Case of an abductor pollicis longus muscle: variation or differentiation?

A variation of the abductor pollicis longus muscle in a 65 year old cadaver was encountered during routine dissection in our department. The muscle was found to split into two bellies and give off two tendons, one of which inserted to the abductor pollicis brevis, opponens pollicis and flexor pollicis brevis muscles. The other tendon inserted to the first metacarpal bone which is considered a normal insertion site for the abductor pollicis longus muscle.     

Bilateral abductor pollicis longus muscle variation. Case report and review of the literature

An abnormal abductor pollicis longus muscle was encountered bilaterally during the dissection of the upper limb of a 26-year-old male cadaver. In the left side, the abductor pollicis longus had seven tendon slips. The medial two inserted into the abductor pollicis brevis, the other five inserted into the base of the first metacarpal bone. In the right side of the case, the abductor pollicis longus was consisted of three bellies. The lateral belly's tendon was the main abductor pollicis longus tendon and inserted into the base of the first metacarpal bone. The medial belly inserted into the abductor pollicis brevis. Between these muscle bellies, there was an intermediate belly. Its tendon was split into two thin slips and inserted into both the abductor pollicis brevis and the opponens pollicis muscles. The number of such accessory tendons has a functional significance in the development of de Quervain's stenosing tendovaginitis and possibly also has a practical significance. This paper is the first to describe seven tendons of the abductor pollicis longus and extensor pollicis brevis in the same compartment.     

人鱼际肌的肌内神经分支分布和肌梭密度研究

目的探索鱼际肌肌肌内神经分支和肌梭密度的分布。方法采用改良Sihler’s肌内神经染色法和HE染色法进行解剖学研究。结果鱼际肌的神经常从肌起端深面入肌,神经入肌后在拇短展肌、拇对掌肌、拇收肌横头内与肌长轴垂直走向,拇收肌斜头和拇短屈肌内沿肌长轴平行走形。80%～82.5%的拇短屈肌和拇指对掌肌接受正中神经和尺神经的双重支配。拇短屈肌浅头和深头、拇收肌横头和斜头有独立的神经支配,可分出神经肌肉亚部。4块肌内神经分支分布密集区多在肌的中部与近端,可见"Y"、"O"、"H"或"U"型等不同的神经吻合形式。鱼际肌肌梭密度高达16.19～27.14个/g,高低顺序为拇指对掌肌拇短屈肌拇短展肌拇收肌。结论鱼际肌肌内神经吻合丰富,肌梭密度高,除拇对掌肌外,其余肌块可作整肌或半肌移植的供体。     

拇短展肌对拇指指骨间关节背伸作用的解剖学研究

目的　为解决胸小肌移植重建拇对掌功能术后出现拇指指骨间关节屈曲畸形提供解剖学依据并寻找解决办法。 方法　在15具尸体手标本上,使拇指处于对掌位时,测量拇指指骨间关节在拇短展肌未切断及切断两种情况下的自然屈曲角度;同时,通过外力作用使拇指指骨间关节分别屈曲处于45°及60°时,分析拇短展肌对拇指指骨间关节屈伸功能的影响。 结果　拇指处于对掌位时,拇短展肌在未切断及切断两种情况下,拇指指骨间关节自然屈曲角度分别为（13.30±2.13）°及（24.03±1.25）°;同时,使拇指指骨间关节屈曲处于45°时,所用外力分别约（0.50±0.08）N及（0.22±0.07）N,而使拇指指骨间关节屈曲处于60°时,所用外力分别约（1.48±0.09）N及（1.15±0.04）N。 结论　拇短展肌对拇指指骨间关节主要起背伸作用,因此胸小肌移植重建拇对掌功能时,应同时重建拇短展肌功能,才有可能纠正在拇对掌功能重建术后出现的拇指指骨间关节屈曲畸形。     

Human motor-unit recruitment during isometric contractions and repeated dynamic movements

Spike-triggered averaging was used to determine the twitch tensions and contraction times of motor units in the abductor pollicis brevis muscle of two human subjects for two directions of isometric contraction: abduction and opposition of the thumb. During isometric contractions in each direction, the threshold force for motor-unit recruitment and the twitch amplitude were correlated linearly. These data suggested that an orderly pattern of recruitment, according to increasing twitch size, describes the function of the human abductor pollicis brevis muscle for each contraction direction. Rank order of motor-unit recruitment in each isometric contraction direction was correlated, but not identical. All units contributed tension in each direction of contraction, so no clear evidence was found for task-dependent motor units. In two subjects, motor-unit recruitment order during isometric contraction of the first dorsal interosseous and abductor pollicis brevis muscles was then compared with that of motor-unit pairs in both muscles during repetitive dynamic movements. Recruitment according to increasing twitch size was largely preserved during the repetitive opening and closing of scissors. The recruitment reversals that were observed were usually between pairs of units with similar thresholds.     

