Bennett Fracture Treatment & Management

Closed reduction and thumb spica cast immobilization are effective in the treatment of Bennett fractures if the reduction can be maintained. The closed reduction technique consists of thumb traction combined with metacarpal extension, pronation, and abduction. Direct downward pressure is applied to the dorsal radial metacarpal base. The strong pull of the APL frequently leads to displacement, necessitating open reduction and internal fixation or closed reduction with percutaneous pinning. More than 1 mm of articular incongruity or persistent CMC joint subluxation after closed reduction indicates the need for surgical treatment.^{[2, 3, 5, 8, 9, 10]}

Generally, closed reduction utilizing the technique described above followed by percutaneous K-wire fixation is successful. Two 0.045-inch K-wires are drilled through the dorsal radial thumb metacarpal base into the reduced volar ulnar fragment. If the fragment is very small, reduction may be maintained by placing the K-wire from the thumb metacarpal into the trapezium or the index metacarpal. Maintaining thumb abduction is essential to preserving the first web space.^[11]

If adequate reduction cannot be achieved utilizing this percutaneous technique, open reduction and internal fixation is performed. An L-shaped incision is made over the subcutaneous border of the thumb metacarpal. The incision is carried down radially to allow for subperiosteal reflection of the thenar musculature and direct visualization of the joint. Towel-clip forceps are extremely valuable in obtaining and temporarily maintaining reduction. Fixation is achieved using either K-wires or mini screws (2.0 mm).^{[2, 3, 5, 8, 9, 12]}

Fluoroscopy was found to often provide erroneous results, compared with plain radiographs and direct examination, in cases of Bennett fracture after closed reduction and percutaneous pinning, according to Capo et al in a study of simulated Bennett fracture in cadavers. This is an important issue, the authors stated, because fluoroscopic examination is often used to determine the adequacy of closed reduction after pinning of Bennett fracture. The assessment of the articular gap, stepoff, and displacement as detected by fluoroscopy is often in error, according to the authors, compared to that detected by plain radiographs and direct examination. The authors noted that restoration of joint congruity is an important factor in the prevention of arthritis in patients with Bennett fracture and that therefore surgical management is generally recommended for displaced intra-articular fractures of the base of the thumb metacarpal.^[10]

A well-molded thumb spica cast is utilized for 2-6 weeks depending on the stability obtained at surgery. Once the cast is discontinued, a thermoplastic splint is fabricated and a protected mobilization program is initiated until fracture healing is complete.

Displaced intra-articular fractures predispose the patient to arthritis and loss of motion within the affected joints. Unfortunately, even after restoration of articular congruity, some patients develop posttraumatic arthritis secondary to the osteocartilaginous injury sustained as a result of the initial trauma.

Loss of motion also occurs following prolonged immobilization. Rigid fixation enables patients to initiate movement sooner postoperatively, minimizing this problem.

Other potential postoperative complications include loss of reduction with recurrent joint subluxation and instability, infection, and sensory nerve injury.

The prognosis for Bennett fractures is most closely related to the amount of energy associated with the original injury. High-energy injuries produce comminution, articular surface damage, and extensive soft-tissue injury, leading to a poor 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.