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.     

Growth in the larval zebrafish pectoral fin and trunk musculature.

After initial patterning, muscle in the trunk and fins of teleosts grows extensively. Here, we describe muscle growth in zebrafish, with emphasis on the pectoral fin musculature. In the trunk, slow muscle fibers differentiate first. In contrast, slow muscle does not appear in the pectoral fin until the beginning of the juvenile period. Mosaic hyperplasia contributes to trunk muscle growth, and new fibers are apparent within the muscle as early as 6 mm standard length. In the pectoral fin muscle, mosaic hyperplasia is not evident at any examined stage. Instead, the predominant mode of hyperplasia is stratified. In larval pectoral fin muscle new fibers appear subjacent to the skin, and this correlates with the expression of myogenic genes such as muscle regulatory factors and Pax7. Our results suggest that regulation of fiber type development and muscle growth may differ in the pectoral fin and trunk.     

Translation and rotation movements of the mandible during mouth opening and closing

To assess the relative contribution of rotation and translation of the temporomandibular condyle‐disc assembly during opening and closing movements, free movements of maximum mouth opening and closing were recorded in healthy subjects (12 men, 14 women) using an optoelectronic three‐dimensional motion analyzer. For each subject, the displacement of the lower interincisal point, the path of the condylar reference point, the degree of rotation around the three orthogonal rotational axes, and the relative contribution of translation and rotation were calculated during all movement of mouth opening and closing. The distance covered by the interincisor point and the rotational angle about the transverse axis at maximum mouth opening were larger in men than in women, but the difference cancelled after correcting for mandibular radius in the sagittal plane; mandibular rotation was always larger than translation, but never approaching 100%; opening and closing translations were similar within sex, but their paths were longer in men than in women (P < 0.05); rotational angles around vertical and sagittal axes were negligible; the linear correlation between maximum mandibular opening and condylar translation was minor and not significant. In normal subjects, mouth opening and closing as modeled at the interincisor point was determined more by mandibular rotation than by translation, but in no occasion a pure rotation was found. The percentage rotation was not identical during mouth opening and closing; female and male paths were not totally coincident; no correlation between maximum mandibular opening and condylar translation was found. Clin. Anat. 22:311–318, 2009. © 2009 Wiley‐Liss, Inc.     

The effect of humeral torsion on rotational range of motion in the shoulder and throwing performance

Several recent studies have found that throwing athletes typically have lower humeral torsion (retroversion) and a greater range of external rotation at the shoulder than non-athletes. How these two parameters are related is debated. This study uses data from a sample of both throwers and non-throwers to test a new model that predicts torsion values from a range of motion data. The model proposes a series of predicted regressions which can help provide new insight into the factors affecting rotational range of motion at the shoulder. Humeral torsion angles were measured from computed tomography scans collected from 25 male subjects. These values are compared to predicted torsion values for the same subjects calculated from both kinematic and goniometric range-of-motion data. Results show that humeral torsion is negatively correlated (goniometric: r = -0.409, P = 0.047; kinematic: r = -0.442, P = 0.035) with external rotational range of motion and positively correlated (goniometric: r = 0.741, P < 0.001; kinematic: r = 0.559, P = 0.006) with internal rotational range of motion. The predicted torsion values are highly correlated (goniometric: r = 0.815, P < 0.001; kinematic: r = 0.617, P = 0.006) with actual torsion values. Deviations in the data away from predicted equations highlight significant differences between high torsion and low torsion individuals that may have significant functional consequences. The method described here may be useful for non-invasively assessing the degree of torsion in studies of the evolution and biomechanics of the shoulder and arm, and for testing hypotheses about the etiology of repetitive stress injuries among athletes and others who throw frequently.     

