an accessory palmaris longus (APL) located in the epifascial plane could be ascribed to an unusual migration of myoblasts during the morphogenesis. Although extremely rare, APL is worth bearing in mind as a possible cause of median nerve compression and etiology of a volar mass in the distal forearm.     

Anomalous course of the median nerve medial to the trochlea and anterior to the medial epicondyle of the humerus.

It is generally assumed that in the cubital region the median nerve is directly medial to the brachial artery and that it lies anterior to the trochlea of the humerus, from which it is separated by the brachialis muscle. Three instances are noted where the median nerve passed medial to the trochlea and anterior to the medial epicondyle, deep to the pronator teres, unilateral in one subject and bilateral in another. Its possible significance in elbow trauma is commented upon.     

Abnormal musculoaponeurotic tunnel in the arm: possible entrapment of the median nerve and brachial artery with high origin of nerve to pronator teres within the tunnel

Median nerve and brachial artery in the arm are not usually overlapped by any structure. Connective tissue bands and muscular slips draping or enclosing this neurovascular bundle have been reported, however, which may produce clinical symptoms of nerve compression and vascular changes. We report an unusual musculoaponeurotic band that originates as the ligament of Struthers but terminates as the brachiofascialis muscle of Wood and in the process may have entrapped both the median nerve and brachial artery. The nerve to pronator teres originates from the median nerve within this tunnel. On histological examination the nerve was flattened and showed some perineurial thickening. In view of the flexor function of brachialis muscle, this anomalous musculoaponeurotic band may be considered a clinically important entity in the causation of idiopathic neurovasculopathy in the hand.     

Innervation of the medial epicondylar muscles: an anatomic study in 50 cases

The median nerve is classically distributed to the medial epicondylar muscles by two branches (superior and inferior) for the pronator teres muscle, a common trunk for the flexor carpi radialis and palmaris longus muscles, and a branch for the flexor digitorum superficialis muscle. The 50 dissections were made by two workers on 30 upper limbs of formolized cadavers and 20 limbs from fresh-frozen cadavers. The innervation of the pronator teres m. was classical in only 26% of cases, and the “normal” pattern for the flexor carpi radialis and palmaris longus mm. was found in only 40% of cases. The innervation of the flexor digitorum superficialis m. was the least subject to variations, a single branch being observed in 68% of cases. We found a solitary medio-ulnar anastomosis of Martin-Gruber to the flexor carpi ulnaris muscle. This study confirmed the great variability of the branches of the median nerve at the elbow, and the importance of identifying them in surgical procedures for transposition of the medial epicondyle.     

Muscle variations and abnormal branching and course of the ulnar nerve in the forearm and hand

During dissection of the right forearm of a 27-year-old female cadaver, variations in the form and insertion of the palmaris longus muscle were observed. The tendon of the palmaris longus muscle, which demonstrated a centrally placed belly, split into two tendons: one inserted into the palmar aponeurosis and the other into the proximal part of the flexor retinaculum. Additionally, we found an accessory muscle extending between the flexor retinaculum and the tendon of the abductor digiti minimi muscle. This accessory muscle was located deep to the ulnar artery but superficial to the superficial and deep branches of the ulnar nerve at the wrist. Finally, an aberrant branch of the ulnar nerve was identified in the forearm; it traveled distally alongside the ulnar artery and in the palm demonstrated communications with common palmar digital nerves from the ulnar and the median nerves. No variations were observed in the contralateral upper limb.     

An accessory belly of the abductor digiti minimi muscle: a case report and embryologic aspects

Accessory fasciculi of the hypothenar muscles have been involved in vascular and nerve compressions. During a routine dissection an accessory belly of the abductor digiti minimi muscle arising from the tendon of the palmaris longus muscle was found in the lower third of the forearm. The accessory fasciculus ran through Guyon’s canal enclosing the ulnar nerve and vessels. It was attached by means of two tendons where the fibres of the abductor digiti minimi muscle ended in a single pennate form. This anatomic variation was associated with a marked reduction of the caliber of the fourth tendon of the flexor digitorum superficialis muscle and a split of the median nerve. The nerve supply arose from the ulnar nerve. A fibrous band originating from this accessory muscular belly was found covering the median nerve. Based on the development of muscles and fibrous structures within the hand and forearm, as well as on our results, we consider the present anomalies as an unusual persistence of an undifferentiated group of mesenchymal cells. These belong to the superficial muscular anlagen layer of the hand, just between the flexor digitorum superficialis muscle blastema (which has the capacity of migration) and that for the abductor digiti minimi muscle.     

