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

https://doi.org/10.1016/j.jse.2010.08.005Get rights and content

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.

Section snippets

Study design

Fourteen pairs of fresh-frozen cadaver upper extremities (28 total specimens) were used for the current study. Each pair of left and right elbows was a matched pair harvested from the same donor. The mean donor age was 84 years (range, 60-97) and 12 of 14 donors were older than 70 years. A low T-type intra-articular distal humerus fracture with a metaphyseal defect was created, and the right or left elbow of each matched pair was randomly chosen for fixation with either orthogonal or parallel

Varus loading

Parallel plate constructs were characterized by significantly higher stiffness compared to the orthogonal constructs during all phases of cyclic loading under a varus moment (repeated measures ANOVA: F-ratio = 17.7, P = .002). The detailed results are presented in Table I and Figure 6.

Macroscopic evaluation demonstrated screw loosening in all (7/7) posterior plates of the orthogonal construct (Figure 7), but in none of the lateral plates of the parallel construct; the difference was significant

Discussion

Stable fixation of distal humerus fractures plays a critical role in avoiding the complications of nonunion, failure of fixation, and stiffness of the elbow.8, 12, 13, 15, 20, 22, 23, 26, 27 However, optimal configuration of dual plate constructs for fixation of distal humerus fractures remains controversial and biomechanical studies have reported conflicting results.4, 10, 14, 30, 31, 32, 33

Helfet and Hotchkiss10 concluded in one of the early biomechanical studies that an orthogonal plate

Conclusions

Parallel plating for fixation of an intra-articular distal humerus fracture with a metaphyseal defect demonstrates higher stiffness and lower rate of implant loosening compared to orthogonal plating in varus cyclic loading, higher ultimate torque in varus loading to failure, and higher ultimate load in axial/sagittal loading to failure. Parallel plating appears to be preferable for fixation of such fractures. Further research is needed to clarify the biomechanical properties of these plate

Disclaimer

Dr Itamura is a speaker for Acumed LLC. (Hillsboro, OR) and has received financial payments or other benefits. The other authors, their immediate families, and any research foundations with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article. No outside funding or grants were received that assisted this study. IRB approval was not required.

Implants for this study were donated by Acumed (Hillsboro,

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