Our cost-effectiveness analysis included 634 participants with stenosis and 601 participants with degenerative spondylolisthesis with associated stenosis. On the basis of follow-up through 14 May 2007, 394 (62%) participants with stenosis and 368 (61%) participants with degenerative spondylolisthesis had surgery. Disease groups were remarkably similar across most characteristics at baseline, except that the degenerative spondylolisthesis group had more women (69% vs. 39%; P < 0.001) and was slightly older (average age, 66.1 vs. 64.6 years; P = 0.021). At baseline, patients in each disease group who went on to have surgery had significantly worse self-rated health trends, health status, and stenosis bothersomeness index scores than patients who received nonoperative treatment but were similar for most other characteristics ().
Baseline Participant Characteristics
For both disease and treatment groups, mean health state values improved over time (). Mean discounted QALYs ranged from 1.33 to 1.55 over 2 years of follow-up ().
Adjusted mean EuroQol EQ-5D health state values and 95% CIs over time, by treatment received
Adjusted Mean Quality-Adjusted Life-Years (QALYs) and Costs (95% CIs) over 2 Years*
Total adjusted mean nonoperative care costs were similar across diagnoses (). Health care visits, reported by 97% of participants, did not differ by treatment or disease group. Approximately half of all participants reported physical therapy; chiropractor visits were infrequent (10% in each group), and 6% reported use of acupuncture. Diagnostic tests were reported more frequently among those treated surgically (among patients with stenosis, 71% for surgery recipients vs. 57% for nonoperative management recipients [P < 0.001]; among patients with degenerative spondylolisthesis, 79% for surgery recipients vs. 56% for nonoperative management recipients [P < 0.001]). For both disease groups, injection use (such as epidural or trigger point) was higher among patients treated nonoperatively (among patients with stenosis, 45% for nonoperative management recipients vs. 30% for surgery recipients [P < 0.001]; among patients with degenerative spondylolisthesis, 46% for nonoperative management recipients vs. 29% for surgery recipients [P < 0.001]). Patterns of medication use showed greater use of nonsteroidal anti-inflammatory medication and cyclooxygenase-2 inhibitors in patients with degenerative spondylolisthesis who received nonoperative management (80%) than in other groups. Narcotic use was higher among those receiving surgery in both groups (among patients with stenosis, 71% of surgery recipients vs. 35% of nonoperative management recipients [P < 0.001]; among patients with degenerative spondylolisthesis, 74% of surgery recipients vs. 29% of nonoperative management recipients [P < 0.001]), whereas use of muscle relaxants was lowest among nonoperatively treated patients with stenosis (5%). Assistive device use was similar in both groups among patients with stenosis (54%). Among patients with degenerative spondylolisthesis, device use was significantly more common in those undergoing surgery (74% for surgery recipients vs. 46% for nonoperative management recipients; P < 0.001), with braces, canes, and walkers reported most commonly.
Total adjusted mean costs for surgical treatment were $26 222 (95% CI, $24 308 to $28 129) for patients with stenosis and $42 081 (CI, $39 800 to $44 373) for patients with degenerative spondylolisthesis (). Most stenosis surgeries (320 of 394 [81%]) were decompressive laminectomies, with mean surgery costs for uncomplicated cases of $7159 (CI, $7133 to $7185). A total of 35 repeated stenosis surgeries were performed on 27 (6.9%) patients, with a mean cost of $19 152 ($10 627 to $27 677) per patient. Fusion was uncommon among patients with stenosis, with only 43 occurrences. Most degenerative spondylolisthesis surgeries (344 of 368 [93%]) involved fusion with instrumentation, with mean costs for uncomplicated cases of $21 489 (CI, $21 318 to $21 660). A total of 48 repeated surgeries were performed on 37 (10.1%) patients, with a mean cost of $17 045 per patient (CI, $13 493 to $20 597).
Work loss costs tended to be higher for surgically treated patients (), with a higher proportion of surgically treated patients reporting any missed work days (among patients with stenosis, 25% of surgery recipients vs. 17% of nonoperative management recipients [P = 0.024]; among patients with degenerative spondylolisthesis, 26% of surgery recipients vs. 10% of nonoperative management recipients [P < 0.001]). Although unpaid caregiver costs were minimal, missed homemaking costs were substantial for both treatment groups and diagnoses.
Incremental cost per QALY gained for surgical treatment relative to nonoperative care was $77 600 for stenosis and $115 600 for degenerative spondylolisthesis (). Study cohort, cost type, and mortality made little difference to the value of surgical intervention (). In contrast, changing surgery cost or estimating effectiveness with the SF-6D led to less favorable cost-effectiveness estimates ().
Adjusted Mean 2-Year Costs, Quality-Adjusted Life-Years (QALYs), and Cost per QALY Gained Relative to Nonoperative Treatment*
Sensitivity Analysis Results
Cost-effectiveness acceptability curves, by disease group and analytic assumption
Examining cost-effectiveness by surgery type, decompression without fusion had the most favorable value among patients with stenosis (). Although fusion surgery was significantly more costly than decompression alone (cost difference, $17 545 [CI, $11 074 to $24 090]), it resulted in no QALY gain over 2 years (QALY difference, −0.01 [CI, −0.14 to 0.11]). In the 48% of bootstrapped samples in which a QALY gain was observed for fusion relative to decompression alone, the mean cost-effectiveness ratio exceeded $4 million.
Fusion with instrumentation surgery in patients with degenerative spondylolisthesis was more costly than laminectomy alone (mean cost difference, $21 266 [CI, $7854 to $32 631), but health outcome did not significantly differ by surgery type (mean QALY difference, 0.01 [CI, −0.21 to 0.24]). In the 66% of samples in which fusion resulted in a QALY gain, it did so at a mean cost per QALY gained of $997 400 (CI, $48 300 to $4 672 000). Relative to nonoperative treatment, instrumented fusion had slightly more favorable economic value than noninstrumented fusion and circumferential fusion seems most efficient, but these differences were not statistically significant (). Comparing instrumented with noninstrumented fusion, costs (difference, $2258 [CI, −$3812 to $7826]) and QALYs (difference, 0.02 [CI, −0.07 to 0.09) did not significantly differ. In the 68% of bootstrapped samples in which instrumentation was associated with a QALY gain, the mean cost was $448 600 per QALY gained (CI, −$177 200 to $1 691 000).