MCP JOINT DISLOCATIONS

Question 1

Most common location for MCP dislocations

Answer 1

Index finger most common

Question 2

Mechanism of injury for MCP dislocations

Answer 2

Hyperextension injury most common

Results in avulsion of volar plate from proximal attachment into MC neck

Question 3

Ligaments of the MCP joint

Answer 3

1. Proper collateral ligament
   - origin = dorsal aspect of MC head
   - insertion = volar aspect of proximal phalanx base
   - taut in flexion
2. Accessory collateral ligament
   - origin = MC head volar to proper collateral ligament
   - insertion = volar plate
   - taut in extension
3. Volar plate
   - thick and fibrocartilageous distally
   - thin and membranous proximally
   - resist hyperextension
4. Dorsal capsule = thin and lax
5. Sagittal bands
   - origin = extensor hood
   - insertion = volar plate and deep transverse MC ligament
   - stabilise extensor tendon

Question 4

Classification of MCP dislocations

Answer 4

Based on direction of dislocation:
1. Dorsal = more common
- hyperextension injuries
- avulsion of volar plate off MC neck
2. Volar 
- hyperextension or hyperflexion injuries
Based on complexity of dislocation:
1. Simple = subluxations
- no soft-tissue interposition
2. Complex = complete 
- proximal phalanx in bayonet apposition to MC head
- interposition of volar plate +/- sesamoids (thumb MCP)

Question 5

Kaplan’s lesion

Answer 5

• Rare lesion most commonly involving IF
• MC head buttonholes volarly into palm between natatory ligaments distally and superficial transverse MC ligament proximally
• Volar plate is interposed in joint

Question 6

6 causes for drop finger

Answer 6

Extensor side:
1. PIN palsy
2. Extensor tendon rupture
3. Extensor tendon subluxation
Flexor side:
1. Locked trigger finger
2. Dupuytren's disease (not in RA patients)
Joint:
Volar MCP dislocation

Question 7

CR maneuver for dorsal MCP dislocations

Answer 7

• Flex wrist to take tension off intrinsic and extrinsic flexors
• Volarly directed pressure over dorsal aspect of P1
• No longitudinal traction = may pull volar plate into joint and block reduction
• Early ROM with dorsal blocking splint

Question 8

CR maneuver for volar MCP dislocations

Answer 8

• Flex MCP joint
• Dorsally directed pressure over volar aspect of P1
• No longitudinal traction = may pull soft-tissue into joint and block reduction
• Immobilise in 30deg flexion for 2 wks, then ROM with dorsal blocking splint