Five-year outcomes from a multi-center prospective randomized controlled trial of minimally invasive interspinous fixation versus open direct decompression for lumbar spinal stenosis

Background Interspinous fixation devices (IFDs) provide indirect decompression and stabilization for lumbar spinal stenosis (LSS) and are potentially less invasive than open decompression, but long-term comparative data are limited. Objective To evaluate the long-term clinical efficacy, safety, and perioperative outcomes of indirect decompression and fusion with an IFD versus standard open surgical decompression in patients with LSS. Methods 48 patients were randomly assigned to IFD or decompression. Primary endpoints were changes in Oswestry Disability Index (ODI), Visual Analogue Scale (VAS) leg and back pain, Zurich Claudication Questionnaire (ZCQ) physical function, walking distance, sit-to-stand repetitions, and analgesic medication usage at 8 weeks, 6, 12, 24, 36, 48, and 60 months compared to baseline. Secondary endpoints included patient and clinician global impression of change (PGIC, CGIC), safety data, perioperative measures, and IFD fusion rate. Results The IFD group (n = 18) demonstrated statistically significant improvements at five years for: ODI: −53%, VAS-leg: −66%, VAS-back: −60%, and ZCQ: −29% (Bonferroni-adjusted α = 0.0071). In the decompression group (n = 25), three of these four measures showed significant improvement: ODI:-60%, VAS-back: −60%, ZCQ: −42%, while VAS-leg (−64%) was not statistically significant. Both groups had mean increases in walking distance (IFD: 69-101%, decompression: 32-56%) and sit-to-stand repetitions (IFD: 25-70%, decompression: 5-59%) throughout the study, though five-year improvements were not statistically significant using the conservative α of 0.0071 for either group. Analgesic medication usage at five years was markedly reduced in both groups from baseline (IFD: 91% reduction, decompression: 76% reduction; p < 0.0001 for both). Perceived participant improvement was favorable throughout the study for both groups (PGIC: IFD: 87%, decompression: 83%; CGIC: 84% for both). Safety data indicated one resolved complication in each group, one surgical revision in the decompression group, and three surgical removals in the IFD group, though all removed IFD devices showed robust bony fusion and no device failures or migrations occurred. All perioperative metrics favored the IFD group: 80% less blood loss (p < 0.001), 57% shorter skin-to-skin time (p < 0.0001), 37% shorter theater time (p < 0.0001), and 41% shorter length of stay (p < 0.05). Conclusion IFD demonstrated durable 5-year efficacy and safety when used in the treatment of LSS, with marked perioperative advantages compared to open decompression. While overall clinical success was comparable for IFD and decompression, these comparisons are exploratory and hypothesis-generating, and larger trials with better retention are needed for definitive comparisons between groups.