The proximal origins of the flexor–pronator muscles and their role in the dynamic stabilization of the elbow joint: an anatomical study

Purpose

The purpose of this study was to anatomically investigate the proximal origin of flexor–pronator muscles (FPMs) and clarify their contribution to dynamic stabilization of the elbow joint during valgus stress.

Methods

52 elbows from 26 donated formalin-fixed cadavers were examined. The pronator teres muscle (PT), flexor carpi radialis muscle (FCR), palmaris longus muscle (PL), flexor digitorum superficialis muscle (FDS), and flexor carpi ulnaris muscle (FCU) were identified, and their proximal origin and relationship to the anterior bundle of the medial ulna collateral ligament (AOL) were macroscopically and histologically investigated.

Results

The PT, FCR, PL, and FDS converged and formed a common tendon at their proximal origin (the anterior common tendon: ACT). The ACT was attached to the medial epicondyle and the joint capsule, just anterior and parallel to the AOL. The histological morphology of the ACT was quite similar to that of the AOL. The ulnar head of the PT was observed in 48 of 52 elbows (92.3 %), just behind the humeral head of PT. It mainly originated from the anterior edge of the sublime tubercle, while the upper part of ulnar head transitioned directly into the thickened joint capsule just anterior to the AOL.

Conclusion

The proximal attachment of the FPMs had a characteristic morphology. According to our results, the ACT and PT might assist the AOL by sharing static and dynamic traction forces applied to the medial elbow joint.     

The cubital tunnel: anatomical study of its distal part

Different levels of ulnar nerve compression have been reported (the medial intermuscular septum, the posterior compartment of the arm, soft tissue or bony abnormalities of the cubital tunnel). In some rare cases, compression can lie in a 10-cm long tunnel, distal to Osborne's ligament, between the humeral head of the ulnar flexor muscle of wrist (FCU) and the medial epicondylar muscles. Only few publications mention this fact as a factor of residual or recurrent symptoms after common surgical procedures. However, a distal pathology of the cubital tunnel has proved to be the only factor of nerve entrapment in our clinical practice. Specific anatomical dissection of this area was carried out to find and classify the anatomical structures that may play a role in ulnar nerve distal compression. Twenty-four embalmed limbs from 13 cadavers were dissected. The purpose of this study was to find anatomical fibrous structures at an average of 10 cm from the medial epicondyle. Anatomical structures were classified into five types: no aponeurosis between the FCU and the medial epicondylar muscles (54.2% of cases), a fibrous band taut between the FCU and the fourth- and fifth-finger ulnar insertions of the flexor digitorum superficialis (FDS) (8.3%), a thin (20.8%) or thick (4.2%) partial aponeurosis between the FCU and the medial epicondylar muscles, and total aponeurosis (12.5%). Anatomical variations of the distal cubital tunnel were divided in five types, but their clinical significance remains unclear.     

A case of an accessory brachialis muscle

Functionally, the brachialis muscle serves a critical role as the primary flexor of the arm at the elbow. However, few reports exist in the literature, which describe variations of this muscle. We present a case of an accessory brachialis muscle (AcBr), found during routine dissection at Harvard Medical School during 2003. The AcBr originated medially from the mid-shaft of the humerus and the medial intermuscular septum. During its course medially, toward the elbow, the AcBr crossed both the brachial artery and the median nerve. The distal tendon split to surround the median nerve before inserting into the common tendon of the antebrachial flexor compartment muscles. Embryological origins and clinical considerations including median nerve entrapment are considered.     