The abductor pollicis longus: relation between innervation, muscle bellies and number of tendinous slips

The aim of this study was to assess the relation between the insertions of the distal tendinous slips, the muscle bellies and the innervation pattern of the abductor pollicis longus (APL) muscle and of the extensor pollicis brevis (EPB). The upper extremities of 31 frozen cadavers were dissected under magnifying lenses to describe the distribution of the posterior interosseous nerve (PION). The number and the distribution of distal tendinous slip insertions of the APL muscle were variable. Two superficial and deep distal tendon groups were noted. The separation into superficial and deep muscular parts of the APL was frequent (87%). The EPB muscle was generally constituted by one muscle belly and one tendinous slip (93.5%). The innervation by the PION to the APL and EPB muscles was classified into five types. The specific innervation between superficial and deep muscular parts of the APL muscle, the specific innervation of the deep muscle bellies and the independence of the superficial and deep distal tendon groups of the APL muscle are arguments in favor of a complex functional role of the APL motor unit in thumb mechanics. However, no independence of the tendinous slips in the two distal tendon groups and no correlation between the number of tendinous slips and muscle bellies or innervation were observed. These limit the functional role of the two independent superficial and deep musculotendinous APL motor units. The use of the APL tendon for interposition arthroplasty, for tendon transfer or tendon translocation seems logical, particularly if using one of the two distal tendon groups.     

Characteristics of the electrophysiological activity of muscles attached to the transverse carpal ligament in carpal tunnel syndrome

The main cause of carpal tunnel syndrome (CTS) remains unknown. Stiffness of the subcutaneous area of the volar aspect of the carpal tunnel is present in many patients and suggests that the stiffness of muscles attached to the transverse carpal ligament is increased. We performed an electrophysiological study to investigate muscle activities and to clarify whether the stiffness of muscles attached to the transverse carpal ligament is involved in the pathogenesis of CTS. The subjects of this study included 16 patients with early CTS showing no motor dysfunction. Both thenar muscles (opponens pollicis, abductor pollicis brevis, and flexor pollicis brevis) and hypothenar muscles (opponens digiti minimi, abductor digiti minimi, flexor digiti minimi brevis) were investigated. Surface electrodes were placed on each muscle, and maximum voluntary contractions with the thumb and little finger in opposition were maintained for 3 seconds in all patients and in 7 control subjects. Electromyographs were subjected to fast Fourier transform analysis, and the root mean square (RMS) and the mean power frequency (MPF) were determined for each muscle. The RMS of the opponens pollicis was significantly less in hands affected by CTS (292.8 μV) than in healthy hands (405.9 μV). The RMS did not differ between affected hands and healthy hands for the other 2 thenar muscles but did differ significantly for the hypothenar muscles. The MPF did not differ between affected hands and healthy hands for any muscle. The results show that electrophysiological differences are present among muscles innervated by the median nerve and that hypothenar muscles originally unrelated to median nerve dysfunction are also affected in early CTS. These results suggest that modulation of muscles attached to the transverse carpal ligament is involved in the pathogenesis of CTS.     

