To investigate the utility of ultrasonography to objectively examine morphological changes (i.e., muscle atrophy and fatty infiltration) of the supraspinatus muscle.
Thirty-four patients were prospectively enrolled in this study. The degrees of muscle atrophy and fat infiltration were measured using ultrasonography 3–4 months after arthroscopic supraspinatus tendon repair. Shoulder function (i.e., shoulder active range of motion, visual analogue scale, and constant score) was examined. Using the symmetricity of the muscles in the human body, the degrees of morphological changes of the supraspinatus muscle were quantitatively measured. The associations between the morphological changes of the supraspinatus muscle and shoulder function were identified.
There were statistically significant differences in the cross-sectional area (CSA) and echogenicity between the surgery and non-surgery sides (p<0.001). The CSA ratio, which represents the degree of muscle atrophy, was associated with shoulder forward flexion, external rotation, and constant score; however, the echogenicity ratio, which represents the degree of fat infiltration, was not associated with shoulder function after surgery.
This study demonstrated that shoulder function could be predicted by evaluating the morphological changes of the supraspinatus muscle using ultrasonography and that objective evaluation is possible through quantitative measurement using the symmetricity of the human body.
Citations
To assess the intrarater and interrater reliability of the supraspinatus thickness measured by ultrasonography (US) in normal subjects and to identify the relationship between the supraspinatus thickness measured by US and cross sectional area (CSA) of the supraspinatus muscle by magnetic resonance imaging (MRI) in hemiplegic patients.
We examined 20 shoulders of normal subjects and 10 shoulders of hemiplegic patients. In normal subjects, one examiner measured the supraspinatus thickness twice by US at the scapular notch and another examiner measured the supraspinatus thickness several days later. The intrarater and interrater reliability of supraspinatus thickness measurements were then evaluated. In hemiplegic patients, the supraspinatus thickness at the scapular notch was measured by US in affected side and compared with CSA of the supraspinatus muscle at the scapular notch and the Y-view of MRI.
One examiner's supraspinatus thickness measurement average was 1.72±0.21 cm and 1.74±0.24 cm, and the other examiner's supraspinatus thickness measurement average was 1.74±0.22 cm in normal subjects. Intraclass correlation coefficients of intrarater and interrater examination were 0.91 and 0.88, respectively. For hemiplegic patients, the supraspinatus thickness measured by US was 1.66±0.13 cm and CSA by MRI was 4.83±0.88 cm2 at the Y-view and 5.61±1.19 cm2 at the scapular notch. The Pearson Correlation Coefficient between the supraspinatus thickness at the scapular notch and the CSA at the Y-view was 0.72 and that between the supraspinatus thickness and CSA at the scapular notch was 0.76.
The supraspinatus thickness measurement by US is a reliable method and is positively correlated with the CSA of the supraspinatus muscle in MRI in hemiplegic patients. Therefore, supraspinatus thickness measurement by US can be used in the evaluation of muscle atrophy and to determine therapeutic effects in hemiplegic patients.
Citations
To evaluate the test-retest reliability of supraspinatus cross-sectional area measurement by ultrasonography.
Both shoulders of 11 normal subjects (22 shoulders in total) were included in this study. The supraspinatus muscle was examined with the arm alongside the body in the coronal oblique and sagittal oblique planes. The occupational ratio of the supraspinatus fossa was measured. To calculate the occupational ratio, the Y view of MRI was reproduced with sonography by locating the suprascapular notch in the coronal oblique plane (in the plane of the scapula) and then rotating the transducer 90° to that plane. The cross-sectional area was measured using the tracing and ellipse tool. The second measurement was performed 7 days after the initial measurement.
The Pearson correlation coefficient and intraclass correlation coefficient between the first and the second occupational ratio measurements were 0.43 and 0.44, respectively, for the tracing method, and 0.53 and 0.47, respectively, for the ellipsoidal method. The difference between the first and second occupational ratio measurement was 4.1±3.9% (0.1-13.2%) for the tracing method, and 4.5±3.4% (0.01-10.5%) for the ellipsoidal method. The maximum difference was 13.2%. The occupational ratio was 86.2±5.3% (70.6-95.8%) for the tracing method and 85.0±5.2% (69.3-96.1%) for the ellipsoidal method.
Supraspinatus occupational ratio by sonography is a low to moderately reliable intrarater method. However, the maximum difference was not significant. The main reason for its low to moderate reliability was the narrow value range. Therefore, the study method should be re-evaluated in stroke patients and in patients with rotator cuff disease. Knowledge of the anatomy is a prerequisite to attain intrarater reliability.
Citations
Measurements of local shoulder muscle function during shoulder abduction are of a great interest in biomechanics research and in ergonomic applications. There have been so many opinions that the supraspinatus muscle acts in synergy with the deltoid muscle as a single unit throughout the shoulder abduction. However the specific actions of deltoid and supraspinatus muscles have been subjects of controversy. Electromyography is an established evaluation method of biomechanical study. It reflects the electrical activity at the muscle membrane level and indirectly the mechanical output of the muscle. The purpose of this study was to evaluate the role of deltoid and supraspinatus muscles during shoulder abduction by the comparison of motor unit action potentials using a quantitative electromyographic analysis method, to provide a good insight into the biomechanics of shoulder abduction.
Motor unit action potentials of deltoid muscle were seen earlier than those of supraspinatus muscle at the time of initiation of shoulder abduction. The Root Mean Square (RMS) voltage of deltoid muscle was increased gradually from 0o to 90o of shoulder abduction, and then decreased gradually above 90o to 180o of shoulder abduction. The RMS voltages of deltoid muscle were significantly higher than those of supraspinatus muscle at each degree of shoulder abduction wholly. There was no differences in the RMS voltages of deltoid muscle, during shoulder abduction between the loading of 1 kg and without loading. However, the RMS voltages of supraspinatus muscle were significantly higher in the loading state than without loading. The Mean Rectified Voltages (MRV) were similar to the RMS voltages of deltoid and supraspinatus muscles during shoulder abduction.
Based on these results, we concluded that the deltoid muscle was not only an initiator but also a major contributor in shoulder abduction, where as the supraspinatus muscle acts as a secondary muscle for the initiation of shoulder abduction and a supporting muscle when there is a resistance against shoulder abduction.
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