High-frequency Quantitative Ultrasound Imaging of Human Rotator Cuff Muscles: Assessment of Repeatability and Reproducibility.

This study evaluated the repeatability and reproducibility of using high-frequency quantitative ultrasound (QUS) measurement of backscatter coefficient (BSC), grayscale analysis, and gray-level co-occurrence matrix (GLCM) textural analysis, to characterize human rotator cuff muscles. The effects of varying scanner settings across two different operators and two US systems were investigated in a healthy volunteer with normal rotator cuff muscles and a patient with chronic massive rotator cuff injury and substantial muscle degeneration. The results suggest that BSC is a promising method for assessing rotator cuff muscles in both control and pathological subjects, even when operators were free to adjust system settings (depth, level of focus, and time-gain compensation). Measurements were repeatable and reproducible across the different operators and ultrasound imaging platforms. In contrast, grayscale and GLCM analyses were found to be less reliable in this setting, with significant measurement variability. Overall, the repeatability and reproducibility measurements of BSC indicate its potential as a diagnostic tool for rotator cuff muscle evaluation.

Three-dimensional evaluation of the transverse rotator cuff muscle's resultant force angle in relation to scapulohumeral subluxation and glenoid vault morphology in nonpathological shoulders.

BACKGROUND: Static posterior subluxation of the humeral head (SPSH) results in glenohumeral osteoarthritis. Treatment strategies for SPSH with or without resulting osteoarthritis remain challenging. There is growing interest in evaluating the rotator cuff muscle volume, fatty infiltration, or forces in osteoarthritic shoulders with SPSH, mainly due to a possible transverse force imbalance. In nonpathological shoulders, the transverse angle of the rotator cuff muscle's resultant force may be associated with scapulohumeral alignment and glenoid vault morphology, despite an assumed transverse force balance. The purpose of this study was to assess the transverse rotator cuff muscle's resultant force angle (TRFA) and its relationship with the scapulohumeral subluxation index (SHSI) and selected glenoid vault parameters using computer modeling. METHODS: Computed tomography scans of 55 trauma patients (age 31 ± 13 years, 36 males) with nonpathological shoulders were analyzed and all measurements performed in 3-dimension. We placed landmarks manually to determine the humeral head center and the rotator cuff tendon footprints. The contours of the rotator cuff muscle cross-sectional areas were automatically predicted in a plane perpendicular to the scapula. Each rotator cuff muscle was divided into virtual vector fibers with homogeneous density. The resultant force vector direction for each muscle, corresponding to the rotator cuff action line, was calculated by vectorially summing the normalized fiber vectors for each muscle, weighted by the muscle trophic ratio. The resultant force vector was projected on the axial plane, and its angle with the mediolateral scapular axis was used to determine TRFA. The SHSI according to Walch, glenoid version angle (GVA), glenoid anteroposterior offset angle (GOA), glenoid depth, glenoid width, and glenoid radius were also evaluated. RESULTS: The mean values for TRFA, SHSI, GVA, GOA, glenoid depth, glenoid width, and glenoid radius were 7.4 ± 4.5°, 54.3 ± 4.8%, -4.1 ± 4.4°, 5.1 ± 10.8°, 3.3 ± 0.6 mm, 20 ± 2 mm, and 33.6 ± 4.6 mm, respectively. The TRFA correlated strongly with SHSI (R = 0.731, P < .001) and GVA (R = 0.716, P < .001) and moderately with GOA (R = 0.663, P < .001). The SHSI was strongly negatively correlated with GVA (R = -0.813, P < .001) and moderately with GOA (R = -0.552, P < .001). The GVA correlated strongly with GOA (R = 0.768, P < .001). In contrast, TRFA, SHSI, GVA, and GOA did not correlate with glenoid depth, width, or radius. CONCLUSION: Despite an assumed balance in the transverse volume of the rotator cuff muscles in nonpathological shoulders, variations exist regarding the transverse resultant force depending on the SHSI, GVA, and GOA. In healthy/nonosteoarthritic shoulders, an increased glenoid retroversion is associated with a decreased anterior glenoid offset.

Wide Resection Preserving Conjoined Tendons of the Rotator Cuff Muscles for Undifferentiated Pleomorphic Sarcoma at the Suprascapular Fossa - A Case Report.

