Compensation strategy of shoulder synergist muscles is not stereotypical in patients with rotator cuff repair.

Rotator cuff tear is a common shoulder injury that causes shoulder dysfunction and pain. Although surgical repair is the primary treatment for rotator cuff tear, it is well recognized that impaired force exertion of muscles connecting to the involved tendon and subsequent complemental change in the force exertion of synergist muscles persist even after repair. This study aimed to identify the compensation strategy of shoulder abductors by examining how synergist muscles respond to supraspinatus (SSP) muscle force deficit in patients with rotator cuff repair. Muscle shear modulus, an index of muscle force, was assessed for SSP, infraspinatus, upper trapezius, and middle deltoid muscles in repaired and contralateral control shoulders of 15 patients with unilateral tendon repair of the SSP muscle using ultrasound shear wave elastography while the patients passively or actively held their arm in shoulder abduction. In the repaired shoulder, the shear modulus of the SSP muscle declined, whereas that of other synergist muscles did not differ relative to that of the control. To find the association between the affected SSP and each of the synergist muscles, a regression analysis was used to assess the shear moduli at the population level. However, no association was observed between them. At the individual level, there was a tendency of variation among patients with regard to a specific muscle whose shear modulus complementarily increased. These results suggest that the compensation strategy for SSP muscle force deficit varies among individuals, being nonstereotypical in patients with rotator cuff injury.

Age-related changes in muscle thickness, echo intensity and shear modulus of the iliocapsularis.

PURPOSE: This study aimed to clarify age-related changes in the iliocapsularis (IC) using indicators of quantity, quality, and mechanical properties. We also compared the age-related changes in the IC and other hip muscles. METHODS: Eighty-seven healthy women (ages: 21-82 years, mean age: 45.9 ± 15.7 years) participated in the experiment. We measured thickness, echo intensity, and shear modulus of the IC, iliacus muscle, rectus femoris, and the thickness and shear modulus of the hip joint capsule. Spearman's rank correlation coefficient was used to measure the association of age with variables measured in the muscles and joint capsule. RESULTS: Thickness of the iliacus muscle and rectus femoris decreased significantly with age, but the thickness of the IC and hip joint capsule showed no significant correlation. The echo intensities of the IC, iliacus muscle, and rectus femoris were positively correlated, which increased with age. Furthermore, the shear modulus of the iliacus, rectus femoris, and hip joint capsule showed an increase with age, whereas the shear modulus of the IC exhibited no correlation with age. CONCLUSION: The muscle quality of the IC changed significantly, unlike that of the iliacus or rectus femoris. Additionally, the correlation with echo intensity was relatively weaker in the IC compared with the iliacus or rectus femoris.

Effect of age on shear modulus, muscle thickness, echo intensity of the upper limb, lower limb, and trunk muscles in healthy women.

PURPOSE: This study aimed to examine the effect of age on the mechanical properties, muscle size, and muscle quality in the upper and lower limb and trunk muscles. METHODS: We evaluated the shear modulus (G), muscle thickness (MT), and echo intensity (EI) of the upper and lower limb and trunk muscles of 83 healthy women (21-83-year-old). The G values of some limb muscles were measured in relaxed and stretched positions. RESULTS: Regarding the effect of age on G at the distinct positions, the G of the upper limb muscles were not significantly correlated with age in the relaxed and stretched positions. In contrast, the G of the iliacus showed a significant negative correlation in both positions. Additionally, the G of the rectus femoris had a significant negative correlation only in the relaxed position. Regarding differences among body parts, the G of the lower limb and oblique abdominal muscles showed a significant negative correlation, but no correlation in the upper limb, rectus abdominis, and back muscles. Moreover, MT showed a significant negative correlation with age in the lower limb, abdominal, and erector spinae muscles, but no correlation was detected in the upper limb and lumbar multifidus muscles. EI had a significant positive correlation in all the muscles. CONCLUSION: The effect of age on G depended on body parts, and the G of the lower limb and oblique abdominal muscles negatively associated with age. Additionally, G in the relaxed position may be more susceptible to aging than G in the stretched position.

Application of statistical parametric mapping for comparison of scapular kinematics and EMG.

