Monday, January 23, 2012

Hand Anatomy: Tips For Learning The Carpal Bones

Learning hand anatomy is important for any medical student. Despite being a relatively small area, the hand contains many structures which leads to many disease patterns. For example, ulnar nerve injuries can cause patterns of findings like Pope's blessing. However, by learning the hand systematically, these diseases can be eventually mastered.

As far as what order to learn hand anatomy, it makes sense to start with the bones as they form the framework which all the other structures course through or attach to. The long bones of the forearm that articulate with the wrist (also called the carpus) are the radius and the ulna, which are on the lateral and medial sides of the forearm, respectively. There are two rows of carpal bones, which will be discussed in further detail below. The distal row articulates with the metacarpals, which are named by the digit they attach to. The metacarpals, in turn, articulate with the proximal phalanges (single: phalanx), which join with the middle and distal phalanges to form the rest of the digits. Note, there is no middle phalanx in the first digit (the thumb).

Proximal: A=Scaphoid, B=Lunate, C=Triquetrum, D=Pisiform
Distal: E=Trapezium, F=Trapezoid, G=Capitate, H=Hamate
Source: Wikipedia
Now about those carpal bones! Starting with the proximal row, there are the scaphoid, lunate, triquetrum, and pisiform. The distal row contains the trapezium, trapezoid, capitate, and hamate. How does anyone go about remembering them? 

Simple! Mnemonics - the most common one being Some Lovers Try Positions That They Cannot Handle:
  • Some - Scaphoid
  • Lovers - Lunate
  • Try - Triquetrum
  • Positions - Pisiform
  • That - Trapezium
  • They - Trapezoid
  • Cannot - Capitate
  • Handle - Hamate
Keep in mind that the first four letters refer to the proximal row, and the second four to the distal row, both from radial/lateral to ulnar/medial side. Like every mnemonic, this one has a downside: there are THREE bones that start with 'T', two of which sound very similar to each other. How does one remember which T goes with which T bone? 
  • For triquetrum, remember that the word in the mnemonic try sounds the same as the first syllable tri-.
  • Remember that, and there are only two T bones left, but they are spelled very similarly. No worries just remember that for trapezium, remember that the bone nearest the THUMB ends in -UM (say it aloud if that is unclear).
  • The remaining T bone has to be trapezoid. 
Hopefully bearing that extra information along with the mnemonic will help you easily master the bones of the wrist. Since we're talking about the bone, here are some extra factoids to keep in mind:
  • The scaphoid is the most commonly fractured bone in the wrist.
  • Also, the scaphoid has retrograde perfusion, so if there is vascular insufficiency, avascular necrosis will go in a proximal to distal, unlike every other bone.
  • The lunate is the most commonly disLocated bone in the wrist. On a lateral film, it looks like a half moon (hence, the name, as luna is Latin for moon). 
Once you've mastered the bones, learning the muscles, nerves, arteries and veins becomes much more straightforward. Knowing the bones is also key for learning all the eponymous fractures that occur at or near the wrist (Boxer's fracture, Bennett's fracture, Rolando's fracture, Colles fracture, Smith fracture, etc.). It takes some amount of practice and repetition, but I have no doubt you can handle it =)

Updated 2015-12-20


  1. I always remembered the trapezium was nearest the thumb, because you need your thumb so you can grab onto the flying trapeze.

  2. Haha, that's a good one too! It really is important to learn the mnemonic well - if you don't use it often, you'll get rusty very quickly.



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