Degenerative spondylolisthesis: Does fusion method influence outcome? four-year results of the Spine patient outcomes research trial

Study Design. Clinical trial subgroup analysis. Objective. To compare outcomes of different fusion techniques treating degenerative spondylolisthesis (DS). Summary of Background Data. Surgery has been shown to be more effective than nonoperative treatment out to 4 years. Questions remain regarding the differential effect of fusion technique. Methods. Surgical candidates from 13 centers in 11 states with at least 12 weeks of symptoms and confirmatory imaging showing stenosis and DS were studied. In addition to standard decompressive laminectomy, 1 of 3 fusion techniques was employed at the surgeon's discretion: posterolateral in situ fusion (PLF); posterolateral instrumented fusion with pedicle screws (PPS); or PPS plus interbody fusion (360°). Main outcome measures were the SF-36 bodily pain (BP) and physical function (PF) scales and the modified Oswestry Disability Index (ODI) assessed at 6 weeks, 3 months, 6 months, and yearly to 4 years. The as-treated analysis combined the randomized and observational cohorts using mixed longitudinal models adjusting for potential confounders. Results. Of 380 surgical patients, 21% (N = 80) received a PLF; 56% (N = 213) received a PPS; 17% (N = 63) received a 360°; and 6% (N = 23) had decompression only without fusion. Early outcomes varied, favoring PLF compared to PPS at 6 weeks (PF: 12.73 vs. 6.22, P < 0.020) and 3 months (PF: 25.24 vs.18.95, P < 0.025) and PPS compared to 360° at 6 weeks (ODI: -14.46 vs. -9.30, P < 0.03) and 3 months (ODI: -22.30 vs. -16.78, P < 0.02). At 2 years, 360° had better outcomes: BP: 39.08 versus 29.17 PLF, P < 0.011; and versus 29.13 PPS, P < 0.002; PF: 31.93 versus 23.27 PLF, P < 0.021; and versus 25.29 PPS, P < 0.036. However, these differences were not maintained at 3- and 4-year follow-up, when there were no statistically significant differences between the 3 fusion groups. Conclusion. In patients with DS and associated spinal stenosis, no consistent differences in clinical outcomes were seen among fusion groups over 4 years.