Bone and Joint Bamboozler 004

There is a fracture involving the articular surface of the base of the right thumb metacarpal. It is slightly displaced and the carpo-metacarpal joint is slightly subluxed as a result.

This is a Bennett fracture, named for the Irish surgeon who introduced antisepsis to Dublin: Edward Halloran Bennett (1837-1907).

It is distinct from the Rolando fracture, which is a comminuted intra-articular Bennet’s fracture with a Y-shaped appearance.

Thumb metacarpal fractures are rare because of the thumb’s inherent mobility. However, when fractures do occur they usually involve the base — and the Bennett fracture is the most common type.

The Bennett fracture usually results from axial loading onto a partially flex thumb metacarpal. This can occur when a fist strikes a solid object.

The ulna portion of the base of the thumb remains in place, whereas the larger radial fragment is radially subluxed or dislocated by the pull of the abductor pollicus longus (APL) muscle. The ulna portion is stabilised by the deep ulnar ligament from the ulna and the anterior oblique ligament from the trapezium.

Routine views of the thumb adequately define the nature of the fragment(s). CT scans may be performed as part of the definitive management work-up.

Late complications:

• joint stiffness and 1st CMCJ arthritis
• malunion

Treatment goals are to achieve articular congruity and stability of the thumb carpo-metacarpal joint.

Initial management:

• RICE
• thumb spica splint
• early referral to a hand specialist

Definitive management options:

• closed reduction alone is unlikely to be successful as CMC stability is compromised by the pull of APL
• closed reduction with percutaneous pinning (most common)
• open reduction and internal fixation (this is also the usual treatment of a Rolando fracture, although external fixation may be performed depending on the size of the fragments).