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BACKGROUND CONTEXT: Although satisfactory clinical outcomes have been reported for degenerative spondylolisthesis using a variety of surgical techniques, its optimal management remains controversial. Laboratory and clinical evidence is emerging that if fusion surgery is undertaken, improved short- and longer-term outcomes may be achieved by correcting any sagittal deformity present. The insert-and-rotate posterior lumbar interbody fusion (PLIF) technique, first described by Jaslow in 1946, may enable surgeons to safely and effectively correct sagittal balance through a single posterior approach. PURPOSE: To examine the clinical outcomes and determine whether the focal sagittal imbalance associated with a degenerative lumbar spondylolisthesis can be safely and effectively corrected using a posterior distraction/reduction technique and insert-and-rotate interbody fusion spacers. STUDY DESIGN/SETTING: A prospective, single-cohort, observational study of the clinical outcomes and retrospective radiological review, in a series of 34 patients with degenerative spondylolisthesis, who underwent surgery between September 2000 and October 2002. PATIENT SAMPLE: Mean age of 65.1 years (range, 35 to 82 years). Thirty-two of the 34 patients underwent surgery principally for the relief of radicular leg pain. The principal indication for the fusion was the prevention of anticipated postdecompression instability in 68% of the patients. Mean preoperative slip was 20.0% (range, 12% to 33%). Mean preoperative focal lordosis was 13.2 degrees. OUTCOME MEASURES: Patients were administered pre- and postoperative clinical outcome surveys recording Visual Analogue Pain Score (VAS), Low Back Outcome Score (LBOS), Short Form (SF)-12 and patient satisfaction questionnaires. Pre- and postoperative measurements of the percentage slip and lumbar lordosis of the involved segments were available on 17 patients. Statistical analysis was done using a two tailed, paired t test. SURGICAL METHODS: Decompressive laminectomy was followed by reduction of the spondylolisthesis using intervertebral disc space distraction and pedicle screw instrumentation. The vertebral bodies were supported with bilateral intervertebral lordotic spacers, inserted on their sides and rotated 90 degrees before placing bone graft to either side of them, within the disc space. RESULTS: Mean follow-up time was 21.2 months (range, 12-32 months). No patients were lost to follow-up. Mean preoperative measures of VAS and LBOS of 5.3+/-2.2 and 24.8+/-15.6, respectively, improved to 2.2+/-2.1 (p<.001) and 44.8+/-18.0 (p<.001) at last follow-up. Thirty-one of 34 patients (91%) considered their outcome to be good or excellent. Mean preoperative slip reduced from 20.2% to 1.7% (92% correction, p<.001). Mean focal lordosis increased from 13.1 to 16.1 degrees (26.0% increase, p=.01). There were no device-related procedural complications. Postoperatively, three patients developed an ileus and one a possible deep wound infection, which settled on antibiotics. One patient required extension of his fusion at 12 months for adjacent segment stenosis. CONCLUSIONS: This series suggests that PLIF for degenerative spondylolisthesis using an insert-and-rotate technique can yield high levels of patient satisfaction with low levels of complications and substantial deformity correction using a posterior only approach. Longer-term outcome studies are required regarding the relevance of the restoration of spinal balance.