Biomechanical comparison of parallel versus 90-90 plating of bicolumn distal humerus fractures with intra-articular comminution

Purpose: To compare the biomechanical properties of 90-90 versus mediolateral parallel plating of C-3 bicolumn distal humerus fractures.

Methods: We created intra-articular AO/Orthopaedic Trauma Association C-3 bicolumn fractures in 10 fresh-frozen matched pairs of cadaveric elbows. We determined bone mineral density of the metaphyseal region with dual-energy x-ray absorptiometry. The matched pairs of elbows were randomly assigned to either 90-90 or parallel plate fixation. We tested anteroposterior displacement at a rate of 0.5 mm/s to a maximum load of ± 100 N for both the articular and entire distal humerus segments. We tested torsional stability at a displacement rate of 0.1 Hz to a maximum torque of ± 2.5 Nm. After cyclical testing, we loaded the specimens in torsion to failure.

Results: There was no significant difference in the bone density of the paired specimens. Compared with parallel fixation, 90-90 plate fixation had significantly greater torque to failure load. Both plating constructs were equally sensitive to bone density. Both techniques had the same mode of failure in torsion, a spiral fracture extending from the medial plate at the metaphyseal-diaphyseal junction. There was no significant difference in the stiffness of fixation of the articular fragment or the entire distal segment in anteroposterior loading.

Conclusions: This study demonstrated that 90-90 and parallel plating had comparable biomechanical properties for fixation of comminuted intra-articular distal humerus fractures, and that 90-90 plating had greater resistance to torsional loading.