Discussion: Isthmic Spondylolisthesis: Reduction vs. In-Situ Fusion?
The issue of neurologic compromise is at the forefront of every surgeon's mind when reduction of Spondylolisthesis is entertained. The cited literature indicates that reduction of grade 3 and 4 Spondylolistheses and Spondyloptoses typically produces neurologic L5 root symptoms in 10 %–20 % of patients.
The study of published approaches to the reduction of Spondylolisthesis reveals evidence of substantial but poorly controlled force being applied to the interspace in the form of posteriorally directed translation as well as distraction. The exact degree of distraction during reduction is not recorded in any of the abovementioned literature. Petraco's study reveals a severe increase in L5 root tension at the time of disc distraction . Their study does show substantial increase in the distance between the L5 pedicle and anterior upper sacrum at the time of reduction. However, the study fails to consider other causes of L5 root injury such as intraoperative trauma to the root, inadequate neural decompression, or lumbosacral ligament compression. The study also assumes that the length of the L5 root is the same as the distance from the pedicle to the anterosuperior border of S1. It should be realized that the total spinal canal length (from L1 to S1) is significantly shortened at the time of reduction. Furthermore, one should appreciate that nerve roots typically slide in and out of the foramen throughout activities of daily living. Actual L5 root tension results from canal lengthening, L5 root stretch, L5 root mobility, degree of disc distraction, and reduction of kyphosis.
The key to a safe reduction is to utilize carefully controlled force and limited distraction amounting to no more than physiological disc space height. Our case series of 22 patients with grade 2 and 3 isthmic Spondylolisthesis reduction utilizing the SOCON Spondylolisthesis Reduction System produced no neurologic deficits. It should be noted that anatomic reduction in 19 of our 22 patients was achieved, whereas all other groups excepting that of Ani have achieved only one third to one half average reduction of the Spondylolisthesis. The SOCON Spondylolisthesis Reduction System achieves precise and controlled reduction through levered forces applied to the L5 and S1 bodies. Simultaneous translation and slip angle correction is achieved via the mechanism of derotation. Studies with long-term follow-up are necessary to clearly substantiate the relative merits and disadvantages of Spondylolisthesis reduction.
Clearly, reduction of grade 4 and 5 Spondylolisthesis is problematic. This study does not address this challenging problem. Substantial evidence has been accumulated to suggest that a significant portion of the surgical trauma involving the L5 roots at the time of Spondylolisthesis reduction may be associated with compression of the L5 roots underneath the lumbosacral ligament. Until the exact etiology of L5 root trauma during Spondylolisthesis reduction is established, routine release of the lumbosacral ligament via an anterior or posterior approach during attempted reduction of grade 4 and 5 Spondylolisthesis seems prudent.
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