aka Bone and Joint Bamboozler 004
A 27 year-old man attempted to smash his fist through a plank of wood as part of an amateur martial arts demonstration. His success was bitter-sweet.
These are the radiographs taken of his right hand:
Q1. Describe the injury?
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.
Q2. What is the eponymous name for this fracture?
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.
Q3. What the typical mechanism of injury?
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.
Q4. What imaging and views are best for this assessing this injury?
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.
Q5. What specific complications should be considered?
- joint stiffness and 1st CMCJ arthritis
Q6. What is the management of this injury?
Treatment goals are to achieve articular congruity and stability of the thumb carpo-metacarpal joint.
- 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).
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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