The study involved analyses using 2, well-described data sources: the Spine Patient Outcomes Research Trial (SPORT), and the National Spine Network (NSN). SPORT is a prospective trial with observational and randomized cohorts of patients with IDH, SpS, and degenerative spondylolisthesis (DS) enrolled at multiple centers.24–26
The NSN includes 28 spine centers that prospectively collected data on patients seen for a wide range of spine problems.27,28
The current study sought to identify patients with the same lumbar spine disorders in the SPORT and NSN data sets who reported they were receiving or applying for disability compensation due to their back problem (excluding patients already permanently disabled), and to compare them with patients in the workforce not receiving or applying for disability compensation (work-eligible comparison group). This study combined data from both sources because survey instruments included many similar variables. By merging data from patients with lumbar radiculopathy due to an IDH or SpS who were categorized according to initial disability and work status, the goal was to identify a large, multistate cohort of patients receiving disability compensation or not with well-described homogeneous clinical conditions. All patients enrolled in NSN and SPORT provided written informed consent at the time of study enrollment, and all study activities were approved by institutional review boards at participating institutions.
Broadly, eligibility for the current study involved categorizing patients in SPORT and NSN according to 1) criteria for lumbar radiculopathy due to an IDH or SpS with or without DS, 2) disability status at study enrollment, and 3) work status at study enrollment. All patients meeting clinical eligibility criteria who were either receiving disability compensation at study enrollment or were classified as work-eligible were selected.
Eligibility Criteria for Lumbar Radiculopathy
Study eligibility with respect to the clinical spine condition was based on inclusion and exclusion criteria for patients enrolled in SPORT. Patients were eligible if they had appropriate symptoms and examination findings confirmed on advanced imaging studies for each of the 3 radicular syndromes, IDH, SpS, and DS. Exclusion criteria for all 3 diagnostic categories were designed to restrict enrollment to patients without prior spine surgery for whom surgery would be appropriate, elective, and acceptably safe (). Patients in SPORT were enrolled between 2000 and 2005.
Figure 1 Eligibility criteria for SPORT and comparison to NSN. , comparable variable in NSN; −, similar variable in NSN; X, no comparable variable available in NSN; IDH, intervertebral disc herniation; SpS, spinal stenosis; DS, degenerative (more ...)
Since NSN enrolled patients with a wide range of spine conditions, eligibility criteria were developed to mirror SPORT. A comparison of eligibility criteria for SPORT and NSN populations are shown in . Exclusion criteria in SPORT without comparable variables in NSN were generally limited to factors necessary for a clinical trial comparing surgical and nonoperative treatment outcomes. As such, the criteria for NSN patients may better reflect clinical practice at these sites. A total of 4858 patients with IDH and 3445 patients with SpS enrolled between 1998 and 2003 were identified. Applying the criteria in , 2294 (47.2%) patients with IDH and 1712 (49.7%) with SpS were excluded.
Disability Status at Study Enrollment
Patients were classified according to self-reported disability compensation status at study enrollment (baseline).21
Programs assessed included WC, Social Security Disability Insurance (SSDI), and other disability compensation (ODC) insurance. Since SSDI reflects a permanent disability state, patients receiving SSDI at enrollment were excluded. Response categories and disability status criteria are shown in . Since patients could respond affirmatively to 1 or more disability programs, patients were considered to be receiving disability if they reported an approved or pending application.
Comparison of disability and work status criteria in SPORT and NSN at study enrollment.
Although patient-reported disability compensation status has been previously validated,21
we compared patient-reported disability status responses to billing records for the subset of eligible patients enrolled at 1 site enrolling patients in SPORT and NSN (total 981 patients: 813 only in NSN, 69 only in SPORT, and 99 in both SPORT and NSN). The payer source for all clinical visits during a period of 2 years before and after the study enrollment date was obtained. Billing data were considered to agree with patient response if there was any payment by WC for those reporting WC and no payment by WC for those not reporting WC. Disagreement was defined as patient and billing records reporting differences for WC status or if the billing record information was missing. Among patients reporting applying for or receiving WC, 148 of 167 (88.6%) had local billing information indicating payment by WC. Thirteen of 19 where patient and billing information differed represented patients who stated they had applied for WC. Among 814 patients reporting not currently receiving or applying for WC, 761 (93.5%) had no billing records indicating payment from WC. Of the 53 patients who reported they had not applied for or were receiving WC but had billing records of WC payments, 15 (28.3%) stated that had received WC in the past but were no longer receiving it, and 10 (18.9%) said they were planning to apply for WC. Agreement for the total validation population was good (kappa = 0.76), and ranged from 0.75 to 0.88 among NSN and SPORT patients.
