Overall, 1244 SPORT participants with lumbar intervertebral disk herniation were enrolled out of 1991 eligible for enrollment (). Five hundred one patients agreed to participate in the randomized controlled trial and are reported in another article in this issue of JAMA
The 743 patients who declined to enroll in the randomized controlled trial comprised the observational cohort. Seven hundred nineteen patients (97%) completed at least 1 follow-up visit and were included in the analysis; between 82% and 89% of enrollees supplied data at each follow-up interval.
Flow Diagram of SPORT Observational Cohort for Herniated Disk: Exclusion, Enrollment, and Follow-up
Five hundred twenty-one patients initially choosing surgery and 222 patients initially choosing nonoperative care were enrolled. For the group initially choosing surgery, 91% received surgery within 6 weeks of enrollment, with an additional 4% receiving surgery by 6 months; at 2 years 4% remained nonoperative. In the group initially choosing nonoperative treatment, 2% underwent surgery in the first 6 weeks; while 16% had surgery by 6 months, and 22% had surgery by 2 years. Overall, 528 patients received surgery during the first 2 years and 191 remained nonoperative ().
Patient Baseline Demographic Characteristic, Comorbidities, Clinical Findings, and Health Status Measures by Treatment Received, and Also Compared With the Patients in the SPORT Randomized Controlled Trial*
The baseline characteristics of participants are shown in , according to whether they actually received surgery during the 2 years of follow-up. A comparison between the SPORT observational and randomized cohorts is also provided.
The study population was a mean age of 41.4 years with a majority being men, of white race, completing some college, and working full-time or part-time; 18% were receiving disability compensation. Ninety-eight percent had classic dermatomal pain radiation. Most of the herniations were at L5-S1, were posterolateral, and were extrusions by imaging criteria.17
At baseline, the surgery group was younger, heavier, less likely to be working, more likely to be receiving disability compensation, and reported fewer comorbid joint problems than those in the nonoperative group. They had more disk extrusions, positive contralateral straight leg raise, and neurological deficits; more severe bodily pain and back pain–related disability; lower levels of physical function; worse sciatica; and more often rated symptoms as getting worse at enrollment than those in the nonoperative group. The final model controlled for age, sex, race, marital status, work status, compensation, body mass index, smoking status, joint problems, migraines, neurological deficit, herniation (type, level, location), baseline score (for SF-36 and ODI), baseline sciatica bothersomeness, baseline satisfaction with symptoms, self-rated health trend, center, and health insurance status.
A variety of nonoperative treatments were used during SPORT. In the observational cohort, 92% received education and counseling, 58% received nonsteroidal anti-inflammatory drugs, 35% received narcotic analgesic agents, 43% underwent physical therapy, and 38% underwent epidural injections.
Surgical Treatment and Complications
The median surgical time was 70 minutes (interquartile range, 15-333 minutes) with an median blood loss of 50 mL (interquartile range, 0-1500 mL). Only 2 patients required transfusions. There were no perioperative mortalities. The most common surgical complication was dural tear in 2% of cases. Reoperation occurred in 7% of cases by 1 year and in 9% of cases at 2 years; more than half were recurrent herniations at the same level.
Main Treatment Effects
Treatment outcomes for the observational cohort are summarized in , , and . Treatment effects were statistically significant in favor of surgery for the primary outcome measures at 3 months: bodily pain (mean change: surgery, 40.9 vs non-operative, 26.0; treatment effect, 14.9; 95% confidence interval [CI], 10.8-18.9), physical function (mean change: surgery, 40.7 vs nonoperative, 25.3; treatment effect, 15.4; 95% CI, 11.6-19.2), and ODI (mean change: surgery, −36.1 vs nonoperative −20.9; treatment effect, −15.2; 95% CI, −18.5 to −11.8); at 1 year: bodily pain (mean change: surgery, 42.8 vs nonoperative, 32.0; treatment effect, 10.8; 95% CI, 6.5-15.0), physical function (mean change: surgery, 44.3 vs nonoperative, 29.2; treatment effect, 15.0; 95% CI, 10.9-19.2), and ODI (mean change: surgery, −37.7 vs nonoperative, −22.4; treatment effect, −15.2; 95% CI, −18.9 to −11.6), and 2 years: bodily pain (mean change: surgery, 42.6 vs non-operative, 32.4; treatment effect, 10.2; 95% CI, 5.9-14.5), physical function (mean change: surgery, 43.9 vs non-operative, 31.9; treatment effect, 12.0; 95% CI, 7.9-16.1), and ODI (mean change: surgery, −37.6 vs nonoperative, −24.2; treatment effect, −13.4; 95% CI, −17.0 to −9.7). The secondary measures of sciatica bothersomeness, satisfaction, and self-rated improvement also demonstrated significant treatment effects. The treatment effects narrowed between 3 months and 2 years but remained significant at all periods. Work status was worse in the surgery group at 6 weeks but this had equalized at 3 and 6 months; work status then showed a small benefit for surgery at 1 year but not at 2 years.
Adjusted Primary and Secondary Outcomes Change Scores, Percent and Treatment Effects for the Intervertebral Disk Herniation Observational Cohort According to Treatment Received*
Main Outcomes at Baseline and Each Follow-up Visit Through 2 Years
Work Status, Satisfaction With Symptoms, Satisfaction With Care, and Self-rated Health Trend at Baseline and Each Follow-up Visit Through 2 Years
Missing Data and Shifting Baselines
The percentages of participants with missing data were equivalent between the groups at each time point with no evidence of differential dropout (). At year 2 the missing data percentages were 17% for the surgery group and 14% for the nonoperative group. Sensitivity analysis was completed comparing our primary analysis using longitudinal models including covariates associated with missed visits with alternative analytic methods using single-imputation of missing data—baseline value carried forward and last value carried forward.15
Treatment effect estimates at 1 year ranged from 9.0 to 11.3 for bodily pain, 14.3 to 15.0 for physical function, −13.9 to −15.2 for ODI, and −2.1 to −2.6 for sciatica. Given these ranges, there appear to be no substantial differences among these methods.
Several alternative approaches for other features of the primary treatment effect analyses were also evaluated. Models using the enrollment values as baseline for the surgically treated group, rather than the visit prior to surgery, and which evaluated outcomes from the time of enrollment rather than the time from surgery, produced similar estimates for the 1-year outcomes. Strategies excluding the nonoperative experience of patients ultimately undergoing surgery or ignoring the correlation between patients contributing both nonoperative and surgical visits showed smaller but still statistically significant treatment effects in favor of surgery. Models without adjustment for baseline differences between the groups showed much larger treatment effects in favor of surgery as would be expected from regression to the mean since the surgery group started out with worse health status scores. Controlling for this regression to the mean in the adjusted models is important for estimating the true treatment effect.