Superficial ulnar artery originating from the brachial artery and its clinical importance

We found a left superficial ulnar artery in the cadaver of a Japanese woman. This anomalous vessel originated from the brachial artery at a site 55 mm distal to the inferior border of the teres major muscle and medial to the median nerve, ran downward and medially superficial to the forearm flexor muscles, and then downward to enter the hand. It formed superficial and deep palmar arches with the radial artery. The clinical importance of the anomalous ulnar artery is discussed.     

Three-headed biceps brachii muscle associated with duplicated musculocutaneous nerve

A unilateral three-headed biceps brachii muscle coinciding with an unusual variant of the musculocutaneous nerve was found during routine dissection of a 79-year-old male cadaver. The supernumerary bicipital head originated from the antero-medial surface of the humerus just beyond the insertion of the coracobrachialis, and inserted into the conjoined tendon of biceps brachii. Associated with this muscular variant was a duplicated musculocutaneous nerve. The proximal musculocutaneous nerve conformed to the normal pattern only in its proximal part, and terminated after innervating the coracobrachialis and biceps brachii muscles. The distal musculocutaneous nerve arose from the median nerve in the lower arm, then passed laterally between the supernumerary bicipital head and the brachialis muscles, supplying both and terminating as the lateral cutaneous nerve of the forearm. The supernumerary bicipital head and the accompanying anomaly of the musculocutaneous nerve seem to be unique in literature.     

Concentric and eccentric muscle strength before,during and after fatigue in 13 year-old boys

Summary The purpose of this study was to investigate the force-producing characteristics of boys aged 13 years in relation to fatigue of elbow flexor muscles. Maximal voluntary force in elbow flexion was measured before and after a muscle endurance test (MET) by using an isokinetic dynamometer isometrically, concentrically and eccentrically at three velocities, i.e. 0.21, 0.52, and 1.05 rad · s^–1. The MET consisted of maximal concentric and eccentric muscle actions performed alternately at 0.52 rad · s^–1 for 50 consecutive trials. Muscle cross-sectional area (CSA) of elbow flexor muscles (biceps brachii and brachialis) was measured by a B-mode ultrasound apparatus. Although eccentric force showed significantly higher values than concentric force during MET, there was no significant difference in the rate of decline in force between the two actions. There was no significant difference in the rate of decline in force after MET for each velocity and muscle action. Isometric, concentric and eccentric force before MET was significantly related to muscle CSA whereas, after MET, concentric force significantly correlated with muscle CSA but there was no significant correlation between muscle CSA and isometric or eccentric force. From our study, it is therefore suggested that in development to maturity, isometric, concentric and eccentric force decrease at the same rate with advancing muscle fatigue; however, there might be differences among muscle actions in facors affecting force development.     

Differences in coordination of elbow flexor muscles in force tasks and in movement tasks

Summary Motor-unit activity in m. biceps brachii, m. brachialis and m. brachioradialis during isometric contractions has been compared with motor-unit activity during slow voluntary (extension and flexion) movements made against external loads. During these slow movements the recruitment threshold of m. biceps motor units is considerably lower than it is during isometric contractions but the recruitment threshold of both m. brachialis and m. brachioradialis motor units is considerably higher. For all three elbow flexor muscles the motor-unit firing frequency seems to depend on the direction of movement: the firing frequency is higher during flexion movements (3 deg/s) and lower during extension movements (−3 deg/s) than during isometric contractions. The relative contribution of the biceps to the total exerted flexion torque during slow voluntary movements is estimated to increase from 36% to about 48% and that of the brachialis/brachioradialis is estimated to decrease from 57% to about 45% compared to the relative contribution of these muscles during isometric contractions. This difference in the relative contribution of the three major elbow flexor muscles is shown to be caused by differences in the central activation in force tasks and movement tasks.     

The effects of wrist muscle vibration on human voluntary elbow flexion-extension movements

Summary The effect of forearm muscle tendon vibration during alternating step flexion-extension movements about the elbow was studied in normal humans. In one experiment, a vibrator was mounted over either the forearm flexor or the extensor muscle. In a second experiment, a vibrator was mounted over either the forearm muscle or the biceps muscle. In both experiments, vibration was applied either to a single muscle or simultaneously to both muscles during elbow flexion-extension movements. After a period of practice, subjects learned the required movements and were able to make them with their eyes closed. Application of vibration to the forearm and the biceps muscle during extension movements produced an undershoot of the required end movement position. Moreover, application of high frequency vibration (100 Hz) to the forearm extensor and flexor muscle produced an overshoot of the required end-movement position. The observed results are consistent with vibration induced activation of muscle spindle receptors not only in the lengthening muscle during movement but also in the forearm muscles. It is suggested that the pattern of distribution of muscle spindle afferent from the forearm muscle onto -motoneurons of muscles acting at the elbow has played an important role of alternating step flexion-extension movements.