A Finite Element Comparison Between Two Sizes of NiTi Commercial Staples Used in Scaphoid Fracture Fixation

Most carpal bone fractures occur in the scaphoid. The most suitable size of NiTi shape memory alloy (nitinol) staples to heal scaphoid fractures was found by comparing two commercially available compression staples (DynaClip™ Bone Fixation System, 10×10 and 14×14 mm). The scaphoid bone was selected for simulating a model in SolidWorks software. To accurately investigate the effect of staple size on the bone the scaphoid was assumed to be a three-layer composite structure consisting of collagen and mineral crystals. The stress distributions along a path located at the waist of the scaphoid were assessed. The finite element analysis was carried out in ABAQUS software based on the nitinol staple shape memory effect and super-elasticity behavior. The results indicated that the smaller size of staples induced a more significant stress on the central zone of the scaphoid, whereas the larger size of staples showed a peak stress concentration on the peripheral zones with a reduced stress concentration at the center. Hence, it is suggested to utilize the two of these staples in different orientations or in parallel with each other to improve the biomechanical behavior of the regenerated bone.