HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Figures Only Full Text (PDF) All Versions of this Article: 2261011818v1 226/1/161    most recent Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Yao, L. Articles by Mehta, U. Search for Related Content PubMed PubMed Citation Articles by Yao, L. Articles by Mehta, U.

Infraspinatus Muscle Atrophy: Implications?¹

¹ From the Department of Radiology, National Institutes of Health, Bldg 10, Rm 1C640, 10 Center Dr, Bethesda, MD 20892-1182 (L.Y.); and Department of Radiology, Georgetown University Medical Center, Washington, DC (U.M.). Received November 13, 2001; revision requested January 28, 2002; final revision received April 30; accepted May 14. Address correspondence to L.Y. (e-mail: yaolawrence@yahoo.com).

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
PURPOSE: To evaluate associated findings in patients who exhibited atrophy of infraspinatus muscle at magnetic resonance (MR) examination of their shoulders to clarify implications of this abnormality.

MATERIALS AND METHODS: With an electronic database search, cases of advanced infraspinatus muscle atrophy in patients who underwent MR imaging during a 1-year period for evaluation of shoulder pain or dysfunction were identified. The analysis was restricted to cases interpreted by one reader who applied a standardized method of reporting. Associated MR imaging findings in these cases were tabulated.

RESULTS: Advanced infraspinatus muscle atrophy was encountered in 51 (4.3%) of 1,191 MR examinations of the shoulder. Tears of the infraspinatus tendon were present in only 27 (53%) of 51 cases. In 46 (90%) of 51 cases, a full-thickness tear was present in the anterior portion of the rotator cuff. In 10 (20%) of 51 cases with infraspinatus muscle atrophy, cuff muscle atrophy was confined to the infraspinatus muscle. Cuff muscle atrophy was isolated to the infraspinatus muscle in four (17%) of 24 cases in which atrophy of the infraspinatus muscle was present despite an intact tendon. In none of the 51 cases was there a mass in the suprascapular or sphenoglenoid notch.

CONCLUSION: Infraspinatus muscle atrophy typically occurs with tendon tears in the anterior aspect of the rotator cuff. Concomitant atrophy in the supraspinatus muscle often is present, but infraspinatus muscle atrophy can occur in isolation, and this finding does not imply that the infraspinatus tendon is ruptured.

© RSNA, 2002

Index terms: Muscles, injuries, 41.4813 • Muscles, MR, 41.121411, 41.121412, 41.121413, 41.4813 • Shoulder, injuries, 41.4813 • Shoulder, MR, 41.121411, 41.121412, 41.121413, 41.4813

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Rotator cuff muscle atrophy is readily detected at magnetic resonance (MR) imaging of the shoulder. This finding is a useful sign of a rotator cuff tendon tear. Rotator cuff muscle atrophy most commonly occurs in the supraspinatus muscle where most cuff tendon tears occur. The presence of cuff muscle atrophy implies that an associated cuff tendon tear is chronic, and because it is chronic, the surgical approach for cuff repair usually is altered (1). Advanced cuff muscle atrophy also has negative prognostic clinical importance for patients who undergo surgical repair of the rotator cuff (2–4).

Atrophy in cuff muscles other than the supraspinatus muscle also regularly occurs, typically when the cuff tears are large. Atrophy localized to the infraspinatus muscle can occur secondary to suprascapular neuropathy and can be caused by either a compressive mass in the suprascapular or spinoglenoid notch (5) or a traction injury to the nerve (6).

We observed that infraspinatus muscle atrophy occurs in the setting of anterior cuff tears, even when the infraspinatus tendon appears uninvolved in the tear. The purpose of this study was to evaluate the associated findings in patients with atrophy of the infraspinatus muscle at MR examination of their shoulders to clarify the implications of infraspinatus muscle atrophy.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Patients
All patients were referred from community-based practices for outpatient MR imaging for evaluation of shoulder pain or dysfunction. An electronic MR imaging patient database was queried for the finding of advanced infraspinatus muscle atrophy. The search was limited to MR images of the shoulder that were interpreted by a single musculoskeletal radiologist who had 10 years of experience in the interpretation of musculoskeletal MR imaging. This reader applied a standardized lexicon to reporting of MR imaging findings. In this context, the term "advanced atrophy" was used only when some degree of fatty involution of the muscle was evident on images. This narrower definition was adopted to reduce subjectivity in case selection. The case accrual time period was 1 year. Our institutional review board does not require its approval or informed consent for this type of study.