Insertion of the pectoralis major into the shoulder joint capsule

The pectoralis major muscle is subject to various morphologies. One presumably very rare variation is insertion of this muscle into the shoulder joint. During the routine dissection of the right upper extremity of an adult male cadaver a distinct separate tendinous insertion into the shoulder joint capsule was identified. This vertical tendon (7 mm×6 cm) traveled just lateral to the long head of the biceps brachii muscle and terminated into the fibrous aspect of the joint capsule without penetrating it. Mechanical traction on the humeral attachment of the pectoralis major resulted in anteroinferior displacement of the shoulder joint capsule. The possible embryologic origin of this variation is discussed. Clinicians may wish to consider potential attachment of the pectoralis major into the capsule of the shoulder joint in diagnosing pathology of this region.     

Hind foot drumming: Volumetric micro-computed tomography investigation of the hind limb musculature of three African mole-rat species (Bathyergidae)

Several species of African mole-rats use seismic signalling by means of hind foot drumming for communication. The present study aimed to create three-dimensional reconstructions and compare volumetric measurements of 27 muscles of the hind limb of two drumming (Georychus capensis and Bathyergus suillus) and one non-drumming (Cryptomys hottentotus natalensis) species of African mole-rats. Diffusible iodine contrast-enhanced micro-computed tomography (diceCT) scans were performed on six specimens per species. Manual segmentation of the scans using VGMAX Studio imaging software allowed for individual muscles to be separated while automatically determining the volume of each muscle. The volume of the individual muscles was expressed as a percentage of the total hind limb volume and statistically compared between species. Subsequently, three-dimensional reconstructions of these muscles were created. Musculus gracilis anticus had a significantly larger percentage of the total hind limb muscle volume in both drumming species compared to the non-drumming C. h. natalensis. Furthermore, several hip and knee extensors, namely mm. gluteus superficialis, semimembranosus, gluteofemoralis, rectus femoris and vastus lateralis, had significantly larger muscle volume percentages in the two drumming species (G. capensis and B. suillus) compared to the non-drumming species. While not statistically significant, G. capensis had larger muscle volume percentages in several key hip and knee extensors compared to B. suillus. Additionally, G capensis had the largest summed percentage of the total hind limb volume in the hip flexor, hip extensor, knee extensor and ankle plantar flexor muscle groups in all the three species. This could be indicative of whole muscle hypertrophy in these muscles due to fast eccentric contractions that occur during hind foot drumming. However, significantly larger muscle volume percentages were observed in the scratch digging B. suillus compared to the other two chisel tooth digging species. Moreover, while not statistically significant, B. suillus had larger muscle volume percentages in several hip extensor and knee flexor muscles compared to G. capensis (except for m. vastus lateralis). These differences could be due to the large relative size of this species but could also be influenced by the scratch digging strategy employed by B. suillus. Therefore, while the action of hind foot drumming seems to influence certain key muscle volumes, digging strategy and body size may also play a role.     

Significance of the latissimus dorsi for shoulder instability. II. Its influence on dislocation behavior in a sequential cutting protocol of the glenohumeral capsule

In a cadaveric instability model that leaves all muscles intact initially, the latissimus dorsi seemed to play a role when complete section of the glenohumeral capsuloligamentous structures did not result in a locked anteroinferior dislocation. The present study was carried out to determine whether the latissimus dorsi does truly affect dislocation in a modified cutting protocol, and to find an anatomic explanation for this apparent behavior. This article (Part II) details the results of a sequential cutting study and relates these results with the anatomic findings of Part I. In 75 shoulders, the influence of the latissimus dorsi on dislocation behavior in the apprehension position after section of all capsuloligamentous structures was examined. After cutting all capsuloligamentous structures, either on the glenoid or on the humeral side, the tendon of either the latissimus dorsi or the subscapularis was cut. Capsular lesions on the glenoid side (20 shoulders) resulted in a locked dislocation in 16 specimens. In the other four shoulders, there was a metastable dislocation after cutting the entire capsule, which did not change after cutting either tendon. With lesions on the humeral side (55 shoulders), three possibilities arose: metastable (17 shoulders), locked anterior (9 shoulders) or locked anteroinferior (29 shoulders) dislocation. This difference in dislocation behavior was related to the variability of the tendon-cartilage distance (TCD) and the type of scapular connection of the latissimus dorsi. A locked anteroinferior dislocation was always observed when the TCD was more than 20 mm, regardless of the type of scapular connection. With a TCD < 20 mm, a metastable dislocation was the result when there was a type 1 scapular connection and a locked anterior dislocation was seen when there was a type 2 scapular connection. The tendon of the latissimus dorsi can restrain the humeral head from dropping inferiorly or can lead to a spontaneous reduction of a dislocation, depending on its anatomy. This effect can only take place in the infrequent situation of humeral avulsion of the glenohumeral ligaments. This may be an explanation for the relative paucity of these lesions in clinical instability series.     