Surgical principles in sarcoma are a wide resection, including surrounding tissues and maximisation of the function of the affected limb. Rotator cuff muscles are biomechanically important structures acting as a force couple in movement of the shoulder joint. Thus, conjoined tendons are essential for motion capability in absence of the supraspinatus muscle. This article reports a case of a large undifferentiated pleomorphic sarcoma (UPS) at the suprascapular fossa in a 78-year-old man. After diagnosis of sarcoma, he underwent wide, en-bloc excision preserving conjoined tendons of rotator cuff muscles and low-dose radiation therapy for surveillance of local recurrence. All dissection was performed to avoid contaminating the tumour and involved the whole supraspinatus except the conjoined tendons. We report a case of UPS at the suprascapular fossa, which showed a good result after a wide resection preserving conjoined tendons of rotator cuff muscles. Level of Evidence: Level V (Therapeutic).

Muscle fatigue response of rotator cuff muscles in different postures.

INTRODUCTION: Muscle fatigue is a leading cause of rotator cuff (RC) pathologies. Scapular orientation affected by changes in the thoracic spine account for differences in body postures leading to altered RC muscle activation. This posture-related alteration in RC muscle activation and its fatigue response needs to be analyzed. MATERIALS AND METHODS: This study included 50 healthy shoulders with no coexisting spine pathologies. Raw data were recorded using electromyography sensors for RC muscles during two isometric maneuvers of abduction and external rotation, performed at 30% maximum voluntary contraction at 30°, 45°, and 90° arm elevation in sitting and standing. The raw data were analyzed in DataLITE® software, and the mean power frequency (MPF) was extracted to analyze the fatigue response of RC muscles. The Wilcoxon signed-rank test and Kruskal-Wallis test with Bonferroni corrections analyzed fatigue differences between postures and various activities. P < 0.05 was considered significant for the results. RESULTS: Supraspinatus muscle demonstrated significant fatigue at 90° of arm elevation in standing as compared to sitting (MPF -5.40: -5.41; P = 0.03) posture. Between the three elevation angles, all the RC muscles showed increased fatigue at 90° (MPF range -5.22 to -6.64). When compared between abduction and external rotation, only infraspinatus showed fatigue in external rotation (MPF range -5.42 to -6.08). Among all the three RC muscles, infraspinatus showed the maximum fatigue of MPF -6.64 when compared to supraspinatus -5.22 and teres minor -5.36. CONCLUSION: The findings indicate that alterations in the body postures and different elevation angles affect the RC muscles' fatigue response.

Proton density fat fraction measurements of rotator cuff muscles: Accuracy, repeatability, and reproducibility across readers and scanners.

PURPOSE: To determine the accuracy, repeatability, and reproducibility of magnetic resonance imaging-based proton density fat fraction (MRI-PDFF) measurements of rotator cuff muscles between two readers and three different scanners. METHODS: Twenty-seven volunteers underwent serial shoulder MRI examinations of both left and right sides on one 1.5-T MRI scanner and two 3.0-T MRI scanners. Two independent readers measured muscular PDFF of the supraspinatus, infraspinatus/teres minor muscle, and subscapularis. MR spectroscopy-based proton density fat fraction (MRS-PDFF) was regarded as the reference standard for assessing accuracy. A "coffee break" examination method was used to test the repeatability of each scanner. Bland-Altman plots, Pearson correlation, and linear regression analysis were used to assess bias and linearity. The Wilcoxon signed-rank test and Friedman test were applied to evaluate repeatability and reproducibility. RESULTS: MRI-PDFF measurements indicated strong linearity (R2 = 0.749) and small bias (-0.18%) in comparison with the MRS-PDFF measurements. A very strong positive Pearson correlation (r = 0.955-0.986) between the PDFF estimates of the two repeat scans indicated excellent repeatability. The PDFF measurements showed high reproducibility, with a strong positive Pearson correlation (r = 0.668-0.698) and a small mean bias (-0.04 to -0.10%) across different scanners. CONCLUSION: MRI-PDFF measurements of rotator cuff muscles were highly accurate, repeatable, and reproducible across different readers and scanners, leading us to the conclusion that PDFF can be a reliable and robust quantitative imaging biomarker for longitudinal or multi-center studies.

Longitudinal MR quantification of the fat fraction within the supraspinatus and infraspinatus muscles in patients with shoulder pain.

