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Hybrid external fixation of the proximal tibia: strategies to improve frame stability
Craig S Roberts1, James C Dodds, Kelvin Perry
1Department of Orthopaedic Surgery, University of Lousville, Lousville, Kentucky 40202, USA. craig.roberts@lousville.edu
Objective:
To determine the specific frame construction strategies that can increase the stability of hybrid (ring with tensioned wires proximally connected by bars to half-pins distally) external fixation of proximal tibia fractures. DESIGN Repeated measures biomechanical testing.
Setting:
Laboratory.
Specimens:
Composite fiberglass tibias.
Methods:
Using the Heidelberg and Ilizarov systems, external fixators were tested on composite fiberglass tibias with a 1-cm proximal osteotomy (OTA fracture classification 41-A3.3) in seven frame configurations: unilateral frames with 5-mm diameter half-pins and 6-mm diameter half-pins; hybrid (as described above), with and without a 6-mm anterior proximal half-pin; a "box" hybrid (additional ring group distal to the fracture connected by symmetrically spaced bars to the proximal rings) with and without an anterior, proximal half-pin; and a full, four-ring configuration. Each configuration was loaded in four positions (central, medial, posterior, and posteromedial).
Main Outcome Measurements:
Displacement at point of loading of proximal fragment.
Results:
The "box" hybrid was stiffer than the standard hybrid for all loading positions. The addition of an anterior half-pin stiffened the standard hybrid and the "box" hybrid.
Conclusions:
The most dramatic improvements in the stability of hybrid frames used for proximal tibial fractures result from addition of an anterior, proximal half-pin.