Carpometacarpal Boss

DESCRIPTION
A carpometacarpal boss is also known as a bossing. It is a bony overgrowth or lump on the back of the wrist at the base of the index (pointer finger) or long (middle finger) metacarpal bones where they join the carpal bones. 
CAUSES
The exact cause is unknown. Some people develop a carpometacarpal (CMC) boss following a traumatic injury or activities that involve repetitive wrist motion such as golf or racquet sports.
SIGNS AND SYMPTOMS
The CMC boss is usually first noticed in young adults between 20 and 40 years of age. It occurs equally in men and women. Usually the boss occurs on one wrist, but occasionally it can be present on both.

Patients notice a firm, immovable bump on the back of the wrist or hand. It can be painless or tender and achy. Pain can occur with upward and downward motion of the wrist. Painful or painless snapping of the tendons that straighten the fingers over the boss can occur. The boss is frequently mistaken for a ganglion cyst because of their similar appearance and location (Figure 1). Some patients can have a ganglion that arises from the boss itself.

An x-ray of a CMC boss is shown in figure 2.  
TREATMENT
The treatment approach depends on how long the boss has been present and what kinds of problems it is causing. If it is painless, nothing further needs to be done. If it is painful, you need to avoid movements and tasks that bring on the pain. Treatment options include:

  • A wrist splint to immobilize and rest the wrist
  • Icing of the painful area
  • Pain relievers such as Motrin or Tylenol
  • Steroid injection into the boss
  • Surgery

Surgery may be recommended if the boss has been painful for an extended period of time, if non-surgical treatment has failed, or if there is painful snapping of the tendons.

Surgery involves removing the boss. Continued pain and swelling is common after surgery, and it may take several weeks to months to improve. In some patients, the pain does not completely go away and the joint may need to be fused, which is a separate surgical procedure.

© 2016 American Society for Surgery of the Hand

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