RATIONALE AND OBJECTIVES: Knowing the natural history of fatty degeneration of rotator cuff muscles is important for estimating the risk and rate of progression to cuff tear arthropathy (CTA). The purpose of this study was to investigate the changes in rotator cuff muscle fatty degeneration over time quantitatively in patients treated conservatively for shoulder pain. MATERIALS AND METHODS: Thirty patients with a baseline and follow-up shoulder MRI, including a 2-point Dixon sequence, which were performed at least 1 year apart, were included. We classified patients into 3 groups: "full-thickness tear" (n = 7), "partial-thickness tear" (n = 13), and "no-tear" (n = 10) groups. The fat fraction in the supra- and infraspinatus muscles, and the rate of change in the fat fraction (ΔFfr) were calculated using the formula "fat fraction of follow-up MRI/fat fraction of initial MRI." We investigated the difference in ΔFfr among the 3 groups and the degree of progression to CTA. RESULTS: Statistically significant differences in ΔFfr within the supraspinatus and infraspinatus muscles were found among full-thickness, partial-thickness, and no-tear groups (2.54 vs 1.02 vs 0.75, p < 0.001 and 1.96 vs 1.07 vs 0.73, p = 0.021, respectively). Overall, 71.4% of the full-thickness tear group showed progression of CTA, and 28.6% of the full-thickness tear group needed reverse shoulder arthroplasty within an average follow-up period of 34 months. CONCLUSIONS: MR quantification, together with the knowledge of change in fatty degeneration over time, may be useful for the management of patients with shoulder pain.

The effect of task rotation on activation and fatigue response of rotator cuff muscles during overhead work.

Overhead work is known as one of the ergonomic risk factors that can lead to shoulder overload and injury. Anatomical alignment of rotator cuff muscles makes them the most vulnerable to injuries during overhead work. In this study, the effect of task rotation, as one of the administrative controls to reduce the risk of injury during overhead work, on the fatigue response of rotator cuff muscles was investigated. Twelve participants performed three submaximal exertions (5, 20, and 35% of maximum voluntary contraction (MVC)) using four task rotation sequences (increasing, decreasing, upward parabolic, and downward parabolic). Median frequency of surface electromyography (EMG), shoulder strength, and ratings of perceived exertion (RPE) were used to study the fatigue response of rotator cuff muscles. Although the average normalized muscle activity was similar in all sequences, the task rotation sequence had a significant effect on the median frequency. The effect of task rotation sequence on the strength and RPE was similar to that of the median frequency but was statistically not significant. The upward parabolic task rotation sequence resulted in the lowest fatigue among all the task sequences. Performing intense exertions apart from each other, warm-up exertions, and the presence of active recovery after the intense exertions could be the factors that produced the lowest fatigue during this sequence.

Sex Differences in Rotator Cuff Muscles' Response to Various Work-Related Factors.

OCCUPATIONAL APPLICATIONSDespite the frequency and cost of rotator cuff injuries among male and female workers, very little is known about the strength, endurance, and perceived exertion and electromyographic response of rotator cuff muscles to different exertion levels. In this study, sex differences were studied using muscle-specific maximal and submaximal exertions of the supraspinatus, infraspinatus, and teres minor muscles. Females showed lower strength and endurance, but higher muscle activity and perceived exertion compared to males. The baseline data presented in this paper can assist ergonomic practitioners in determining the worker capacity to ensure that physically-demanding shoulder exertions can be performed without incurring injurious stress. Such data is also essential to establish population norms for the better design of workplace tasks.

TECHNICAL ABSTRACTBackground: Baseline strength, endurance, perceived exertion, and muscle activity data are essential to characterize sex-specific responses of the rotator cuff muscles to the workplace tasks to minimize risk of injury due to overexertion. Purpose: This study was conducted to measure sex differences in strength, endurance time, activity, fatigue, and perceived exertion for the rotator cuff muscles. Method: Muscle-specific maximum voluntary contractions (MVCs) were used to measure the maximum torque for the supraspinatus, infraspinatus, and teres minor muscles among 10 male and 10 female participants. Four submaximal exertions (15, 30, 45, and 60% MVC) were used to measure differences in endurance time, muscle activation, fatigue, and perceived exertion between sexes. Surface electromyography was used to measure muscle activity and fatigue. Results: Strength was the highest for the infraspinatus followed by teres minor and supraspinatus regardless of sex. Strengths for females were 70, 50, and 48% that of males for the infraspinatus, supraspinatus, and teres minor muscles, respectively. Muscle activity was significantly higher for females than males during the sub-maximal exertions. Among males, muscles with higher activity developed fatigue faster. Females exhibited lower endurance during all sub-maximal exertions. Perceived exertion ratings showed an increasing trend with %MVC, and females exceeded an acceptable limit at lower %MVC levels compared to males. Conclusions: Sex differences observed in this study suggest that a safe level of %MVC level for females is approximately 15% lower compared to males.