Identification of two accessory muscle bundles with anomalous insertions in the flexor side of the right forearm

During dissection practice held at Kyorin University School of Medicine in 2004, two anomalous muscles were observed on the Rt-forearm-flexor-side of an 83-year-old man. The results of this investigation are reported. One accessory muscle originated from the tendinous insertion of the biceps brachii and medial epicondyle. After passing through the deep layer of the pronator teres, it became tendinous, passing towards the trapezium and second metacarpal base. Its two origins fused superficial to the ulnar artery distal to the cubital fossa, and it merged with the deep region of the pronator teres. More distally, the accessory muscle formed a belly before again becoming tendinous and bifurcated, one branch attaching to the trapezium and the other fusing with the belly of the second accessory muscle. These findings suggested that this accessory muscle was similar to Gantzer's muscle. The other accessory muscle arose distal to the origin of the flexor pollicis longus and inserted onto the second metacarpal base. In addition, from the distal side of its origin, a small muscle bundle was formed and became tendinous. It fused with the insertion tendon of the first accessory muscle to the trapezium. The second accessory muscle was thought to be deep radial carpal flexor.     

Strategies for muscle activation during isometric torque generation at the human elbow

1. We studied the patterns of electromyographic (EMG) activity in elbow muscles of 14 normal human subjects. The activity of five muscles that act in flexion-extension and forearm supination-pronation was simultaneously recorded during isometric voluntary torque generation, in which torques generated in a plane orthogonal to the long axis of the forearm were voluntarily coupled with torques generated about the long axis of the forearm (i.e., supination-pronation). 2. When forearm supination torques were superimposed on a background of elbow flexion torque, biceps brachii activity increased substantially, as expected; however, brachioradialis and brachialis EMG levels decreased modestly, a less predictable outcome. The pronator teres was also active during pure flexion and flexion coupled with mild supination (even though no pronation torque was required). This was presumably to offset inappropriate torque contributions of other muscles, such as the biceps brachii. 3. When forearm supination torque was superimposed on elbow extension torque, again the biceps brachii was strongly active. The pronator teres also became mildly active during extension with added pronation torque. These changes occurred despite the fact that both the pronator and biceps muscles induce elbow flexion. 4. In these same elbow extension tasks, triceps brachii activity was also modulated with both pronation or supination loads. It was most active during either supination or pronation loads, again despite the fact that it has no mechanical role in producing forearm supination-pronation torque. 5. Recordings of EMG activity during changes in forearm supination-pronation angle demonstrated that activation of the biceps brachii followed classic length-tension predictions, in that less EMG activity was required to achieve a given supination torque when the forearm was pronated (where biceps brachii is relatively longer). On the other hand, EMG activity of the pronator teres did not decrease when the pronator was lengthened. Triceps EMG was also more active when the forearm was supinated, despite its having no direct functional role in this movement. 6. Plots relating EMG activity in biceps brachii, brachialis, and brachioradialis at three different forearm positions revealed that there was a consistent positive near-linear relationship between brachialis and brachioradialis and that biceps brachii is often most active when brachioradialis and brachialis are least active. 7. We argue that, for the human elbow joint at least, fixed muscle synergies are rather uncommon and that relationships between muscle activities are situation dependent.(ABSTRACT TRUNCATED AT 400 WORDS)     

Intermuscular aponeuroses between the flexor muscles of the forearm and their relationships with the ulnar nerve

Introduction

The aim of this study was to clarify the morphological characteristics of the intermuscular aponeurosis between the flexor carpi ulnaris (FCU) and flexor digitorum superficialis (FDS; IMAS), and that between the FCU and flexor digitorum profundus (FDP; IMAP), and their topographic relationships with the ulnar nerve.

Materials and methods

Fifty limbs of 38 adult cadavers were studied.

Results

The IMAS extended along the deep surface of the FCU adjoining the FDS, having the appearance of a ladder, giving off “steps” that decreased in width from superficial to deep around the middle of the forearm. Its proximal part divided into two bands connected by a thin membrane, and was attached to the medial epicondyle and the tubercle (the most medial prominent part of the coronoid process of the ulna), respectively. The IMAP extended deep between the FCU and FDP from the antebrachial fascia, and its distal end was located on the posterior border of the FCU. The IMAP became broader toward its proximal part, and its proximal end was attached anterior and posterior to the tubercle and the olecranon, respectively. The ulnar nerve passed posterior to the medial epicondyle and then medial to the tubercle, and was crossed by the deep border of the IMAS at 58.3 ± 14.1 mm below the medial epicondyle.

