Elbow ossification occurs at the six elbow ossification centers in a reproducible order. Being familiar with the order of ossification of the elbow is important in not mistaking an epicodylar fracture for a normal ossification center.
The order of appearances of the elbow ossification centres is highly reliable and in most individuals, is consistent: capitellum, radial head, internal epicondyle, trochlea, olecranon and external epicondyle.
The order of "I" and "T" are most important to remember - the trochlea ossification center should not appear before the internal (medial) epicondyle ossification centre. If you can see a trochlea but no internal epicondyle, then you need to look very hard for the avulsed ossification center.
Two counting methods are taught to help remember the ages at which the ossification centers appear: 1 - 3 - 5 - 7 - 9 -11 (simple) and 1 - 5 - 7 - 10 - 10 - 11 (more accurate).
- capitellum - 1 year
- radial head - 3 years
- medial epicondyle - 5 years
- trochlea - 7 years
- olecranon - 9 years
- lateral epicondyle - 11 years
Therefore, if the trochlear center is present, but there is no medial epicondyle then you are most likely looking at a medial epicondylar fracture where the ossification centre has been avulsed and displaced. This is extrememly important since these injuries should be seen by an orthopaedic surgeon and internally fixed.
Elbow ossification: article - mnemonic