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Background and Aims Suprascapular nerve entrapment syndrome (SSNES) is a neuropathy caused by compression of the nerve. Previous research has demonstrated that it often causes the weakness of supraspinatus muscles, as well as pain of the shoulder. We considered that the supraspinatus muscle cross-sectional area (SMCSA) might be a morphological parameter to analyze SSNES.

Methods We acquired supraspinatus muscle data from 10 patients with SSNES and from 10 control subjects who revealed no evidence of SSNES. T1-weighted sagittal magnetic resonance imaging of the shoulder (MRI-S) images were acquired. We analyzed the supraspinatus muscle thickness (SMT) and SMCSA at the shoulder on the MRI-S using our image analysis program. The SMCSA was measured as the whole supraspinatus muscle cross-sectional area that was most hypertrophied in the sagittal MRI-S images. The SMT was measured as the thickest level of supraspinatus muscle.

Results The mean SMT was 20.05 ± 1.85mm in the normal group and 18.16 ± 1.58mm in the SSNES group. The mean SMCSA was 653.24 ± 100.55mm2 in the normal group and 503.06 ± 117.89mm2 in the SSNES group. SSNES patients had significantly lower SMT (p < 0.001) and SMCSA (p < 0.001) than the normal group. ROC curve analysis suggested that the best cut-off scores of the SMT was 18.49 mm, with 70.0% sensitivity, 70.0% specificity, and an AUC of 0.80 (95% CI, 0.60-0.99). The optimal cut-off value of the SMCSA was 612.60mm2, with 80.0% sensitivity, 80.0% specificity, and AUC of 0.85 (95% CI, 0.68-1.00).

Conclusions The SMCSA test is more sensitive than the SMT test.