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Construct-construct "rail technique" decreases screw strain during spinal deformity corrective maneuvers across a
Alekos A Theologis1, Jason DePhillips2, Izabella T Lachcik2
1Department of Orthopaedic Surgery, University of California - San Francisco (UCSF), 500 Parnassus Ave, MUW 3Rd Floor, San Francisco, CA, 94143, USA. alekos.theologis@ucsf.edu.
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.