Conclusion

The deep border of the IMAS and aberrant tendinous structure passing across the ulnar nerve, or the parts of the IMAS and IMAP passing posterior to the ulnar nerve are potential causes of ulnar nerve compression.

     

Elbow torques and EMG patterns of flexor muscles during different isometric tasks.

This paper examines the torque responses and EMG activity levels in four muscles acting at the elbow joint during different combinations of one- and two- degree of freedom isometric torque production (single and dual tasks, respectively). Flexor and supinator/pronator torques and surface EMG signals from m. biceps brachii, m. brachialis, m. brachioradialis and m. triceps brachii were measured in 16 male subjects while they performed maximal effort isometric contractions of pure flexion, pure supination, pure pronation, combined flexion and supination and combined flexion and pronation. In the single tasks, the torque responses were consistent with task requirements, but the dual task results were surprising in that flexor torque levels were reduced as compared to pure flexion, while supinator/pronator torque levels were as high or higher than in pure supination or pronation. Muscle activity levels varied with task, and could not always explain the differences observed in torque responses. These data are discussed within the framework of subpopulations of task-specific motor units within each muscle. The implications of such task-specific muscle units are related to musculoskeletal modelling and previous EMG - torque relationships found at the elbow.     

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.     

膝内侧稳定结构的解剖特征与软组织平衡的关系

目的:观测国人膝内侧结构解剖学特点,为膝关节置换术中内侧结构软组织平衡的松解策略选择提供形态学依据.方法:80例固定及20例新鲜成人膝关节标本,解剖观察内侧结构的组成及其位置与形态学特点.结果:膝关节内侧面支持结构包括内侧副韧带复合体和半膜肌复合体等结构,可分为3层.内侧副韧带复合体包括内侧副韧带(medial collateral ligament,MCL)深、浅两层,可分为前纵部和后斜部两部分.MCL前纵部以间接止点形式融入胫骨平台关节面下50～60 mm,鹅足深方的胫骨内侧骨面骨膜,长约92mm,中部宽约15mm后斜部纤维以腱板起于股骨内卜髁后侧,下止点弥散;在关节间隙处,后斜部纤维与其深方第3层(内侧关节囊)愈着,被半月板、冠状韧带固定.MCL深层实际上为膝内侧关节囊增厚,自股骨内上髁下半周缘骨面垂直向下走行,连接内侧半月板,止于胫骨平台内侧缘中点关节面下0.8～1.5cm骨面,并与半膜肌腱横臂融合.膝关节后内侧区域为半膜肌腱鞘和半膜肌腱的9处附丽所加强,维持膝关节后内侧角稳定.结论:基于膝关节内侧结构解剖特点,膝关节置换术中软组织平衡可以做到微创化、选择性的松解.尽量保护其结构和功能的完整对术后功能有重要意义.     

Toward direct biocontrol using surface EMG signals: control of finger and wrist joint models

Increased interest in virtual reality (VR) and telemanipulation has created a growing need for the development of new interfacing devices for measuring controlling actions of the human hand. The objective of the present study was to determine if surface electromyography signals (SEMG) from the flexor digitorum superficialis (FDS), and flexor carpi ulnaris (FCU) generated during flexion-extension of the human index finger and wrist can be used for controlling the flexion-extension of the finger and wrist of a simple geometric computer model. A simple geometric computer model of finger and wrist joints was developed. Eighteen subjects controlled the computer model using the SEMG signals from their FDS and FCU. The results indicate that the SEMG signals from the FDS and FCU muscles can be used as a direct biocontrol technique for controlling the finger and wrist models. This study establishes the proof of concept for direct biological control of the dynamic motion of the finger and wrist models for use in virtual reality environments and telemanipulation.     