A study on the immediate effects of neuromuscular electrical stimulation on the corticospinal tract excitability of the infraspinatus muscle.

BACKGROUND: Rotator cuff muscles are structurally and functionally different from other upper-limb muscles because they are responsible for glenohumeral joint stability. Neuromuscular electrical stimulation (NMES) induces excitability changes (increase or decrease) of the corticospinal tract (CST) in the peripheral muscles, such as those of the finger. However, it remains unclear whether similar results are obtained when targeting the infraspinatus muscle, which has properties that differ from other muscles, in healthy subjects. OBJECTIVE: We investigated the immediate effects of NMES on the corticospinal excitability of the infraspinatus muscle, a rotator cuff muscle, in healthy subjects. METHODS: Thirteen healthy right-handed men (mean age: 26.77 ± 2.08 years) participated in this study. The motor evoked potentials (MEPs) and the maximum compound muscle action potential (Mmax) were recorded before NMES to the right infraspinatus and within 15 minutes after the end of the NMES. RESULTS: NMES on the infraspinatus muscle significantly increased its MEP amplitude (Pre: 0.45 mV [0.33-0.48]; Post: 0.54 mV [0.46-0.60] (median [lower quartile to higher quartile]); p= 0.005) but had no effect on Mmax (Pre: 2.95 mV [2.59-4.71]; Post: 3.35 mV [2.76-4.72]; p= 0.753). CONCLUSIONS: NMES application to the infraspinatus muscle increases CST excitability without producing immediate changes in the neuromuscular junction or muscle hypertrophy.

Localization of the centers of intramuscular nerve dense regions of the rotator cuff muscles: a guide for botulinum toxin A injection for spasticity accompanied by shoulder pain / Localización de los centros de las regiones densas del nervio intramuscular de los músculos del manguito rotador: una guía para la inyección de toxina botulínica A por espasticidad con dolor de hombro

To accurately localize the centers of intramuscular nerve dense regions (CINDRs) of rotator cuff muscles. Twenty adult cadavers were used. The curves on skin connecting the superior angle of scapula with the acromion, and with the inferior angle of scapula were designed as the horizontal (H) and longitudinal (L) reference lines, respectively. One side of the rotator cuff muscles were removed and subjected to Sihler's staining to show intramuscular nerve dense regions, and the contralateral muscles' CINDRs were labeled with barium sulfate and scanned by computed tomography (to determine body surface projection points (P)). The intersection of the longitudinal line from point P to line H, and that of the horizontal line from point P to line L, were recorded as PH and PL, respectively. The projection of CINDRs on the anterior body surface across the saggital plane was defined as P' and the line connecting P to P' was recorded as Line PP'. Percentage positions of CINDRs of PH and PL on lines H and L, and the depths on line PP' were determined under the Syngo system. Two, four, one, and one CINDRs were identified in supraspinatus, infraspinatus, teres minor, and subscapularis muscles, respectively. The positions of PH of these CINDRs on the H-line are as follows: supraspinatus, 25.43 % and 26.59 %; infraspinatus, 53.85 %, 34.63 %, 35.96 % and 58.17 %; teres minor, 74.50 %; and subscapularis, 20.33 %. The PL on the L-line: supraspinatus, 11.09 % and 14.83 %; infraspinatus, 21.59 %, 27.93 %, 48.55 % and 57.52 %; teres minor, 68.28 %; and subscapularis, 52.82 %. The depth on line PP': supraspinatus, 24.83 % and 25.40 %; infraspinatus, 21.55 %, 16.10 %, 10.01 % and 8.14 %; teres minor, 13.27 %; and subscapularis, 22.88 %. The identification of these CINDRs should provide the optimal target position for injecting botulinum toxin A to treat rotator cuff muscles spasticity accompanied by shoulder pain and to improve the efficiency and efficacy of blocking target localization.

