Introduction: Interspinous process fixation (ISPF) is a minimally disruptive adjunct to circumferential spinal arthrodesis. Whether ISPF is a suitable alternative to pedicle screw fixation (PSF) for that indication is unknown. This trial was conducted to answer that question.
Methods: This was a prospective randomized controlled multi-center (11 investigators) study of 103 subjects receiving single-level interbody fusion with supplemental ISPF (n=66) or PSF (n=37) for the treatment of degenerative disc disease +/- low grade spondylolisthesis. The randomization ratio was 2:1, ISPF (Aspen MIS Fusion System, Zimmer Biomet Spine) to PSF subjects. The PSF approach (MIS or open; unilateral or bilateral) and interbody access approach (lateral or anterior) were per investigator institutional standard-of-care. Perioperative outcomes, patient reported outcomes, and radiographic/CT fusion assessment outcomes were collected through 12months (study duration: 24months). Comparative analysis was performed using a linear mixed model (p<0.05).
Results: No statistically significant differences were observed between cohorts with respect to change in patient reported outcome scores (ODI, SF-36, ZCQ, and NRS/VAS) from baseline to 1.5, 3, 6, or 12months. ISPF subjects did demonstrate a greater mean decrease in ODI across all follow-up time points.
Radiographic/CT assessment of vertebral translation (=3mm), angular motion (=5deg.), subsidence, intervertebral bone bridging, and BSF classification demonstrated comparable fusion outcomes between cohorts. 92% of ISPF subjects exhibited bone formation between the ISPF device plates that bridged the spinous processes.
Posterior device-related complication was minimal in both cohorts (ISPF=2; PSF=1).
Conclusions: ISPF subjects demonstrated comparable outcomes to PSF as an adjunct to circumferential lumbar interbody fusion. At one year, clinically advantageous trends across all follow-up metrics were noted with ISPF including bone formation in both the anterior and posterior aspects. Longer-term outcome will be needed to ascertain its durability.
Patient Care: How will your research improve patient care?
Should the long-term outcomes achieved with ISPF compare favorably to those with PSF, ISPF may be less invasive and more efficacious for posterior fixation as an adjunct to lumbar interbody fusion. Given its minimally disruptive nature and ease of placement, patients would have the potential to experience less iatrogenic complication while achieving comparable or favorable long-term outcomes.
Learning Objectives: By the conclusion of this session, participants should be able to discuss/identify…
1) Outcome trends achieved with adjunctive ISPF in circumferential fusion
2) Patient demographics/pathologies for which ISPF may be advantageous
3) Similarities and differences between outcomes achieved with adjunctive ISPF or PSF