Muscle coactivation before and after the impact phase of running following isokinetic fatigue

Context:

The effects of fatigue on impact loading during running are unclear, with some authors reporting increased impact forces and others reporting decreased forces.

Objective:

To examine the effects of isokinetic fatigue on muscle cocontraction ratios about the knee and ankle during running.

Design:

Cross-sectional study.

Setting:

Neuromechanics laboratory.

Patients or Other Participants:

Female middle-distance runners (age  =  21.3 ± 1.93 years) with at least 5 years of training experience.

Intervention(s):

Participants ran on the treadmill at 3.61 m/s before and immediately after the fatigue protocol, which consisted of consecutive, concentric knee extension-flexion at 120°/s until they could no longer produce 30% of the maximum knee-extension moment achieved in the familiarization session for 3 consecutive repetitions.

Main Outcome Measure(s):

Electromyographic (EMG) amplitude of the vastus medialis (VM), biceps femoris (BF), gastrocnemius (GAS), and tibialis anterior (TA) was recorded using surface electrodes. Agonist∶antagonist EMG ratios for the knee (VM∶BF) and ankle (GAS∶TA) were calculated for the preactivation (PR), initial loading response (LR₁), and late loading response (LR₂) phases of running. Hip-, knee-, and ankle-joint angular displacements at initial foot contact were obtained from 3-dimensional kinematic tracings.

Results:

Fatigue did not alter the VM∶BF EMG ratio during the PR phase (P > .05), but it increased the ratio during the LR₁ phase (P < .05). The GAS∶TA EMG ratio increased during the LR₁ phase after fatigue (P < .05) but remained unchanged during the PR and LR₂ phrases (P > .05).

Conclusions:

The increased agonist EMG activation, coupled with reduced antagonist EMG activation after impact, indicates that the acute decrease in muscle strength capacity of the knee extensors and flexors results in altered muscle-activation patterns about the knee and ankle before and after foot impact.     

肩关节外侧三角肌及深部血管神经的解剖观测

目的 了解肩关节囊外侧三角肌形态及其深面的血管神经的走向及分布,为肩关节及其周围手术入路提供解剖学依据。方法 对30具成人尸体60侧上肢标本进行解剖观测。结果1.三角肌起点弧长(22.5±3.9)cm,中线长(15.2±2.3)cm;2.腋神经前支长(2.9±0.7)cm,其分支主要分布支配三角肌前部和外侧部;3.腋神经前支与肩峰至三角肌粗隆连线之交点位于肩峰平面下方(6.1±1.3)cm。结论肩关节及周围手术时,其手术切口和分离三角肌纤维的远侧点不应超过上述范围,以防止损伤腋神经前支。     

Anomalous stabilizing action of Ca on sphincter smooth muscle of the rat iris

This paper concerns the first measurement of spontaneous electrical activity in the smooth muscle cells of the mammalian iris sphincter. Although the membrane potential was quite stable, at –59 mV, under physiological conditions in vitro, bursts of rhythmic electrical activity occurred when barium was substituted for all of the calcium in the medium (Ba-Krebs' solution). These bursts consisted initially of spike potentials, but these were followed by a long-lasting depolarization. Although the amplitude of the spike potentials did not decrease even when the external Na concentration was lowered to 25 mM, addition of a small amount of Ca (>0.3 mM) to the Ba-Krebs' depressed the rhythmic contractions which followed the cessation of the spike potentials. Strontium also depressed the rhythmicity but to a lesser extent. These results show that the smooth muscle of the rat iris sphincter has an ability to generate spike potentials, and that the properties of the latter differ from those observed in other smooth muscles; i.e. the activity is suppressed by Ca ions at far lower concentrations than those in the physiological enviroment. This anomalous effect is presumably due to the stabilizing action of Ca.     

