Fatigue-induced glenohumeral and scapulothoracic kinematic variability: Implications for subacromial space reduction

Superior humeral head translation and scapula reorientation can reduce the subacromial space. While these kinematic abnormalities exist in injured populations, the effect of muscle fatigue is unclear. Additionally, these mechanisms were typically studied independently, thereby neglecting potential covariance. This research evaluated the influence of upper extremity muscle fatigue on glenohumeral and scapulothoracic kinematics and defined their relationship. Radiography and motion tracking systems captured these kinematic relationships, during scapula plane elevation, both before and after fatigue. Fatigue-induced changes in humeral head position, scapular orientation and the minimum subacromial space width were measured. High inter-subject variability existed for each measure which precluded identification of mean differences at the population level. However, significant scapular upward rotation occurred following fatigue (p = 0.0002). Despite similar population mean results, between 39% and 57% of participants exhibited fatigue-related changes in disadvantageous orientations. Additionally, correlations between measures were generally fair (0.21–0.40) and highly dependent on elevation, likely attributed to the variable fatigue responses. Overall, the data confirms that fatigue-induced changes in kinematics poses highly variable risk of subacromial impingement syndrome across individuals. Thus, solely considering the “average” or mean population response likely underestimates potentially injurious fatigue consequences.     

Altered activity of the serratus anterior during unilateral arm elevation in patients with cervical disorders

Altered activity in the axioscapular muscles is considered to be an important feature in patients with neck pain. The activity of the serratus anterior (SA) and trapezius muscles during arm elevation has not been investigated in these patients. The objectives of this study was to investigate whether there is a pattern of altered activity in the SA and trapezius in patients with insidious onset neck pain (IONP) (n = 22) and whiplash associated disorders (WAD) (n = 27). An asymptomatic group was selected for baseline measurements (n = 23).Surface electromyography was used to measure the onset of muscle activation and duration of muscle activity of the SA as well as the upper, middle, and lower trapezius during unilateral arm elevation in the three subject groups. Both arms were tested.With no interaction, the main effect for the onset of muscle activation and duration of muscle activity for serratus anterior was statistically significant among the groups. Post hoc comparison revealed a significantly delayed onset of muscle activation and less duration of muscle activity in the IONP group, and in the WAD group compared to the asymptomatic group. There were no group main effects or interaction effects for upper, middle and lower trapezius.This finding may have implications for scapular stability in these patients because the altered activity in the SA may reflect inconsistent or poorly coordinated muscle activation that may reduce the quality of neuromuscular performance and induce an increased load on the cervical and the thoracic spine.     

Convergences in Scapula Morphology among Small Cursorial Mammals: An Osteological Correlate for Locomotory Specialization

Small cursorial mammals, such as lagomorphs, elephant shrews, and the more cursorial caviomorph rodents, share both the similar locomotor gait of rapid half-bounding and a similar scapula anatomy of a long, slender, caudally projecting metacromion process. This scapular morphology is also present in some notoungulates (extinct endemic South American ungulates), in rabbit-like taxa such as Propachyruchos. In the rabbit Oryctolagus this elongated metacromion process serves to increase the moment arm of the acromiotrapezius and levator scapulae ventralis muscles, which we propose may aid in scapula stabilization and resisting ground reaction forces during the landing phase onto a single forelimb in half-bounding. A long, slender metacromion process is thus an osteological correlate of locomotor specialization, that of rapid half-bounding in small to medium-sized mammals.     

3D reconstructions of quail–chick chimeras provide a new fate map of the avian scapula

Limbed vertebrates have functionally integrated postcranial axial and appendicular systems derived from two distinct populations of embryonic mesoderm. The axial skeletal elements arise from the paraxial somites, the appendicular skeleton and sternum arise from the somatic lateral plate mesoderm, and all of the muscles for both systems arise from the somites. Recent studies in amniotes demonstrate that the scapula has a mixed mesodermal origin. Here we determine the relative contribution of somitic and lateral plate mesoderm to the avian scapula from quail-chick chimeras. We generate 3D reconstructions of the grafted tissue in the host revealing a very different distribution of somitic cells in the scapula than previously reported. This novel 3D visualization of the cryptic border between somitic and lateral plate populations reveals the dynamics of musculoskeletal morphogenesis and demonstrates the importance of 3D visualization of chimera data. Reconstructions of chimeras make clear three significant contrasts with existing models of scapular development. First, the majority of the avian scapula is lateral plate derived and the somitic contribution to the scapular blade is significantly smaller than in previous models. Second, the segmentation of the somitic component of the blade is partially lost; and third, there are striking differences in growth rates between different tissues derived from the same somites that contribute to the structures of the cervical thoracic transition, including the scapula. These data call for the reassessment of theories on the development, homology, and evolution of the vertebrate scapula.     