Con el objetivo de localizar con precisión los centros de las regiones densas del nervio intramuscular (CRDNI) de los músculos del manguito rotador, se utilizaron veinte cadáveres adultos. Las curvas en la piel que conectan el ángulo superior de la escápula con el acromion y con el ángulo inferior de la escápula se determinaron como líneas de referencia horizontales (H) y longitudinales (L), respectivamente. Se extrajo de un lado los músculos del manguito rotador y se sometió a la tinción de Sihler para mostrar regiones densas de nervios intramusculares, y los CRDNI de los músculos contralaterales se marcaron con sulfato de bario y se escanearon mediante tomografía computarizada (para determinar los puntos de proyección de la superficie corporal (P)). La intersección de la línea longitudinal desde el punto P a la línea H, y de la línea horizontal desde el punto P a la línea L, se registraron como PH y PL, respectivamente. La proyección de CRDNI en la superficie del cuerpo anterior a través del plano sagital se definió como P 'y la línea que conecta P a P' se registró como Línea PP '. Las posiciones porcentuales de los CRDNI de PH y PL en las líneas H y L, y las profundidades en la línea PP 'se determinaron bajo el sistema Syngo. Se identificaron dos, cuatro, uno y un CINDR en los músculos supraespinoso, infraespinoso, redondo menor y subescapular, respectivamente. Las posiciones de PH de estos CRDNI en la línea H son las siguientes: supraespinoso, 25,43 % y 26.59 %; infraspinatus, 53,85 %, 34,63 %, 35,96 % y 58,17 %; redondo menor, 74,50 %; y subescapular, 20,33 %. El PL en la línea L: supraespinoso, 11.09 % y 14.83 %; infraspinatus, 21,59 %, 27,93 %, 48,55 % y 57,52 %; redondo menor, 68.28 %; y subescapular, 52,82 %. La profundidad en la línea PP ': supraespinoso, 24,83 % y 25,40 %; infraspinatus, 21,55 %, 16,10 %, 10,01 % y 8,14 %; redondo menor, 13.27 %; y subescapularis, 22,88 %. La identificación de estos CRDNI debería proporcionar la posición objetivo óptima para inyectar la toxina botulínica A para tratar la espasticidad de los músculos del manguito rotador acompañada de dolor en el hombro y para mejorar la eficiencia y la eficacia del bloqueo de la localización del objetivo.

Muscle Contributions to Upper-Extremity Movement and Work From a Musculoskeletal Model of the Human Shoulder.

Musculoskeletal models enable movement scientists to examine muscle function by computing the mechanical work done by muscles during motor tasks. To estimate muscle work accurately requires a model that is physiologically plausible. Previous models of the human shoulder have coupled scapula movement to humeral movement. While coupled movement produces a stereotypical scapulohumeral rhythm, it cannot model shrugging or independent movement of the scapula and humerus. The artificial coupling of humeral elevation to scapular rotation permits muscles that cross the glenohumeral joint, such as the rotator-cuff muscles and deltoids, to do implausible work to elevate and rotate the scapula. In reality, the motion of the scapula is controlled by thoracoscapular muscles, yet the roles of these muscles in shoulder function remains unclear. To elucidate the roles of the thoracoscapular muscles, we developed a shoulder model with an accurate scapulothoracic joint and includes scapular muscles to drive its motion. We used the model to compute the work done by the thoracoscapular muscles during shrugging and arm elevation. We found that the bulk of the work done in upper-extremity tasks is performed by the largest muscles of the shoulder: trapezius, deltoids, pectoralis major, and serratus-anterior. Trapezius and serratus anterior prove to be important synergists in performing upward-rotation of the scapula. We show that the large thoracoscapular muscles do more work than glenohumeral muscles during arm-elevation tasks. The model, experimental data and simulation results are freely available on SimTK.org to enable anyone to explore our results and to perform further studies in OpenSim 4.0.

A semi-automated quantitative CT method for measuring rotator cuff muscle degeneration in shoulders with primary osteoarthritis.

