gms | German Medical Science

Objectives/Interrogation: Evaluate the mechanical properties of unicortical and bicortical fixations in a model of intra-articular fracture of the distal end of the radius, classified as AO 23C3, under simulated physiological loads.

Hypotheses:

1.

The mechanical behavior of the model using unicortical screws in the fixation of volar plates in intra-articular fractures of the distal end of the radius is equivalent to the model using bicortical screws.

2.

Cyclic loading, using a frequency of 1 Hz per 1000 cycles, affects the mechanical behavior of volar plate fixation models in intra-articular fractures of the distal end of the radius using unicortical and bicortical screws.

Methods: Fourty-four fourth-generation left-hand radius models (Sawbones; model 3407) were used in this study.

In each model, a volar plate was used for variable angle distal radius (Matrix 54-25276; Stryker, Freiburg, Germany) in a systematic and reproducible way, ensuring distal screw placement in the subchondral bone.

All bone models, in their proximal region, were included with JET® polymethylmethacrylate cement.

After inclusion, the bones were sent to the Precision Office to perform cuts to simulate bone failure, characterizing a fracture of the distal radius in 4 parts with a wedge of dorsal metaphyseal resection.

The 10 mm dorsal base wedge in the metaphyseal region was made to characterize instability.

The models were divided into six groups, so that each model underwent only one type of test, thus it did not affect any of the overlapping tests. Three groups had unicortical assembling and three groups with bicortical assembling. Each of the groups received seven models.

The mechanical tests were axial compression (AC), dorsal flexion (DF), and volar flexion (VF).

After the first static test, the models underwent a cyclic loading to simulate the wrist movements during the six-week period after fracture.

Then another static test.

After tests in the elastic phase, the models underwent extreme loads until failure occurred, each group in its corresponding type of test.

Results and Conclusions: According to our results and comparing them to the literature, we agree that at least 75% length of the unicortical screw has mechanical properties similar to those of the bicortical screw in volar plate assembling of the distal radius, thus we recommend using unicortical screws in intra-articular fractures of the distal end of the radius.