Carpal Boss (Carpometacarpal Boss)

A hard, fixed, non-mobile lump on the dorsum of the wrist at the bases of the index and middle metacarpals is most likely a carpal boss, which is a symptomatic bony prominence - an osteophyte or exostosis - at the second and third carpometacarpal joints, representing localised osteoarthritis, sometimes with an associated accessory ossicle, the os styloideum. The most important distinction is from a dorsal wrist ganglion: a ganglion is soft, mobile, often transilluminates, fluctuates in size and sits more proximally over the scapholunate region, whereas a carpal boss is hard, fixed and bony at the CMC bases and becomes more prominent when the wrist is flexed. I would confirm the diagnosis with a dedicated carpal boss view - a lateral radiograph with the wrist about 30 to 40 degrees supinated and ulnar-deviated, which profiles the dorsal osteophyte - and use CT if I needed to plan surgery. Management is non-operative first, because the lump itself is harmless: reassurance, activity modification, a wrist splint, non-steroidal anti-inflammatories and a corticosteroid injection, and most settle or are tolerated. If pain is refractory, the operation is simple excision of the bony exostosis with any overlying ganglion, which gives reliable results with low recurrence. The pitfall to avoid is excessive bone resection, which can destabilise the carpometacarpal joint, so I would resect the prominence while preserving CMC stability, and reserve a fusion for the rare case of secondary instability rather than performing it routinely.