Abstract
Suprascapular nerve entrapment (SNE) syndrome is a commonly overlooked cause of shoulder weakness and pain. It frequently causes weakness over the posterior and lateral and posterior aspects of the shoulder, as well as pain of infraspinatus muscles. Therefore, we considered that the infraspinatus muscle cross-sectional area (IMCSA) might be a new morphological parameter to analyze SNE syndrome. We assumed that the IMCSA is an important morphologic parameter in SNE syndrome diagnosis. We acquired infraspinatus muscle data from 10 patients with SNE syndrome and from 10 healthy subjects who had undergone magnetic resonance imaging of the shoulder and who revealed no evidence of SNE syndrome. We analyzed the infraspinatus muscle thickness (IMT) and IMCSA at the shoulder on the imaging of the shoulder using our image analysis program. The IMCSA was measured as the whole infraspinatus muscle cross-sectional area that was most atrophied in the sagittal S-MR images. The IMT was measured as the thickest level of infraspinatus muscle. The mean IMT was 29.17 ± 2.81 mm in the healthy subjects and 25.22 ± 3.19 mm in the SNE syndrome group. The mean IMCSA was 1321.95 ± 175.91 mm2 in the healthy group and 1048.38 ± 259.94 mm2 in the SNE syndrome group. SNE syndrome patients had significantly lower IMT (P < .001) and IMCSA (P < .001) than the healthy group. The ROC curve shows that the optimal cutoff point of the IMT was 26.74 mm, with 70.0% sensitivity, 70.0% specificity, and an AUC of 0.83 (95% CI, 0.65–1.00). The best cutoff value of the IMCSA was 1151.02 mm2, with 80.0% sensitivity, 80.0% specificity, and AUC of 0.87 (95% CI, 0.69–1.00). The IMT and IMCSA were both significantly associated with SNE syndrome. And the IMCSA was a highly sensitive diagnostic tool.
Keywords: cross-sectional area, diagnosis, infraspinatus muscle, suprascapular nerve entrapment syndrome, thickness
1. Introduction
Suprascapular nerve entrapment (SNE) syndrome is a rare neuropathy.[1,2] Symptoms due to nerve system dysfunction are based on atrophy of the infraspinatus and supraspinatus muscles supplied by the suprascapular nerve.[3–6] Traumatic injuries such as, clavicular fracture, scapular fracture, shoulder dislocations, and the acromioclavicular joint, or proximal humerus fractures are common causes of nerve damage. The diagnosis of SNE syndrome is typically based on interview, physical examination, medical imaging (ultrasonography, X-ray), or electrodiagnostic study.[4] The diagnosis must be differentiated from cervical disc injury, cervical spinal cord disease, brachial plexus disease, and the damage to the rotator cuff.[7] Thus, exact diagnosis and management is important to prevent SNE syndrome.
Magnetic resonance imaging of the shoulder (MRS) is very useful for analysis of the atrophy of the infraspinatus muscle.[8] Treating physicians consider the MRS findings when analyzing morphological changes in the infraspinatus muscle when they decide on treatment choices. Previous research has assessed the infraspinatus muscle using a simple measurement at the “halfway” of the infraspinatus muscle. However, a partial and an asymmetrical atrophy of the infraspinatus muscle can occur anywhere. Thus, a measurement error bias could occur. In contrast to the infraspinatus muscle thickness (IMT), the cross-sectional area of the infraspinatus muscle will not suffer from measurement error bias, because the IMCSA the cross-sectional area of the infraspinatus muscle. Therefore, to analyze atrophy of infraspinatus muscle, we created the IMCSA as a novel image analysis tool to diagnose SNE syndrome. We assumed that the IMCSA will be an important image analysis parameter in SNE syndrome diagnosis.
2. Methods
2.1. Participants
This observational study protocol was reviewed and approved by the Institutional Review Board.
The inclusion criteria were that the subjects for the SNE syndrome group must:
Each patient had a history of arm/shoulder heaviness or weakness.
