Biomechanical Analysis of Anterior Spinal Instrumentation Constructs for Lumbar Fusions

Corrective surgery for scoliosis with anterior instrumentation can be accomplished with different constructs: single rod, single rod with interbody cages and dual rods. These varying constructs are most often used in the lumbar spine to generate a fusion mass while retaining the natural lordosis of the lumbar region (Sweet, 1999). In a pediatric population or in smaller adults, two screws cannot often be implanted into a single vertebral body due to the body’s limited size. Previous work has compared the rigidity of one rod versus two rods (Kaneda, 1996) but no information exists directly comparing the stability of a single rod augmented with an interbody cage against a dual rod construct (Glazer, 1997). This study was initiated to determine stiffness differences in extension, lateral bending and axial torsion between 4 possible lumbar constructs: a single rod (Group 1), a single rod plus interbody cages (Group 2), two rods (Group 3) and two rods plus interbody cages (Group 4).