Carpal Pronation and Supination Changes in the Unstable Wrist

Area of Science:

• Orthopedic Surgery
• Biomechanics
• Hand Surgery

Background:

• Limited understanding of scaphoid and lunate motion changes after scapholunate interosseous ligament (SLIL) injury.
• Investigating these changes may elucidate failures in SLIL reconstructions and guide new surgical techniques.

Purpose of the Study:

• To quantify scaphoid pronation and lunate supination increases after simulated SLIL injury.
• To assess concurrent changes in extensor carpi ulnaris (ECU) force during wrist motion.

Main Methods:

• Cadaveric wrist study with SLIL sectioning and volar or dorsal ligamentous division.
• Dynamic wrist motion (flexion/extension, radioulnar deviation, dart-throwing) with scaphoid/lunate motion and ECU force measurement.
• Comparison of motion and force changes between volar and dorsal ligamentous sectioning groups.

Main Results:

• Significant increases in scaphoid pronation and lunate supination observed post-ligament sectioning.
• Lunate motion changes differed significantly between volar and dorsal ligament sectioning groups; scaphoid motion changes did not.
• Increased extensor carpi ulnaris (ECU) force was required to achieve pre-sectioning wrist motion levels.

Conclusions:

• Simulated damage to scapholunate stabilizers alters carpal supination/pronation dynamics.
• Increased ECU force requirement may be linked to these observed carpal kinematic changes.
• Surgical SLIL reconstruction should consider correcting scaphoid pronation and lunate supination, particularly with dorsal stabilizer involvement.