The evolution of bite force in horned lizards: the influence of dietary specialization

Dietary specialization is an important driver of the morphology and performance of the feeding system in many organisms, yet the evolution of phenotypic specialization has only rarely been examined within a species complex. Horned lizards are considered primarily myrmecophagous (ant eating), but variation in diet among the 17 species of horned lizards (Phrynosoma) makes them an ideal group to examine the relationship between dietary specialization and the resultant morphological and functional changes of the feeding system. In this study, we perform a detailed analysis of the jaw adductor musculature and use a biomechanical model validated with in vivo bite force data to examine the evolution of bite force in Phrynosoma. Our model simulations demonstrate that bite force varies predictably with respect to the gape angle and bite position along the tooth row, with maximal bite forces being attained at lower gape angles and at the posterior tooth positions. Maximal bite forces vary considerably among horned lizards, with highly myrmecophagous species exhibiting very low bite forces. In contrast, members of the short‐horned lizard clade are able to bite considerably harder than even closely related dietary generalists. This group appears to be built for performing crushing bites and may represent a divergent morphology adapted for eating hard prey items. The evolutionary loss of processing morphology (teeth, jaw and muscle reduction) and bite force in ant specialists may be a response to the lack of prey processing rather than a functional adaptation per se.     

老年人左、右手喝水动作的运动特性研究

目的通过采集和分析人体三维运动数据,研究老年人左、右手喝水动作的运动学特性。分析左、右手动作的差异,为镜像康复设备的设计和精准康复训练方案的制定提供数据支持和理论基础。方法选取16名右利手的老年人为实验对象,实验对象分别用左、右手完成喝水动作。应用运动捕捉系统采集实验者上肢的三维运动轨迹,分析实验对象在喝水动作中,左、右肩、肘、腕关节的三维运动角度和角速度的相关性。结果左、右手在肩关节的矢状轴角度、肘关节的屈伸角度、肩关节的旋内旋外角度、肘关节旋内旋外的角度上具有高度相关性(相关系数r0.8);在肩关节冠状轴的角度、腕关节掌屈背伸的角速度上具有低度相关性(0.3r0.5);在肩关节冠状轴的角速度上具有微弱相关性(0.1r0.3);在其余上肢的关节角度和角速度上具有显著相关性(0.5r0.8)。结论健康老年人在完成喝水动作中,主要利用肩关节的旋内旋外活动和肘关节的屈伸、旋内旋外活动。右手在关节屈伸角度的运动幅度上大于左手,而在关节旋内旋外角度的运动幅度方面小于左手。在镜像康复机器人设计和康复轨迹规划中,应尊重左、右手的差异,实现精准康复的目的。     

电子镇痛仪电信号传导机制模型建立与分析

目的:分析电子镇痛仪电流信号在手臂肌肉内的信号传导情况,为电刺激镇痛提供理论依据。方法:结合人体解剖学与组织结构学,在COMSOL Multiphysics 5.5有限元仿真软件中,利用圆台、圆柱、椭球为几何实体,建立电子镇痛仪数值仿真有限元模型。在频域环境下,通过注入载波信号分别为100 kHz、1 MHz、10 MHz,幅度为±20 mA的电流信号,以此分析信号在手臂中的传播机制。结果:随着载波频率的不断增加,集肤效应越来越明显,信号在电极接触处皮肤部分越来越集中,容积导体内部的扩散性也将失去一致性。在100 kHz时,随着离电极中心的通信距离逐渐增加,信号在手臂内部信号扩散变得越来越均匀。结论:在电子镇痛仪实施肌肉酸痛治疗过程中,通信频率越高,信号越难以进入机体内部,信号一致性越差。因此,在实施电流镇痛过程中,信号电极应尽量布置在镇痛靶向区域附近。     