足部相关肌肉、肌腱组织材料弹性模量的测定

背景：目前,几乎所有足部三维有限元模型的材料参数均来自国外研究,尚未见有关国人组织材料参数的测量与报道。 目的：对国人足部的相关肌肉、肌腱材料做测量,获得初步的参数数据。 方法：解剖成年女性左小腿足新鲜标本拇长屈肌及其肌腱、拇短屈肌内外侧头、拇长伸肌及其肌腱、拇收肌横头及斜头、拇展肌,分别测量和计算各试样的截面积和位于夹具之间的长度并记录数值,将标本加载载荷,1个测样反复测量4次,采集强度极限、最大载荷等数据,以及载荷-位移曲线。根据胡克定律,计算各标本的弹性模量。 结果与结论：共得到了包括拇长伸肌、拇长屈肌、拇收肌、拇展肌横头和斜头、拇短屈肌内外侧头、拇长屈肌腱、拇长伸肌腱9个样本的相关测量数据,主要包括长度、宽度、厚度、横截面积、最大载荷、强度极限和弹性模量。中国组织工程研究杂志出版内容重点：生物材料;骨生物材料; 口腔生物材料; 纳米材料; 缓释材料; 材料相容性;组织工程全文链接：     

The innervation of deep muscles of the human forearm extensors]

The innervation of four deep muscles of the human forearm extensors (the abductor pollicis longus, the extensor pollicis brevis, the extensor pollicis longus, and the extensor indicis muscles) were investigated in 24 bodies (48 sides) from those used in the 1989 and 1990 student courses in gross anatomy dissection at the Iwate Medical University School of Medicine. The forearm extensor muscles and the deep branch of the radial nerve were dissected intensively in the student courses in gross anatomy and were removed afterwards. The four deep muscles of the human forearm extensors and the nerves innervating the muscles were observed while they were immersed in the water and with use of a stereomicroscope--with the assistance of which they were drawn. In six sides the intramuscular nerve supply was also examined carefully and drawn. The results were as follows. 1. The nerves to the four deep muscles of the forearm extensors arose usually from the deep branch of the radial nerve after emerging the supinator muscle and sending branches to superficial forearm extensors. In some cases a nerve or nerves to the superficial forearm extensors were observed arising from the deep branch of the radial nerve after sending one or more branches to the deep forearm extensor muscles, or from the branches to the deep muscles themselves. However they were split easily from the deep branch of the radial nerve and from the branches to the four deep forearm extensors proximally near to the emerging of the deep branch from the supinator muscle. Therefore, it was considered to be constant that the nerves to the four deep forearm extensors arose from the deep branch of the radial nerve after branching to the superficial forearm extensors. 2. The radial group of the deep forearm extensors (the abductor pollicis longus and the extensor pollicis brevis muscles) was innervated usually by one branch that arose from the deep branch of the radial nerve just after emerging from the supinator and giving off branches to the superficial forearm extensors. This branch ran on the dorsal (extensor) surface of the abductor pollicis longus muscle distally, sending many twigs to this muscle, and entered into the muscle at various distances from the origin (Figs. 1-6). The abductor pollicis brevis muscle was innervated by some twigs that ran usually inside but occasionally outside of the abductor pollicis longus muscle (Figs. 7-10).(ABSTRACT TRUNCATED AT 400 WORDS)     

Biometry of thenar muscle origins on the flexor retinaculum

The transverse carpal ligament (TCL), the main part of the flexor retinaculum, serves as an anchor for the thenar muscles: abductor pollicis brevis (APB), superficial head of the flexor pollicis brevis (sFPB), and opponens pollicis (OPP). Biomechanically, the thenar muscles rely on their TCL anchoring to transmit muscle contractions distally for thumb force and motion production, and reciprocally, muscle contraction interacts with the TCL at the proximal end through the origins. However, scarce knowledge exists regarding the distribution pattern of the thenar muscle origins. The purpose of this study was to understand the anatomical interface between the thenar muscles and TCL by examining the origin distributions of the individual muscles. Ten cadaveric specimens were dissected for digitization of the muscle origins and TCL volar surface. Digitized data were used for mesh reconstruction and calculation of surface areas and centroids. The origin areas for APB, sFPB, and OPP were 105.8 ± 30.3, 64.6 ± 15.2, and 245.9 ± 70.7 mm², respectively. The surface area of the TCL was 386.2 ± 86.9 mm². The origin areas of APB and OPP on the TCL were comparable, 18.4 ± 4.8% and 17.3 ± 9.6% of the TCL area, respectively. The origin locations for APB, sFPB, and OPP were in proximal-radial quadrant of the TCL, on distal aponeurosis outside the TCL, and around the ridge of trapezium, respectively. The knowledge of the anatomical interface provides a foundation for the understanding of biomechanical interactions between the muscles and ligaments and pathomechanical implications.     

