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Optimal Fixation of the Capitellar Fragment in Distal Humerus Fractures.

OBJECTIVES
To determine if orthogonal or parallel plate position provides superior fixation of the separate capitellar fragment often present in intra-articular distal humerus fractures. We hypothesized that orthogonal plating would provide stiffer fixation given a greater number of opportunities for capitellar fixation as well as screw trajectories perpendicular to the fracture plane offered by a posterolateral plate compared to a parallel plate construct.


METHODS
Ten matched pairs of cadaveric distal humeri were used to compare parallel and orthogonal plating in a fracture gap model with an isolated capitellar fragment. The capitellum was loaded in 20 of flexion utilizing a cyclic, ramp-loading protocol. Fracture displacement was measured using video tracking software. The primary outcome was axial stiffness for each construct. Secondary outcomes included maximum axial and angular fracture displacement.


RESULTS
The parallel plate construct was more than twice as stiff as the orthogonal plate construct averaged across all loads (1464.8±224.0 N/mm vs 526.3±90.8 N/mm, p<0.001). Average axial fracture displacement was 0.15±0.03 mm versus 0.53±0.10 mm for parallel versus orthogonal plating, respectively (p=0.003). Angular fracture displacement was minimal for both constructs (0.009±0.001 deg vs 0.028±0.006 deg for parallel vs orthogonal constructs).


CONCLUSIONS
Despite fewer points of fixation, a parallel plate construct provided stiffer fixation with less displacement of the simulated capitellar fracture fragment than an orthogonal plate construct in this biomechanical study. In the setting of an articular fracture, in which absolute stability and primary bone healing are desirable, parallel fixation should be considered even in fractures with a separate capitellar fragment if the size of fragment and fracture orientation allows.