Construct-construct "rail technique" decreases screw strain during spinal deformity corrective maneuvers: a mechanical analysis.

Abstract

Purpose: To compare screw strains adjacent to a simulated spinal osteotomy between segmental compression (SC) and cantilever bending (CB) to SC and CB performed over a construct-to-construct lateral accessory rod ("rail").

Methods: 10 PCF foam blocks were instrumented with 6 polyaxial pedicle screws, each with a linear strain gage. SC and CB were performed over a traditional construct (midline rods) or over a construct-to-construct lateral accessory rod. Real-time screw strains were collected and peak strains were reported and compared between corrective techniques.

Results: Strains in screws closest to the osteotomy were significantly less during "rail" compression compared to traditional SC. Maximum screw strains were significantly lower during "rail" SC (p < .001) and CB (p = 0.003) compared to traditional SC and CB, respectively. Total screw strain was more evenly distributed over all 6 screws during "rail" compression and CB compared to traditional techniques, which concentrated strain at individual screws adjacent to the osteotomy.

Conclusions: Performing SC and CB across an accessory construct-to-construct lateral ("rail") rod resulted in significantly lower strain on individual pedicle screws adjacent to a simulated spinal osteotomy compared to traditional SC and CB. As such, the "rail" may lessen risk of screw pull-out and screw plow during maneuvers to correct spinal deformities. Future work focused on building upon this controlled study in cadaveric specimens will be important to validate these findings in more clinically relevant scenarios.