An uncommon form of the rare extensor carpi radialis accessorius.

Two accessory muscles were found in the lateral compartment of the forearm while dissecting a 92-year-old female cadaver. One of these originated from the extensor carpi radialis brevis, became tendinous and travelled between the two radial extensor tendons. It inserted independently into the second metacarpal bone, and may be regarded as an extensor carpi radialis intermedius. The other accessory muscle originated from the extensor carpi radialis longus, passed superficially over the parent tendon and inserted into the abductor pollicis brevis. This variation appeared to be a rare extensor carpi radialis accessorius, an additional muscle, which usually arises from below the extensor carpi radialis longus and inserts into the first metacarpal bone. Various forms of the accessorius have been described previously, including one that inserts into the abductor pollicis brevis. The tendon of the accessory muscle described in this study passed through its own dorsal tunnel under the extensor retinaculum, making it an uncommon form of the rare accessorius.     

Static dynamometer for the measurement of multidirectional forces exerted by the thumb

The functioning of a static dynamometer designed to measure simultaneous forces exerted by the thumb in the vertical and horizontal axes is described. The analysis of the output signals by a desktop computer program provides information regarding the forces generated in eight directions covering a plane transverse to the thumb by 45° increments. In 12 normal female subjects, the maximum voluntary torques exerted at the trapezo-metacarpal joint of the thumb were examined and the muscle activation patterns of the interosseus, flexor pollicis brevis and adductor pollicis brevis muscles were recorded in one subject. Torques and muscle activation patterns were depicted using polar plots. Dynamometric data indicate that strength varies with direction and that higher torques are obtained in directions that bring the thumb towards the palm, i.e. flexion, adduction, combined flexion-adduction and extension-adduction. Patterns of muscle activity vary according to the direction evaluated suggesting that strength depends on the number of activated muscles as well as the relative force contribution of each muscle.     

足底内侧和外侧群肌的肌内神经整体分布模式及临床意义

目的 揭示足底内侧和外侧群肌的肌内神经整体分布模式,探讨其临床意义。 方法 24具成年尸体,完整取下足底内侧和外侧群肌,采用改良Sihler染色显示肌内神经分布模式。 结果 母收肌的神经支从肌止端的深面入肌,而 母展肌、母短屈肌、小趾展肌和小趾短屈肌的神经支常从肌起端的深面入肌。母展肌中有1个半月形和1个长方形的肌内神经密集区（INDR）;母收肌横头内有2个肾形INDRs,斜头内有1个肾形和1个长方形的INDR;母短屈肌、小趾展肌和小趾短屈肌内均有2个长方形的INDRs。这5块肌均可分为2个神经肌肉亚部,但各肌的INDR及其中心点在肌长上的百分位置不同。结论 上述结果可为外科手术免于神经损伤,肌移植的选材匹配,以及注射肉毒毒素A阻滞这些肌肉的痉挛提供形态学指导依据。     

Multiple variations in the region of Mm. extensores carpi radialis longus and brevis.

While dissecting the body of an 80-year-old female we observed multiple variations in the right region of Mm. extensores carpi radialis longus and brevis. The M. extensor carpi radialis longus gave origin to an accessory head. The tendon of this accessory head passed through a separate tunnel in the extensor retinaculum and inserted in the middle of the first metacarpal bone. Concerning its function, this accessory head of the M. extensor carpi radialis longus could be regarded as an additional abductor pollicis. The M. extensor carpi radialis brevis had an accessory tendon lying underneath the main tendon of this muscle. The accessory tendon joined with the main tendon just when undercrossing Mm. abductor pollicis longus and extensor pollicis brevis. Afterwards the tendon lay in the second tunnel of the extensor retinaculum and inserted in the base of the third metacarpal. In her lifetime the individual's tabatière probably must have been conspicuously pronounced at its radial margin.     

