Negative Ulnar Variance Lessens DRUJ Instability After DRUJ Disruption: A Biomechanical Analysis

Area of Science:

• Orthopedic Surgery
• Biomechanics
• Anatomy

Background:

• Distal radioulnar joint (DRUJ) stability is crucial for forearm function.
• Ulnar variance (UV), the relative length of the ulna to the radius, is a known factor influencing DRUJ mechanics.
• Understanding UV's role in DRUJ stability is essential for treating wrist injuries.

Purpose of the Study:

• To biomechanically investigate the influence of ulnar variance (UV) on distal radioulnar joint (DRUJ) stability.
• To assess stability changes before and after sectioning of the DRUJ stabilizing structures.

Main Methods:

• Ten cadaveric forearm specimens were used.
• Baseline UV was measured, and radial translation was assessed using motion capture during a simulated Shuck test.
• A radial osteotomy was performed, and stability was re-evaluated at +4 mm, 0 mm, and -4 mm UV states before and after sectioning of the volar radioulnar ligaments and triangular fibrocartilage complex (TFCC).

Main Results:

• Sectioning of the volar radioulnar ligaments and TFCC significantly increased radial translation across all UV states.
• The ulnar negative (-4 mm) state demonstrated significantly lower radial translation compared to the positive (+4 mm) and neutral (0 mm) UV states after sectioning.
• No significant differences in translation were observed between UV groups when the DRUJ was intact.

Conclusions:

• Fixation at -4 mm ulnar negativity significantly decreased radial translation after sectioning of key stabilizing structures.
• Ulnar variance does not affect DRUJ stability when the joint is intact.
• Negative ulnar variance may play a protective role in DRUJ instability following ligamentous and TFCC disruption.