Predicting time on prolonged benefits for injured workers with acute back pain.

INTRODUCTION: Some workers with work-related compensated back pain (BP) experience a troubling course of disability. Factors associated with delayed recovery among workers with work-related compensated BP were explored. METHODS: This is a cohort study of workers with compensated BP in 2005 in Ontario, Canada. Follow up was 2 years. Data was collected from employers, employees and health-care providers by the Workplace Safety and Insurance Board (WSIB). Exclusion criteria were: (1) no-lost-time claims, (2) >30 days between injury and claim filing, (3) <4 weeks benefits duration, and (4) age >65 years. Using proportional hazard models, we examined the prognostic value of information collected in the first 4 weeks after injury. Outcome measures were time on benefits during the first episode and time until recurrence after the first episode. RESULTS: Of 6,657 workers, 1,442 were still on full benefits after 4 weeks. Our final model containing age, physical demands, opioid prescription, union membership, availability of a return-to-work program, employer doubt about work-relatedness of injury, worker's recovery expectations, participation in a rehabilitation program and communication of functional ability was able to identify prolonged claims to a fair degree [area under the curve (AUC) = .79, 95% confidence interval (CI) .74-.84]. A model containing age, sex, physical demands, opioid prescription and communication of functional ability was less successful at predicting time until recurrence (AUC = .61, 95% CI .57, .65). CONCLUSIONS: Factors contained in information currently collected by the WSIB during the first 4 weeks on benefits can predict prolonged claims, but not recurrent claims.

Second-order estimating equations for the analysis of clustered current status data.

With clustered event time data, interest most often lies in marginal features such as quantiles or probabilities from the marginal event time distribution or covariate effects on marginal hazard functions. Copula models offer a convenient framework for modeling. We present methods of estimating the baseline marginal distributions, covariate effects, and association parameters for clustered current status data based on second-order generalized estimating equations. We examine the efficiency gains realized from using second-order estimating equations compared with first-order equations, issues of copula misspecification, and apply the methods to motivating studies including one on the incidence of joint damage in patients with psoriatic arthritis.

Risk factors for axial inflammatory arthritis in patients with psoriatic arthritis.

OBJECTIVE: Axial involvement is an important manifestation of psoriatic arthritis (PsA). We aimed to identify risk factors associated with the presence of axial PsA (AxPsA) in patients with PsA. METHODS: Patients with AxPsA (bilateral sacroiliitis >or= grade 2/unilateral sacroiliitis >or= 3 and inflammatory neck/back pain or limited spinal mobility) at first clinic visit were identified from the University of Toronto PsA clinic database. Risk factors associated with the presence of AxPsA were determined. Subsequently, patients without AxPsA at first clinic visit were identified. Under a multistate framework, the proportion of patients with PsA who subsequently developed AxPsA was estimated robustly using marginal methods and a Markov model. Risk factors at baseline that were associated with future development of AxPsA were identified through multiplicative time-homogeneous Markov models. RESULTS: Our study included 206 patients. Fifty patients had AxPsA at first clinic visit. HLA-B*27, radiographic damage to peripheral joints, and elevated erythrocyte sedimentation rate (ESR) increased odds of having AxPsA, while family history of PsA decreased the odds. One hundred fifty-six patients did not have AxPsA at first clinic visit. On followup, 28 developed AxPsA, and 11 died. We estimated that after 10 years of followup, 15% would develop AxPsA. Nail dystrophy, number of radiographically damaged joints, periostitis, and elevated ESR increased the risk of developing AxPsA, while swollen joints decreased the risk. CONCLUSION: These results suggest that severe peripheral arthritis and HLA-B*27 are risk factors for AxPsA.