Evaluation of Neural Tension at the Time of Spondylolisthesis Reduction

This series of short papers on isthmic spondylolisthesis is well-written, concise, and well-referenced. I agree almost universally with the points raised by Dr. Kozak. In our center we also add free run EMG monitoring for the lumbosacral roots during reduction of isthmic spondylolisthesis. While many techniques have been described, the technique of distraction/translation and levered reduction appear to be the two most popular and enjoy the lowest complication rates, albeit certainly not zero. The reader should not forget the possibility of performing an in situ arthrodesis with a fibula drilled from sacrum through the endplate and into the body of L5 (modified Speed procedure) for high grade slips. This can be supplemented by posterior instrumentation and posterolateral fusion and also enjoys a very high success rate without a substantive neurologic complication rate. Dr. Kozak is to be complimented on his thoughtful and comprehensive reviews. The surgeon should be mindful of the challenges of these procedures prior to translating the results of surgeon advocates to their own practice.

Dr. Kozak provides a thorough, yet concise review of the entity of isthmic spondylolisthesis. The various etiologies of nerve root compression from the disorder are well-described, as is the risk of neurological deterioration with reduction of high-grade slippage. Emphasis should be placed on visualization and assessment of tension and compression of the involved nerve roots (i.e. L5 in L5/S1 spondylolisthesis) during reduction. Shortening of the spinal column with a sacral dome osteotomy for example, and avoidance of large structural interbody grafts, may help to lessen the incidence of deficits related to tension on the nerve roots. Although we routinely employ free-running EMGs at our institution, they may not detect stretch injuries at the time of surgery. Direct nerve root stimulation has been advocated as a technique to assess the integrity of the nerve root at the time of reduction (Shufflebarger, et al.) and may be more effective in that regard. The importance of the lumbosacral ligament is not often alluded to and is a valuable point of this article. In previous series, L4-sacrum or more cephalad levels of arthrodesis was often advocated for lumbosacral spondylolisthesis. The advantage of a reduction maneuver is that monosegmental fusion can be achieved perhaps lessening the long-term consequences of adjacent segment degeneration. More important than translation reduction is the restoration of sagittal alignment as measured by slip angle. As pointed out by Dr. Kozak, long-term studies will perhaps point to the benefits of reduction of isthmic spondylolisthesis.