OTA 1998 Posters

Tension Wire Position for Hybrid External Fixation of the Proximal Tibia

Paul Tornetta, III; Douglas Tiburzi; Jeffrey Geller; Kenneth Koval; Fred Kummer, Boston University Medical Center and Hospital for Joint Disease Institute, New York, NY

Purpose: Hybrid external fixation has become more popular in the treatment of complex tibial plateau fractures. The purpose of this study was to examine a new placement scheme for the tension wires in an attempt to increase resistance to flexion and extension forces.

Methods: In the first part of the study, two configurations of 3 wires proximally were used with a 3 half pin distal configuration. The standard, with the crossing point in the middle of the bone, and the new configuration with the same starting positions posteriorly but exiting just medial and lateral to the tubercle. Thus, the wires were oriented more in the sagittal plane and crossed more anteriorly. Placement of the third wire, which is in the transverse plane, posteriorly creates a triangle of intersection points within the proximal tibia. The second part compared the stronger of the two arrangements in the first part with two oblique thin wires and an anteromedial half pin proximally. All specimens were cadaveric tibiae with a proximal 2 cm gap subjacent to the tubercle and underwent biaxial testing on an Instron machine. Compression, torque, and anterior, posterior, medial, and lateral bending were tested for each configuration.

Results: The newer wire configuration was significantly stiffer in anterior bending (167%, p<0.001) and in posterior bending (139%, p<0.05) but not different in any other parameter. The addition of an anteromedial half pin increased the stiffness in medial bending by 20% (p<0.001) but did not affect stiffness in any other parameter.

Discussion: Placement of the oblique tensioned wires closer to the sagittal plane via more anterior exit points adjacent to the tubercle increases the ability of the frame to withstand the strong flexion and extension forces present in proximal tibia fractures. The addition of a half pin did not add to the stability in this plane and increased the stiffness only in medial bending. This new configuration allows for a greater angular spread of the wires and avoids the need for a half pin which is difficult to place clinically.

Conclusion: We suggest the use of this new wire configuration for proximal tibial fractures treated with hybrid fixation in order to better resist bending moments in the sagittal plane.