Solution to Unknown Case #17 – Short 4th and 5th Metacarpals Differential Diagnosis

History: 15 year old boy with hand pain. 

Short 4th and 5th metacarpals: Radiograph of the left hand shows the 4th and 5th metacarpals are abnormally shorter than the other metacarpals. Additionally, the third metacarpal is abnormally bowed.

This is a case of short 4th and 5th metacarpals. Shortened 4th and 5th metacarpals is diagnosed by the metacarpal sign, which involves drawing a line through the heads of the 4th and 5th metacarpals. If the line intersects the head of the third metacarpal, then it is a positive metacarpal sign and diagnostic of a shortened 4th and 5th metacarpals. The metacarpal sign unfortunately can be positive in normal individuals about 10% of the time.

The differential diagnosis of shortened 4th and 5th metacarpals (which has also been referred to as “knuckle-knuckle-dimple-dimple” on physical exam), is as follows

1. Idiopathic
2. Post-traumatic or infectious
3. Turner syndrome
4. Pseudohypoparathyroidism and pseudopseudohypoparathyroidism
5. Basal Cell Nevus Syndrome – Gorlin Syndrome
6. Hereditary Multiple Exostosis Syndrome
7. Homocystinuria

The cause in this case was idiopathic, which is the most common.