Bennett’s Fracture: Base of the Thumb
Posted on Fri, Jan 13, 2012 @ 05:55 AM
History
In 1882, Edward Hallaran Bennett, MD, described this fracture of the base of the first metacarpal. It is the most common of thumb metacarpal fractures. Bennett described the anatomic details of the fracture and suggested that early diagnosis and treatment are imperative to prevent loss of function of this highly mobile joint. Bennett said his fracture "passed obliquely across the base of the bone, detaching the greater part of the articular surface, and "the separated fragment was very large and the deformity that resulted there-from seemed more a dorsal subluxation of the first metacarpal". Interestingly, Bennett was also the surgeon that introduced Lister’s concept of asepsis into Ireland.
Mechanism of Injury
Axial loading of a partially flexed thumb metacarpal causes this injury. This type of compression along the metacarpal bone is often sustained when a person punches a hard object, such as the skull or tibia of an opponent, or a wall. It can also occur as a result of a fall onto the thumb such as that sustained by Bears quarterback Jay Cutler while trying to make a tackle during the 2011 season. Indeed, this injury is fairly common in football and rugby, and males outnumber females by 10:1.
Problem
This fracture separates the important volar oblique ligament along with a portion of the joint surface of the base of the thumb metacarpal from the rest of the thumb metacarpal, and without this stabilizer, the joint can subluxate or dislocate under the pull of the APL tendon. Without prompt and appropriate treatment, this intra-articular fracture may result in an unstable arthritic joint with subsequent loss of strength, motion, and pain. Because the thumb carpometacarpal (CMC) joint is critical for pinch and opposition, this injury may severely affect overall function of the hand.
Presentation
Patients present with swelling and pain at the thumb base after an impact injury to the thumb. On examination, motion is limited and CMC instability is frequently noted with gentle stress of the thumb metacarpal.
Workup
Xrays are usually adequate to make the diagnosis of this injury. Occasionally, special views will be useful to assess for fragmentation, and computed tomography, or CT, can be helpful in defining the degree of fragmentation (comminution) or if there is impaction of the joint surface.
Treatment
Closed reduction and thumb spica cast immobilization are effective in the treatment of Bennett fractures if the reduction can be maintained and the fracture fragment very small. The strong pull of the APL frequently leads to displacement, necessitating surgical intervention. Frequently, surgery is the most reliable method of stabilizing these fractures. In many cases, surgery can be done without incisions and under Xray control, using two small pins to stabilize the fracture after restoring normal position. Large and displaced fracture fragments may need an open incision and use of screws or pins. These operations are done as ambulatory or out-patient surgery, and pins will typically be removed in 4 to 6 weeks. The patient is usually casted during this interval following
which bracing and therapy will be initiated.
Prognosis
The outcome after Bennett fractures is most closely related to the amount of energy associated with the original injury. High-energy injuries that produce extensive comminution, articular surface damage, and extensive soft-tissue injury, will tend to have a less successful outcome. With anatomic restoration of the joint surface and reestablishment of stability, the outcome is routinely good, especially in low-energy injuries with simple fracture patterns and limited soft-tissue involvement.
-- Lee