1. Posterolateral versus Posterior Interbody Fusion in Isthmic Spondylolisthesis Introduction Spondylolisthesis is a heterogeneous disorder characterised by subluxation of a vertebral body over another in sagittal plane. Its most common form is isthmic spondylolisthesis (IS). The nerve root deficits and leg pains involve foraminal stenosis caused by a combination of fibrocartilaginous mass at the isthmic defect, disc and osteophyte of the slipped body. Instrument-assisted posterolateral fusion (PLF) and posterior lumbar interbody fusion (PLIF) are used as two common techniques for the treatment of IS. This study aims to compare clinical outcomes of PLF with posterior instrumentation and PLIF with posterior instrumentation in the treatment of grades I and II of IS. We performed a randomized prospective study in which 80 patients out of total of 85 patients with lumbar IS, 18 men and 62 women aged 18-65, were eligible to participate and were randomly allocated to one of 2 groups: PLF with posterior instrumentation (n=40) or PLIF with posterior instrumentation (n=40). A 1-year follow-up period was planned from March 2010 to March 2011. Fusion was performed by using bone chips, achieved from the resected lamina, mixed with synthetic bone substitute granules. Isthmic spondylolisthesis No previous spine operation Age between 18 and 65 Failed conservative therapy Non-isthmic spondylolisthesis Need to perform discectomy in PLF group Infection Generalized bone disease Static and functional lumbar spine plain X-rays, four views: anteroposterior (AP), lateral, right and left obliques, in which features relevant to spondylolisthesis, including percentage of subluxation, severity of slip, slippage angle, and height of intervertebral disc space were evaluated. Successful fusion was defined as the integrated ossification at the fusion bed without motion in a dynamic graph. The Oswestry low back pain disability (OLBP) scale and visual analogue scale (VAS) were used to evaluate the quality of life (QOL) and pain, respectively. The Fisher exact test was used to evaluate fusion rate and Mann- Whitney U-test was used to compare categorical data. Fusion in PLIF group was significantly better than PLF group (P=0.012). Improvement in low back pain was statistically more significant in PLF group (P=0.001). Incidence of neurogenic claudication was significantly lower in PLF group (P=0.004). In PLF group, there was no significant correlation between slip Meyerding grade and disc space height, radicular pain, and low back pain. There was no significant difference in postoperative complications at the 1-year follow-up period. Intraoperative blood loss in PLIF was significantly more than PLF procedure (P=0.04). P valueMean ± SDMean RankGroupsParameter 0.001 25.34±9.3651.00PLF Reduction in Low Back Pain 17.10±12.9833.11PLIF Our findings suggest that PLF with posterior instrumentation provides better clinical outcomes compared to PLIF with posterior instrumentation. Improvement of low back pain in PLF group was more significant than PLIF group in our study. The number of the patients who had complaints of neurogenic claudication 1 year after the operation was significantly more in PLIF group with posterior instrumentation than PLF. It seems that fusion alone is not sufficient for the reduction of low back pain. More manipulation of osseous tissue, end plates, dura, and neural structures in PLIF is the main cause of more LBP in this procedure compared with PLF, in spite of better fusion rate in PLIF. Compared with PLIF, the improvement in low back pain and QOL was better in patients who underwent PLF with posterior instrumentation. PLF with posterior instrumentation is recommended in patients with IS because this procedure is simple, with less neurological deficits, less blood loss, and better clinical outcomes. Majid Reza Farrokhi, MD; Abdolkarim Rahmanian, MD; Mohammad Sadegh Masoudi, MD* Shiraz Neurosciences Research Center, Neurosurgery Department, Shiraz University of Medical Sciences, Shiraz, Iran Materials and Methods Inclusion Criteria Results P valueMean ± SDMean RankGroupsParameter 0.138 6.59±1.7946.19PLF Radicular Pain 6.02±1.8338.44PLIF Exclusion Criteria Radiological Evaluation Statistical Analysis Discussion Conclusion http://snrc.sums.ac.ir neuroscien@sums.ac.ir *masoudims@sums.ac.ir