Dislocation of MCP Joints
Dislocations of the Metacarpophalangeal (MCP) joints, or "knuckles," are less common than IP dislocations but more problematic. The Index finger is most commonly affected.
1. Classification
- Simple Dislocation: Subluxation. The phalanx is hyperextended (60-90 degrees) but the joint surfaces are still in contact. Can be reduced closed.
- Complex (Irreducible) Dislocation: The Volar Plate gets interposed between the metacarpal head and phalanx.
- Kaplan's Lesion: Specifically refers to complex dislocation of the Index finger.
2. Clinical Features
The Puckering Sign:
In a complex dislocation, there is a dimple (puckering) in the palmar skin near the MCP crease. The metacarpal head is prominent in the palm.
In a complex dislocation, there is a dimple (puckering) in the palmar skin near the MCP crease. The metacarpal head is prominent in the palm.
3. Management
- Simple: Closed reduction (Flex wrist + push phalanx).
- Complex: Requires Open Reduction. DO NOT pull (traction) as it tightens the "noose" of tendons around the neck.
25 Practice MCQs
Q1. The most commonly dislocated MCP joint is:
Answer: B). Due to its exposure and lack of support.
Q2. Complex dislocation means:
Answer: A). Usually the Volar Plate blocks return.
Q3. The primary structure preventing reduction in complex dislocation is:
Answer: A). It gets stuck inside the joint.
Q4. Kaplan's Lesion refers to dislocation of:
Answer: A). Often entrapped by Flexor tendons and Lumbricals.
Q5. Why is traction contraindicated in complex dislocation?
Answer: A). Makes reduction harder. Push, don't pull.
Q6. "Puckering" of skin in the palm indicates:
Answer: A). Pathognomonic sign.
Q7. The direction of dislocation is almost always:
Answer: A). Due to hyperextension injury.
Q8. Surgical approach for complex dislocation is usually:
Answer: B). Dorsal is safer (avoids neurovascular bundle), Volar gives better view of pathology.
Q9. The "Noose" in Kaplan's lesion is formed by:
Answer: A). They trap the metacarpal head.
Q10. Thumb MCP dislocation is often associated with:
Answer: A). Instability is common.
Q11. Post-reduction splinting position:
Answer: A). Allow flexion, block extension > 30 degrees.
Q12. Simple dislocations have the phalanx positioned at:
Answer: A). Complex dislocations show parallel alignment (Bayonet).
Q13. Digital nerve injury is:
Answer: A). The nerve is stretched over the MC head.
Q14. Buddy taping is useful in rehab to:
Answer: A). Standard practice.
Q15. Recurrent instability is:
Answer: A). Stiffness is the main problem, not instability.
Q16. Mechanism of injury:
Answer: A). Fall on hand.
Q17. Brewerton View X-ray is used for:
Answer: A). Specialized view for MCP heads.
Q18. A "Locked" MCP joint (unable to extend) suggests:
Answer: A). Not always a full dislocation.
Q19. Volar dislocation is:
Answer: A). Would require extreme flexion force.
Q20. The Natatory Ligament contributes to:
Answer: A). Along with superficial transverse ligament.
Q21. In complex dislocation, the metacarpal head is:
Answer: A). Very prominent.
Q22. How soon should motion start after simple reduction?
Answer: A). To prevent stiffness.
Q23. The collateral ligaments are tight in:
Answer: A). Cam effect. Immobilize in flexion to prevent shortening.
Q24. Gamekeeper's thumb involves the:
Answer: A). Of the thumb MCP.
Q25. Main risk of Dorsal approach surgery:
Answer: A). But it spares the nerves.
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