Locked plates reduce displacement of vertically unstable pelvic fractures in a Mechanical Testing Model

Biomechanical evaluation of location and mode of failure in three screw fixations for a comminuted transforaminal sacral fracture model

Background

Pelvic ring–comminuted transforaminal sacral fracture injuries are rotationally and vertically unstable and have a high rate of failure.

Objective

Our study purpose was to use three-dimensional (3D) optical tracking to detect onset location of bone–implant interface failure and measure the distances and angles between screws and line of applied force for correlation to strength of pelvic fracture fixation techniques.

Methods

3D relative motion across sacral–rami fractures and screws relative to bone was measured with an optical tracking system. Synthetic pelves were used. Comminuted transforaminal sacral–rami fractures were modelled. Each pelvis was stabilised by either (1) two iliosacral screws in S1, (2) one transsacral screw in S1 and one iliosacral screw in S1 and (3) one trans-alar screw in S1 and one iliosacral screw in S1; groups 4–6 consisted of fixation groups with addition of anterior inferior iliac pelvic external fixator. Eighteen-instrumented pelvic models with right ilium fixed simulate single-leg stance. Load was applied to centre of S1 superior endplate. Five cycles of torque was initially applied, sequentially increased until permanent deformation occurred. Five cycles of axial load compression was next applied, sequentially increased until permanent deformation occurred, followed by axial loading to catastrophic failure. A Student t test was used to determine significance (p < 0.05).

Results

The model, protocol and 3D optical system have the ability to locate how sub-catastrophic failures initiate. Our results indicate failure of all screw-based constructs is due to localised bone failure (screw pull-in push-out at the ipsilateral ilium–screw interface, not in sacrum); thus, no difference was observed when not supplemented with external fixation.

Conclusion

Inclusion of external fixation improved resistance only to torsional loading.

Translational Potential of this Article

Patients with comminuted transforaminal sacral–ipsilateral rami fractures benefit from this fixation.

Crossover external fixator for acetabular fractures: a cadaver study

BACKGROUND

Dislocated acetabular fractures in polytraumatized patients are very challenging cases to deal with. Temporary stabilization by skeletal traction is difficult in these patients. A more effective solution can be an external fixation.

OBJECTIVE

The authors designed a new crossover external fixation frame for acetabular fracture. The aim of this study is the biomechanical testing of this frame on human cadavers.

METHODS

This study is an experiment on ten human cadavers. The acetabular fracture C2.2 was created. The stabilization effect of external fixation was compared with stabilization by large distractor. Femoral heads' shifts caused by standardized manipulation with the cadaver were obtained from X-ray pictures.

RESULTS

The mean total shift in stabilization technique by external fixation was 2.56 (1-4) mm. In stabilization by large distractor, the mean of the total shift after cadaver manipulation was 5.11 (0-10) mm. No significant differences were found between stabilization by external fixation and by large distractor (p = 0.066).

CONCLUSIONS

The stabilization of acetabular fracture C2.2 by a crossover external fixator is as effective as large distractor. The crossover external fixation could be a suitable solution for the temporary stabilization of acetabular fractures in polytraumatized patients. Subsequent studies including clinical trials are necessary to confirm the authors' suggestion.