This study included 51 subjects (28 women, 23 men), and the mean age was 66 years ± 11.5 (SD) (age range, 32–86 years).

Imaging
MR imaging was performed with 0.3 T in 392 patients with one machine (Airis I; Hitachi Medical Systems America, Twinsburg, Ohio), in 245 patients with another machine (MRP 7000, Hitachi Medical Systems America), and in 455 patients with a third machine (Airis II, Hitachi Medical Systems America) or with 0.35 T in 99 patients with a fourth machine (Opart; Toshiba America Medical Systems, Tustin, Calif). All were open MR imaging units. A standardized imaging protocol was used, and images were obtained with the following sequences: coronal oblique T1-weighted spin echo (repetition time msec/echo time msec, 450–550/25) and T2-weighted fast spin echo (repetition time msec/echo time msec [effective] 2,000–2,200/75–90; echo train length, four), transverse three-dimensional gradient echo (40–50/22–23; flip angle, 30°), and sagittal oblique short inversion time inversion-recovery (STIR) (repetition time msec/echo time msec/inversion time msec, 1,750–2,000/25–35/80).

Image Evaluation
Associated findings at MR imaging, as documented in the report database, were tabulated. Cases were not reviewed again for this data collection. The MR imaging findings that were tabulated included the extent of rotator cuff tendon tears (specific tendon involvement), ruptures of the long-head biceps tendon, the presence of periarticular masses, and advanced atrophy in other rotator cuff muscles. For purposes of the analysis, only complete, retracted ruptures of the long-head biceps tendon were classified as ruptures. Advanced atrophy in cuff musculature was diagnosed when fatty involution was depicted on MR images, as discussed for the infraspinatus.

The clinical database in each patient was also queried for a history of prior shoulder surgery or trauma to the shoulder, as routinely reported by the patients at the time of their MR imaging examination. Sex and age of the patients were also recorded.

Data Analysis
Patients with infraspinatus muscle atrophy were classified into two groups: those with a partially or completely ruptured infraspinatus tendon (group 1), and those with an intact infraspinatus tendon (group 2). The differences in the rate of MR imaging and clinical features between the groups was tested with either the ² or the Fisher exact test. Differences in age were tested with a t test.

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
During the study period, 1,191 MR examinations of the shoulder were identified in 1,172 subjects. Of these 1,172 subjects, 51 shoulders in 51 subjects (4.4%) exhibited MR imaging evidence of advanced infraspinatus muscle atrophy (Figure).

View larger version (159K): [in this window] [in a new window] [Download PPT slide]   (A-D) Infraspinatus muscle atrophy in a large anterior cuff tear. (A) Transverse gradient-echo MR image (45/23; flip angle, 10°) demonstrates an intact infraspinatus tendon (arrow). (B) Sagittal STIR MR image (1,750/35/80) demonstrates large anterior cuff tear (arrowheads). Infraspinatus tendon (arrow) remains intact. (C) Coronal fast spin-echo T2-weighted MR image (2,100/75; echo train length, four) demonstrates a retracted full-thickness tear (arrow) of the supraspinatus tendon, with atrophy (*) of the supraspinatus muscle belly. (D) Coronal T1-weighted spin-echo MR image (540/25) demonstrates associated atrophy (*) and fatty involution of the infraspinatus muscle belly.

In 10 (20%) of 51 cases of infraspinatus muscle atrophy, the cuff muscle atrophy was isolated to the infraspinatus muscle. In 41 (80%) of the 51 cases, atrophy was present in other portions of the rotator cuff (Figure). Associated muscle atrophy was in the supraspinatus muscle (33 cases [65%]), supraspinatus and subscapularis muscles (seven cases [14%]), or in the subscapularis muscle alone (one case [2%]). None of the 51 cases of infraspinatus muscle atrophy exhibited teres minor muscle atrophy.

