An interventional study of EXPLOR-3 in Knee Osteoarthritis, sponsored by Mark van Loo. Not yet recruiting at 1 site in Netherlands. Open to participants aged 45 Years to 70 Years. Per ClinicalTrials.gov, last updated 2026-10-28.
Sponsored by Mark van Loo · Not applicable, Interventional, and Treatment
Knee osteoarthritis (OA) is a leading cause of pain, disability, and reduced physical functioning worldwide. Although physiotherapy and physical activity are recommended as first-line treatments, many individuals with knee OA do not achieve or maintain recommended levels of physical activity. As a result, the benefits of evidence-based physiotherapy are often not fully realized. To improve physical activity participation, effective behaviour change interventions are needed.
Theory-informed interventions have the potential to enhance physiotherapy outcomes by targeting the psychological determinants that influence physical activity behaviour. One well-established framework is the Theory of Planned Behaviour (TPB), which proposes that behaviour is primarily influenced by behavioural intention, attitude, subjective norms, and perceived behavioural control. To translate these determinants into intervention content, behaviour change techniques (BCTs) can be systematically selected using tools such as the Behaviour Change Intervention Ontology (BCIO), Mechanisms of Action Ontology (MoAO), and Theory and Techniques Tool (TaTT). This approach may improve the effectiveness and sustainability of behaviour change interventions.
The present study therefore aims to evaluate the potential of a TPB-based behaviour change intervention as an addition to guideline-recommended physiotherapy for individuals with knee OA. The primary objective is to determine whether this theory-driven intervention can improve physical activity levels and reduce sedentary behaviour. A secondary objective is to explore the behavioural mechanisms through which these changes occur.
The study will employ a randomized, concurrent, multiple-baseline single-case experimental design (SCED). Participants with knee OA will receive a six-week physiotherapy intervention consisting of usual guideline-based care supplemented with a TPB-based behaviour change component. Physical activity and sedentary behaviour will be continuously assessed using ActiGraph accelerometers. In addition, behavioural determinants, pain, and functional limitations will be repeatedly measured to evaluate potential mechanisms of action and clinical effects. Findings from this study may contribute to the development of more effective, theory-informed physiotherapy interventions aimed at promoting sustainable physical activity behaviour in people with knee OA.
3,292 studies on the registry are indexed under Osteoarthritis, Knee; 623 are open to participants now.
This study's planned enrollment of 20 is below the median of 68 across 2,714 interventional studies indexed under Osteoarthritis, Knee.
Browse Osteoarthritis, Knee studies →This is the only study on the registry with Mark van Loo as lead sponsor.
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Exclusion Criteria:
Multiple baseline phase. Participants will complete repeated measures during this phase. The duration of this phase will be randomized to 7, 10 or 14 days. Participant will not receive treatment during this phase. The measurements from this phase will be used a control to the data that will be collected within the treatment phase (Phase B).
The intervention will consist of the guideline-recommended treatment protocol, supplemented with a behaviour change component designed to enhance treatment effectiveness by targeting key determinants of behaviour change. The behaviour change component is intended to complement, rather than replace, the standard treatment. In accordance with usual clinical practice, the content and delivery of the guideline-based treatment will be tailored to the individual needs, goals, and clinical presentation of each participant. Tailoring of the treatment will be performed by the treating physical therapist.
Behavioral: EXPLOR-3
Follow-up period of three months takes place after phase B. Participant will not receive treatment during this period.
The behaviour change component will be developed based on the TPB. Selection of corresponding MoAs and BCTs will be guided by the BCIO, the MoA Ontology, and the TaTT. Within the TPB framework, three MoAs are known to predict intention and actual behavior. Accordingly, the intervention applies a stepwise, phased approach when implementing TPB within a physiotherapy context aimed at increasing physical activity (≥150 minutes of moderate physical activity per week). The intervention first targets individuals' attitudes toward the behavior (treatment phase 1, duration 1-2 weeks), followed by enhancement of perceived behavioral control (treatment phase 2, duration 2-3 weeks), and subsequently aims to strengthen behavioral intention (treatment phase 3, duration 2 weeks). For each phase, specific BCTs will be selected to align with the corresponding MoAs (based on link within TaTT) and will be tailored to individual patient needs, as assessed by the physical therapist.
Also known as: Guideline care complementary behaviour change intervention
Change in physical activity (ActiGraph GT3x) from Phase A to Phase B to Phase A'.
Physical activity will be assessed using ActiGraph GT3x (ActiGraph, Pensacola, Florida) triaxial accelerometers. Participants will be instructed to wear the accelerometer on their thigh while they are awake during the A and B phase and the last 5 days of the A' phase. Physical activity thresholds will be used to distinguish between sedentary behaviour and light, moderate and vigorous physical activity.
Time frame: Daily measurements for 7-8 weeks (A+B Phase) and the last 5 days of the follow-up phase (Phase A'). Duration of follow-up phase is 12 weeks.
Change in sedentary behaviour (ActiGraph GT3x) from Phase A to Phase B to Phase A'.
Sedentary behaviour will be assessed using ActiGraph GT3x (ActiGraph, Pensacola, Florida) triaxial accelerometers. Participants will be instructed to wear the accelerometer on their thigh while they are awake during the A and B phase and the last 5 days of the A' phase. Physical activity thresholds will be used to distinguish between sedentary behaviour and light, moderate and vigorous physical activity.
