The Bennet fracture is a fracture of the base of the thumb metacarpal (aka 1st metacarpal) that involves the articular surface of the 1st carpometacarpal joint. It is distinct from the Rolando fracture, which is a comminuted intra-articular Bennet’s fracture with a Y-shaped appearance.
The Bennett fracture is named for the Irish surgeon who introduced antisepsis to Dublin: Edward Halloran Bennett (1837-1907).
Mechanism and Pathophysiology
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.
The important complications occur late:
- joint stiffness and 1st CMCJ arthritis
- axial loading of a partially flexed thumb, e.g. fist strike
- local tenderness and swelling at the base of the 1st metatarsal
- limited range of motion at the 1st carpometacarpal joint due to pain
- 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.
Treatment goals are to achieve articular congruity and stability of the thumb carpo-metacarpal joint.
- thumb spica splint
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).
- early analgesia
- early referral to a hand specialist
- patients may be discharged from the ED prior to subsequent outpatient surgery
References and Links
Journal articles and Textbooks
- Marx JA, Hockberger R, Walls RM. Rosen’s Emergency Medicine: Concepts and Clinical Practice, 7th edition (2009) Mosby, Inc. [mdconsult.com]
- Schwartz DT, Reisdorff. Emergency Radiology, McGraw-Hill, 2000.
- Simon RR, Sherman SC, Koenigsknecht SJ. Emergency Orthopedics — The Extremities (5th edition), McGraw-Hill, 2007.
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