Introduction: Investigators quantified in-vitro stability of the novel technique of inserting both cortical screws (CS) and pedicle screws (PS) in the same vertebral level using a robotic-assisted guidance system to improve posterior fixation in patients with severe osteopenia and vertebral compression fracture (VCF). Multi-rod reconstruction techniques have been shown to maximize posterior fixation, but at present, utilize a single pedicle screw anchor point to support multiple rods. Recent studies have demonstrated the radiographic feasibility for such a dual screw trajectory for posterior lumbar spinal instrumentation; however, biomechanical characterization of the technique is presently lacking.
Methods: Operative constructs (L2-L4) included intact; bilateral PS with two rods (PS 2-rod); bilateral PS with four rods using rod-to-rod connectors (PS 4-rod); bilateral PSCS dual screw fixation with two rods affixed only at the PS (PSCS 2-rod); and bilateral PSCS dual screw fixation with rods affixed at PS and CS (PSCS 4-rod). VCF was simulated at L3. Load control (±7.5Nm) testing was performed in flexion-extension (FE), lateral bending (LB), and axial rotation (AR) (n=7).
Results: In FE and LB, for both groups, the following general trend was observed: intact > 2-rod > 4-rod. In LB, PS and PSCS 2-rod fixation reduced intact motion to 27.7% and 39.0%, respectively (both p<0.05); 4-rod fixation further reduced motion to 24.0% and 26.2%, respectively (both p<0.05). The FE and AR results were not significant (p>0.05).
Conclusions: The present study provided the first biomechanical evaluation of a novel dual screw technique in a VCF model. Multi-rod reconstruction increased stability, regardless of single or dual screw technique. While 4-rod reconstruction with dual screws provided the most fixation in FE and AR, the additional bony anchor points did provide improved stability in comparison to the use of 4-rod reconstruction with PS and rod-to-rod connectors.
Patient Care: This study proposed a new dual screw surgical technique in treatment of vertebral compression fractures in the lumbar spine. Inadequate reduction in range of motion of the lumbar spine after a compression fracture can result in construct failure and may require removal of the instrumentation and revision surgery. This novel dual screw technique has the potential to improve the stabilization of the lumbar spine and reduce the risk of instrumentation failure. Patient care can be improved with decreased pain caused by construct failure and lower ratesof revision surgery. With the popularity of posterior instrumentation in spinal fusion, improvements in surgical technique can have widespread influence and impact a significant portion of the population.
Learning Objectives: By the conclusion of this session, participants should be able to:
1) Describe the arrangement of the dual screw technique involving both a cortical screw and pedicle screw in the same vertebral level with multi-rod support.
2) Discuss, in small groups, potential biomechanical and clinical advantages for the dual screw technique in vertebral compression fractures over traditional techniques.