Bennett's fracture

Definition/Description

A Bennett fracture, also known as a Bennett fracture-dislocation, is an intra-articular fracture of the base of the first metacarpal which leads to dislocation of the first carpometacarpal joint (CMCJ). The fracture involves the joint between the first metacarpal and the proximal carpal bone, the trapezium. The fracture is unstable and has an inadequate reduction/fixation which leads to long term consequences such as osteoarthritis, weakness and / or loss of function.

Clinically Relevant Anatomy

The first CMCJ is unique, it has only an articulation between the trapezium and the base of the first metacarpal. The articulation is saddle-shaped which allows greater motion. The ligaments in this joint are the anterior (volar) and posterior oblique ligaments, the anterior and posterior intermetacarpal ligaments, and the dorsal radial ligament. The anterior oblique ligament is the most important for stability in the carpo-metacarpal joint.

Differential Diagnosis

Other common injuries involving the first metacarpal include Rolando fractures, extra-articular fractures and gamekeepers thumb

The first differentiation clue can be found during the inspection/palpation of the location of the injury. Bennett fractures are associated with pain and weakness of the pinch grasp and swelling and ecchymosis over the carpal metacarpal joint of the thumb. The patient will be unable to perform functional tasks such as tying a shoe or using a key. Possible complications can be infection, malunion or nonunion, arthritis and stiffness with contracture.

Examination

If a Bennett fracture is suspected, the subjective history of the patient should include trauma to the hand or thumb followed by immediate pain and swelling or ischemia. The most common mechanism of injury is axial force (compression) applied to the thumb whilst in flexion.

On physical examination a Bennett's fracture of the first carpo metacarpal joint may present with:

• visible deformity if the fracture is displaced
• pain and swelling +/- ecchymosis over carpo metacarpal joint of the thumb
• tenderness to touch
• warmth over area in acute phase
• decreased pinch grasp and decreased grip strength¹³ 

Although X-ray films can be used to diagnose this condition, a CT scan should be ordered to evaluate the extent of the damage. On these CT scans a Bennett fracture will present can as an intra-articular fracture and dislocation of base of the first metacarpal. Even though there is a dislocation there should still be a small fragment of the first metacarpal that continues to articulate with trapezium.

Medical Management

Bennett fractures have several options of management. Each treatment has it’s advantages and disadvantages.

Type I - Closed Reduction

The first type of management is closed reduction and plaster casting. This is a non-invasive procedure and remains the first option if possible.The major issue in closed reduction is to obtain and maintain adequate fracture reduction to allow healing in an anatomical position. Consequences of an inaccurate reposition are pain and grip weakness in short term and osteoarthritis of the first metacarpal joint in long term. Hence it is recommended to let these fractures be treated by specialist hand surgeons.
All the variant methods of closed reduction involve traction on the thumb to pull metacarpal distally with concurrent pressure pushing the metacarpal base medially to return it to anatomical position. Closed reduction is performed under adequate analgesia/sedation follow by plaster cast immobilization for ±6 weeks. A cast with the thumb in a moderate adduction and opposition is most effective by reducing the fracture fragments.

Type II - K-wires

A second method of reduction involves reduction of the fracture followed by percutaneous insertion of a Kirschner wire through the base of the metacarpal across the joint and into the trapezium to hold the reduction in place. The wire remains in place for about 4 weeks after which a rehabilitation program is started.

Type III - Open Reduction

This last treatment is necessary when there is a significant displacement (>3mm).Type III involves an open reduction, which involves opening up the fracture and reduction under direct vision followed by insertion of either Kirschner wires (Fig1) or lag screws in order to hold the reduction in place. Like the second type of management, after the reduction there is an immobilization period of 4 weeks.
This type is preferable where there is a large proximal fragment and that ORIF should be used where the fracture is irreducible or a Kirschner wire is unable to be passed across the fracture.

Physical Therapy Management

Generally, hand fractures are treated by immobilization with a cast or splint regardless of whether surgical or conservative treatment was required. Physical therapists and / or occupational therapists are usually heavily involved in creating and adapting these in consultation with the treating team or surgeon. Protocols for rehabilitation must be based upon stability of the fracture and fracture management (operative or nonoperative).

Following the immobilisation period, physiotherapists and specialist hand therapists are involved in the facilitation of restoring maximal function to the hand.
. Modalities employed include cryotherapy, joint mobilisation, strengthening & flexibility exercises, dexterity re-education and specific education. Exercise intensity and complexity should be progressed appropriately following designated protocol usually provided by the surgeon. Evidence supports the positive impact of early physiotherapy intervention to facilitate optimal return to function and return to work/sport in hand fractures.