Age / Sex : 33 / M

Age / Sex :
33/M

Chief complaint :

Tender hard mass of wrist (Duration : 5 months)

1) What is your impression?

Two weeks later, you can see the final diagnosis with a brief discussion of this case.

* Send Application Answers to In Sook Lee, MD ([email protected])

Courtesy :

carpal boss

Discussion

Findings:

1)     Plain radiographs of the wrist show the dorsal bony protuberance at the carpometacarpal joint.

2)     Sagittal and volume rendering CT images show the dorsal osteophytes from the base of the third metacarpal bone and the capitate at the carpometacarpal joint.

Differential Diagnosis:

Diagnosis:  

Carpal boss (or carpometacarpal boss)

Discussion:

The carpal boss, an unmovable protuberance of bone on the dorsum of the hand, is a relatively common clinical entity. The carpal boss appears as a bone mass at the base of the second or third metacarpals, or both, and their articulations with the trapezoid and the capitate. The lesion may occur with or without a specific history of injury to this region. This bony protuberance may represent degenerative osteophyte formation and/or the presence of an os styloideum, an accessory ossification center that occurs during embryonic development. Occasionally, the os styloideum is completely isolated. More commonly it is fused to the second or third metacarpal (m/c), to the capitate or to the trapezoid.

The major axis of stress in the normal wrist is in the region of the second and third metacarpals, capitate, and the scapholunate joint. Since the third metacarpocapitate joint receives great stress during normal wrist function, degenerative joint disease may result from inability of this abnormal joint configuration to withstand the normal daily stress placed upon it. Typically this condition will begin to show itself in the third or fourth decade. The clinical differential diagnosis for a hard lump in the area of a carpal boss includes a ganglion, localized fibrosis or subcutaneous calcification.

Radiologically carpal boss shows osteophyte or bony protuberance from the dorsal surface of metacarpal base, capitate, and/or trapezoid at carpometacarpal joint or accessory ossicle (os styloideum) at metacarpal base. Radiographically, the view that best profiles the separate os styloideum is a lateral view utilizing 30° supination and ulnar deviation of the wrist.

 When this condition is symptomatic, patients present with complaints of pain and limitation of motion of the affected hand. The symptoms of carpal boss may result from an overlying ganglion or bursitis, an extensor tendon slipping over this bony prominence, or from osteoarthritic change at this site.

References:

1. Conway WF, Destouet JM, Gilula LA, Bellinghausen HW, Weeks PM. The carpal boss: an overview of radiographic evaluation. Radiology 1985;156:29-31

2. Hazlett JW. The third metacarpal boss. International orthopaedics 1992;16:369-371