Burning/radiating discomfort to the back or neck.
Shoulder movement impairments.
Loss of shoulder range of motion.
Atrophy of infraspinatus muscles.
Patients were excluded if they reported:
previous shoulder and elbow fracture history.
previous shoulder and elbow surgery.
No available of MRS.
The participants were an SNE syndrome group comprising 10 patients. There were 8 (80.0%) male and 2 (20.0%) female, with a mean age of 43.90 ± 15.57 years (range, 20–57 years) (Table 1). To contrast the IMT and IMCSA between subjects without and with SNE syndrome, we enrolled a healthy group consisting of subjects who wanted to take MRS for accurate diagnosis. The healthy group was patients who had shoulder discomfort and wanted to undergo MRS. There were no abnormal findings on MRS in the healthy group.
Table 1.
Comparison of the demographic characteristics of the normal and SNE syndrome groups.
| Variable | Healthy group n = 10 |
SNE syndrome group n = 10 |
Statistical significance |
|---|---|---|---|
| Gender (male/female) | 6/4 | 8/2 | NS |
| Age (yrs) IMT (mm) |
42.70 ± 13.28 29.17 ± 2.81 |
43.90 ± 15.57 25.22 ± 3.19 |
NS P < .001 |
| IMCSA (mm2) | 1321.95 ± 175.91 | 1048.38 ± 259.94 | P < .001 |
IMCSA = infraspinatus muscle cross-sectional area, IMT = infraspinatus muscle thickness, NS = not statistically significant (P > .05), SNE syndrome = suprascapular nerve entrapment syndrome.
In the normal group, 10 subjects (6 men and 4 women) were enrolled with an average age of 42.70 ± 13.28 years (range, 20–67 years).
2.2. Imaging parameters
Using a 3.0T MRS system (Siemens vision) and and 3T Ingina scanners (Philips Healthcare, Eindhoven, Netherlands), we obtained sagittal T1-weighted images. The MRS imaging parameters were as follows: flip angle 35°, field of view 160 cm × 160 cm, repetition time 619.0 ms, number of signals averaged = 2, echo time 13.0 ms, 3 > echo train length, slice thickness 3.00 mm, matrix size 512 × 307, and scan time 4 minutes 32 seconds.
2.3. Image analysis
The IMT and IMCSA measurements were performed by the 18 years experienced specialist. T1-weighted sagittal TSE MRS images were acquired for visualization of the most atrophied infraspinatus muscle. IMT and IMCSA were measured at MRS (INFINITT, Incheon, Simgokro, Republic of Korea) using the INFINITT Picture Archiving and Communication System (PACS). INFINITT PACS also offers a diagnostic viewer with enterprise imaging solutions. Sagittal T1-weighted MRS images showed a tortuous appearance of the infraspinatus muscle. We measured the IMCSA as the cross-sectional area of the muscle margin of the infraspinatus muscle that was the most atrophied area in the MRS images. And, we also measured the IMT at the midline between the insertion and origin (Fig 1A and B). We have added 3D reconstruction image of shoulder (Fig. 2).
Figure 1.
Measurement of both infraspinatus muscle thickness (IMT) (white arrow) (A) and infraspinatus muscle cross-sectional area (IMCSA) (white arrow) (B) was acquired on MR T1 weighted images.
Figure 2.
3D reconstruction image of shoulder. The blue plane is the slicing plane; infraspinatus muscle thickness (IMT) and infraspinatus muscle cross-sectional area (IMCSA).
2.4. Statistical analysis
IMT and IMCSA between SNE syndrome and normal subjects were compared using independent t tests. The optimal cutoff point is identified by the significant AUC of ROC analysis. A value of P < .05 was considered statistically significant. All statistical analyzes were performed using Windows version 22.0 (IBM/SPSS, Inc., Incheon, Korea).
