Mechanical consequences of scaphotrapeziotrapezoid fusion studied by computational modelling.

Scaphotrapeziotrapezoid arthrodesis is a controversial surgical procedure for wrist disorders and its biomechanical effect remains unclear. This study investigated scaphotrapeziotrapezoid fusion based on a previously validated whole-wrist finite element model to simulate arthrodesis by creating a unified bone complex from the three bones (scaphoid, trapezium and trapezoid) in the joint. The model was analysed under physiological grasping loads to examine axial load distributions and articular contact pressures at the radioscaphoid and radiolunate interfaces. The fused complex becomes a major load-bearing structure, while radiocarpal contact pressures at both the radioscaphoid and radiolunate interfaces show reductions compared with the intact model. This altered load distribution pattern suggests significant biomechanical adaptations after the procedure and supports its use for scapholunate instability and the treatment of Kienböck's disease.