The effect of EMG biofeedback training on muscle activation in an impingement population

Subacromial impingement syndrome (SAIS) is one of the most diagnosed causes of pain in the upper extremity. The purpose of this study was to investigate muscle activity between asymptomatic and SAIS shoulders on the same subject while understanding the effectiveness of EMG biofeedback training (EBFB) on bilateral overhead movements. Ten participants (7 male), that tested positive for 2/3 SAIS clinical tests, volunteered for the study. Bilateral muscle activity was measured via electrodes on the upper trapezius (UT), lower trapezius (LT), serratus anterior (SA), and lumbar paraspinals (LP). Participants performed bilateral scapular plane overhead movements before and after EBFB. EBFB consisted of 10 bilateral repetitions of I, W, T, and Y exercises focused on reducing UT and increasing LT and SA activity. Prior to EBFB, no significant difference in muscle activity was present between sides. A significant main effect of time indicated that after EBFB both sides exhibited reduced UT activity at 60° (p = 0.003) and 90° (p = 0.036), LT activity was increased at all measured humeral angles (p < 0.0005), and SA muscle activity was increased at 110° (p = 0.001). EBFB in conjunction with scapular based exercise effectively alters muscle activity of asymptomatic and symptomatic scapular musculature.     

Measurement of Dynamic Scapular Kinematics Using an Acromion Marker Cluster to Minimize Skin Movement Artifact

The measurement of dynamic scapular kinematics is complex due to the sliding nature of the scapula beneath the skin surface. The aim of the study was to clearly describe the acromion marker cluster (AMC) method of determining scapular kinematics when using a passive marker motion capture system, with consideration for the sources of error which could affect the validity and reliability of measurements. The AMC method involves placing a cluster of markers over the posterior acromion, and through calibration of anatomical landmarks with respect to the marker cluster it is possible to obtain valid measurements of scapular kinematics. The reliability of the method was examined between two days in a group of 15 healthy individuals (aged 19-38 years, eight males) as they performed arm elevation, to 120°, and lowering in the frontal, scapular and sagittal planes. Results showed that between-day reliability was good for upward scapular rotation (Coefficient of Multiple Correlation; CMC = 0.92) and posterior tilt (CMC = 0.70) but fair for internal rotation (CMC = 0.53) during the arm elevation phase. The waveform error was lower for upward rotation (2.7° to 4.4°) and posterior tilt (1.3° to 2.8°), compared to internal rotation (5.4° to 7.3°). The reliability during the lowering phase was comparable to results observed during the elevation phase. If the protocol outlined in this study is adhered to, the AMC provides a reliable measurement of upward rotation and posterior tilt during the elevation and lowering phases of arm movement.     

肩胛骨性别的判别分析

就青岛出土已知性别成年肩胛骨84例(男66,女18)进行了12项测量,从中挑选出肩胛形态宽(X1),肩胛宽(X2),肩胛冈长(X3)和关节盂长(X4)四个变量,按Fisher法进行判别分析,其中有五种组合方式其判别率均在92.9％以上,而X3与X4两因素判别率最优,高达97.62％。此法简便,准确,具有较高的实用价值。     

对华南地区男性成年颅骨、锁骨、肩胛骨和髋骨与身高关系的研究

作者对近年在华南地区收集的70具成年男性完整骸骨的颅围、锁骨最大长、肩胛骨形态宽及髋骨最大长进行了测量。相关分析表明,各测量项目与身高的相关系数均有非常显著的意义(p<0.01)。进而建立了相应的回归方程。用70例已知生前身高的国人骸骨对这些回归方程进行了检验。结果表明,本文所建立的这些回归方程均有一定的实用价值。     

The role of Emx2 during scapula formation

The scapula is subdivided into head, collum, and blade. Due to the expression pattern of Emx2 and the absence of the scapula blade in Emx2 knockout mice, it has been suggested that Emx2 is involved in the formation of the scapula. Micromanipulation experiments revealed that ectoderm ablation over the somites does not affect Emx2 expression but inhibits the formation of the scapula blade indicating that Emx2 is not sufficient to induce scapula blade formation. Furthermore, we show that the formation of the scapula head is dependent, scapula blade formation independent of FGFR-1-mediated signaling. Overexpression of Emx2 does not influence scapula blade formation but leads to the development of an additional posterior digit in the anterior border of the limb. Taken together, the data presented implicate that Emx2 expression is necessary but not sufficient for the development of the scapula blade. It is not a marker for scapula development but rather provides positional information along the proximodistal and anterior-posterior limb axes, whereas the specificity of the developing skeletal elements is determined by the concerted interaction of Emx2 with other factors.