Force Transfer through the Scaphotrapeziotrapezoid (STT) Joint.

Area of Science:

• Orthopedics
• Biomechanics
• Anatomy

Background:

• The scaphotrapeziotrapezoidal (STT) joint is crucial for force transmission from the thumb and fingers to the proximal carpal row.
• While STT joint osteoarthritis is common, its mechanical role in wrist function is not fully understood.

Purpose of the Study:

• To model normal wrist types and predict scaphotrapeziotrapezoidal (STT) joint motion under applied loads.
• To investigate the biomechanical differences in STT joint movement between Type 1 and Type 2 wrist morphologies.

Main Methods:

• Utilized computed tomography scans from five Type 1 and five Type 2 wrists to create 3D models.
• Applied a 200-N force to the trapezoid and capitate bones to simulate knuckle push-up loading conditions.
• Employed finite element analysis to predict and quantify bony movements within the STT joint.

Main Results:

• Significant differences in STT joint motion were observed between Type 1 and Type 2 wrists when loading the index and middle fingers.
• Type 1 wrists showed greater anterior-posterior movement, while Type 2 wrists exhibited more medial-lateral and proximal-distal motion.
• The trapezium in Type 1 wrists moved more in the coronal plane, and the trapezoid in Type 2 wrists showed greater distal-to-proximal movement (p=0.03).

Conclusions:

• Distinct patterns of STT joint motion exist between Type 1 and Type 2 wrists under load.
• Type 2 wrists demonstrate increased radial movement, approaching the scaphoid and scapholunate ligament.
• These findings offer a potential biomechanical explanation for degenerative changes and could inform arthritis prevention strategies.