Bennett's Fracture Fracture of the Base of the Thumb

The metacarpal bone at the base of your thumb and the trapezium bone in your wrist meet to form the carpometacarpal (CMC) joint.  Smooth cartilage covers the ends of the metacarpal and trapezium.  The cartilage allows the bones to glide easily during motion.  Strong ligaments and muscles hold the CMC joint in position and provide a combination of mobility and stability.
 
Your thumb joint is the only joint in your hand that can move in all directions.  Your thumb can move up and down, in and out, and rotate slightly to touch your fingers (opposition).  You move your thumbs hundreds of times each day.  The movements of the thumb allow it to work as an anchor to help the fingers hold objects.  The thumb works as a grip when you use a hammer or hold a glass.  The thumb also acts as a stabilizer to allow your fingers to manipulate items.  You use such precision movements for such activities as counting coins and handwriting.  A tendon that attaches to the base of the thumb metacarpal, called the abductor pollicis longus, is responsible for the joint dislocation that can occur with a Bennett’s fracture.

A Bennett’s fracture occurs when the metacarpal bone in the thumb breaks and dislocates at the base of the thumb.  This injury occurs when a force is placed on the thumb when it is slightly bent.  Bennett’s fractures can result from any significant forces placed on the base of the thumb, such as sports, falls and accidents.

A Bennett’s fracture causes your thumb to feel painful and stiff.  Your thumb area will swell.  Your thumb may be unstable and therefore difficult to move normally.  Over time, it is common for an old Bennett’s fracture that is poorly treated to develop arthritis.  This is because the joint at the base of the thumb is not realigned properly.

Your doctor can diagnose a Bennett’s fracture by examining your hand and taking X-rays.  In some cases, a computed tomography (CT) scan may be used to provide a more detailed image.