Musculoskeletal disorders (MSD) and mental disorders (MD) are common among working-age individuals, and reduced work ability is often a problem that influences functioning in working life. Having MSD and MD is also a common cause of seeking health care and these conditions account for the majority of sick leave in most western countries. The overall aims of the thesis were to increase knowledge about biopsychosocial assessment of health, functioning and work ability for individuals with MSD and MD seeking care. A further aim was to gain better understanding of praxis behaviour in the rehabilitation process for sick-listed patients by evaluating patient-reported work ability, type of interventions given, usefulness of interventions, and return to work.

This thesis comprises four studies based on two different cohorts. A cross-sectional design was used for studies I and II, which included 210 individuals diagnosed with MSD and MD seeking occupational health services. Data collection consisted of questionnaires to patients on self-reported health, functioning, work conditions, work ability and reports of professional assessment of diagnosis, main clinical problem, recommended intervention and sick leave. Studies III (n=699) and IV (n=810) were based on a longitudinal cohort study, ReWESS, with a 3-month follow-up comprising individuals who sought primary health care or occupational health services for MSD or MD and were sick-listed. The data collection included repeated questionnaires to the patients on self-reported health, functioning, work conditions, work ability, type and usefulness of intervention and return to work.

There was an association between the professional biopsychosocial assessment and patients’ self-reported measures of health, functioning and work ability in clinical reasoning. Self-reported health and work measures can complement the expert-based diagnosis. Patients who had MSD and MD with co-morbid conditions reported more problems with mental functioning, had higher psychological demands at work and reported poorer work ability compared with those with MSD only. Patients with co-morbid conditions also had worse outcome compared to having mental disorders only. Psychosocial problems and activity limitations concerning social interaction skills were a frequent problem. This can be identified in clinical screening by physiotherapists in dialogue with the patient using the Patient-Specific Functional Scale. Three-quarters of sick-listed individuals with MSD or MD returned to work within 90 days. The treatment approach to sick-listed persons is still very medical and clinically oriented. Access to work-related interventions seems to be limited in the early rehabilitation process and may not be equal in practice. Those who were younger, had higher educational level and reported stronger health resources were favoured. There is a need to strive for access to work-related interventions.

Return to work was associated with receiving combined clinical- and work-related interventions for patients with MD, and with better health-related quality of life, positive return to work expectations and better work ability for patients with MSD. Factors associated with return to work can be identified using self-reported measures. Patients with MD who received a combination of work-related and clinical interventions perceived best usefulness and best effect of health care contacts on work ability. Patients with MSD did not report as good usefulness. There seems to be a gap between scientific evidence and praxis behaviour in the early rehabilitation process; unimodal rehabilitation was widely applied, use of a multimodal treatment approach was limited and only one-third received work-related interventions. For patients with MSD, behavioural treatment seems to be underutilized in clinical practice considering the effect it may have on developing coping strategies and reducing symptoms. In order to meet recommendations in guidelines, physical activity needs to increase as a treatment strategy for patients with MD. A clinical implication is that the rehabilitation process needs to adopt a broader perspective for patients with MSD and MD to include patients’ individual health-related needs, aspects of employment and work conditions. Still, it remains a challenge to understand who needs what type of intervention.