BACKGROUND: Rotator cuff muscle degeneration is an important parameter to consider when planning shoulder arthroplasty. HYPOTHESIS: We hypothesized that rotator cuff muscle degeneration is correlated with scapulohumeral subluxation in patients planned for anatomical total shoulder arthroplasty (TSA). MATERIALS AND METHODS: We developed a semi-automated quantitative CT method to measure rotator cuff muscle degeneration, and retrospectively analyzed 107 preoperative shoulder CT scans of patients with primary osteoarthritis. On a standardized sagittal-oblique CT slice perpendicular to the scapular axis, two observers measured the cross-sectional areas of residual rotator cuff muscle tissues, normalized by the estimated area of healthy muscles. Muscle degeneration was quantified in a semi-automated manner, and divided into atrophy and fatty infiltration. Scapulohumeral subluxation was determined in 3D as the distance between the humeral head center and the glenoid surface center, projected on the same CT slice, and normalized by the humeral head radius. We tested all potential correlations between muscle degeneration and scapulohumeral subluxation. RESULTS: Muscle degeneration, primarily due to atrophy, predominated in the supraspinatus; it varied from 0.8% to 88.8%. Scapulohumeral subluxation varied from 2.5% to 72.9%, and was mainly in a posterior and postero-superior orientation. There was a significant but weak correlation between the amount of subluxation and both supraspinatus (R=0.207, P=0.032) and infraspinatus (R=0.225, P=0.020) degeneration. Inter- and intra-observer reproducibility of muscle degeneration measurements were both excellent (ICCs range=0.955-0.987 and 0.971-0.988, respectively). CONCLUSION: This new semi-automated CT method allows to quantitatively and reproducibly measure rotator cuff muscle degeneration in shoulders with primary osteoarthritis. Muscle degeneration is weakly correlated with scapulohumeral subluxation in patients planned for anatomical TSA. LEVEL OF EVIDENCE: Level IV. TYPE OF STUDY: Diagnostic retrospective study.

Shoulder muscle activity during the modified dynamic relocation test and side-lying shoulder external rotation: a cross-sectional study on asymptomatic individuals.

OBJECTIVES: (1) to compare activity levels between monitored muscles during the dynamic relocation test (DRT); (2) to assess changes in muscle activation variability over 10 trials; (3) to assess within-muscle difference activity levels between the DRT and the unloaded side-lying shoulder external rotation exercise. METHODS: This is a cross-sectional, laboratory-based, repeated measures study. Thirty asymptomatic individuals performed the DRT and unloaded side-lying external rotation. The order of exercises was randomized. Superficial electromyography was used for recording the supraspinatus, infraspinatus, middle deltoid, posterior deltoid, pectoralis major, and latissimus dorsi muscles. The main outcome measures were mean muscle activity, expressed as % of maximal isometric voluntary contraction. RESULTS: We found significant between-muscles differences in activity (Ft = 14.11, p < 0.001) during the DRT. Post hoc analysis suggested between-trial variability did not change over the 10 trials, (F = 18.2, p < 0.001). Within-muscle comparisons between the DRT and side-lying shoulder external rotation suggested significant differences between these exercises (F = 32.37, p < 0.001). CONCLUSIONS: considering the monitored muscles, supraspinatus, infraspinatus, pectoralis major, and latissimus dorsi are the main muscles contracting during the DRT. Of all monitored muscles, supraspinatus muscle was the only one presenting higher activity levels during the DRT when compared to the unloaded side-lying shoulder external rotation.

Composition of Muscle Fiber Types in Rat Rotator Cuff Muscles.

The rat is a suitable model to study human rotator cuff pathology owing to the similarities in morphological anatomy structure. However, few studies have reported the composition muscle fiber types of rotator cuff muscles in the rat. In this study, the myosin heavy chain (MyHC) isoforms were stained by immunofluorescence to show the muscle fiber types composition and distribution in rotator cuff muscles of the rat. It was found that rotator cuff muscles in the rat were of mixed fiber type composition. The majority of rotator cuff fibers labeled positively for MyHCII. Moreover, the rat rotator cuff muscles contained hybrid fibers. So, compared with human rotator cuff muscles composed partly of slow-twitch fibers, the majority of fast-twitch fibers in rat rotator cuff muscles should be considered when the rat model study focus on the pathological process of rotator cuff muscles after injury. Gaining greater insight into muscle fiber types in rotator cuff muscles of the rat may contribute to elucidate the mechanism of pathological change in rotator cuff muscles-related diseases. Anat Rec, 299:1397-1401, 2016. © 2016 Wiley Periodicals, Inc.

Reliability and Limits of Agreement of the Supraspinatus Muscle Anatomical Cross-Sectional Area Assessment by Ultrasonography.

