Evaluation of the Reduction and Association of the Scaphoid,Capitate,and Lunate Procedure: A Biomechanical Analysis

Abstract

Background:

This study evaluates whether augmentation of the reduction and association of the scaphoid and lunate (RASL) procedure with a temporary scaphocapitate (SC) screw will improve the stability of the carpus and scapholunate (SL) joint. Primary endpoint was SL joint diastasis with simulated clenched fist grip.

Methods:

Twelve cadaveric wrists were subjected to repeated cycles at a range of physiologic transcarpal axial forces simulating clenched-fist loading. We measured SL joint motion in scapholunate interosseous ligament (SLIL)-intact wrists and after transecting the SLIL. Outcomes measured included static diastasis and cyclic motion diastasis, defined as the change in SL diastasis from zero newtons to peak force during clenched-fist loading. The RASL procedure was tested with and without the addition of the SC screw. Repeated-measures analysis of variance and Sidak’s tests were used to analyze results.

Results:

No failures were observed in either group when examined manually and radiographically. Static diastasis results showed reduction and association of the scaphoid, capitate, and lunate (RASCL) reduced the scaphoid and lunate more anatomically, resembling SLIL-intact wrists, while RASL over-reduced the scaphoid and lunate. RASCL had less cyclic motion diastasis than the RASL. The RASCL cyclic motion mimicked the SLIL-intact model while RASL cyclic motion was not significantly different from the SLIL injury model

Conclusions:

The addition of the SC screw decreased SL joint diastasis under simulated clenched-fist loading. Reduction and association of the scaphoid, capitate, and lunate is a biomechanically stronger construct allowing for more robust healing of secondary carpal stabilizers; however, it requires SC screw removal prior to weight bearing.