肘部断层解剖学研究

目的为肘部临床影像学诊断提供解剖学依据。方法利用40侧成人尸体肘部,制作成横、矢、冠三个方位的连续断层标本,观测肘关节所在各断面的结构安排,关节腔宽度。结果肱尺关节腔为0.70±0.44mm,肱桡关节腔为0.69±0.44mm,桡尺近侧关节腔为0.90±0.56mm;关节软骨厚度,骨关节软骨厚度为1.15±0.35mm,尺骨关节软骨厚度为1.04±0.16mm,桡骨关节软骨厚度为0.98±0.17mm;侧副韧带尺侧副韧带厚度为1.38±0.42mm,桡侧副韧带厚度为1.32±0.42mm。结论肘部横、矢、冠断层能从三维角度清晰地显示肘关节各关节腔、关节软骨、侧副韧带,以及正中神经、尺神经及桡神经与肘关节的关系。     

肘关节内侧副韧带生物力学及临床研究

目的：探讨肘关节内侧副韧各组成成分在肘关节稳定中的作用及手术治疗内侧副韧带损伤的临床效果。方法：收60例4％福尔马林溶液防腐保存的正常成人尸体肘关节标本，仔细解剖出肘关节内侧副韧带的前束、后束和斜束，随机分为5组，然后通过生物力学研究，分别观察肘关节内侧副韧带各组成部分在肘关节不同屈曲角度下对肘外翻角度的影响，并在此基础上临床治疗内侧副韧带损伤伴肘关节不不稳定患者11例，随访其疗效。结果：肘关节内侧副韧带前束在肘关节屈曲过程中，在抗外翻应力方面起主要作用而单纯后束或斜束损伤对肘关节内侧稳定影响小大；11例肘关节内侧副韧带损伤患者经手术修复前束，肘关节功能恢复良好．未见遗留内侧不稳定。结论：肘关节内侧副韧带前束是肘关节内侧稳定的主要结构，临床上当肘关节内侧副韧带损伤时应重点修复或重建前束以稳定肘关节。     

New insight into the iliofemoral ligament based on the anatomical study of the hip joint capsule

The iliofemoral ligament, which plays an important role in hip joint stability, is formed on the anterosuperior region of the hip joint capsule. Although the tendon and deep aponeurosis of the gluteus minimus and iliopsoas are partly connected to the same region of the capsule, the precise location of the connections between the joint capsule and the tendons and deep aponeuroses remains unclear. The locations of the tendinous and aponeurotic connections with the joint capsule may clarify whether the iliofemoral ligament can be regarded as the dynamic stabilizer. This study investigated the relationships between the anterosuperior region of the joint capsule and the tendon and deep aponeurosis of the gluteus minimus and iliopsoas. Fourteen hips from nine cadavers (five males; four females; mean age at death 76.7 years) were analyzed. Ten hips were macroscopically analyzed, and four were histologically analyzed. During macroscopic analysis, the joint capsule was detached from the acetabular margin and the femur, and its local thickness was measured using microcomputed tomography (micro-CT). The gluteus minimus tendon was connected to the joint capsule, and the lateral end of this connection was adjoined with the tubercle of the femur at the superolateral end of the intertrochanteric line. The deep aponeurosis of the iliopsoas was also connected to the joint capsule, and the inferomedial end of its anterior border corresponded with the inferomedial end of the intertrochanteric line. In the micro-CT analysis, capsular thickening was observed at the base of the connection to the gluteus minimus tendon and at the anterior border of the deep aponeurosis of the iliopsoas. A histological study showed that the gluteus minimus tendon and the deep aponeurosis of the iliopsoas were continuous with the hip joint capsule. Based on the morphology of the tendinous and aponeurotic connections, local capsular thickening and histological continuity, the transverse and descending parts of the iliofemoral ligament were the joint capsules, with fibers arranged according to the connection with the gluteus minimus tendon and the deep aponeurosis of the iliopsoas, respectively. Therefore, the so-called iliofemoral ligament could be regarded as the dynamic stabilizer, with the ability to transmit the muscular power to the joint via the capsular complex. This anatomical knowledge provides a better understanding of the hip stabilization mechanism.     

