What wrist movement is most likely to be increased in a patient with a severe tear of the medial collateral ligament (MCL) of the wrist?

Increased Abduction is Most Likely with Medial Collateral Ligament Tear of the Wrist

A severe tear of the medial collateral ligament (MCL) of the wrist would most likely result in increased abduction movement.

Anatomy and Function of the Medial Collateral Ligament of the Wrist

The medial collateral ligament (also known as the ulnar collateral ligament) of the wrist serves as a primary stabilizer of the ulnar side of the wrist. This ligament:

• Connects the ulnar styloid process to the triquetrum and pisiform bones
• Provides stability against radial deviation (abduction) forces
• Works with other ligaments to maintain proper carpal alignment

Mechanism of Increased Abduction with MCL Tear

When the MCL is severely torn:

1. The primary restraint against radial deviation (abduction) is compromised
2. The wrist loses its normal ulnar-sided stability
3. The carpus can move excessively in the radial direction (abduction)

According to the American College of Radiology guidelines, ligamentous tears can cause dynamic instability 1. The MCL specifically prevents excessive abduction, so when torn, this movement becomes abnormally increased.

Diagnostic Imaging for MCL Tears

For suspected MCL tears, several imaging modalities can be utilized:

• CT arthrography: Highest sensitivity (nearly 100%), specificity, and accuracy for detecting ligament tears 2
• MR arthrography: Good accuracy but less sensitive than CT arthrography for partial tears 2
• 3T MRI: Better diagnostic capability than 1.5T MRI with sensitivities of 65-89% for ligament tears 2
• Ultrasound: Variable sensitivity (46-100%) for ligament tears, can be enhanced with dynamic "clenched fist" maneuvers 2

Clinical Presentation

A patient with a severe MCL tear would typically present with:

• Pain on the ulnar side of the wrist
• Instability with increased abduction (radial deviation) movement
• Tenderness over the ulnar aspect of the wrist
• Possible clicking or clunking with wrist movement
• Decreased grip strength

Differential Diagnosis

It's important to distinguish MCL tears from other wrist injuries:

• Scapholunate ligament tears (affect midcarpal stability)
• Lunotriquetral ligament tears (affect midcarpal stability)
• TFCC (triangular fibrocartilage complex) injuries
• Kienböck's disease (avascular necrosis of the lunate)

Common Pitfalls in Diagnosis

1. Overlooking dynamic instability: Static radiographs may appear normal in partial tears 2
2. Failing to perform stress tests: Dynamic testing is crucial to reveal instability
3. Misinterpreting imaging: CT arthrography has the highest sensitivity for ligament tears, but MRI is often ordered first 1
4. Not considering mechanism of injury: Forceful radial deviation or a fall on an outstretched hand with the wrist in ulnar deviation often causes MCL tears 3

In conclusion, when the medial collateral ligament of the wrist is severely torn, the primary restraint against abduction is compromised, resulting in increased abduction (radial deviation) movement. This is the most characteristic finding in patients with this injury.