Table 2 Outcome measures and study instruments

Patient characteristics

Sociodemographic data, anthropometric data, other baseline data

Variables and definitions according to the International Standard Set of Outcome measures for patients with hip or knee OA [29]

IG, C

t0

Technical affinity towards electronic devices

Self-report questionnaire on subjective technical affinity (Technical Affinity – Electronic Devices (TA-EG)) [31]

IG, C

t0

Outcome expectations

Expectation for Treatment Scale (ETS, German version) [30]

IG, C

t0

Fear of Movement

Tampa Scale for Kinesiophobia (German Version, TSK-GV) [32]

IG, C

t0

Health outcome measures

Patient reported outcome measures (PROMS)

Subscale knee pain (Co1° outcome)

Knee Osteoarthritis Outcome Score KOOS [24, 25]: A disease related questionnaire asking for patient’s opinion about their complaints

IG, C

t0, t1

Subscale function in daily living (ADL) (Co1° outcome)

Knee Osteoarthritis Outcome Score KOOS [24, 25]: A disease related questionnaire asking for patient’s opinion about their complaints

IG, C

t0, t1

Subscales symptoms, function in sport and recreation (Sport/Rec), knee-related quality of life (QoL)

Knee Osteoarthritis Outcome Score KOOS [24, 25]: A disease related questionnaire asking for patient’s opinion about their complaints

IG, C

t0, t1

Patient’s global assessment

Patient Global Assessment of osteoarthritis – Knee [33]

IG, C

t0, t1

Health related quality of life

VR-12 Questionnaire [34]

IG, C

t0, t1

Subjective assessment of overall change, change in pain and function

Transition question according to Angst, Benz [35]

IG, C

t1

Objective outcome measures

Functional strength measure for the lower extremities

30-s Chair Stand Test [36]

IG, C

t0, t1

Concomitant care

Treatment progression

Variables and definitions according to the International Standard Set of Outcome measures for patients with hip or knee OA [29]

IG, C

t0, t1

Care utilization

IG, C

t0, t1 + after 4 and 8 weeks

Perceived human-digital interaction, patient satisfaction

Usability of the app

- mHealth App Usability Questionnaire (MAUQ) [37]

- 1 item from Harder, Holroyd [38] (Item B1)

IG

t1

Patient satisfaction with the app

Patient satisfaction questionnaire (ZUF-8) [39]

IG

t1

Patient satisfaction with the results of the treatment

Satisfaction with the results [29]

IG, C

t1

Logfiles

Adherence to exercise

Logfiles relate to adherence to overall training sessions and each exercise

IG

continuously during intervention phase

Rating of perceived exertion (RPE) during exercising

Entry into the app after each exercise and after the training using an adapted RPE-Scale (NRS 0–10)

IG

continuously during intervention phase

Rating of perceived pain before, during and after exercising

Entry into the app before/after the training and after each exercise using a faces pain scale referring to the numbers 0, 2, 4, 6, 8, 10

IG

continuously during intervention phase

Safety aspects

Exercise related pain

Frequency, duration, intensity

IG, C

t1

Adverse event report

Direct contact to study personal

IG, C

if reported