Carpal boss may occur secondary to:
-
os styloideum (an accessory ossicle of the wrist)
- hypertrophied bony protuberance on the dorsal surfaces of the base of the second or third metacarpals, near the capitate and trapezium, as in this case, there's elongation of the 3rd metacarpal base and the trapezoid bone with secondary pseudoarthrosis.
Degenerative changes at the site of the pseudoarthrosis are also common, as in this case.