The Internet Journal of Minimally Invasive Spinal Technology 2009 : Supplement II - to IJMIST Vol III No 4
Mitchell Hardenbrook
Citation: M. Hardenbrook : Inter-spinous Process Fixation for Degenerative Pathology of the Lumbar Spine. The Internet Journal of Minimally Invasive Spinal Technology. 2009 Supplement II - to IJMIST Vol III No 4
Fusion has been an accepted surgical treatment for degenerative pathology of the lumbar spine. This has traditionally been enhanced through the use of pedicle screw and rod instrumentation. Though this instrumentation has improved the rate of fusion, it has also resulted in numerous adverse outcomes. Placement of pedicle screw requires a wide surgical exposure with intraoperative muscle stripping resulting in significant morbidity. Additionally, the pedicle is in close proximity of the adjacent un-fused facet joint. Placement of pedicle screws often results in iatrogenic injury of the adjacent facet at the cephalad of the construct. This fact combined with the rigidity of the screw-rod construct has lead to accelerated degeneration of the adjacent levels. This has been reported as high as 30% incident. This raises a number of questions. First, can alternative fixation be utilized to avoid the pedicle? This would reduce the need for a wide surgical exposure and reduce the risk of iatrogenic injury to the adjacent facet. Second, would a less rigid construct reduce the rate of adjacent segment degeneration while providing enough stability to enhance surgery? Iter-spinous process fixation allows for posterior fixation as an adjunct to lumbar fusion. It has the benefit of providing fixation with only minimal midline muscle dissection. Biomechanical testing shows inter-spinous fixation to be equal in stiffness to pedicle screw/rod fixation when paired with anterior interbody fusion in flexion and extension. However, there is less rigidity in lateral bending and rotation in the inter-spinous process fixation. Biomechanical testing of the adjacent level to inter-spinous process more closely matches the intact disc when compared to the adjacent level of the rod-screw construct. Early evaluation has demonstrated improved perioperative clinical outcomes.
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