59. Does attachment of the dorsolumbar fascia to a spinous process prosthesis affect kinematics at the operative and adjacent levels? An in vitro human cadaveric model

BACKGROUND CONTEXT Postlaminectomy kyphosis, disc herniations, and/or spondylolisthesis are documented complications following multilevel laminectomy. Removal of the spinous processes and ligaments in multilevel laminectomy disrupts the normal kinematics of the spine, increase segmental motion and risk of “hypermobility-related” complications. The current study utilized a novel testing methodology, where specimens retained all local paraspinal muscle, dorsolumbar fascia and skin layers, to quantify multidirectional flexibility properties of the lumbar spine following destabilization, reconstruction of the posterior arch and reattachment of the posterior fascia to a spinous process prosthesis (SP-P). PURPOSE The purpose of the current investigation was to quantify changes in multidirectional flexibility at the operative and adjacent lumbar motion segments following multilevel laminectomy and implantation of a spinous process prosthesis. STUDY DESIGN/SETTING In vitro human cadaveric model and multidirectional flexibility testing. PATIENT SAMPLE Not applicable. OUTCOME MEASURES Not applicable. METHODS Eight lumbopelvic spines (T9-sacrum) were utilized in this investigation. Specimens retained all paraspinal musculature, ligaments, fascia and skin layers. Multidirectional flexibility testing included pure moment loading at ±10Nm in flexion-extension, lateral bending, and axial rotation. Following analysis of the intact spine, treatment groups included: (1) L2-L4 laminectomy without fascia closure, (2) L2-L4 laminectomy with fascia closure, and (3) L2-L4 SP-P (n=3 prostheses) attached to pedicle screws with fascia closure to the prostheses with suture. Range of motion (ROM) at the superior adjacent (T12-L2), operative (L2-L5), and inferior adjacent (L5-S1) levels was compared using a Repeated Measures Analysis of Variance and Bonferroni post hoc test. Significance was indicated at p≤0.05. RESULTS There were no significant changes in ROM at the superior or inferior adjacent levels between reconstructions under any loading modality. For the operative L2-L5 levels, flexion-extension motion was significantly greater for the laminectomy (156.57±38.89%) and laminectomy with fascia closure (147.11±35.93%) reconstructions compared to intact. The laminectomy reconstruction also demonstrated significantly greater lateral bending motion (110.65±6.43%) compared to intact. In axial rotation, the laminectomy (157.95±18.27%), laminectomy with fascia closure (160.54±21.39%), and SP-P (159.36±18.38%) reconstructions observed greater motion when compared to intact (p CONCLUSIONS Re-establishing the posterior arch and attachment to a spinous process prosthesis restored flexion-extension motion at the operative levels following multilevel laminectomy. The results add value to the concept of robust closure of posterior dorsolumbar layers and stress the importance of preserving or replacing the posterior arch to decrease operative level motion. FDA DEVICE/DRUG STATUS Crosslink (Approved for this indication).