Rotator Cuff: Supraspinatus (empty can test)

The rotator cuff is composed of four muscles

  1. Supraspinatus – abduction
  2. Infraspinatus – external rotation
  3. Teres minor – external rotation
  4. 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.

The anatomical snuff box and deQuervain’s tenosynovitis

The anatomical snuff box is among one of the most fun-named anatomic structures, it’s called the snuff box because people used to put snuff (tobacco) in it.

If you have dinky little hands like me, the snuff box is pretty prominent (as you can see in the doodle since that’s my left hand). The borders are the extensor pollicis longus posteriorly, extensor pollicis brevis and abductor pollicis longus anteriorly and the radial stylus process proximally. If you poke around the snuff box you can feel both the scaphoid and the trapezium as well as the radial artery. Like the rest of the forearm and hand, the snuff box is chock full of way too many structures. The radial nerve is deep in the box while the dorsal cutaneous branch of the radial nerve lies superficially to the extensor pollicis longus. The cephalic vein also originates in the snuff box.

DeQuervain’s Tenosynovitis
This is when the tendons of the extensor pollicis brevis and abductor pollicis longus get inflamed (usually due to overuse, particularly gripping/grasping). Any maneuver that causes these tendons to activate (ie extending the thumb against resistance) causes pain along the lateral side of the wrist and forearm. The classic test is Finkelstein’s maneuver, in which a fist is made over the thumb and the wrist is ulnarly deviated. This stretches the tendons over the radial styloid causing significant pain.

Bones and joints of the hand and wrist

Of course the majority of the bones in the hand we pretty straight forward. You have your metacarpals, appropriately named first through fifth and the same goes with the phalanges. The important thing to remember is that the thumb is phalanges-challenged and only has two instead of three. The reason this can mess people up is that in the thumb only has one interphalangeal (IP) joint whereas the fingers have a proximal interphalangeal (PIP) joint and a distal interphalangeal (DIP) joint.

It’s usually the CMC joint of the thumb (AKA the TMC joint because it’s an articulation between the trapezium and 1st metacarpal) that gives women grief in later life as its prone to arthritis.

Then there are the carpal bones (8 in total)

  • S – scaphoid
  • L – lunate
  • Tq – triquetrum
  • P – pisiform
  • Tm – trapezium
  • Td – trapezoid
  • C – capitate
  • H – hamate

There are plenty of mnemonics to remember them, the one I learned was Some Lovers Try Positions That They Can’t Handle (which goes from thumb across one row and then from the thumb across the more distal row)

The radioulnar joint is one of the articulation points for supination and pronation and the radiocarpal joint is the articulation for extension and flexion.

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