What ligament injury could be caused by a fracture at the base of the fifth proximal phalange of the right ring finger?

Collateral Ligament Injury Associated with Fifth Proximal Phalanx Base Fracture

A fracture at the base of the fifth proximal phalanx commonly causes injury to the collateral ligament, particularly the radial collateral ligament of the metacarpophalangeal joint. 1

Mechanism and Associated Ligament Injuries

The base of the fifth proximal phalanx serves as an attachment site for important ligamentous structures, with fractures in this area frequently involving:

1. Collateral ligament injuries:

   • Radial collateral ligament is most commonly affected due to the ulnar-directed force that typically causes these fractures
   • Complete or partial tears may occur at the ligament's insertion on the base of the proximal phalanx 1

2. Volar plate injuries:

   • May occur concomitantly with collateral ligament injuries
   • Can lead to greater extension lag when combined with collateral ligament rupture 2

3. Joint capsule disruption:

   • Often accompanies more severe fracture-dislocations
   • Can lead to joint instability if not properly addressed

Diagnostic Imaging

MRI is the gold standard for evaluating associated ligamentous injuries with proximal phalanx fractures:

• MRI Hand: Ideal for evaluating tendon and ligament injuries with high sensitivity and specificity 1

  • For collateral ligament injuries of the lesser metacarpophalangeal joints, MRI has a sensitivity of 67% and specificity of 91%
  • MR arthrography increases sensitivity to 75% and specificity to 98% 1

• Ultrasound: Can be useful for dynamic assessment of joint stability

  • Allows direct visualization of metacarpophalangeal joint malalignment 1
  • Can identify collateral ligament tears, though less sensitive than MRI

Treatment Implications

The presence of collateral ligament injury affects the management approach:

1. Conservative treatment:

   • Buddy taping to the adjacent fourth digit with immediate mobilization can be effective for stable fractures 3
   • This approach focuses on function rather than exact anatomical reduction
   • Results in high patient satisfaction and good functional outcomes 3

2. Surgical intervention:

   • Indicated when there is significant joint instability or irreducible subluxation
   • Repair of both the fracture and torn collateral ligament may be necessary 4
   • Outcomes are generally good but extension lag is more common when collateral ligament injury is present 2

Rehabilitation Considerations

Early finger motion is essential to prevent complications:

• Begin with protected motion exercises to prevent stiffness 5
• Implement a home exercise program focusing on active and passive range of motion 5
• Monitor for development of extension lag, which is more common with combined collateral ligament injuries 2

Potential Complications

Patients with combined fracture and collateral ligament injury are at higher risk for:

• Greater extension lag compared to isolated fractures 2
• Joint instability if the ligament injury is not properly addressed
• Malrotation (reported in approximately 6% of cases) 3
• Chronic pain and decreased grip strength
• Post-traumatic arthritis with inadequate treatment

Follow-up Protocol

Regular monitoring is essential:

• Radiographic assessment at 3 months to evaluate fracture healing 5
• Regular assessment of range of motion, particularly extension
• Monitoring for signs of joint instability or malrotation

In summary, fractures at the base of the fifth proximal phalanx commonly involve the radial collateral ligament of the metacarpophalangeal joint. While many cases can be managed conservatively with buddy taping and early mobilization, the presence of significant ligament injury may necessitate surgical intervention to restore joint stability and function.