3. Results
Demographic characteristics assessed were age at date of sex and diagnosis. Significant differences were not found in the demographic data. The mean IMT was 29.17 ± 2.81 mm in the healthy subjects sand 25.22 ± 3.19 mm in the SNE syndrome group. The mean IMCSA was 1321.95 ± 175.91 mm2 in the healthy group and 1048.38 ± 259.94 mm2 in the SNE syndrome group. SNE syndrome patients had significantly lower IMT (P < .001) and IMCSA (P < .001) than the healthy group (Table 1). Optimal cutoff values are identified by the significant AUC of the curve analysis (IMT was 26.74 mm, with 70.0% sensitivity, 70.0% specificity, and an AUC of 0.83 (95% CI, 0.65–1.00)) (Table 2 and Fig. 2). The optimal cutoff point of the IMCSA was 1151.02 mm2, with 80.0% sensitivity, 80.0% specificity, and AUC of 0.87 (95% CI, 0.69–1.00) (Table 3 and Fig. 3).
Table 2.
Each cutoff threshold, sensitivity and specificity of the IMT.
| IMT (mm) |
Sensitivity (%) |
Specificity (%) |
|---|---|---|
| 18.06 | 0.0 | 100 |
| 25.39 | 50.0 | 90.0 |
| 26.74* | 70.0 | 70.0 |
| 28.24 | 80.0 | 60.0 |
| 29.45 | 90.0 | 50.0 |
| 32.98 | 100 | 10.0 |
IMT = infraspinatus muscle thickness.
The optimal cutoff score on the receiver operating characteristic curve.
Table 3.
Each cutoff threshold, Sensitivity and Specificity of the IMCSA.
| IMCSA (mm2) |
Sensitivity (%) |
Specificity (%) |
|---|---|---|
| 658.52 | 10.0 | 100 |
| 1012.08 | 40.0 | 100 |
| 1151.02* | 80.0 | 80.0 |
| 1154.78 | 80.0 | 70.0 |
| 1213.81 | 80.0 | 60.0 |
| 1486.32 | 100 | 20.0 |
IMCSA = infraspinatus muscle cross-sectional area.
The most suitable cutoff score on the receiver operating characteristic curve.
Figure 3.
The best cutoff score for IMCSA was 1151.02 mm2 versus 26.74 mm of IMT, with sensitivity 80.0% versus 70.0%, specificity 80.0% versus 70.0%. IMT AUC of 0.83 (95% CI, 0.65–1.00). IMCSA AUC of 0.87 (95% CI, 0.69–1.00).
4. Discussion
The most important finding of our study was to find out the role of the IMCSA in SNE syndrome. We demonstrated that the IMCSA had 80.0% sensitivity and 80.0% specificity for predicting SNE syndrome. In contrast, the IMT had 70.0% sensitivity, 70.0% specificity.
SNE syndrome, is a condition which is due to damage and irritation to the suprascapular nerve. This condition can result in weakness, pain, or both depending on the cause. The suprascapular nerve has a sensory and motor innervation. Its motor innervation is to the supraspinatus and infraspinatus muscles.[9–11] Traumatic injuries such as, clavicular fracture, scapular fracture, shoulder dislocation, the acromioclavicular joint, or proximal humerus fractures are common causes of nerve damage. Another cause of SNE include iatrogenic damages during exertional overload in physical or athletes laborers, surgical procedures, tuberous changes of this area. One important cause is that symptoms due to nerve irritation are based on progressive atrophy of the infraspinatus muscle, which is supplied by the scapular nerve.[12–14] Thus, analysis of infraspinatus muscle is very important. However, there is no study to analyze infraspinatus muscles objectively.
