Risk of Fracture at External Fixator Pin Hole After Lateral Tibial Plateau Fracture Plating: A Biomechanical Comparison of Different Screw Configurations.

BACKGROUND

External fixation of tibial plateau fractures commonly provides temporary stabilization before definitive fixation with plate and screws. The purpose of this study was to determine if an external fixator pin hole distal to a tibial plate in a synthetic fracture model would increase the risk of fracture after fixation. Another objective was to determine the ideal configuration when placing tibial plate screws near an external fixator pin hole.

METHODS

Thirty synthetic tibiae were tested and evenly divided into 5 groups. Tibial plateau plates were placed with 4 different screw configurations for the distal-most screw near the external fixator pin hole. The 5 groups tested were control (fixation with no external fixator hole), unicortical (distal fixation with a unicortical locking screw), bicortical (distal fixation with a bicortical locking screw), oblique (distal fixation with an oblique cortical screw angled 30° proximally from the external fixator hole), and hole-bridging (hole-bridging fixation in which the plate was placed bridging the external fixator hole). The bone surrogates were potted and tested using an Instron 8874 Testing System.

RESULTS

There was a significant difference in failure load among the 5 groups (p = 0.005). The mean peak loads were 1,259 N (control), 835 N (unicortical), 831 N (bicortical), 943 N (oblique), and 993 N (hole-bridging). There was a higher failure load in the control group compared with the bicortical group (p = 0.007) and the unicortical group (p = 0.007). There was no difference in failure load between the control group and the hole-bridging group (p = 0.16) and the oblique group (p = 0.067).

CONCLUSIONS

External fixator pin holes distal to a tibial plateau plate may increase the risk of tibial fracture through the pin hole. This risk may be mitigated by placing the distal screw oblique and angled proximally away from the external fixator pin hole or by placing the external fixator pin proximally with subsequent bridging of the external fixator pin hole with the plate.