Construct-construct "rail technique" decreases screw strain during spinal deformity corrective maneuvers across a thoracic vertebral column resection: a cadaveric analysis.

PURPOSE: To biomechanically compare screw strains above and below a vertebral column resection (VCR) during segmental compression (SC) and cantilever bending (CB) performed via traditional methods and a novel, construct-to-construct accessory rod ("rail") technique.

METHODS

Eight cadaveric torsos underwent a VCR with 250 kyphosis at T8 with pedicle screws implanted three levels above and below the VCR (T5-7; T9-11). Four screws (T6, T7, T9, T10) were instrumented with strain gauges to capture screw strains during SC and CB. Both deformity corrective maneuvers were performed over a traditional construct (central rod) and over a construct-to-construct accessory ("rail") rod. Real-time screw strains were collected and peak strains were compared between corrective techniques.

RESULTS

Strains in screws closest to the VCR were significantly less during "rail" compression compared to traditional SC (T7: p = 0.015). Maximum screw strains were significantly lower during "rail" SC and CB compared to traditional SC (T6: p = 0.037; T7: p = 0.015) and CB (T6: p = 0.018; T9: p < 0.001). Total screw strain was more evenly distributed over all screws during "rail" compression and CB compared to traditional techniques, which concentrated strain at individual screws adjacent to the VCR.

CONCLUSIONS

Performing segmental compression and cantilever bending across a lateral accessory construct-to-construct ("rail") rod resulted in significantly lower strain on individual pedicle screws adjacent to a thoracic VCR compared to traditional SC and CB. As such, the "rail" may lessen risk of screw pull-out and screw plough during maneuvers to correct spinal deformities across a VCR.