The Optimal Location to Measure Scapholunate Diastasis on Screening Radiographs

Area of Science:

• Orthopedics
• Radiology
• Anatomy

Background:

• Scapholunate diastasis measurement lacks standardized location and normal values, limiting clinical utility.
• Previous methods are hindered by inconsistent measurement points and reference ranges.

Purpose of the Study:

• Determine the optimal site for measuring scapholunate gap during sequential ligament injuries.
• Compare plain radiography with fluoroscopy for accuracy.
• Assess interrater reliability in scapholunate diastasis measurements.

Main Methods:

• Cadaveric forearms underwent sequential ligament transections (scapholunate, radioscaphocapitate, scaphotrapezium-trapezoid).
• Plain radiographs and fluoroscopic images were captured in neutral and 30° ulnar deviation.
• Multiple reviewers measured the scapholunate interval at three distinct locations; interrater reliability was assessed.

Main Results:

• Measurements in the middle of the scapholunate joint demonstrated the lowest error margins across all imaging types, ligament states, and wrist positions.
• Normal wrists showed mean scapholunate measurements below 2.0 mm at the joint's midpoint.
• Fluoroscopy identified more significant instability stages than plain radiographs at the midpoint.

Conclusions:

• Measuring the scapholunate interval at the joint's midpoint using fluoroscopy in neutral or 30° ulnar deviation effectively detects ligamentous disruptions.
• A scapholunate interval measurement below 2.0 mm at the midpoint is indicative of a normal range.