Superficial brachial artery crossing over the ulnar and median nerves from posterior to anterior: Embryological significance

A rare variation of the superficial brachial artery was found in the right arm of an 82-year-old male cadaver in student dissection practice. In this case, the axillary artery passed normally between the medial and lateral roots of the median nerve and then bifurcated into a large superficial brachial artery and the deep brachial artery (A. brachialis profunda). The superficial brachial artery passed medially to the ulnar nerve and then crossed over to take a lateral course to the median nerve at the midpoint of the upper arm. It finally divided into the radial and ulnar arteries at the cubital fossa. The deep brachial artery terminated as the inferior ulnar collateral artery. These findings indicate that the present variant was a well-developed medial type of the superficial brachial artery that gave off the ulnar and radial arteries. The anatomical and embryological significance of the findings are discussed.     

Distribution of recurrent inhibition in the human upper limb

The distribution of homonymous and heteronymous recurrent inhibition among the motor nuclei innervating the main muscles of the human upper limb has been investigated in 25 healthy subjects. Homonymous recurrent inhibition was studied with a specially designed electrophysiological method with paired H-reflexes, previously described by Bussel & Pierrot-Deseilligny (1977), combined with a pharmacological study using a cholinergic agonist, the l -acetylcarnitine (Rossi & Mazzocchio 1991). These methods were used to investigate the Flexor Carpi Radialis (FCR), Extensor Carpi Radialis (ECR), Opponens Pollicis (OP) and Abductor Digiti Minimi (ADM) motor nuclei. In the Deltoid, Triceps, Flexor Carpi Ulnaris (FCU) and Extensor Carpi Ulnaris (ECU) motor nuclei in which it was impossible to evoke clearly distinguishable H-reflexes, homonymous recurrent inhibition was studied with the PSTH technique: homonymous recurrent inhibition was found in Deltoid, Triceps, FCR, FCU, ECR, ECU motor nuclei but not in OP and ADM motor nuclei. Heteronymous recurrent inhibition was studied with the PSTH technique in the Deltoid, Biceps, Triceps, FCR, ECR, FCU, ECU, Flexor Digitorum Communis (FDC), Extensor Digitorum Communis (EDC) motor nuclei as well as those innervating the intrinsic muscles of the hand. The following results were obtained: (1) motor neurones innervating muscles acting at digits do not receive any heteronymous recurrent inhibition; (2) motor neurones innervating muscles acting at the wrist give recurrent inhibition to motor nuclei of proximal muscles but do not receive any recurrent projections from the latter; and (3) motor neurones innervating proximal muscles (acting at shoulder or elbow) are interconnected by recurrent inhibition and receive heteronymous recurrent projections from some wrist muscles but not from intrinsic hand muscles.     

小儿上肢动脉干的测量分析

采用从初生到身长为150cm的重尸180具,分为六个组.分别测量了小儿上肢动脉干各段的长度和起始部外径,经统计学分析处理,初步得出从初生到青春前期各生长发育时期小儿的上肢动脉干长度和外径的系统资料,填补了有关方面的空白.其结果表明:1.小儿上肢动脉干的长度和外径随年龄增长而增加,组间差有显著性意义,并与成人资料相衔接,2.两侧锁骨下动脉长度和外径的均数存在侧差,左侧锁骨下动脉较右侧锁下动脉长(左:右=1 .25:1),较右侧锁骨下动脉稍细(左.右=1:1.04);3. 左、右两侧腋动脉、肱动脉、桡动脉和尺动脉的长度和外径均数相差无几,t检验无显著位差异,两侧基本对称.     

