In vivo virtual investigation of the implant location for scaphoid fractures

INTRODUCTION: Scaphoid fractures still have high rate of nonunion, mainly due to the tenuous blood supply and only primary bone healing. Rigid fixation facilitates this kind of bone healing and is considered as vital as protection of the blood supply. The optimal implant (screw) location should meet the requirements for researcher's biomechanical findings on fracture stability. MATERIALS AND METHODS: Raw CT-scanned data of eight volunteers' wrists were imported into Mimics. The 3D scaphoid was segmented out and calculated, then opened in Geomagic Studio. Four fracture planes (proximal, oblique waist, horizontal waist and distal) simulating common broken scaphoid were created. Mimicking scaphoid implants (screws), the longest, the sub-longest, and central and eccentric cylinders perpendicular to each fracture plane were created. Whole and inside-fragmental length, and the relative location of each cylinder were measured and analyzed. RESULTS: The longest (28.5 ± 1.6 mm) cylinder was significantly longer than the sub-longest (25.4 ± 1.4 mm). Several eccentric perpendicular cylinders (so short or cutting out of the scaphoid) couldn't be created. Some proximal inside-fragmental lengths ranged from 3.0 to 5.1 mm. Several central perpendicular cylinders intersected with the longest one. Several central and eccentric perpendicular cylinders were outside of the proximal scaphoid non-contact region. CONCLUSION: The results of this study showed that scaphoid fracture images from CT scan can be calculated and yield the optimal implant location.