Tension wire position for hybrid external fixation of the proximal tibia.

OBJECTIVE

To compare a new configuration of proximal wires for hybrid external fixation with the standard configuration.

DESIGN

Biomechanical testing of five matched pairs of fresh cadaveric tibia.

INTERVENTION

The authors compared the standard tension wire configuration of the three proximal wires with a more sagittal orientation of the oblique wires. A second study compared the new configuration with two wires and an offset half-pin. A two-centimeter segmental defect was created just distal to the tibial tubercle and the tibias fixed in a Montecelli Spinelli (Howmedica, NJ, U.S.A.) hybrid frame. The constructs were biomechanically tested using an Instron servohydraulic biaxial testing machine.

RESULTS

There was a significant 67 percent decrease in displacement during anterior posterior bending and a significant 40 percent decrease in displacement in posterior bending with the new configuration compared with the standard configuration (p < 0.05). The differences in stability in all other testing modes were not significant. There was no significant difference between the new configuration and the two wire and off-set half-pin configuration.

CONCLUSION

We recommend anterior placement of the oblique tension wires in the proximal tibia to more effectively resist bending in the sagittal plane, which is the most common deforming force on proximal metaphyseal fractures.