Subchondral Bone Radiodensity Patterns in the Glenoid Fossa of Ape and Human Scapulae

Regions of denser subchondral bone deep to a joint's articular surface indicate locations where the joint experiences relatively higher or more frequent compressive trans‐articular forces than less dense regions. Human clinically focused studies have hypothesized that regional variation of acquired with computed tomography osteoabsorptiomety (CT‐OAM), in the scapular glenoid fossa (GF) is specifically related to forces arising from everyday rotator cuff muscle function. We test this hypothesis by investigating the relationship between rotator cuff function and GF HiRD subchondral bone patterns in a broader comparative context. CT‐OAM was used on scapulae of chimpanzees, gibbons and humans to visualize HiRD subchondral bone patterns and assess regional (anterior–posterior; superior–inferior) differences in HiRD concentrations within each group. Like patterns observed in humans, ape GFs show HiRD concentrations in anterior, posterior and superior regions. Gibbons exhibit significantly larger concentrations anteriorly, probably serving as a skeletal correlate of increased subscapularis activity during humeral internal rotation during arm‐swinging locomotion. Chimpanzees exhibit relatively larger areas posteriorly (though not statistically significant), conceivably serving as a correlate of increased infraspinatus activity during humeral external rotation and retraction during knuckle‐walking. All groups show relatively larger HiRD areas superiorly, likely correlating with forceful humeral abduction (rather than adduction) during routine upper limb use across behaviors. Subchondral bone HiRD patterns in the GF appear to correspond with normal and unbalanced rotator cuff activity and force production not only in humans, but also in other primates, thereby corroborating their value in human clinical studies and functional morphology research. Anat Rec, 301:776–785, 2018. © 2017 Wiley Periodicals, Inc.     

Movements of the elbow and shoulder during pronation of the forearm

It is known that medial and lateral movements of the lower end of the ulna occur during pronation and supination of the forearm, but there is little clear evidence as to where these movements originate. Twenty normal subjects pronated their forearm about either an undefined, lateral, or medial axis. Measurements were made from paired photographs taken at increments of 45° during the movement. Abduction of the ulna always occurred but its magnitude did not vary significantly with differing axes of pronation. During pronation about an undefined axis the abduction at the elbow produced a lateral movement of the ulna which was usually appropriate for the axis of pronation in use. Medial or lateral rotation of the humerus was used to increase or decrease the amount of lateral movement of the lower end of the ulna to suit the requirements of pronation about a medial or lateral axis.     

Morphology of the Upper Esophageal Sphincter or Cricopharyngeus Muscle Revisited

Histological examination of specimens from 22 donated elderly cadavers and 15 human fetuses revealed that the cricopharyngeus muscle (CPM) provided (1) posterior circular muscle fibers adjacent to the external aspect of the uppermost esophageal circular muscle and (2) a thin anterior sling connecting to that same muscle. Another thick lateral bundle of longitudinal muscle originated independently from a fascia covering the posterior cricoarytenoideus muscle, extended laterally and posteriorly, and occupied a space after the CPM had disappeared at the anterolateral angle of the esophagus below the cricoid. The thick fascia contained abundant elastic fibers along the internal surface of the pharyngeal constrictors (posteromedial elastic lamina), but was interrupted or discontinued near the cricoid origin of the CPM. As no submucosal smooth muscles or elastic fibers were connected to it, the CPM did not accompany a specific elastic structure at the interface between the pharyngeal and esophageal muscles. In fetuses, the medial half of the CPM was inserted into the cricoid while the lateral half continued to the sternothyroideus muscle or ended at a fascia covering the cricothyroideus. These anterolateral ends provided a mechanical load for longitudinal growth of the pharyngeal constrictors. Consequently, the CPM was unlikely to develop and grow to form the upper esophageal sphincter, and the muscle bundle crossing the lateral aspect of the pharyngo-esophageal junction appeared to have a secondary passive role as a sphincter. This situation contrasts with that of another sphincter in the human body formed from striated muscle. Clin. Anat., 33:782–794, 2020. © 2019 Wiley Periodicals, Inc.