A 7 year old male presents to the ED with isolated right elbow pain three hours after falling on his out-stretched right arm while roller blading. The patient did not sustain any other trauma to his head, neck or trunk. He has not complained of any numbness or tingling in his right hand post-injury.
The right upper extremity from the clavicle to the tip of the fingers is atraumatic in appearance without any obvious angulation or swelling. The patient exhibits full range of motion about the shoulder and wrist. There is no tenderness over the anatomic “snuffbox” region.
The elbow has no obvious swelling, and the elbow circumference (of the affected arm) is equal to the elbow circumference of the non-affected arm. There is very mild, diffuse tenderness about the right elbow (without any specific point tenderness). He has no pain with active elbow flexion, extension, supination, or pronation.
Although you clinically do not suspect any fracture of the right elbow region, the patient’s mother is very anxious and demands an x-ray of her son’s elbow.
Radiographs of the right elbow are obtained.
How many ossification centres are present in this radiograph and what are the names of these ossification centres?
All six ossification centres are present in their expected anatomic positions – capitellum, radial head, internal (medial) epicondyle), trochlear, olecranon, external (lateral) epicondyle.
Are the ossification centres in their correct (expected) anatomic positions?
Yes, all ossification centres are in the correct place.
Are there any fractures present in this radiograph, and if so where?
There is no evidence of elbow effusion. Normal anterior humeral line and a normal radiocapitellar line.
Overall radiographic interpretation: Normal right elbow with normal ossification centres.
Discussion & Teaching Points
- There are 6 ossification centres around the elbow joint. These ossification centres all appear at different ages and they all fuse to the adjacent bones at various ages. It is not clinically important to memorise the specific ages of when these ossification centres appear or fuse. However, it is clinically important to realise that the ossification centres always appear in a specific sequence.
- The mnemonic of the order of appearance of the individual ossification centres is C-R-I-T-O-E: Capitellum, Radial head, Internal (medial) epicondyle, Trochlea, Olecranon, External (lateral) epicondyle.
- Remember that the anatomic position of the body places the upper extremities in external rotation (supination at the elbows) such that the antecubital fossa faces anteriorly. Thus, the external epicondyle is on the radial side of the elbow, while the internal epicondyle is on the ulnar side of the elbow.
- The ages at which these ossification centres appear are highly variable, but as a general guide, remember 1-3-5-7-9-11 years. Note that our patient in this case is 7 years old but all six ossification centres are present. This illustrates that this age sequence is just a guide since the age ranges are highly variable.
- Knowing the C-R-I-T-O-E mnemonic is helpful in determining whether a small piece of bone about the elbow joint represents an avulsion fragment or an ossification centre. The ossification centres always appear in the order specified in the mnemonic C-R-I-T-O-E.
- Example: If you see only three accessory bony fragments about an elbow joint, these bony pieces should be in the areas of the capitellum, radial head and the internal (medial) epicondyle. If one of the three bony fragments is in the area where you would expect to see the external epicondyle, then that piece actually represents an avulsion fracture of the distal, lateral humerus, rather than a normal external epicondyle.
- Whenever evaluating an injured extremity, the most important aspect of the examination is to assess the neurovascular integrity of the affected extremity.
- Always remember to palpate the entire extremity (including the clavicles) in all children who present after falling on the out-stretched arm.
- Always remember to document whether or not the patient who has fallen on the out-stretched hand has any tenderness over the anatomic “snuffbox” (scaphoid bone). Any patient with tenderness over the scaphoid (navicular) bone must be treated (splinted with orthopaedic referral) as an occult scaphoid fracture until proven otherwise (even if the initial scaphoid views do not reveal any evidence of a fracture).