boss or simply metacarpal boss is a common finding of a
dorsal radial prominence of the middle and/or index
carpometacarpal joint. It is benign, usually painless
and usually does not require treatment.
The term "Boss" is derived from the French "bosse" meaning bump, swelling or tumor.
Symptoms, if present, may resolve without treatment. If they don't, options include:
|Click on each image for a larger picture|
appearance, here more prominent over the index
accentuated with clenched fist and wrist flexion.
fist xray tangential view profiles the prominence,
here with an exostosis of the metacarpal base.
with "kissing osteophytes"
with exostosis from the capitate.
painless, they may give rise to symptoms from
arthritic type joint pain or from tendon snapping.
This patient had persistent pain and tendon irritation
from index extensor tendons snapping over the
|In this case, the
index extensor tendons lie radial to the boss at
|but snap to the
ulnar side when gripping.
|This was treated
by shaving down the prominence. Here are the same
maneuvers a year after surgery.
shows smooth contour.
intraoperative view of dorsal bone recontouring of the
metacarpal and capitate. Periosteum was closed over
the exposed medullary bone.
|Some patients have
joint inflammation associated with this, as
demonstrated on this bone scan:
|Xray of the above
patient's symptomatic hand.
|Carpometacarpal arthrodesis is an option for failure of other treatment.|
|For most people,
metacarpal boss is simply an exaggeration of a normal
contour. This patient has no symptoms. Interestingly,
despite an apparent larger prominence on the right
hand, Xrays shown below show a larger bony prominence
on the left.
|Why do we develop
They may arise from irritation of the wrist extensor tendons which insert into the index and middle metacarpal bases.
They may also have to do with the presence of the middle metacarpal styloid process, which is a unique feature of the human hand and the human genus homo. Below, "O" points to the same area comparing the gorilla hand (no styloid) to the Neandertal hand (styloid present).
process is located right where a boss is most likely
importance of the styloid is that it helps stabilize
the middle metacarpal to the carpus, creating the
"fixed unit" of the hand as described by Littler. This
increases strength of grip and impact of a punch.
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