Scapular kinematics and EMG are frequently measured as a functional assessment of the shoulder. Previous studies have compared interval averaging for these time series data, but it is not clear whether this method exactly captures the dynamics of scapular kinematics and muscle activity. Statistical parametric mapping (SPM) can be used to compare time series data. The purpose of this study was to investigate whether there is a difference between the results of SPM and interval averaging (every 10° or 30°) in comparing scapular kinematics, EMG, and EMG ratio. Scapular kinematics and EMG of the upper trapezius (UT), middle trapezius (MT), and lower trapezius (LT) and serratus anterior (SA) were measured in 21 healthy males. Tasks included arm raising and lowering with or without load, and we compared scapular kinematics, EMG, and EMG ratio in the loaded and unloaded conditions. Results suggest disagreement between SPM and interval averaging. Characteristic results are that for scapular kinematics during lowering SPM showed a decrease in upward rotation in only the regions 113-65° and 42-30°, while interval averaging showed a decrease in all range. For EMG during lowering, SPM results were not significantly different in SA over 50-48 and 45-30°, while interval averaging suggested increased activity in all ranges. For EMG ratio during raising, SPM showed no significant difference, while interval averaging showed a decrease in UT/LT during the latter period. These results indicate that SPM provides better resolution regarding effect regions than interval averaging, and suggest that SPM may improve shoulder function assessment accuracy.

Effective stretching position of the coracobrachialis muscle.

An increase in the stiffness of the coracobrachialis muscle can restrain proper movement of the glenohumeral joint and scapula during arm elevation. Therefore, muscle stiffness should be reduced through stretching. The aim of this study was to determine the effective stretching position of the coracobrachialis muscle using ultrasound shear wave elastography imaging to evaluate the stiffness of individual muscles. Eighteen healthy young men participated in this study. The shear modulus of the coracobrachialis muscle was measured at the following eight shoulder positions: i) 20° abduction (Rest), ii) maximal external rotation at 90° abduction (ER2), iii) maximal internal rotation at 90° abduction (IR2), iv) maximal flexion (Flex), v) maximal extension (Ext), vi) maximal horizontal abduction at 90° abduction (Hab), vii) maximal horizontal abduction and maximal external rotation at 90° abduction (HabER), and viii) maximal horizontal abduction and maximal internal rotation at 90° abduction (HabIR). The shear modulus in each position was compared with that of Rest using the Wilcoxon signed-rank test, and a multiple comparison test was performed among the positions that exhibited significant difference. The shear modulus of all stretching positions was significantly higher than that of Rest, except for Flex. Moreover, the shear moduli of IR2, Ext, Hab, HabER, and HabIR were significantly higher than that of ER2. The shear modulus of Ext was significantly higher than that of HabIR. The coracobrachialis muscle could be stretched effectively at IR2, Ext, Hab, HabER, and HabIR. Among these positions, Ext, Hab, and HabER are recommended for clinical settings.

Assessment of Edematous Changes Using Three-Dimensional Body Scanning and Segmental-Bioelectrical Impedance Spectroscopy.

Purpose: The primary purpose of this study was to clarify the occurrence of sites of edematous changes using the measured circumferences of the thigh and lower leg via three-dimensional (3D) body scanning. The secondary purpose was to determine the relationship between the volume changes using 3D body scanning and the resistance changes as indicator of extracellular water (ECW) via segmental-bioelectrical impedance spectroscopy (S-BIS). Methods and Results: Fifteen healthy women participated. Limb circumferences were measured using 3D body scanning at 10% intervals between 50% and 80% in the thigh circumference and between 0% and 80% in the lower leg circumference. The resistance of the ECW component (RECW) and total body water (RTBW) was measured using S-BIS in the thigh and lower leg segments. These measurements were conducted at baseline and 6 hours postobservation. A paired t-test was conducted for the differences in these parameters, and the effect sizes (ESs) were calculated using Cohen's d. Correlations between changes in segmental volume and RECW were analyzed. Measurement-site circumferences and segmental volume significantly increased in the lower leg at postobservation but not in the thigh. The ES of circumference changes in the lower leg's central region were larger (ESs were 0.40-0.71 at 30%-50%) than in other regions. A significant correlation was observed between changes in segmental volume and RECW of the lower leg (ρ = -0.79, p < 0.001). Conclusions: Assessing the circumference using 3D body scanning, we found the edematous changes to be significant in the lower leg's central regions. Moreover, volumetry using 3D body scanning can detect edematous change in the lower leg.