The ossification centre for the internal (ie medial) epicondyle is the point of attachment of the forearm flexor muscles. Vigorous muscle contraction may avulse this centre (see p. 105). The most common injury mechanism is a fall on an outstretched hand. Avulsions also occur in children who are involved in throwing sports, hence the term “little leaguer’s elbow”.

When a major displacement of the internal epicondyle occurs the bone can become trapped within the elbow joint. This is a well recognised complication of a dislocated elbow, occurring in 50% of cases following an elbow subluxation or dislocation. A major avulsion is easy to overlook when an elbow has been transiently dislocated and then reduces spontaneously^5,6 because the detached epicondyle may, on the AP radiograph, be mistaken for the normally positioned trochlear ossification centre (p. 105).

I before T. Though the CRITOL sequence may vary slightly there is a constant: the trochlear (T) centre always ossifies after the internal epicondyle. Therefore apply this rule: if the trochlear centre (T) is visible then there must be an ossified internal epicondyle (I) visible somewhere on the radiograph. If the internal epicondyle is not seen in its normal position then suspect that it is trapped within the joint.

This line helps you to detect a supracondylar fracture with posterior displacement (pp. 106–108).