Left: Snail                                                Right: Left scaphoid, view from the radius-ish

For this week’s edition of OsteoMenagerie, we have the scaphoid, a bone of the wrist that clearly looks like a snail. Appropriately given last week’s OsteoMenagerie, another term for the scaphoid is the navicular, because it is similarly positioned to the tarsal bone of the same name. However, I find the doubling of names confusing, and the ‘s’ in Scaphoid is a “handy” (get it? get it?) reminder that this wrist bone bears a striking resemblance to a Snail.

When the hand is in SAP, the scaphoid is the most superior and proximal carpal, which reminds me – I have a useful mnemonic for remembering the order of the carpal rows that I’ll share soon! Additionally Wikipedia notes that it is about the size of a cashew, which makes me never want to eat cashews again, frankly.

Left: Left scaphoid, view from capitate                                     Right: A different snail

Siding Tips: While this may make me a bad anatomist (Editor’s Note: It does make her a bad anatomist), when I’m working with whole carpals I rarely rely on their anatomical relationships, but instead use cheap tricks to identify and side them. Once I know that I’ve got a scaphoid, I orient it so that the tubercle is the “head” of the snail and the smooth indentation for the capitate is facing me. Whichever side of the snail’s head the shell falls on is the side the bone is from. In the drawing above, the bulk of the “shell” falls to the left of the snail’s head when the smooth indentation for the capitate is facing the observer, so the bone is from the left. If you doubt me (or find my logic confusing), verify with White & Folkens’ HBM, p. 229.

Original images found here: 1 & 2 & 3.