Biomechanical alterations in the carpal arch and hand muscles after carpal tunnel release: A further approach toward understanding the function of the flexor retinaculum and the cause of postoperative grip weakness

The difference between maximal and minimal distance covered (the distance between the trapezium ridge and hamate hook; moment exerted on structures: I Nm) by an intact flexor retinaculum (FR; minimum, 3.3 ± 0.1 cm; maximum, 3.7 ± 0.2 cm) and the increase in the maximal distance on carpal tunnel release (CTR; increase, 1.6 ± 0.2 mm) were significant. Under an external supination moment, the distance between the attachments of the trapeziopisiform band increased after CTR. Under external pronation and ulnar abduction moments, the distance between the attachments of the scaphoideohamate band increased after CTR. The CTR resulted in an anatomic attachment loss for the following muscles: the superficial head of the flexor pollicis brevis (shortening by ∼25%, relative to rest length), the ulnar part of the abductor pollicis brevis (with opposition and adductory functions, ∼20%), the opponens pollicis (∼20%), the middle part of the abductor pollicis brevis (∼7%), and the opponens digiti minimi (∼10%). Preoperative and postoperative (2–7 weeks after surgery) measurements of the reaction force of the distal phalanx (under isometric thumb opposition and finger II–IV flexion with extended carpal joint) led to differentiation of three groups: (1) significant strength loss—the patients showed difficulties with grasping, lifting, twisting off lids and caps, screwing, pulling ropes, and pinching; (2) no significant change in force values; and (3) a significant increase in strength (patients who could grip more firmly). © 1996 Wiley-Liss, Inc.     

A variation in the organization of abductor pollicis longus

The abductor pollicis longus (APL) muscle has been studied bilaterally in 50 cadavers. A variation in the organization of the muscle was found bilaterally in 15 of the 50 specimens. The novel muscular arrangement gives the appearance of being an additional muscle belly arising from the lateral aspect of the distal portion of the typical abductor pollicis longus muscle belly. This variation in the arrangement also creates a retinacular-like tunnel which encases the tendons of the extensor carpi radialis longus and the extensor carpi radialis brevis muscles. To the authors' knowledge, this arrangement has not been cited in the recent medical literature. An understanding of this unusual finding may be clinically relevant in describing the dorso-lateral compartment of the distal forearm. © 1996 Wiley-Liss, Inc.     

A dynamic model of the hand with application in functional neuromuscular stimulation

Potential hand function in people with tetraplegia was evaluated using a three-dimensional dynamic mathematical model. The model was used to evaluate hand positioning, grasp force, and the outcome of surgeries such as tendon transfers and joint fusion, in situations typical of those encountered when using functional neuromuscular stimulation to restore function in people with tetraplegia. In the model, the hand is treated as a jointed multibody system. Each joint is subjected to muscle moments, passive joint moment, and moments due to grasp forces. Model simulations showed that function was highly dependent on both muscle strength and joint passive moments. The potential for tendon transfers, such as the Zancolli-lasso and intrinsic-plasty, to improve hand function was demonstrated, but their value is subject-dependent. It was also shown that activation of multiple thumb muscles (adductor pollicis, abductor pollicis brevis, and flexor pollicis longus) without interphalangeal joint fusion can provide convenient lateral pinch posture with ∼70% more grip force than a currently used method, which includes joint fusion but requires only one muscle. Finally, a grasp protocol was introduced and shown successful in palmar grasp and hold of movable cylindrical objects using only extrinsic muscles, provided the fingers could be extended sufficiently to enclose the object.     

用于显露前臂骨间膜的桡骨背侧入路应用解剖

目的 找出显露前臂骨间膜的最佳入路.方法 用卡尺测量了30例成人上肢,测量项目如下:桡骨头至旋后肌腱弓处骨间背神经的长度(LHA);桡骨头到旋后肌管下口之间骨间背神经的长度(LHS);骨间背神经从旋后肌管下口至桡骨外缘的距离(DSR);骨间背神经从旋后肌管下口至尺骨内缘的距离(DSU);骨间背神经最外侧分支穿拇长展肌处至桡骨外缘的距离(DSP).结果 LHA、LHS、DSR、DSU和DSP的测量结果分别为19.3±4.4mm(11mm～29mm)、53.4±5.2mm(45mm～62mm)、9.7±3.1mm(4mm～15mm)、22.8±3.5mm(20mm～28mm)和7.5±1.6mm(5mm～9mm).牵开拇长展肌、拇短伸肌和拇长伸肌,于桡侧腕短伸肌与指伸肌之间显露前臂骨间膜中1/3和远1/3段.结论 桡骨背侧入路可较少剥离肌肉和软组织,能方便、安全显露前臂骨间膜中1/3和远1/3段.