The rotator cuff is composed of four muscles
- Supraspinatus – abduction
- Infraspinatus – external rotation
- Teres minor – external rotation
- Subscapularis – internal rotation
Rotator cuff injuries are incredibly common and it is helpful to figure out which of the four muscles is the major source of the problem (there is of course the possibility that multiple ones are injured/irritated).
For the supraspinatus (innervated by the suprascapular nerve C5,6) you can do the “empty can test“. The patient holds out the affected arm (abducts) with elbow extended and wrist pronated. Like they were, in fact, pouring out a can of soda (or “pop” as we call it here). The examiner then pushes down on the extended arm and the patient tries to resist. Pain or weakness is a positive test.