Abstract
Posterior only approaches for spinal deformity are increasingly popular and posterior spinal release is utilized to gain flexibility for correctional maneuvers. Prior biomechanical data support the use of facetectomy and rib head resection for gaining flexibility in the sagittal and coronal planes but to date there has been no quantification of stiffness reduction provided by these techniques for axial correction through a pedicle screw construct. We sought to determine the contribution of posterior spinal releases (facetectomy, rib head resection) on axial plane stiffness. Four fresh-frozen human cadavers were instrumented with fixed angle pedicle screws in the thoracic spine. The torque needed to produce 25° axial deflections at individual spinal segments (levels T5-T11) was measured using a custom needle deflection torque device attached to commercially available vertebral rotating construct. After the intact specimen was tested, torque measurements were repeated following a full facetectomy and posterior rib head resection Complete facetectomy resulted in an 18% decrease of torque needed to produce 25° of axial deformity compared to the intact specimen (P<0.001). Rib resection added an additional 36% decrease in torque (P<0.001). Complete facetectomies (Ponte or Smith-Petersen osteotomies) decrease the force required to rotate spinal segments with respect to the axial plane by approximately one-fifth. Posterior rib head resection should be considered to further loosen the spine if additional axial correction is desired.
Highlights
Posterior only approaches for spinal deformity are increasingly popular, with surgeons utilizing more extensive posterior releases, such as Ponte or Smith-Petersen Osteotomies (SPOs) to improve correction [1]
Purpose Posterior only approaches for spinal deformity are increasingly popular and posterior spinal release is utilized to gain flexibility for correctional maneuvers
Prior biomechanical data support the use of facetectomy and rib head resection for gaining flexibility in the sagittal and coronal planes but to date there has been no quantification of stiffness reduction provided by these techniques for axial correction through a pedicle screw construct
Summary
Posterior only approaches for spinal deformity are increasingly popular, with surgeons utilizing more extensive posterior releases, such as Ponte or Smith-Petersen Osteotomies (SPOs) to improve correction [1]. Though originally described to shorten the posterior column for sagittal correction, may serve to improve axial flexibility of the spinal segment. Extensive posterior spinal release with osteotomy was described in 1945 by Smith-Petersen for correction of kyphosis associated with ankylosing spondylitis [9]. This osteotomy involves resection of the interspinous ligament, spinous processes, ligamentum flavum, and facet joints as well as the inferior portion of the lamella.
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