The purpose of this study was to evaluate the reliability and limits of agreement for assessment of the anatomical cross-sectional area (ACSA) of the supraspinatus muscle using B-mode ultrasonography. Sixteen participants were examined with two different protocols, on two different days. There were no statistically significant differences (p > 0.05) in ACSA values between days 1 and 2 or between protocols 1 and 2; the average intra-class correlation coefficient ranged from 0.93 to 0.96. The limits of agreement for supraspinatus ACSA were, in both protocols, about ± 1 cm(2). Our findings revealed that both protocols had high reliability in distinguishing differences of about 1 cm(2) between groups or after interventions and that ultrasonography can be used for experimental designs in which the expected changes in ACSA would be higher than 14%.

Effects of height and load weight on shoulder muscle work during overhead lifting task.

Few musculoskeletal models are available to assess shoulder deeper muscle demand during overhead lifting tasks. Our objective was to implement a musculoskeletal model to assess the effect of lifting height and load on shoulder muscle work. A musculoskeletal model scaled from 15 male subjects was used to calculate shoulder muscle work during six lifting tasks. Boxes containing three different loads (6, 12 and 18 kg) were lifted by the subjects from the waist to shoulder or eye level. After optimisation of the maximal isometric force of the model's muscles, the bio-fidelity of the model was improved by 19%. The latter was able to reproduce the subjects' lifting movements. Mechanical work of the rotator cuff muscles, upper trapezius and anterior deltoid was increased with lifting load and height augmentation. In conclusion, the use of a musculoskeletal model validated by electromyography enabled to evaluate the muscle demand of deep muscles during lifting tasks.

Arterial variations of the subclavian-axillary arterial tree: its association with the supply of the rotator cuff muscles / Variaciones arteriales del árbol arterial subclavio-axilar: su asociación con la irrigación del manguito de los rotadores

The subclavian-axillary arterial tree is responsible for the arterial supply to the rotator cuff muscles as well as other shoulder muscles. This study comprised the bilateral dissection of the shoulder and upper arm region in thirty-one adult and nineteen fetal cadaveric specimens. The variable origins and branching patterns of the axillary, subscapular, circumflex scapular, thoracodorsal, posterior circumflex humeral and suprascapular arteries identified in this study corroborated the findings of previous studies. In addition, unique variations that are unreported in the literature were also observed. The precise anatomy of the arterial distribution to the rotator cuff muscles is important to the surgeon and radiologist. It will aid proper interpretation of radiographic images and avoid injury to this area during surgical procedures.

El árbol arterial subclavio-axilar, es responsable del suministro arterial de los músculos correspondientes al manguito de los músculos rotadores, así como de otros músculos del hombro. Este estudio comprende la disección bilateral del hombro y la región superior del brazo en 31 cadáveres adultos y 19 fetos. Las variables y patrones del origen, ramificación de las arterias axilar, subescapular, circunfleja escapular, toracodorsal, circunfleja humeral posterior y supraescapular, identificados en este estudio, corroboran los hallazgos de estudios anteriores. Además, se observaron variaciones únicas no comunicadas previamente en la literatura. La anatomía precisa de la distribución arterial de los músculos del manguito de los músculos rotadores es importante para el cirujano y el radiólogo. Esta información constituirá una ayuda para la adecuada interpretación de imágenes radiológicas y para evitar lesiones en esta área durante los procedimientos quirúrgicos.

Arterial supply to the rotator cuff muscles / Suministro arterial de los músculos del manguito rotador

The arterial supply to the rotator cuff muscles is generally provided by the subscapular, circumflex scapular, posterior circumflex humeral and suprascapular arteries. This study involved the bilateral dissection of the scapulohumeral region of 31 adult and 19 fetal cadaveric specimens. The subscapularis muscle was supplied by the subscapular, suprascapular and circumflex scapular arteries. The supraspinatus and infraspinatus muscles were supplied by the suprascapular artery. The infraspinatus and teres minor muscles were found to be supplied by the circumflex scapular artery. In addition to the branches of these parent arteries, the rotator cuff muscles were found to be supplied by the dorsal scapular, lateral thoracic, thoracodorsal and posterior circumflex humeral arteries. The variations in the arterial supply to the rotator cuff muscles recorded in this study are unique and were not described in the literature reviewed. Due to the increased frequency of operative procedures in the scapulohumeral region, the knowledge of variations in the arterial supply to the rotator cuff muscles may be of practical importance to surgeons and radiologists.

