Evaluation of Various Fixation Methods in Acute Scapholunate Dissociation, A Finite Element Study.

Objective: This study aimed to compare the outcomes of fixing scapholunate with pins and screws in parallel, convergent, and divergent orientations.

Materials and methods: In this computer simulation study, the CT scan images of a healthy subject were used to construct a 3D model of the wrist joint using MIMICS software. The imposed force to scaphoid and 3D model lunate bones, as well as the scapholunate angle and distance, were compared in different surgical techniques using parallel, divergent, and convergent pins and screws.

Results: In the absence of external force, the imposed stress applied to the scaphoid and lunate bones in cases of parallel pins and screws were 7.5MPa, 5.08MPa (pins), 1.134MPa, and 1.151MPa (screws), and 10.90MPa, 10.90MPa (pins), 9.7MPa, and 34.1MPa (screws) for 50N flexion force. The imposed stress in this approach is significantly lower compared to other interventions. Better outcomes were seen regarding scapholunate angle and scapholunate distance in using parallel pins or screws as well.

Conclusion: In conclusion, implementing parallel pins and screws for scapholunate fixation had better results in terms of achieving carpal stability in scapholunate dissociation. However, fixation with pins and screws showed a statistically significant difference. Furthermore, a wide range of motion exercises with no additional forces can be used in the rehabilitation of patients undergoing this surgery.