骨间前神经综合征的局部解剖学研究

目的 搪塞骨间前神经综合征的解剖学基础。方法 解剖４８例（左右各２４侧）成人防固定标本。结果 骨间前神经主干邻近腱性结构有旋前圆肌纤维桥（５８．３％），尺骨头浅面腱膜（９３．７％），联合腱板（８３．３％）和指浅屈肌纤维弓（９１．２％），横过骨间前神经的拇长岂副头（６６．７％），及少 尺侧血管、小束肌肉或纤维结构。７７％骨间前神经干走在桡骨颈前方结论 骨间的神经主干邻近的腱性结构及距离桡骨颈近可能是     

Capsular attachment of the brachialis muscle (Portal’s muscle): an anatomical and functional study

There is a paucity of information regarding the detailed anatomy of the capsular part of the brachialis muscle in the extant literature. Our current study seeks to further elucidate the presence, morphology, and potential function of this muscle. Thirty-six cadaveric upper extremities underwent dissection of their anterior elbow joint capsule with special attention to any fibers attaching onto it from the brachialis muscle. We found that the majority of fibers of the brachialis simply passed superficial to the anterior elbow joint capsule. The highest concentration of fibers was noted to be onto the anteromedial joint capsule via connective tissue and not direct muscle attachment. No specimen was found to have a distinct muscle belly associated with these connections to the joint capsule. On all sides, such fibers were simply deeper attachments of the brachialis muscle. Following tension on these deeper fibers, retraction of the joint capsule was not noted. We would speculate, based on our study, that these fibers of the brachialis do not represent a separate muscle per se and do not retract the anterior elbow joint capsule with flexion of the forearm as has been theorized. These data may be of use to surgeons who operate this region so that attention to preservation of such fibers may be of less importance.     

指背腱膜的功能解剖及临床意义

目的：进一步探讨指背腱膜的构成特点及临床意义。方法：在30只成人手标本上，通过模拟手术，对指背腱膜的构成特点进行了应用解剖学观测。结果：指背腱膜的构成复杂，其中的外侧腱束、外侧束、外侧腱和中央束在手指畸形的发生中有着特殊的临床意义。外侧腱束主要形成伸近节指间关节的功能解剖机制；其与外侧束形成的密切纤维联系而具有协同外侧腱的功能；该腱束与屈肌腱鞘有联系又使其具有平衡屈肌和伸肌肌力的作用。中央束在指背腱膜的整体协调、畸形的发生及矫正过程中起着重要的功能。结论：通过对指背腱膜的解剖研究，可用以解释因指屈、伸肌腱平衡被破坏后所形成的畸形，并可进一步探讨畸形的发生机理和解决这些畸形的新术式。     

A case of median nerve descended on the surface of the pronator teres muscle

We report a case in which the left median nerve passed downwards on the surface of the pronator teres muscle in a 70-year-old male cadaver examined during student dissection practice in 2001 at Nihon University School of Medicine. In the present case, the lateral cord of the median nerve is formed of only the middle trunk, C7 and did not include upper trunk, C5, 6. The upper trunk continued the musculocutaneous nerve, but it did not participate in the median nerve. In the cubital fossa, the median nerve descended on the surface of the pronator teres muscle. The pronator teres muscle had an additional head which arose from the medial intermuscular septum. The brachial artery passed between the humeral head and the additional head. It suggested the relevance that the first branch from the median nerve to the forearm flexor muscle group is the union covered with the common ensheathing epineurium. It consisted of the pronator teres muscle branch, the flexor carpi radialis muscle branch, and the branch to the proximal belly of the muscle bundle of the flexor digitorum superficialis muscle (FDS) for the second digit (II-p), which also supplies the palmaris longus muscle. The branch to the FDS for the third to the fifth digit and the anterior interosseous nerve branch arose from the back of the median nerve following the first branch, and the two branches connected mutually. And the median nerve had a branch to the distal belly of the muscle bundle of the FDS for the second digit (II-d) in its more distal part.     

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.