Reliability of the supraspinatus muscle thickness measurement by ultrasonography

Abstract

Objective: 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.

Method: 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.

Results: 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 cm(2) at the Y-view and 5.61±1.19 cm(2) 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.

Conclusion: 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.

Keywords: Magnetic resonance imaging; Reliability; Supraspinatus; Thickness; Ultrasonography.

Fig. 1

Evaluation of the supraspinatus muscle using ultrasonography. Surface anatomy of left shoulder (A) and placement of ultrasonographic probe (B). We identified the scapular notch on the monitor in parallel to the action of supraspinatus muscle and rotated the probe parallel to the AC line. After we observed cross section of the supraspinatus muscle on the monitor, We calculated the distance (d) between the AC line and the lateral side of the probe. C: Coracoid process, AC: Acromion, SS: Scapular spine, A: Acromial angle, AC line: Line between A and C, d: The closest distance between AC line and lateral side of ultrasonographic probe.

Fig. 2

Evaluation of the supraspinatus muscle using ultrasonography. Ultrasonographic findings of supraspinatus muscle which is parallel to the muscle line of action (A) and parallel to AC line (B) in normal subject. The arrow indicates scapular notch. AC line: Line between acromial angle and coracoids process, SS: Supraspinatus, T: Trapezius, A: Acoustic shadowing of clavicle, B: Acoustic shadowing of scapular spine, C: Mid-point of distance between A and B, D: Upper border of supraspinatus muscle, E: Lower border of supraspinatus muscle. Distance between D and E corresponds with supraspinatus muscle thickness in this study.

Fig. 3

Cross sectional area measurement of affected supraspinatus muscle by magnetic resonance imaging at the Y-view (A) and the suprascapular notch (B) in hemiplegic patients.