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A Comparison of Plate versus Screw Fixation for Segmental Scaphoid Fractures: A Biomechanical Study.
Jill Goodwin, MD1; Castaneda, BSE1; Ryan Shelhamer, MD1; Liam Bosch, BA1; Scott Edwards, MD2
1University of Arizona College of Medicine, Phoenix, Phoenix, AZ, 2The CORE Institute, Phoenix, AZ
Introduction: Volar locking plate fixation may offer several advantages over headless screw fixation for scaphoid nonunion, or segmental or comminuted fractures: (1) increased surface area for bony healing; (2) preserved vascularity; (3) maintenance of a gap to allow the use of pure cancellous grafts, which are more biologically active than cortico-cancellous grafts. Cancellous graft, however, provides little structural integrity, and no previous study has examined the volar plate’s strength of fixation and resistance to collapse. The purpose of this study is to compare headless screw and locking plate fixation of segmental scaphoid fractures, and to determine whether either fixation provides a greater mechanical advantage in osteoporotic bone.
Materials & Methods: 16 matched pair cadaver scaphoids were dissected from a range of osteoporotic and non-osteoporotic bone, confirmed with T-scores using DEXA. Scaphoids from each matched pair were randomly assigned to either volar locking plate or compression screw fixation. A 3-mm segment of bone was circumferentially excised from each scaphoid waist to simulate the segmental defect frequently encountered in scaphoid nonunions and comminuted fractures. Implants were applied and each specimen was then trialed on a load frame in axial compression. Load to failure was defined as the load required to achieve complete gap closure. Mechanism of failure, load to failure, and percent gap maintenance were recorded for each trial. Ultimate failure loads were compared between fixation methods using ANOVA.
Results: Gap closure occurred in all trials. Difference in load to failure was not statistically significant between plate and screw fixation in either non-osteoporotic or osteoporotic cadaver specimens (µ = 118.903N, 114.058N, 184.974N, and 131.488N for osteoporotic plate and screw fixation, and non-osteoporotic plate and screw fixation, respectively; p = .4655). Percent gap maintenance was substantially higher for plate fixation than for screw fixation (µ = 40% versus 4% gap maintenance for plate and screw fixation, respectively; p < 0.01).
Conclusion: In scaphoid fractures with segmental defect, plate and screw fixation demonstrate similar loads to failure, but plate fixation performs superiorly to screw fixation for gap maintenance after an applied load to failure. From a biomechanical standpoint, plates maintain gaps, and subsequently scaphoid height, in segmental fracture patterns more predictably than headless screws. The authors advocate for consideration of plate fixation in complex scaphoid fractures to maintain scaphoid height, especially when using non-structural pure cancellous grafts.
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