Posterior Lumbar Interbody Fusion with Interspinous Fastener Provides Comparable Clinical Outcome and Fusion Rate to Pedicle Screws

Objective: To investigate the clinical feasibility and validity of interspinous fastener (ISF) for lumbar degenerative diseases. Methods: From October 2013 to March 2014, a total of 46 patients suffering from lumbar degenerative diseases underwent posterior lumbar interbody fusion (PLIF) randomly augmented by ISF or pedicle screws. The clinical outcome was primarily measured by Oswestry Disability Index (ODI) score. The minimal clinical important difference (MCID) was defined as an eight-point decrease in ODI. The second clinical outcome measurement was Japanese Orthopedic Association (JOA) score. Interbody fusion rates were evaluated by lumbar plain radiograph and computed tomography (CT) scan. Complications were also compared between groups. Statistical analyses were performed by SPSS version 13.0. Sample size calculation was performed before the study. The type I error a was set at 0.05 and the type II error beta at 0.1. Based on these assumptions and adding 10% for possible drop-outs, sample size calculations indicated that a total of 46 patients were required for the study. Parametric data was compared by independent t-test and categorical variables were compared using.2-tests or Fisher exact tests depending on the sample size. A P-value of less than 0.05 was considered significantly statistically different. Fleiss kappa coefficients were calculated for intra-observer and inter-observer reliability. Results: A total of 43 patients completed the follow-up, with 22 cases in the ISF group and 21 patients in the pedicle screws group, respectively. Less intraoperative blood loss and shorter operation time were observed in the ISF group. The mean ODI significantly declined in both groups, with the ISF group's decreasing from preoperative 43.3 +/- 8.2 to 21.4 +/- 3.5 at 24-month follow-up and the pedicle screws group's decreasing from preoperative 42.9 +/- 7.9 to 22.5 +/- 3.8 at 24-month follow-up, respectively. The ODI changes between groups had no statistical difference (P > 0.05). Of the 43 patients, 33 patients achieved an MCID. The bone fusion rate was 77.3% according to X-rays and 68.2% according to CT scans in the ISF group, and 81.0% according to X-rays and 76.2% according to CT scans in the pedicle screws group at the final follow-up. The intra-observer and inter-observer reliability assessed by the kappa value were 0.93 and 0.89, respectively. One patient in the pedicle screws group demonstrated screw loosening at the 6-month follow-up but was asymptomatic. One patient with spondylolisthesis in the ISF group demonstrated cage subsidence during the follow-up but also without related symptoms. Conclusion: The less invasive ISF combined with PLIF provided comparable clinical outcome and a similar bone fusion rate to pedicle screws. The ISF could potentially serve as a new alternative for lumbar degenerative diseases.