Bennett Fracture 

Updated: Sep 07, 2018
Author: Mark E Baratz, MD; Chief Editor: Harris Gellman, MD 

Overview

Background

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

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.

Anatomy

The thumb affords prehensile abilities that were essential in human evolution. The bony anatomy of the thumb consists of two 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 two 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 abductor pollicis longus (APL).

Pathophysiology and Etiology

The thumb is a highly mobile border digit. For that reason, injury to this ray is common. Thumb CMC joint stability is maintained by five 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.

A Bennett fracture occurs when an axial force is transmitted through a partially flexed thumb metacarpal.[6] 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 APL.

Prognosis

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.

 

Presentation

History and Physical Examination

Patients present with swelling and pain at the thumb base.

On examination, motion is limited and carpometacarpal (CMC) joint instability is frequently noted with gentle stress of the thumb metacarpal.

 

Workup

Imaging Studies

Obtain standard posteroanterior (PA), lateral, and oblique radiographs in patients with suspected fractures or dislocations of the thumb. Traction radiography may be used to assess the degree of comminution in appropriate fractures (eg, Bennett, Rolando, comminuted metacarpal base fractures; see the images below).

Radiograph of a Bennett fracture. Radiograph of a Bennett fracture.
Rolando fracture. This is differentiated from a Be Rolando fracture. This is differentiated from a Bennett fracture because of the presence of intra-articular comminution.

Radiographs of the carpometacarpal (CMC) joint are obtained by placing the palmar surface of the hand flat on the imaging plate for a true lateral view, allowing accurate assessment of the CMC joint. Pronate the hand and wrist approximately 20-30º, and direct the imaging beam obliquely at 15º in a distal-to-proximal direction centered over the trapeziometacarpal joint.

A broken V sign may be present on the lateral radiograph, indicating disruption of the normal V that is formed by the radial aspect of the trapeziometacarpal articulation. This may indicate undetected CMC joint subluxation.

Tomography or computed tomography (CT) can help define the degree of comminution within a fracture, as well as suspected impaction of the articular surface.

 

Treatment

Approach Considerations

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. More than 1 mm of articular incongruity after closed reduction is an indication for operative intervention.

Contraindications for closed treatment include the following:

  • Open fracture
  • Unstable fracture
  • Unsuccessful closed reduction with residual articular incongruity greater than 1 mm
  • Instability and joint subluxation

Nonoperative Therapy

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 abductor pollicis longus (APL) frequently leads to displacement, necessitating open reduction and internal fixation (ORIF) or closed reduction with percutaneous pinning. More than 1 mm of articular incongruity or persistent carpometacarpal (CMC) joint subluxation after closed reduction indicates the need for surgical treatment.[2, 4, 7, 8, 9]  This degree of articular incongruity is associated with an increased rate of articular degeneration in the thumb CMC joint over time.[2, 4, 10, 11]

Surgical Therapy

Generally, closed reduction utilizing the technique described above followed by percutaneous Kirschner wire (K-wire) fixation is successful. Two 0.045-in. 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.[12] (See the image below.)

Percutaneous pinning of a Bennett fracture. Percutaneous pinning of a Bennett fracture.

If adequate reduction cannot be achieved by means of this percutaneous technique, ORIF is performed. An L-shaped incision is made over the subcutaneous border of the thumb metacarpal. The incision is carried down radially to allow 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 by using either K-wires or mini-screws (2.0 mm).[2, 4, 7, 8, 13, 14, 15]

Zhang et al reported success with open tension band wiring as a fixation option for the treatment of Bennett fractures.[16] Mahmoud et al reported good results from performing ORIF of Bennett fractures in young, active manual laborers, using a K-wire and wire loop construct to achieve anatomic reduction.[17]  Arthroscopically assisted percutaneous screw fixation has been described.[18, 19, 20]

Postoperative Care

Capo et al, in a study of simulated Bennett fracture in cadavers, evaluated the accuracy of fluoroscopic examination in determining the adequacy of closed reduction after pinning of Bennett fracture.[9] They found that assessment of the articular gap, stepoff, and displacement, as detected by fluoroscopy, was often erroneous in comparison with the results of plain radiography 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 surgical management therefore is generally recommended for displaced intra-articular fractures of the base of the thumb metacarpal.

Complications

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.

Long-Term Monitoring

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