Review Question - QID 216799

This patient has a posterior labral tear with an adjacent paralabral cyst that is leading to compression of the spinoglenoid notch and will affect the infraspinatus muscle only.

The suprascapular nerve innervates the supraspinatus and infraspinatus muscles. It first crosses under the transverse scapular ligament and impingement at this location leads to denervation of both the supraspinatus and infraspinatus. As the nerve progresses through its course, it traverses the spinoglenoid notch to innervate the infraspinatus muscle. Therefore, compression at the spinoglenoid notch only affects the infraspinatus. The most common etiology of spinoglenoid notch compression is a paralabral cyst associated with a labral tear. Patients describe vague, deep shoulder pain and will have weakness with external rotation with the arm by the side when the infraspinatus is affected. MRI is useful in identification of these lesions and surgical decompression is usually required in cases of mechanical impingement.

Martin et al. reviewed the results of nonoperative management in patients with suprascapular neuropathy. They utilized physical therapy and evaluated the patients at an average of 4 years out from their diagnosis, with 5 patients reporting excellent results, 7 good results, and 3 opting for operative management. They concluded that if there was no well defined lesion compressing the nerve, suprascapular neuropathy should be managed non-operatively.

Piasecki et al. reviewed suprascapular neuropathy and the relevant anatomy, noting it is relatively uncommon. They note it is particularly vulnerable to compression at the suprascapular and spinoglenoid notches in addition to the possibility of traction neuropathy following overhead sports or retracted rotator cuff tear. They recommend initial nonoperative management in the absence of a compression lesion, but with discrete nerve compression do recommend early operative intervention for decompression.

Figure A is a Sagittal T1 shoulder MRI demonstrating the normal musculature of the shoulder girdle. The structures labeled are as follows: (1) Deltoid (2) Subscapularis (3) Supraspinatus (4) Infraspinatus (5) Teres Minor.

Incorrect Answers:
Answer 1: Structure #2 is the subscapularis, which is innervated by the upper and lower subscapular nerves and would not be affected in this patient.
Answer 2: Structure #3, the supraspinatus, is innervated by the suprascapular nerve, although the site of impingement, in this case, is distal to its innervation, therefore, it would not be affected.
Answer 4: The deltoid (structure #1) and teres minor (structure #5) are innervated by the axillary nerve, which would not be affected in this case.
Answer 5: Both the supraspinatus (structure #3) and infraspinatus (structure #4) would be affected in cases where the suprascapular nerve was compressed at the suprascapular notch, not the spinoglenoid notch as in this question.