A total of 414/ 634 (65.3%) SpS, 391/601 (65.1%) DS and 789/1,192 (66.2%) IDH participants underwent surgery. Examination of baseline participant characteristics by treatment received over 4 years () shows that surgically treated patients, in general, were younger; more frequently perceived that their problem was getting worse; and had a definite surgical preference compared with non-operatively treated participants.
Baseline participant characteristics by disease group and treatment received within 4 years.
Among surgically treated patients, reoperations were not common. For SpS, 43 (10.4%) patients underwent 47 additional surgeries; for DS, 48 (12.3%) patients had 52 additional surgeries, and for IDH 70 (8.9%) patients had 82 repeat surgeries. In each case, the majority of repeat surgeries were within 2 years of the initial surgery with a substantial minority occurring after 2 years, including 32.6% of SpS, 20.8% of DS and 24.4% of IDH repeat procedures.
Higher health state values were observed over time among surgically treated patients, than among non-operatively treated patients (). Mean quality-adjusted life years over the 4-year study period ranged from 2.66 to 3.24 (). QALY differences between treatment groups over 4 years were 0.22 (95%CI: 0.15, 0.34) for SpS; 0.34 (95%CI: 0.30, 0.47) for DS; and 0.34 (95%CI: 0.31, 0.38) for IDH.
Figure 1 Adjusted mean EQ-5D health state values and 95% confidence intervals over time by treatment received for A) spinal stenosis, B) degenerative spondylolisthesis with stenosis and C) intervertebral disc herniation disease groups. Treatment groups are compared (more ...)
Adjusted* mean 4-year costs (95% CI), QALY (95%), and cost QALY gained by patients group and type of surgery relative to non-operative treatment.
Adjusted total mean costs remained higher for surgically treated patients than for non-operatively treated patients across all patient groups (). Cost differences between treatment groups over 4 years were $13,147 (95%CI: $9,168, 21,716) for SpS; $22,127 (95%CI: $13,149, $38,317) for DS; and $6,994 (95%CI: $1,900, $11,237) for IDH. Examination of costs by treatment received showed somewhat different patterns over time (). Ongoing direct medical costs were observed for all groups () with similar expenditure patterns between treatment groups within each disease category (data not shown). The largest ongoing costs occurred for DS patients, who had higher ongoing indirect costs among non-operatively treated patients ().
Mean costs and 95% confidence intervals by time period and treatment received for each disease group and type of cost: A) Direct medical costs, B) Indirect costs.
The cost per QALY gained for surgery relative to non-operative care was lowest for those with IDH ($20,600) and highest for those with DS ($64,300) (). Only 23 DS patients underwent decompression alone and only 47 SpS patients underwent fusion surgery, making definitive comparisons between procedures within disease groups impractical. Among those with SpS, fusion surgery’s cost per QALY gained relative to non-operative care was $257,600 with a very wide confidence interval (). Among those with DS, fusion surgery’s cost per QALY gained relative to non-operative care was $66,300.
When type of instrumentation was examined for DS patients who underwent instrumented fusion, no statistically significant differences in QALY outcomes were found. The cost-effectiveness of each type of instrumentation relative to non-operative treatment was comparable at approximately $65,000 to $75,000 per QALY gained.
In sensitivity analyses, mortality adjustment, method of QALY estimation, and limiting the analysis to surgeries occurring within 2 years had little impact on cost-effectiveness estimates (). While study cohort (randomized vs. not) had little impact on cost-effectiveness for DS or IDH, in the SpS group the randomized cohort cost per QALY gained was somewhat higher at $124,700. Estimates remained below $125,000 per QALY gained across disease groups when higher surgery costs were used.
Sensitivity analysis results shown as mean cost per QALY gained (95% confidence interval) for surgery relative to non-operative care by disease group as analytic assumptions are varied.