607 participants enrolled in the DS SPORT trial (304 in the randomized cohort and 303 in the observational cohort). Of these, 34.9% (212) were non-operative patients and 395 were treated surgically. Of the 395 surgical cases, 380 (96%) had surgical descriptive data and at least one follow up: 21% (N=80/380) had a PLF; 56% (N=213/380) had a PPS; 17% (N=63/380) had a 360°; and 6% (N=23/380) had a decompressive laminectomy only. In the 360° fusion group, 35% underwent an anterior-posterior procedure while 65% underwent a posterior procedure including PLIF and TLIF. These were not independently analyzed due to the small size of these sub-sub-groups. Given the small size of the decompression-only group, they are not considered in this analysis. The proportion of enrollees who supplied data at each follow-up interval ranged from 70% to 99% with losses due to dropouts, missed visits, or deaths ().
Figure 1 Exclusion, Enrollment, Randomization and Follow-up of Trial Participants The values or surgery, withdrawal, and death are cumulative over four years. For example, a total of 3 patients in the group assigned to surgery died during the 4-year follow-up (more ...)
summarizes baseline characteristics of the three fusion groups. Statistically significant differences were seen between the groups in age; race; work status; osteoporosis; neurologic deficits; and stenosis level, location and severity (). Several significant baseline differences appear to be driven by the 360° group. Compared to the other fusion groups the 360° group was: younger; more likely to be working; less likely to report osteoporosis; had lower rates of stenosis at L3-4; less severe stenosis; less central stenosis; and had lower scores on the SF-36 mental component summary scale. There were no other significant differences in baseline characteristics or functional health status between groups.
Baseline demographic characteristics and comorbidities according to treatment received.
These observations highlight the need to control for baseline differences in the adjusted models. Based on the selection procedure for variables associated with treatment, missing data and outcomes, the final as-treated models controlled for the following covariates: age; gender; BMI; compensation status; depression; joint problems; hypertension; current symptom duration; number of moderate/severe stenotic levels; baseline stenosis bothersomeness; enrollment center; and baseline score for each outcome.
Surgical Treatment and Complications
The mean surgical times for the three fusion groups ranged from 157 to 274 minutes, PLF having the shortest time and 360° the longest (). Mean estimated blood loss ranged from 499 cc to 666 cc and was lowest for PLF and highest for PPS. Intra-operative blood replacement was lowest in PLF but did not reach statistical significance (p=0.098); however, there was a difference in the postoperative transfusion rates (14% for PLF versus 26% for PPS and 17% for 360°, p=0.05). The most common surgical complication was dural tear, which was highest for PPS (12% versus 9% PLF and 2% 360°, p=0.047). This may reflect the fewer number of operative levels and severity of stenosis in the 360° group. The 4-year re-operation rate did not significantly differ across the three groups (P=0.27).
Operative treatments, complications and events for DS 4yr fusion.
Over four years, there were 16 documented deaths across the three fusion groups (); 8 PLF, 8 PPS and 0 360° compared to expected numbers based on age-specific mortality rates of 7, 16, and 3, respectively7
for the general population. A Cox model comparing the three fusion treatment mortality rates adjusting for patient age, gender and wait time for surgery was not statistically significant (Wald
= 2.71, p = 0.259). However, the hazard ratio for PLF referenced to PPS was 2.30 (95% CI 0.85 to 6.17), which would be clinically significant; this result approached statistical significance at p < 0.10 with a 90% CI of 1.001 to 5.265. All 16 deaths were independently reviewed and 12 were judged not to be treatment-related; 2 deaths were of unknown cause; and 2 were judged as potentially related to treatment. For these 2 potentially related deaths, 1 was in the PLF group and occurred 32 days after surgery due to respiratory distress; the other, in the PPS group, occurred 82 days after surgery due to sepsis.
Main Treatment Effects
All three fusion groups demonstrated significant changes compared to baseline in all primary outcomes (BP, PF and ODI) out to four years (). The patterns of change are depicted in . Overall, there were some varying differences between groups during the early time periods and no significant differences between any of the groups in later time periods.
Comparison of Fusion Techniques by Primary Outcome Measures
Summary of fusion group pattern of results for the SF-36 Bodily Pain (BP) and Physical Function (PF) scales and the Oswestry Disability Index (ODI)
For SF-36 BP, the groups were similar at the early time points, though at 1-year there was a trend toward a difference between the three groups overall (p<0.10) with the 360° fusion demonstrating a slightly larger improvement than PLF (38.99 vs. 30.7; p=0.04) and PPS (38.99 vs. 32.32; p=0.06) in pair-wise comparisons. At 2-years the groups were significantly different (p<0.008), with 360° having significantly better outcomes than PLF (39.08 vs. 29.17; p=0.01) and PPS (39.08 vs 29.13; p=0.003); however, no significant differences were seen between fusion types at 3 years (p<0.79) or 4 years (p<0.74). The outcomes of PLF and PPS were similar in all pair-wise comparisons.
For SF36 PF, there were trends toward early differences at 6 weeks (p<0.07) and 3 months (p<0.08), slightly favoring PLF over PPS (6 weeks 12.73 vs. 6.22; p=0.02 and 3 months 25.24 vs. 18.95; p=0.03). Pair-wise differences between PLF and 360°, or PPS and 360° were not significant at these early time points. No differences between the groups were seen at 1 year but the 360° group had better outcomes at 2 years compared to both PLF (31.93 vs. 23.27; p=0.02) and PPS (31.93 vs. 25.29; p=0.04). There were no significant differences between the groups at 3 or 4 years but there was a trend toward worse outcomes in PPS at 4 years.
For ODI, differences between the three fusion groups were observed at 6-weeks (p<0.10), 3-months (p<0.042), and 1-year (p<0.036). In pair-wise analysis, PPS demonstrated significantly greater improvement than 360° at 6 weeks (−14.46 vs.−9.30, p < 0.03) and 3 months (−22.30 vs. −16.78, p < 0.02). At 1-year PLF was worse than PPS (−20.92 vs.−26.33, p < 0.02) and 360° (−27.61, p < 0.03). Again, no significant differences were seen between any of the groups at 3 and 4 years.
The Stenosis Bothersomeness Scale revealed no statistically significant differences between PLF and 360°, and slightly worse outcomes in PPS compared to 360° that were statistically significant at 2 years (p=0.009) but not at other time points. Back pain bothersomeness showed a similar pattern with somewhat worse outcomes in PPS compared to 360° at 2 and 3 years but not at other time points (). There were no significant differences across fusion groups in satisfaction with symptoms or care at any of the 5 follow-up time intervals (data not shown).
Summary of fusion group pattern of results for Stenosis Bothersomeness and Back Pain Bothersomeness Indices.
Fusion status classifications were reported for 74% (282/380) of the cases. Of the 282 fusion classifications, 89.7% were classified based on plain radiographs only, 3.9% indicated that classification included CT, and the remaining 6.4% indicated that classification included some “other” method.
As illustrated in , solid fusion was the predominate classification. However, across the three treatment approaches, the solid fusion ratings were significantly different,
= 10.69, p <0.005. Follow-up tests using logistic regression methods revealed that the PLF group had a significantly lower solid fusion rate (67.24%) compared to both the PPS (85.29%, p < 0.004) and the 360° (87.04%, p < 0.017) approaches, respectively. The difference in solid fusion rates for the two instrumented approaches was not significant (85.29% vs. 87.04%, p < 0.75).
Fusion Status for SPORT DS Fusion Subgroups