Interspinous process fixation vs. pedicle screw fixation

Kee D Kim

Kee D Kim explores new one-year outcomes data supporting the use of interspinous process fixation as an alternative to the use of pedicle screws.

Do we still need to use pedicle screws as an adjunct to interbody fusion? Supplemental pedicle screw fixation became a standard of care after suboptimal outcomes from standalone threaded cylindrical interbody cages popularised during the 1990s. This may sometimes be unnecessary with advances in standalone interbody technology. Wide-footprint anterior and lateral lumbar cages allow for good disc height restoration with distraction of annulus and longitudinal ligaments, and indirect neural decompression. However, an adjunctive posterior fixation is still desirable in many cases. Interspinous process fixation (ISPF) may be a lower risk and less challenging alternative to pedicle screw fixation. Until now, no prospective, randomised study has been performed comparing the two as an adjunct to circumferential fusion.

Our study was designed as a noninferiority randomised trial to compare the outcomes between ISPF and pedicle screw fixation when treating symptomatic disc degeneration and/or mild spondylolisthesis (≤grade II) in a real-world practice. We used the Aspen system (Zimmer Biomet) for ISPF. To best represent the current diverse surgical practice, investigators chose the posterior approach (minimally invasive or open pedicle screw placement), fixation type (unilateral or bilateral pedicle screws) and interbody approach (anterior or lateral). A randomisation of 2:1—ISPF to pedicle screw fixation (control) patients—was used. The non-inferior margin was 10 Oswestry Disability Index (ODI) points in accordance with previously reported values of minimal clinically-important difference. The primary outcome measure was ODI, and secondary outcome measures included perioperative outcomes, patient reported outcome scores (Short Form-36 survey, Zurich Claudication Questionnaire and Visual Analogue Scale) complication/revision profiles, and fusion.

While two-year follow-up data will not be available until June 2016, our podium talk at the 2016 ISASS meeting offered a detailed look at outcomes through one year. As may be a surprise to some, follow-up outcomes with ISPF were comparable and often favourable to those of pedicle screw fixation in most metrics.

ISPF demonstrated a mean ODI decrease of 3.6 points greater than pedicle screw fixation patients at 12 months. Mean ODI decrease was also greater for ISPF patients at earlier follow-up of six weeks, three months, and six months (p≥0.12). No significant differences were observed between either cohort for mean improvement in patient-reported outcomes. Brantigan, Steffee and Fraser interbody fusion scores were not significantly different (p=0.33) as assessed by an independent radiology group (mean 11.4 months).

Interestingly, 93% of ISPF patients demonstrated fusion, supporting robust interspinous bony fusion as support for the overall strength of the construct. Two ISPF (3%) and four pedicle screw fixation subjects (10.8%) required secondary surgical interventions, with one symptomatic pseudoarthrosis in each cohort.

Two-year follow-up will be telling with respect to the maintenance and longevity of outcomes. At one year, however, data supports the use of ISPF as an adjunct to circumferential fusion.


Kim K et al. Presented at the International Society of the Advancement of Spine Surgery Annual Meeting: General Session MIS-1 (6–8 April 2016, Las Vegas, USA).

Kee D Kim is chief of spinal neurosurgery and co-director of the Spine Center at the University of California Davis Health System, Sacramento, USA