Presentation
Hard swelling on the dorsal aspect of the hand
Patient Data
Small bony protuberance is seen dorsal to the carpometacarpal joints, best appreciated on the lateral view. The alignment and the joint spaces are maintained.
CT study shows that the bony protuberance is originating from the dorsal aspect of the capitate bone and articulates with the base of the 3rd metacarpal bone. The location and appearance of this bony structure is compatible with accessory ossicle (os styloideum). Mild degenerative changes are noted between the capitate, base of the 3rd metacarpal bone and between the capitate and the trapezoid bones.
3D volume rendering images redemonstrate the carpal boss.
Case Discussion
Bony protuberance between the capitate and the 2nd or 3rd metacarpal bases can cause palpable fixed prominence dorsal to the wrist. These findings are in keeping with a carpal boss. Differential diagnosis would include carpometacarpal joint osteoarthritis. Carpal boss may result in degenerative changes at the pseudoarticulation, ganglion formation, adventitial bursitis or irritation of the extensor tendons.