title: Biomechanical demands on posterior fusion instrumentation during lordosis restoration procedures.
abstract: OBJECTIVE The goal of this study was to investigate the forces placed on posterior fusion instrumentation by 3 commonly used intraoperative techniques to restore lumbar lordosis: 1) cantilever bending; 2) in situ bending; and 3) compression and/or distraction of screws along posterior fusion rods. METHODS Five cadaveric torsos were instrumented with pedicle screws at the L1-5 levels. Specimens underwent each of the 3 lordosis restoration procedures. The pedicle screw pullout force was monitored in real time via strain gauges that were mounted unilaterally at each level. The degree of correction was noted through fluoroscopic imaging. The peak loads experienced on the screws during surgery, total demand on instrumentation, and resting loads after corrective maneuvers were measured. RESULTS A mean overall lordotic correction of 10.9 ± 4.7° was achieved. No statistically significant difference in lordotic correction was observed between restoration procedures. In situ bending imparted the largest loads intraoperatively with an average of 1060 ± 599.9 N, followed by compression/distraction (971 ± 534.1 N) and cantilever bending (705 ± 413.0 N). In situ bending produced the largest total demand and postoperative loads at L-1 (1879 ± 1064.1 and 487 ± 118.8 N, respectively), which were statistically higher than cantilever bending and compression/distraction (786 ± 272.1 and 138 ± 99.2 N, respectively). CONCLUSIONS In situ bending resulted in the highest mechanical demand on posterior lumbar instrumentation, as well as the largest postoperative loads at L-1. These results suggest that the forces generated with in situ bending indicate a greater chance of intraoperative instrumentation failure and postoperative proximal pedicle screw pullout when compared with cantilever bending and/or compression/distraction options. The results are aimed at optimizing correction and fusion strategies in lordosis restoration cases.
authors.affiliation: Kaiser Permanente Medical Center, Oakland;
authors.forename: Calvin C
authors.initials: CC
authors.lastname: Kuo
authors.affiliation: The Taylor Collaboration, San Francisco;
authors.forename: Audrey
authors.initials: A
authors.lastname: Martin
authors.affiliation: Sierra Pacific Orthopedics, Fresno;
authors.forename: Connor
authors.initials: C
authors.lastname: Telles
authors.affiliation: The Taylor Collaboration, San Francisco;
authors.forename: Jeremi
authors.initials: J
authors.lastname: Leasure
authors.affiliation: Redwood Orthopaedic Surgery Associates, Santa Rosa;
authors.forename: Alex
authors.initials: A
authors.lastname: Iezza
authors.affiliation: UCSF Department of Neurological Surgery, San Francisco;
authors.forename: Christopher
authors.initials: C
authors.lastname: Ames
authors.affiliation: SF Orthopaedic Residency Program, San Francisco; and.|St. Mary's Spine Center, San Francisco, California.
authors.forename: Dimitriy
authors.initials: D
authors.lastname: Kondrashov
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D004868:Equipment Failure; D005471:Fluoroscopy; D006801:Humans; D008141:Lordosis / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D065289:Pedicle Screws; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods*; D016896:Treatment Outcome
keywords: balance; bending; cantilever; correction; fusion; intraoperative; lordosis; lumbar; posterior; sagittal