Aim:Although conventional posterior lumbar interbody fusion (PLIF) using pedicle screws accomplish successful outcomes, pedicle screw related complications were sometimes noted. SPIRE™ was invented as interspinous fixation device (ISD) to replace pedicle screw. This study is to evaluate the clinical and radiological outcomes in patients underwent unilateral PLIF using SPIRE™ compared with pedicle screw.Material and Methods:All consecutive patients who shows medically intractable lumbar degenerative disease with unilateral radiculopathy and mild instability were enrolled. Thirteen patients underwent the PLIF using SPIRE™ (ISD group), and age, gender, and index level matched patients underwent the PLIF using pedicle screw (PS group) were recruited as 1:1 ratio. Pain, Oswestry Disability Index (ODI), disc height, and slippage were evaluated. Results:Both PS and ISD groups revealed significant improvement and there was no significant difference between them (back pain, p=0.18; leg pain, p=0.51; ODI, p=0.82). Although the ISD group showed spondylolisthesis for the first 3 months after the surgery, there is no significant difference compared with the PS group (p=0.65). Disc height decreased in both the ISD group (10.8mm→7.7mm) and the PS group (12.8mm→10.8mm), and this difference had statistical significance (p<0.01). In aspect of perioperative outcomes, the ISD group displayed better outcomes than the PS group (blood loss, p<0.001; surgery time, p=0.017). Conclusion:SPIRE fixation for PLIF demonstrate a comparable clinical outcomes with pedicle screw. It may be weak to fix, but acceptable. This technique may be an alternative technique to the patients with unilateral radiculopathy and mild instability.