The carpal bone ossify aka turn into bone aka magically become visible on an x-ray in a predictable order.
The easiest way to remember is that it starts at the capitate (smack dab in the middle) and then goes in a ulnarly-directed spiral. I was going to say “clockwise” or “counter-clockwise” but that would depend on which side of which hand you were looking at. So capitate, followed by hamate and then down to triquetrum and so on. Except for the pisiform, being a sesamoid bone it gets left behind and only develops years later.
- Capitate: 1-3 months
- Hamate: 2-4 months
- Distal radius: 1 year
- Triquetrum: 2-3 years
- Lunate: 2-4 years
- Scaphoid: 4-6 years
- Trapezium: 4-6 years
- Trapezoid: 4-6 years
- Distal ulna: 5-6 years
- Pisiform: 8-12 years
I included the distal radius and distal ulna in there for good measure.
I know I could have been fancier with changing the length of the metacarpals or their growth plates, but it was more fun to make the animated gif.