Multiple imaging techniques, such as plain X-ray, MRS, computed tomography, and shoulder ultrasonography, are available.[15–18] However, it is difficult to evaluate SNE syndrome by means of imaging modalities, because of the lack of a reliable objective imaging parameter. And, atrophied infraspinatus muscle has been considered to be a major morphologic parameter of SNE syndrome. However, the infraspinatus muscle exhibits wavy or curved contours, ligamentous discontinuities, variable signal intensity, contour elongation, and muscle irregularities within areas of atrophy.[19] Therefore, a single measurement may result in an incorrect measurement. IMCSA, which measures the total cross-sectional area of the infraspinatus muscle, was thought to be able to predict SNE syndrome through the cross-sectional area of the infraspinatus muscle, unlike IMT. Ultimately, we demonstrated that IMCSA is superior to IMT as a morphological measurement tool for SNE syndrome. Eventually, we demonstrated that the IMCSA is better than the IMT as a morphological measurement tool of SNE syndrome. In the current original research, we demonstrated that the IMCSA had 80.0% sensitivity 80.0% specificity for predicting SNE syndrome. In contrast, the IMT had 70.0% sensitivity, 70.0% specificity, and an AUC of 0.83. These results show that IMCSA predicts SNE syndrome better than IMT.
This study has many limitations. First, SNE syndrome has a variety of causes, including trauma, rotator cuff damages, repetitive overhead activities, and the supraspinatus and/or infraspinatus muscles.[20–30] However, we only focused on the infraspinatus muscle. Second, there may be incorrect measurements of IMCSA and SMT in MRS. Despite efforts to analyze these morphological measurements to best represent the supraspinatus on sagittal image sections, the sagittal images evaluated to measure cross-sectional images may be inconsistent due to differences in cut level or angle of the MRS. It is caused by individual anatomical differences and technical issues. Third, alternative imaging tools to evaluate SNE syndrome include ultrasonography, intraosseous ganglion, computed tomography, and superior transverse shoulder ligament, but only IMCSA and IMT measurements of MRS were analyzed in this study protocol. Fourth, functional instability was not considered. This is because functional instability is a subjective finding that can vary depending on interpretation. Efforts are being made to create objective morphological indicators.
Despite these limitations, this is the first study to document an association between IMCSA and SNE syndrome.
5. Conclusion
The aim of this observational study was to assess the role of the IMCSA in SNE syndrome. We demonstrated that the IMCSA had high sensitivity (80.0%), high specificity (80.0%), and an AUC of 0.87 (95% CI, 0.69–1.00) for predicting SNE syndrome. The IMT and IMCSA were both significantly associated with SNE syndrome. And the IMCSA was a highly sensitive diagnostic tool.
Acknowledgments
The all authors thank the International ST. Mary`s Hospital.
Author contributions
Conceptualization: Young Uk Kim.
Data curation: Young Uk Kim.
Formal analysis: Jaeho Cho, Young Uk Kim.
Funding acquisition: Jaeho Cho, Young Uk Kim.
Investigation: Hojin Shin, Young Uk Kim.
Methodology: Jaeho Cho, Young Uk Kim.
Project administration: Jaeho Cho, Young Uk Kim.
Resources: Hyunhae Kim, Young Uk Kim.
Software: Young Uk Kim.
Visualization: Sunyoung Moon.
Writing – original draft: Jungmin Yi, Woobin Choi, Keum Nae Kang.
Abbreviations:
- IMCSA
- infraspinatus muscle cross-sectional area
- IMT
- infraspinatus muscle thickness
- MRS
- magnetic resonance imaging of the shoulder
- SNE syndrome
- suprascapular nerve entrapment syndrome
The authors have no conflicts of interest to disclose.
The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.
How to cite this article: Cho J, Yi J, Kim H, Moon S, Choi W, Kang KN, Shin H, Kim YU. Diagnosis of suprascapular nerve entrapment syndrome based on the infraspinatus muscle cross-sectional area on shoulder MRI. Medicine 2024;103:29(e39066).
Contributor Information
Jaeho Cho, Email: jaehotv@gmail.com.
Jungmin Yi, Email: jminyi19@gmail.com.
Hyunhae Kim, Email: leiga11@ish.ac.kr.
Sunyoung Moon, Email: tjsdudm19@naver.com.
Woobin Choi, Email: binrosa0413@gmail.com.
Keum Nae Kang, Email: cleanbinu@gmail.com.
Hojin Shin, Email: daniel.shin@emory.edu.
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