The Intercalated Segment: Does the Triquetrum Move in Synchrony With the Lunate?

Area of Science:

• Biomechanics
• Orthopedics
• Anatomy

Background:

• The carpal bones, specifically the lunate and triquetrum, are often modeled as an intercalated segment.
• Understanding their relative motion is crucial for carpal mechanics and stability.

Purpose of the Study:

• Quantify relative motion between the lunate and triquetrum during functional wrist movements.
• Examine the impact of wrist laxity on triquetral motion.

Main Methods:

• Utilized a digital database of carpal kinematics from 10 healthy volunteers.
• Compared radiolunate and radiotriquetral (RT) rotation axes during radioulnar deviation (RUD) and flexion-extension (FE).
• Assessed triquetral motion relative to the radius against passive FE range of motion as a measure of wrist laxity.

Main Results:

• The radiolunate and RT rotation axes differed by less than 20° in most movements, except radial deviation and initial hammering.
• Triquetral rotation axis orientation varied with passive wrist range of motion during radioulnar deviation.

Conclusions:

• Lunate and triquetrum movement is not always synchronous, particularly during radioulnar deviation.
• These findings challenge existing biomechanical models of carpal function.
• Individual motion differences may affect lunotriquetral arthrodesis outcomes and carpal instability.