Biomechanical evaluation of parallel versus orthogonal plate fixation of intra-articular distal humerus fractures

Background: Orthogonal and parallel plate constructs are used for fixation of intra-articular distal humerus fractures but optimal plate configuration remains controversial. The purpose of this study was to compare the biomechanical properties of orthogonal versus parallel plate constructs in a cadaver distal humerus fracture model. Material and methods: An intra-articular distal humerus fracture with a metaphyseal defect was created in 14 matched pairs of cadaver elbows. Paired specimens were fixed with either orthogonal or parallel plates from a single elbow plating system using nonlocking screws. Using a novel testing protocol, loading was applied to the forearm and was transmitted to the distal humerus through intact collateral ligaments, olecranon, and radial head. Seven matched pairs were tested under varus loading and seven under axial/sagittal loading. Each specimen underwent cyclic loading first, followed by loading to failure. Results: Parallel plate constructs had significantly higher stiffness than orthogonal ones during cyclic varus loading (P = .002). Screw loosening occurred in all posterior plates of orthogonal constructs but in no plates of parallel constructs (P = .001). Parallel constructs had significantly higher ultimate torque in varus loading to failure (20.7 vs 15.9 Nm, P = .008), and higher ultimate load in axial/sagittal loading to failure (1287.8 vs 800.0 N, P = .03). Discussion: Parallel plating of intra-articular distal humerus fractures with a metaphyseal defect demonstrates superior biomechanical properties compared to orthogonal plating, and may be preferable for fixation of these fractures. Level of evidence: Basic Science Study, Biomechanical Study. (C) 2011 Journal of Shoulder and Elbow Surgery Board of Trustees.