The Biomechanical Behavior of Fixation Options in Short Segment Radius and Ulna Diaphyseal Fractures

Plate fixation of radius and ulna shaft fractures has evolved due to a more complete understanding of the biology and mechanics. Screw fixation across six cortices has been adopted as the standard, purported to provide the optimal biological and mechanical environment for healing; however, recent investigations have proposed that four cortices of fixation may be sufficient. These recommendations are intended for segments of optimal length; however, it is less clear how these options perform in short segment fixation. Our objective was the determine the biomechanical behavior of fixation options for short segment diaphyseal fractures of the radius and ulna.

Synthetic epoxy-formulated bones were prepared using a five-hole straight titanium plate with 3.5 mm locking and compression screws. Consistent with the recommendation of six cortices, we defined a construct of optimal length to be one with a single compression screw in three consecutive oblong holes (series 1). Series 2, 3, and 4 were configurations for short segment fixation. Torsional load to failure was applied to all samples.

The mean load to failure in series 4 was 2.5% higher than series 1. The mean load to failure in series 1 was 2.7% higher than series 2. All samples failed by spiral fracture of the bone through the screw holes.

Our results demonstrated that short segment fixation with six or eight cortices had stability comparable to a standard length segment with six cortices of fixation. Further, the use of locking screws did not improve torsional resistance. Across all testing series, utilization of two screws in a single oblong hole did not affect the failure mechanism.

The current findings suggest that increasing the number of cortices from six to eight has the potential to mitigate suboptimal length in short segment diaphyseal fixation.