Table 1 Description of the three components according to the TIDieR checklist

Why

The employee and the occupation health physician get to know each other. Any further questions about the intervention, study participation, data protection, confidentiality and the voluntary nature of participation are clarified during the initial consultation. The employee should make an informed decision about participating in the two-day diagnostics at the rehabilitation center. An initial needs analysis and joint goals for participation in the intervention should be developed based on the employee’s report of health and contextual factors. Finally, the occupational health physician needs to clarify the eligibility of the employee for study participation

Occupational health physicians have an important linking function in the initiation and monitoring of rehabilitation processes due to their in-company knowledge and skills, and can support the return-to-work process directly in the workplace [19]

Diagnostic measures are needed to develop recommendations for adapting the employee’s job environment and to improve work participation. Comprehensiveness is necessary so as to understand the underlying health problem, which is often complex and has bio-psycho-social causes and consequences, and to derive appropriate interventions. Work-related assessments are carried out in order to plan and design therapeutic measures individually and to align them to the actual workplace

Social counseling provides information on various possibilities for supporting work participation and individual occupational and social problems

Coaching approaches in the final meeting and tests for optional therapeutic measures are used to improve the participant’s self-reflection skills, resilience, and motivation. A resource-based approach aims to activate available skills

The occupation health physician and the employee should discuss the recommendations for action derived from the rehabilitation center to secure employment and improve work ability. These recommendations are to be recorded during joint goal setting. The other stakeholders who need to be involved in realizing the recommendations need to be clarified

Involving occupational health physicians in the rehabilitation and return-to-work process can improve the success of rehabilitation, increase sustainable stay-at-work and reduce sick leave [13]

What (materials)

Guidelines for initial one-on-one consultation; computerized documentation; questionnaire for the collection of medical data and job demands; “Analysis of needs and objectives” worksheet; study information; informed consent form (in duplicate); baseline questionnaire

Equipment at the rehabilitation center for the performance of work-related diagnostics; final report of the two-day diagnostics in the rehabilitation center; questionnaire at the end of the two-day diagnostics

Guidelines for follow-up consultations; “Recommendations and agreement on objectives” worksheet; computerized documentation; final report of the two-day diagnostics in the rehabilitation center

What (procedures)

The employee meets with the occupational health physician in the practice or their office, or directly in the company for an initial one-on-one consultation. The consultation includes the following elements: information and consent from the employee to participate in the study, completion of the baseline questionnaire, examination of the employee's current health limitations and work ability, and completion of a description of job demands. The completed documents are sent to the study coordinator in the rehabilitation center after the consultation

The program of the two-day diagnostics in the rehabilitation center is arranged by the study coordinator in consultation with the rehabilitation team on the basis of the patient information resulting from the initial consultation

Physiotherapeutic and psychotherapeutic diagnostics, social counseling and a final meeting communicating the results to the participant are necessary elements of the two days. The physiotherapeutic diagnostics include an evaluation of functional capacity. The content is based on anamnestic symptoms and job demands. The psychotherapeutic diagnostics include psychosomatic exploration in order to identify pathological disorders, psychosomatic comorbidity and relevant functional limitations. The social counseling examines the individual’s work–life situation and provides socio-legal guidance and advice concerning further assistance within the social security system

Other optional elements are provided in order to test therapeutic action possibilities and strengthen self-care competences. These include seminars on sports and exercise, nutrition, sleep hygiene, as well as psychoeducational groups on depression, pain or stress management, and participation in occupational therapy or autogenic training

, Specific recommendations for action to maintain work participation are developed by the rehabilitation team in a case conference, and recorded in a final report

The occupational health physician and the employee have at least one and up to four follow-up consultations, as required, within five months after the two-day diagnostics. The occupation health physician accompanies the employee in realizing the recommendations for action that were developed based on the results of the two-day diagnostics. The first follow-up consultation should take place as soon as possible after the two-day diagnostics. The other three follow-up consultations are held at regular intervals to review and, if necessary, update, needs, goals and the involvement of other stakeholders. Questions from the occupational health physician can be clarified with the medical contact person at the rehabilitation center if necessary

Who (provided)

Occupational health physician

Interdisciplinary team at a rehabilitation center (i.e. physicians, physiotherapists, psychotherapists, occupational therapists and social counselors) and a study coordinator

Occupational health physician

How

In presence and individually

In presence and individually

In presence, digitally or by telephone and individually; if necessary, with the involvement of other stakeholders (e.g., employer or employee representative)

Where

In the practice of the occupational health physician or directly in the company

Inpatient or outpatient in one of three rehabilitation centers in the German states of Hamburg, Mecklenburg-Western Pomerania and Schleswig–Holstein

In the occupational health physician’s practice or directly in the company

When and how much

Once with a duration of up to two hours

Two days with an overall mean therapy dose of nine hours

Up to four consultations, with a duration of one hour each within five months of the end of the two-day diagnostics in the rehabilitation center

Tailoring

Not planned

The dose of the diagnostic measures is fixed. Individual treatments trials are tailored to the needs of the participants, which are derived from the initial consultation with the occupational health physician

As needed, up to four consultations can be conducted to implement the recommendations

How well

The initial one-on-one consultation is described in guidelines to ensure standardized implementation

The initial one-on-one consultation is documented by the occupational health physician in a standardized manner. The occupational health physicians were trained to conduct the consultations and in the required computerized documentation before the randomized controlled trial began

All diagnostic components were developed by the interdisciplinary project team (i.e. rehabilitation center, research institution and German Pension Insurance North) in 2020 to ensure standardized implementation. The interdisciplinary team were trained to conduct a standardized comparison of job demands and individual work ability before the randomized controlled trial began

Regular video conferences will be held with the study coordinators to support the accuracy of the intervention throughout the process. At the end of the two-day diagnostics and at the six-month follow-up, all participants are asked which intervention components they received during the intervention using standardized questionnaires

The follow-up consultations are described in guidelines to ensure standardized implementation

The follow-up consultations are documented by the occupational health physician in a standardized manner. The occupational health physicians were trained to conducti the consultations, and in the required computerized documentation before the randomized controlled trial began

Guided interviews will be conducted with participants during the follow-up consultation phase, asking which intervention elements participants received and how they could be improved, in order to assess treatment fidelity