Work Status at Study Enrollment
To create an appropriate comparison group for patients identified as receiving disability compensation, patients not classified as WC or ODC but who could have a future work-related disability were identified. This was accomplished by classifying patients according to self-reported work status at study enrollment. Response categories and work status criteria are shown in . Patients were “work- eligible” if they were 1) currently working, 2) not working because of back problems, or 3) unemployed (since they could return to work after finding a new job). Patients were excluded if they reported they were retired, disabled from another condition, were a homemaker or student, or if they did not report their employment status.
Initial Treatment Designation
Treatment status was categorized at baseline as surgical or nonoperative based on treatment assignment or choice. For patients enrolled in SPORT, treatment assignment was based on participation in the randomized controlled trials or an observational cohort. Patients agreeing to randomization received their treatment assignment, surgical or nonoperative, at the time of study enrollment. Patients not choosing to be randomized but agreeing to participate in the observational cohort study designated their treatment choice at the time of study enrollment. Since NSN was not designed as a clinical trial, no formal treatment assignment or designation was required at study enrollment. Therefore, initial treatment designation for this study was based on the evaluating physician reporting that surgery was “recommended” or “scheduled” for a patient at baseline.
All patients completed baseline questionnaires at the time of study enrollment. Participating investigators also provided baseline clinical information. Patients reported a broad range of socioeconomic information. Because the goal of this study is to compare nonclinical factors that differentiate patients receiving WC or not, domains considered in this analysis include demographic information, disability status, work status, economic information, and expectations for treatment. Other domains representing clinical baseline status that are available in these data sets will be evaluated in future analyses.
For each socioeconomic domain, baseline variables from the SPORT and NSN were assessed, including their response categories. Mapping of variables and responses among the 2 data sources was performed (see Appendix, available online through Article Plus). In general, most variables in NSN were available in the SPORT data set, but as a major clinical trial, SPORT collected additional variables not included in the NSN survey questionnaires. For example, more detailed information about work status, income sources, and treatment expectations/preferences were available in SPORT.
Baseline variables were compared for patients in WC and work-eligible comparison groups. Initial analyses compared responses by WC status separately according to data source (SPORT or NSN), clinical cohort (IDH or SpS), and initial treatment (surgical or nonoperative). Since findings were similar for those in WC and work-eligible groups, the combined population was used with all comparisons controlling for data source, clinical cohort, and initial treatment. Although SPORT enrolled patients with SpS and DS into separate treatment cohorts, this study merged these patients into 1 group since the underlying process is degenerative and the population represents older working individuals. For baseline variables that were only available in the SPORT data set, adjusted comparisons controlled for clinical cohort, initial treatment, and study cohort (randomized or observational).
χ2 tests were used to compare the percentage of work-eligible patients with WC and ODC according to 1) data source (SPORT or NSN), 2) clinical cohort (IDH or SpS/DS), 3) initial treatment designation (surgical or nonoperative), and 4) for SPORT patients, study cohort (randomized or observational). To identify baseline variables independently associated with WC status, preliminary selection from each of the 5 socioeconomic domains was separately performed using stepwise multiple logistic regression models developed with a P value threshold of 0.1 for entry and 0.05 for retention. Variables meeting these criteria were then entered into new models using the same criteria. Separate models were created for combined and SPORT only data sets. Association among baseline variables and WC status (the dependent variable) are reported as odds ratios and 95% confidence intervals. All statistical analyses were performed using a commercial software package (Statistical Analysis System, SAS Institute, Cary, NC).