Purpose Functional restoration programs (FRPs), for patients with chronic disabling occupational musculoskeletal disorders (CDOMDs), have consistently demonstrated positive socioeconomic treatment outcomes, including decreased psychosocial distress and increased work return. The pre-treatment length of disability (LOD), or time between injury and treatment admission, has been shown to influence FRP work outcomes. Some studies have found that shorter LOD is associated with better work outcomes. However, few studies have actually examined cohorts with LOD duration longer than 18 months. This present study evaluated the effects of extended LOD (beyond 18 months) on important treatment outcomes. Methods A total cohort of 1413 CDOMD patients entered an FRP. Of those, 312 did not complete the program, so they were eliminated from outcome analyses. The 1101 patients who completed the FRP were classified based on LOD: Late Rehabilitation (LR, 3–6 months, n = 190); Chronic Disability (CD, 7–17 months, n = 494); and Late Chronic Disability (LCD). The LCD, in turn, consisted of four separate subgroups: 18–23 months (LCD-18, n = 110); 24–35 months (LCD-24, n = 123); 36–71 months (LCD-36, n = 74); and 72+ months (LCD-72, n = 110). Patients were evaluated upon admission and were reassessed at discharge. Those patients who chose to pursue work goals post-treatment (n = 912) were assessed 1-year later. Results Longer LOD was associated with less likelihood of completing the FRP (p < .001). Compared to the other LOD groups, a relatively large percentage of patients (47%) in the longest- disability group were receiving social security disability benefits. Associations were found between longer LOD and more severe patient-reported pain, disability, and depressive symptoms at treatment admission. At discharge, symptom severity decreased for these patient-reported variables in all LOD groups (p < .001). Using binary logistic regressions, it was found that LOD significantly predicted work-return (Wald = 11.672, p = .04) and work-retention (Wald = 11.811, p = .04) after controlling for covariates. Based on the LOD groups, the percentage of patients returning to, and retaining work, ranged from 75.6 to 94.1%, and from 66.7 to 86.3%, respectively. The odds of LCD-24 and LCD-72 patients returning to work were 2.9, and 7.4, respectfully, less likely, compared to LR patients. Furthermore, the odds of LCD-24 and LCD-72 patients retaining work were 3.3 and 3.8 times, respectively, less likely, compared to LR patients. Conclusions Long LOD was a risk factor for FRP non-completion, and was associated with more severe patient-reported variables, including pain intensity and perceived disability. Furthermore, long LOD was a significant predictor for work outcomes at 1 year following FRP discharge. Nevertheless, a large percentage of longer LOD (>24 months) patients had returned to work within the year after discharge (above 85%), and had retained at least part-time work 1-year later (above 66%). These results support the effectiveness of the FRP in mitigating the effects of extended LOD in a large percentage of long-term LOD patients.
