 As such, the muscles usually involved are the supraspinatus and infraspinatus, which are both innervated by the suprascapular nerve.Involvement of the deltoid is more variable, as it is innervated by the axillary nerve.The differential focuses on distinguishing it from similar entities such as quadrilateral space syndrome, which involves the teres minor and variably the deltoid, and suprascapular nerve impingement at the spinoglenoid notch, which predominantly involves the infraspinatus.