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Mechanical Testing of Epiphysiodesis Screws

Normandin BM, Tennent DJ, Baldini TH, Blanchard AM, Rhodes JT

Orthopedics, 2018

Abstract

Epiphysiodesis is performed to treat leg-length discrepancies and angular deformities in children. However, when placed across a physis to modulate growth, screws can bend or break postoperatively. This study evaluated the mechanical properties of 3 different screw designs commonly used when performing an epiphysiodesis. Six 4.0-mm cannulated, fully threaded; six 4.0-mm cannulated, partially threaded; and six 4.0-mm noncannulated, partially threaded cancellous screws underwent cantilever bending and tension testing in a simulated physis. All screws were tested in simulated cancellous bone foam blocks. All testing was performed using a servo-hydraulic testing machine to determine stiffness and ultimate load. For statistical analysis, one-way analysis of variance with Tukey's honestly significant difference test in post hoc analysis was used to assess significant differences among groups (P<.05). The noncannulated, partially threaded screws had a significantly lower stiffness than the 2 cannulated screw types in the tension test (P<.001) and bending test (P<.001). Additionally, the noncannulated, partially threaded screws had significantly higher ultimate load to failure than the 2 cannulated screw types in the tension test (P<.001) and the cannulated, partially threaded screws in the bending test (P=.045). The results indicate that noncannulated, partially threaded screws have a higher ultimate load capacity and are less stiff than both cannulated, partially threaded screws…

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