BIOMECHANICAL ANALYSIS OF 3 SURGICAL APPROACHES FOR LUMBAR BURST FRACTURES USING SHORT-SEGMENT INSTRUMENTATION

Burst fractures of the lumbar spine that are located below the thoracolumbar junction present a challenge when operative management is indicated. Short-segment instrumentation offers the advantage of incorporating fewer motion segments in the fusion, but may not provide adequate long-term stabilization. The goal of this study was to assess the axial stiffness and torsional rigidity of several short-segment instrumentation procedures. Compressive axial stiffness and torsional rigidity were measured in six intact porcine lumbar spines (Ll-L5). A corpectomy was performed to simulate a burst fracture injury and decompression. Posterior instrumentation, posterior instrumentation with an anterior strut (a wood block), and anterior instrumentation with an anterior strut one level above and one level below the fracture site were applied as treatment strategies. VSP plates (Acromed, Cleveland, OH) for posterior instrumentation and the Kaneda system (Acromed, Cleveland, OH) for anterior instrumentation were used. Load-displacement and torque-angle plots were generated and used to calculate 144 estimates of axial stiffness and 144 estimates of torsional rigidity for these constructs. These analyses showed that, in comparison with the intact spine, posterior instrumentation alone was an average of 76% less stiff axially, posterior instrumentation with an anterior strut was 3% more stiff (not significantly different from intact), and anterior instrumentation with an anterior strut was 15% more stiff. Posterior instrumentation alone was an average of 30% less rigid in torsion, posterior instrumentation with an anterior strut was 26% less rigid, and anterior instrumentation with an anterior strut was 24% less rigid than the intact spine. These results suggest that short-segment posterior instrumentation alone does not restore the stiffness or rigidity of the injured spine to the stiffness and rigidity of the intact spine. Further, these results suggest that the reconstruction of the anterior column with a rigid strut is an important adjunct to posterior or anterior instrumentation.