Instrumented fusion, improves fusion rates, eliminates the need for postoperative braces and allows early mobilization. However, there are some drawbacks, as a larger surgical exposure, greater blood loss, nerve injury, etc. The increased stiffness of fused segments reduces the bone mineral content in adjacent vertebrae, and biomechanical studies indicated that increased stress at the levels adjacent to the fusion may increase adjacent segment pathology. Objective: To evaluate the efficacy and safety of unilateral pedicle screw fixation with posterolateral fusion (as a means to decrease the stiffness of the instrumented segment) for the treatment of one segment degenerative 2nd degree lumbar spondylolisthesis. Methods: This prospective study of forty three properly selected patients with one segment (L4-5 or L5-S1) degenerative 2nd degree lumbar spondylolisthesis underwent posterior decompression with unilateral pedicle screw fixation and posterolateral bony fusion from July 2008 to March 2013 in Mabarra hospital and Kuwaiti hospital and the follow-up period was a year. Results: Unilateral fixation shortens the operation time, limits the surgical exposure, reduces the blood loss, reduces the risk of nerve
root injury, reduces medical expenses and shortens hospital stay. At the same time this technique one year post operatively, achieved solid bony fusion as that of bilateral pedicle screw fixation with posterolateral fusion. Conclusion: This technique seems to be an effective and safe procedure for the treatment of one segment degenerative 2nd degree lumbar spondylolisthesis when compared with widely used bilateral instrumented fusion.