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Glendale Adventist Medical Center
1509 Wilson Terrace
Glendale, CA 91206
Ph: (818) 409-8000

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What is a Bennett thumb fracture? I get that my thumb is broken -- just not what a Bennet break means.

The thumb is made up of three bones: the metacarpal (bone closest to the wrist), the proximal phalanges (middle bone), and the distal phalanges (tip of the thumb). The CMC joint (an abbreviation for carpometacarpal joint) of the thumb is where the metacarpal bone of the thumb attaches to the trapezium bone of the wrist. This joint is sometimes referred to as the basal joint of the thumb. The CMC is the joint that allows you to move your thumb into your palm, a motion called opposition. A Bennett fracture is a break in the metacarpal bone at the thumb base where it attaches to the trapezium bone of the wrist. It causes two separate bone fragments. One of those fragments is still attached to the ligament there. the rest of the metacarpal bone gets pulled away by the abductor pollicis longus muscle of the thumb. If you had a fracture in this same location that resulted in many bone fragments (not just two), it would be a Rolando fracture. This is still a form of Bennett fracture, just more complex. The surgeon will have to pin (or wire) the bone back together and hold it in place (usually with a cast) until healing takes place. Without surgical treatment, this type of fracture is not likely to heal. Arthritis at the carpometacarpal (CMC) joint is a potential problem without treatment (and sometimes even with treatment).


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