Of the 51 subjects with infraspinatus muscle atrophy, only 27 (53%) had a partial- or full-thickness tear of the infraspinatus tendon (group 1). Twenty-four (47%) of 51 subjects with infraspinatus muscle atrophy had no evidence of an infraspinatus tendon tear (group 2). These two groups did not differ significantly in age, sex, the incidence of antecedent shoulder trauma, or the incidence of prior shoulder surgery (Table).

In none of the 51 cases was a mass or cyst identified in the suprascapular or spinoglenoid notch areas.

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Rotator cuff muscle atrophy, particularly in the setting of impingement syndrome, is a conspicuous MR imaging finding that commonly heralds advanced cuff tendon disease. Our results suggest that this finding, when encountered in the infraspinatus muscle, does not consistently imply that there is an abnormality in the infraspinatus tendon itself. However, in almost all cases, the finding does indicate a rupture in the anterior aspect of the cuff where most tears begin.

The finding of infraspinatus muscle atrophy has been recognized clinically and at MR imaging in cases of suprascapular nerve palsy. Injury to the suprascapular nerve can result when a ganglion cyst or perilabral cyst compresses the nerve in the suprascapular or spinoglenoid notch areas. Such cysts usually occur secondary to an abnormality in the superior or posterosuperior aspects of the glenoid labrum. No such cysts were encountered in the MR imaging examination of our patients who had infraspinatus muscle atrophy. Suprascapular nerve palsy can also result from a traction mechanism in competitive athletes involved in overhead activities, such as volleyball (6). Our patients were not referred for examination by specialized sports medicine practices, and our patient population did not include, in large part, competitive athletes.

Investigators (7) who performed computed tomography also described the development of infraspinatus muscle atrophy in anteriorly located cuff tears. The results of that study indicated that infraspinatus atrophy was a negative prognostic indicator. Patients with infraspinatus muscle atrophy tended not to recover infraspinatus muscle bulk and function even after successful surgical cuff repair, while supraspinatus muscle atrophy and strength was more reversible. The reasons for the vulnerability of the infraspinatus muscle to atrophy and the lack of resilience of this muscle to recover strength and function after cuff repair are intriguing. Researchers (8) who created lesions in rabbits also documented the development of infraspinatus muscle atrophy after selective detachment of the supraspinatus tendon. The subscapularis muscle in these rabbits did not develop atrophy (8).

Disuse that may accompany a painful shoulder is not an adequate explanation for the infraspinatus muscle atrophy that we describe. In our cases, there was universal sparing of the teres minor muscle and only occasional involvement of the subscapularis muscle. Ten (20%) of our patients with infraspinatus muscle atrophy did not have atrophy in the supraspinatus muscle. Perhaps an anterior cuff tear alters the biomechanics of the glenohumeral mechanism in a manner that compromises the suprascapular nerve. If so, the atrophy of the infraspinatus muscle that occurs with an intact tendon may have a neuropathic basis. An electromyographic study in the patients reported by Goutallier et al (7), however, did not reveal impairment of the suprascapular nerve.

While the use of one experienced reader may represent a study limitation, in a strictly retrospective database survey of this type, it actually facilitated the systematic collection of reliable patient data. This reliability is predicated on the use of a standardized method of reporting (9), as employed by the reader in this study. The abstraction of only "advanced" infraspinatus atrophy was designed to reduce subjectivity in case selection. Early cases of atrophy that were manifested exclusively on fat-suppressed T2-weighted or STIR MR images were excluded because they might be confused with muscle strain injuries. The conservative nature of the criteria for muscle atrophy used in this survey should be considered in interpreting the data.

In summary, infraspinatus muscle atrophy does occur in the absence of a rupture of the infraspinatus tendon. Our case experience suggests that compressive neuropathy of the suprascapular nerve is a comparatively uncommon cause for infraspinatus muscle atrophy. Infraspinatus muscle atrophy typically occurs in association with full-thickness anterior cuff tendon tears, where atrophy in muscles of other involved tendons also may be present. Atrophy of the infraspinatus muscle can occur in isolation even when the infraspinatus tendon is intact, and this phenomenon cannot be adequately explained as a consequence of disuse. Findings in the study by Goutallier et al (7) suggest that the presence of infraspinatus muscle atrophy has independent prognostic importance for patients who are undergoing a cuff repair, as reflected by a higher rate of retearing of the cuff tendon and diminished active external rotation in these patients.

