Outcomes in cases of lumbar degenerative spondylolisthesis more than 5 years after treatment with minimally invasive decompression: examination of pre- and postoperative slippage, intervertebral disc changes, and clinical results
Authors: Mori Gen , Mikami Yasuo , Arai Yuji , Ikeda Takumi , Nagae Masateru , Tonomura Hitoshi , Takatori Ryota , Sawada Koshiro , Fujiwara Hiroyoshi , Kubo Toshikazu 
Published: November 2015

OBJECT
There are reports that fusion is the standard treatment of choice for cases of lumbar degenerative spondylolisthesis (LDS) associated with lumbar spinal canal stenosis with a large degree of slippage. The reasons why, however, have not been clarified. On the other hand, it is known that the progress of slippage decreases and restabilization occurs over the natural course of LDS. Therefore, if minimally invasive decompression could be performed, there would be little possibility of it influencing the natural course of LDS, so it would not be necessary to include preoperative percentage slip in the criteria for the selection of fusion. This study examined the course of LDS cases more than 5 years after treatment with minimally invasive decompression to determine whether pre- and postoperative slippage and disc changes influence the clinical results.

METHODS
A total of 51 intervertebral segments in 51 cases with the chief complaint of radicular or cauda equina symptoms due to lumbar spinal canal stenosis were examined after prospective treatment with minimally invasive decompression for LDS. The mean age of the patients at the time of surgery was 66.7 years and the mean follow-up period was 7 years 4 months. Minimally invasive decompression was performed regardless of the degree of low-back pain or percentage slip. The outcome variables were clinical results and changes in imaging findings.

RESULTS
Over the follow-up period, postoperative percentage slip increased and disc height decreased, but the Japanese Orthopaedic Association score improved. Regardless of the preoperative percentage slip, disc height, or degree of intervertebral disc degeneration or segmental instability, the clinical results were favorable. In the high preoperative percentage slip group, low disc height group, and progressive disc degeneration group, there was little postoperative progress of slippage. In the group with a postoperative slippage increase of more than 5%, slippage increased significantly at postoperative year 2, but no significant difference was observed at the final follow-up.

CONCLUSIONS
When minimally invasive decompression was performed to treat LDS, the postoperative change in slippage was no different from that during the natural course. Furthermore, regardless of the degree of preoperative slippage or intervertebral disc degeneration, the clinical results were favorable. Also, the higher the preoperative percentage slip and the more that disc degeneration progressed, the more the progress of postoperative slippage decreased. Because the postoperative progress of slippage decreased, it is believed that even after minimally invasive decompression, restabilization occurs as it would during the natural course. If minimally invasive decompression can be performed to treat LDS, it is believed that preoperative percentage slip and intervertebral disc degeneration do not have to be included in the appropriateness criteria for fusion.