title: Lateral mass versus hybrid construct for cervical laminectomy and fusion.
abstract: Spine stabilization after C3-C7 laminectomy can be accomplished with many instrumentation options. A hybrid construct using lateral mass screws from C3 to C5 and pedicle screws at C7 can potentially maximize strength and solve the spatial constraints introduced by the placement of C6 lateral mass screws and C7 pedicle screws. Seven cadaveric cervical spines from C2 to T2 were potted in a custom testing apparatus. Differential variable reluctance transducers were placed on C6 and C7 to measure linear displacement. Specimens were loaded in flexion, extension, lateral bending, and axial torque at 1.5 Nm. A wide laminectomy was then performed, and specimens were randomized to first receive either the bilateral C3-C7 lateral mass screw construct or a hybrid construct with C3-C5 lateral mass screws and C7 pedicle screws. All specimens were tested with both constructs. Normalized deformation (mean±SD) for the lateral mass screw vs the hybrid pedicle screw constructs in the sagittal plane was 7.46%±5.48% vs 5.68%±3.67%, respectively (P=.237). Coronal deformation for lateral mass screw vs the hybrid pedicle screw constructs was 19.2%±10.9% vs 13.6%±9.53% (P=.237). Axial rotation deformation for lateral mass vs pedical screw constructs was 85.9%±83.3% vs 74.7%±58.1%, respectively (P=.868). Despite data reported in the literature indicating a higher pullout strength of pedicle screws and improved strength of hybrid pedicle screw constructs compared with lateral mass screw constructs, a hybrid construct taking spatial constraints and increased danger of pedicle screw placement above C7 into account showed no improvement in motion compared with a lateral mass screw construct.
authors.affiliation: Department of Orthopaedic Surgery, University of North Carolina, Chapel Hill, NC 27599, USA. conor.regan@gmail.com
authors.forename: Conor M
authors.initials: CM
authors.lastname: Regan
authors.forename: Steven
authors.initials: S
authors.lastname: Emmanuel
authors.forename: Christoph
authors.initials: C
authors.lastname: Hornik
authors.forename: Paul
authors.initials: P
authors.lastname: Weinhold
authors.forename: Moe R
authors.initials: MR
authors.lastname: Lim
mesh_terms: D001696:Biomechanical Phenomena; D001863:Bone Screws; D002102:Cadaver; D002574:Cervical Vertebrae / Q000503:physiopathology / Q000601:surgery*; D006801:Humans; D007796:Laminectomy / Q000295:instrumentation*; D013123:Spinal Fusion / Q000295:instrumentation*