Bennett Fracture 

In 1882, Edward Hallaran Bennett, MD, described the fracture of the base of the first metacarpal that bears his name. 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.^{[1, 2, 3, 4, 5]}

Images depicting Bennett fracture are shown below.

Unless properly recognized and treated, this intra-articular fracture subluxation may result in an unstable arthritic joint with secondary loss of motion and pain. Because the thumb carpometacarpal (CMC) joint is critical for pinch and opposition, this injury may severely affect function.

Frequency

The thumb is a highly mobile border digit. For that reason, injury to this ray is common.

Axial loading of a partially flexed thumb metacarpal causes this injury.^[6]

Thumb CMC joint stability is maintained by 5 ligaments and the articular contours. The most critical of these stabilizers is the volar oblique ligament. This ligament courses from the volar lip of the trapezium to the volar ulnar corner of the thumb metacarpal base. The injury occurs when an axial force is transmitted through a partially flexed thumb metacarpal. The portion of the metacarpal onto which the volar oblique ligament inserts remains in anatomic position, and the remainder of the articular base subluxates in a dorsal, radial, and proximal direction because of the pull of the abductor pollicis longus (APL).

Patients present with swelling and pain at the thumb base. On examination, motion is limited and CMC instability is frequently noted with gentle stress of the thumb metacarpal.

Closed reduction and thumb spica cast immobilization can be effective in the treatment of some Bennett fractures. Generally, cases characterized by small avulsion fractures and minimal articular incongruity and instability can be managed in this fashion. These patients must be carefully monitored with serial radiography. The strong pull of the abductor pollicis longus (APL) frequently leads to displacement. As a result, open or closed reduction combined with internal fixation is frequently required. More than 1 mm of articular incongruity after closed reduction is an indication for operative intervention. This degree of articular incongruity is associated with an increased rate of articular degeneration in the thumb CMC joint over time.^{[2, 3, 5, 7]}

The thumb affords prehensile abilities that were essential in human evolution. The bony anatomy of the thumb consists of 2 phalanges and a metacarpal, which articulates with the trapezium bone in the distal carpal row. The metacarpal is actually a primordial phalanx.

The CMC joint consists of an articulation between the trapezium and the metacarpal base composed of 2 reciprocally interlocking saddles with perpendicular longitudinal axes. Ligamentous stability at the trapeziometacarpal joint is maintained by the anterior (volar) and posterior oblique ligaments, the anterior and posterior intermetacarpal ligaments, and the dorsal radial ligament. The anterior (volar) oblique ligament originates on the trapezium and inserts into the volar ulnar beak of the thumb metacarpal. This is the most important ligament in maintaining CMC stability. The dorsal ligament is not as strong as the volar ligament but is reinforced by the APL.

Contraindications to closed treatment include an open fracture, an unstable fracture, unsuccessful closed reduction with residual articular incongruity greater than 1 mm, or instability and joint subluxation.