	FOOTNOTES

 
Abbreviation: STIR = short inversion time inversion-recovery

Author contributions: Guarantor of integrity of entire study, L.Y.; study concepts and design, L.Y.; literature research, U.M.; clinical studies, L.Y., U.M.; data acquisition, U.M.; data analysis/interpretation, L.Y., U.M.; statistical analysis, L.Y.; manuscript preparation, definition of intellectual content, editing, revision/review, and final version approval, L.Y.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 

1. Warner JJ, Goitz RJ, Irrgang JJ, Groff YJ. Arthroscopic-assisted rotator cuff repair: patient selection and treatment outcome. J Shoulder Elbow Surg 1997; 6:463-472.[Medline]
2. Iannotti JP, Bernot MP, Kuhlman JR, Kelley MJ, Williams GR. Postoperative assessment of shoulder function: a prospective study of full-thickness rotator cuff tears. J Shoulder Elbow Surg 1996; 5:449-457.[CrossRef][Medline]
3. Gazielly DF, Gleyze P, Montagnon C. Functional and anatomical results after rotator cuff repair. Clin Orthop 1994; 304:43-53.
4. Thomazeau H, Boukobza E, Morcet N, Chaperon J, Langlais F. Prediction of rotator cuff repair results by magnetic resonance imaging. Clin Orthop 1997; 344:275-283.
5. Fehrman DA, Orwin JF, Jennings RM. Suprascapular nerve entrapment by ganglion cysts: a report of six cases with arthroscopic findings and review of the literature. Arthroscopy 1995; 11:727-734.[Medline]
6. Ferretti A, De Carli A, Fontana M. Injury of the suprascapular nerve at the spinoglenoid notch: the natural history of infraspinatus atrophy in volleyball players. Am J Sports Med 1998; 26:759-763.[Abstract/Free Full Text]
7. Goutallier D, Postel JM, Bernageau J, Lavau L, Voisin MC. Fatty muscle degeneration in cuff ruptures: pre and postoperative evaluation by CT scan. Clin Orthop 1994; 304:78-83.
8. Fabis J, Kordek P, Bogucki A, Mazanowska-Gajdowicz J. Function of the rabbit supraspinatus muscle after large detachment of its tendon: 6 week, 3 month, and 6 month observation. J Shoulder Elbow Surg 2000; 9:211-216.[CrossRef][Medline]
9. Yao L, Nelson MC, Blease S, Platenberg C. Standardizing the MRI report: recommendations and guidelines for evaluation of the knee, shoulder, cervical spine, and lumbar spine. (abstr) 2000; 217(P):619.

This article has been cited by other articles:

				I OZTOPRAK, B OZTOPRAK, C GUMUS, H EGILMEZ, and M F ERKOC An abdominal muscular fold mimicking tumour Br. J. Radiol., January 1, 2009; 82(973): e1 - e2. [Abstract] [Full Text] [PDF]

				K. Strobel, J. Hodler, D. C. Meyer, C. W. A. Pfirrmann, C. Pirkl, and M. Zanetti Fatty Atrophy of Supraspinatus and Infraspinatus Muscles: Accuracy of US Radiology, November 1, 2005; 237(2): 584 - 589. [Abstract] [Full Text] [PDF]

				J. M. Mellado, J. Calmet, M. Olona, C. Esteve, A. Camins, L. Perez del Palomar, J. Gine, and A. Sauri Surgically Repaired Massive Rotator Cuff Tears: MRI of Tendon Integrity, Muscle Fatty Degeneration, and Muscle Atrophy Correlated with Intraoperative and Clinical Findings Am. J. Roentgenol., May 1, 2005; 184(5): 1456 - 1463. [Abstract] [Full Text] [PDF]

This Article Abstract Figures Only Full Text (PDF) All Versions of this Article: 2261011818v1 226/1/161    most recent Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Yao, L. Articles by Mehta, U. Search for Related Content PubMed PubMed Citation Articles by Yao, L. Articles by Mehta, U.