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A Comparison of Headless Screw, Locking Plate, and Non-Locking Plate Fixation for Simulated Scaphoid Defects: A Biomechanical Study
Jill A. Goodwin, MD; Patricia Drace, MD; Scott G. Edwards, MD; Paulo Castaneda, MD
Banner University Medical Center- Phoenix, Phoenix, AZ

Introduction: Headless screw fixation is the current gold standard of surgical repair for scaphoid fractures. However, maintaining reduction of certain types of scaphoid fractures is challenging with a compression screw. Plate fixation has been used clinically with success and may offer superior fixation in some cases of scaphoid fractures, particularly those with comminution, nonunion, segmental bony defects, and osteopenic or osteoporotic bone. To date, no biomechanical evaluations have compared plates with headless screw fixations.

Methods: Polyurethane models were fashioned to simulate scaphoids with 3mm segmental defects. Defects were bridged by one of three constructs: a locking plate, a non-locking plate, or a headless compression screw. Three samples for each fixation construct were tested for both normal bone density (20PCF) and osteopenic bone density (10PCF). Constructs were stressed in axial compression at a 45 angle to mimic the load that a scaphoid encounters in a neutral wrist. Load to failure was recorded as the load at which the 3mm segmental defect was closed. These loads were compared between fixation methods using ANOVA to test the null hypothesis, and a post-hoc t-test to determine statistical significance.

Results: Gap closure occurred in all trials. In simulated normal bone, there were no statistically significant differences in load to failure between fixation methods (?=125.607N, 89.287N, 133.05N for locking plate, non-locking plate, and screw fixation, respectively; p = 0.1983). In simulated osteoporotic bone, the locking plate had a 28 percent greater load to failure as compared to screw fixation (? = 52.34N vs. 40.792N, p = 0.0426). Other differences between fixation methods in osteoporotic bone were not statistically significant.

Conclusions: While all methods of fixation perform similarly in normal bone, locking plate fixation performs superiorly to screw fixation in simulated osteoporotic bone. As this is a biomechanical study with simulated bone, the clinical relevance of these results cannot be determined conclusively. It can be inferred from this study that locking plate fixation is at least equivalent to the current gold standard headless screw fixation in a scaphoid fracture with segmental defect. If open reduction and internal fixation of a scaphoid fracture with segmental defect is indicated, plate fixation is a reasonable alternative from a biomechanical standpoint. Plate fixation may be more structurally resilient to hardware failure, especially if cancellous bone graft is used. In lower density bone, locking plates may also be superior to screw fixation for prevention of gap closure and subsequent carpal collapse.

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