El suministro arterial a los músculos del manguito rotador generalmente es proporcionado por las arterias subescapular, circunfleja escapular, circunfleja humeral posterior y supraescapular. Se realizó la disección bilateral de la región escapulo humeral de 31 especímenes cadavéricos adultos y 19 fetos. El músculo subescapular estaba irrigado por las arterias subescapular, supraescapular y circunfleja escapular. Por otra parte, la arteria supraescapular irrigaba a los músculos supra e infraespinoso. Observamos que los músculos infraespinoso y redondo menor fueron irrigados por la arteria circunfleja escapular. Además de las arterias de origen y sus ramas, observamos que los músculos del manguito rotador son irrigados por la arteria escapular dorsal y las arterias torácica lateral, toracodorsal y circunfleja humeral posterior. Las variaciones en la irrigación de los músculos del manguito rotador registrados en este estudio son únicos y no existe una descripción referente a ellos en la literatura revisada. Debido a la mayor frecuencia de los procedimientos quirúrgicos en la región escápulohumeral, el conocimiento de las variaciones de la irrigación de los músculos del manguito rotador puede ser de importancia práctica para cirujanos y radiólogos.

MUSCLE VOLUME AND STRENGTH CHARATERISTICS OF THE ROTATOR CUFF AND DELTOID MUSCLES IN ASYMPTOMATIC BASEBALL PITCHERS / 体力科学

The purpose of this study was to investigate muscle volume (MV) and strength characteristics of the rotator cuff (supraspinatus, infraspinatus, teres minor, and subscapularis) and deltoid muscles in each shoulder of asymptomatic baseball pitchers. Twelve collegiate baseball pitchers (PG) and ten male students (CG) who never played an overhand sports volunteered to participate in this study. Magnetic resonance imaging (Straits II, Hitachi Medico, 1.5 T) was used to measure the MV of rotator cuff and deltoid muscles in both shoulders of each subject. Since the individual muscles were difficult to identify on MRI scans, the infraspinatus and teres minor were analyzed as one infraspinatus muscle. Shoulder abduction (ABD), external rotation (ER), and internal rotation (IR) strengths were measured each side using a hand-held dynamometer (Power Track II, Jtech Medical Industry) . The MV of deltoid muscle was significantly larger value on the dominant side (DOM) than on the non-dominant side (NDOM) in both the PG and CG groups (p<0.05) . However, no significant differences in the MV of the rotator cuff muscles and the measured shoulder strength (ABD, ER, and IR) were observed between both sides in either group. Similarly, no significant differences in the DOM/NDOM ratio of the muscle volume and the measured shoulder strength were observed between the two groups. These results suggest that the rotator cuff muscle volume and strength does not differ in both sides of the PG, and DOM/NDOM ratios of the rotator cuff muscle volume and strength of the PG does not differ in those of the CG.

Electromyographic analysis of shoulder muscles during shoulder external rotation with reference to load magnitude / 体力科学

Electromyographic muscle activities of the shoulder muscles during shoulder external rotation with reference to load magnitude were studied in 8 healthy male subjects without history of shoulder injuries. In addition, we discussed the relationship between rotator cuff muscles and superficial muscles. The subjects performed shoulder external rotation from 60°internal rotation to 45° external rotation at 20° of shoulder abduction and 20° of flexion. A Cybex dynamometer used to prescribe angle and velocity of the shoulder movement. At the same time, intramuscular wire electrodes were inserted into the supraspinous, infraspinous and teres minor muscles, and then surface electrodes were placed over the posterior deltoid and middle trapezius muscles. The load magnitude ranged 2-18 Nm and the angle velocity was set at 15 deg/sec. The rotator cuff muscles became significantly to be activated from 2 Nm (the supraspinous and infraspinous m.) and from 4-5 Nm (the teres minor m.) compared with the muscle activity during non-load. The superficial muscles became significantly to be activated from 4-7 Nm (the posterior deltoid m.) and from 3-6 Nm (the middle trapezius m.) compared with the muscle activity during non-load. Within the load range (18 Nm 46.8% MVC), %iEMG of the rotator cuff muscles was always larger than that of the superficial muscles. Therefore, we concluded that the contribution of the rotator cuff muscles was larger than that of the superficial muscles up to 3-4 Nm, and activities of the superficial muscles increased gradually from 3-4 Nm during shoulder external rotation.