Time frame: Daily measurements for 7-8 weeks (A+B Phase) and the last 5 days of the follow-up phase (Phase A'). Duration of follow-up phase is 12 weeks.
Change on the Knee Injury and Osteoarthritis Outcome Score from phase A to phase B to follow-up.
The Knee Injury and Osteoarthritis Outcome Score (KOOS) comprises five subscales: 1) Pain (9 items), 2) Symptoms (7), 3) Activities of Daily Living (17), 4) Sport/Rec (5), and 5) knee related Quality of Life (4). Questions are scored 0-100 (worst-best). Internal consistency is adequate (pooled Cronbach's α≈0.70-0.95) and test-retest reliability high (ICCs ≈0.85-0.90). Content validity is condition and age sensitive: ADL is more relevant in older OA cohorts and Pain in painful conditions.
Time frame: At start of baseline, after 3 weeks and 6 weeks of treatment and at the end of the follow-up phase. Follow-up phase is 12 weeks.
Change on the Patient Specific Functional Scale (PFPS) from phase A to phase B to follow-up.
The PSFS is a patient reported, individualized measure in which patients nominate two activities and rate difficulty on an 11 point scale (0-10); higher scores reflect better function. Test-retest reliability across musculoskeletal conditions (e.g., ICC ≈0.82-0.97) is reported good to excellent. Construct/concurrent validity is supported via correlations with the RMQ, NDI, and SF 36, and predictive validity for return to work outcomes.
Time frame: At start of baseline, after 3 weeks and 6 weeks of treatment and the end of the follow-up phase. Follow-up phase is 12 weeks.
Change on the Numeric Pain Rating Scale (NPRS) from phase A to phase B to follow-up.
The NPRS is a unidimensional self report of pain intensity, typically using 0-10 anchors ("no pain" to "pain as bad as you can imagine"). Scores generally correspond to VAS, though not perfectly interchangeable. The NPRS is widely used in pain research and its psychometric characteristics are reported to be good.
Time frame: At start of baseline, after 3 weeks and 6 weeks of treatment and at the end of the follow-up phase. Follow-up phase is 12 weeks.
Change in subjective norms from phase A to phase B to follow-up.
Subjective norms are part of the Theory of Planned Behaviour construct and will be measured as a moderator. Description: BCIO: Perceived evaluative behavioral norm (BCIO:006041) Definition: A \<perceived norm\> regarding whether a behaviour is appropriate and correct for people who belong to a particular group. https://bciosearch.org/BCIO\_006041 Subjective norms will be measured with a single item (m-Path mobile application). Question: "People in my environment consider it important to engage in 2.5 hours of moderately intensive physical activity per week." (strongly disagree(0) - strongly agree(100))
Time frame: At start of baseline, after 3 weeks and 6 weeks of treatment and at the end of the follow-up phase. Follow-up phase is 12 weeks.
Change in attitude towards physical activity from phase A to phase B to follow-up.
Attitude towards the behaviour is part of the Theory of Planned Behaviour construct and will be measured as a mediator. BCIO: Attitude towards a behaviour (BCIO:050329) Definition: An \<attitude\> in which the entity that is the attitude object is a behaviour. https://bciosearch.org/BCIO\_050329 Attitude towards physical activity will be measured with a single item (m-Path mobile application). Question: "For me, 2.5 hours per week of moderately intensive physical activity is…" (not important(0)-very important(100))
Time frame: Twice a week during Phase A and B. One time at the end of the follow-up phase(Phase A'). Follow-up phase is 12 weeks.
Change in perceived controllability of physical activity levels from phase A to phase B to follow-up.
Perceived controllability is part of the Theory of Planned Behaviour construct and will be measured as a mediator. Description: BCIO: Belief about control over behaviour (BCIO:006152)\[Mv20.1\] Definition: A \<belief\> about one's capabilities and opportunities within an environmental system to perform a behaviour or achieve the outcomes resulting from a behaviour. https://bciosearch.org/BCIO\_006152 Perceived controllability will be measured with a single item (m-Path mobile application). Question: "I currently have control over how physically active I am." (strongly disagree(0) - strongly agree(100))
Time frame: Daily measurements twice a day during Phase A and B (7-8 weeks). Also twice a day during the last 5 days of the follow-up phase (Phase A'). Follow-up phase is 12 weeks.
Change in intention from phase A to phase B to follow-up.
Intention is part of the Theory of Planned Behaviour construct and will be measured as a mediator. Description: BCIO: Behavioral intention (BCIO:006016) Definition: A \<mental disposition\> to commit to enact or not enact a behaviour. https://bciosearch.org/BCIO\_006016 Intention will be measured with a single item (m-Path mobile application). Question: "I will be physically active within the next few hours." (strongly disagree (0) - strongly agree(100))
Time frame: Daily measurements twice a day during Phase A and B (7-8 weeks). Also twice a day during the last 5 days of the follow-up phase (Phase A'). Follow-up phase is 12 weeks.
Plan to share: Undecided
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Start is estimated for Oct 2026; primary completion for Dec 2027, 13 months later.
Of 1,111 non-industry interventional studies with no phase under Osteoarthritis, Knee, half reached primary completion within 18 months of starting (the median), counting those still running; a quarter within 8 and three quarters within 36. This study's planned 13 months is below that.
Counting every sponsor, half of 1,251 studies reached it within 18 months; a quarter within 8 and three quarters within 36.
How these figures are worked out, and which studies are left out of them.
From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
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