Bennett's Fracture-Dislocation
Bennett's Fracture is an intra-articular fracture-dislocation of the base of the 1st Metacarpal (Thumb). It is highly unstable due to the pull of the muscle tendons.
1. Anatomy of Failure
The fracture creates two fragments:
- Small Volar-Ulnar Fragment: Stays in place, held by the strong Volar Oblique Ligament (Beak Ligament).
- Large Shaft Fragment: Dislocates radially, proximally, and dorsally due to the pull of the Abductor Pollicis Longus (APL) muscle.
2. Management
- Conservative: Rarely successful due to APL pull.
- Surgical:
- CRPP: Closed Reduction and Percutaneous Pinning (K-wires).
- ORIF: Open Reduction with small screws (if fragment is large enough).
25 Practice MCQs
Q1. Bennett's fracture involves which bone?
Answer: A). Fracture-dislocation of the thumb base.
Q2. Is Bennett's fracture intra-articular?
Answer: A). Involves the CMC joint of the thumb.
Q3. Which muscle pulls the shaft fragment proximally and radially?
Answer: A). The main deforming force.
Q4. The small volar-ulnar fragment is held in place by:
Answer: A). This ligament attaches to the trapezium.
Q5. Mechanism of injury is:
Answer: A). E.g., Punching or falling.
Q6. Conservative treatment often fails because:
Answer: A). The APL constantly displaces it.
Q7. Percutaneous pinning (CRPP) usually involves pins passing through:
Answer: A). To anchor the thumb base.
Q8. Adductor Pollicis muscle contributes to displacement by:
Answer: A). Works with APL to deform the fracture.
Q9. Failure to treat Bennett's fracture leads to:
Answer: A). Painful arthritis at the base of thumb.
Q10. Which fracture is considered a "Comminuted Bennett's"?
Answer: A). Y or T shaped intra-articular fracture.
Q11. "Baby Bennett" fracture refers to:
Answer: A). Similar mechanics but on the little finger side.
Q12. How many fragments are typical in a classic Bennett's fracture?
Answer: A). If >2, it is likely Rolando's.
Q13. Is thumb spica cast sufficient?
Answer: B). Reduction is hard to maintain without pins.
Q14. Reduction maneuver involves:
Answer: A). Reversing the deforming forces.
Q15. Surgical screws used are typically:
Answer: A). The bone fragments are small.
Q16. Acceptable articular step-off is:
Answer: A). While 0 is ideal, <1mm is tolerated.
Q17. CMC joint of the thumb is what type of joint?
Answer: A). Allows high mobility but prone to instability.
Q18. Wagner incision is used for:
Answer: A). An L-shaped incision at the thumb base.
Q19. Pins are typically removed at:
Answer: A). Once clinical union is achieved.
Q20. Stiffness of the CMC joint after Bennett's:
Answer: A). Patients adapt well even with some loss of motion.
Q21. Winterstein's fracture is:
Answer: A). Often transverse or oblique, easier to treat than Bennett's.
Q22. Can Bennett's fracture be treated with traction alone?
Answer: A). Obsolete method.
Q23. Gamekeeper's Thumb differs because:
Answer: A). Ligament vs Bone, MCP vs CMC.
Q24. Arthritis post-Bennett's fracture is treated with:
Answer: A). Removal of trapezium is a common procedure.
Q25. Rehabilitation focuses first on:
Answer: A). Restoring functional pinch.
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