The Preliminary Effectiveness of Personalized Physiotherapy Grounded in a Process-Based Therapy Framework in People With (Sub)Acute Neck Pain: a Protocol for a Mixed-methods Single-case Research Design

This study employs a replicated mixed-methods single-case experimental design (MMSCR) with a convergent, parallel approach, in which quantitative and qualitative data are collected concurrently and subsequently integrated. The protocol was developed in accordance with the Single-Case Reporting Guideline in Behavioural Interventions (SCRIBE) 2016 and the Mixed Methods Reporting in Rehabilitation & Health Sciences (MMR-RHS) guidelines.

Rationale Non-specific neck pain (NSNP) is a multifactorial condition in which physical, behavioral, cognitive, and contextual processes vary between patients, change over time, and continuously interact. A standardized treatment approach is therefore inherently limited. Personalized physiotherapy grounded in a Process-Based Therapy (PBT) framework aims to address this by continuously identifying which modifiable biopsychosocial processes are most relevant for an individual patient at a given moment, and selecting interventions that most efficiently target those processes. To make this approach feasible in daily primary care practice, a treatment protocol was developed together with a data-driven Clinical Compass, consisting of clinical indicators of modifiable biopsychosocial processes. This study is designed to obtain a first estimate of the preliminary effectiveness of this approach and to examine the fidelity with which it is delivered, prior to larger-scale evaluation.

Study design The quantitative component follows a nonconcurrent AB single-case experimental design (SCED) with repeated measurement, replicated systematically across 11 participants (11 SCEDs). Each participant undergoes a predetermined phase sequence: a baseline phase (A) followed by an intervention phase (B). The baseline phase spans three weeks with a minimum of nine measurement points; the intervention phase lasts a minimum of two weeks with a minimum of six measurement points, with actual duration depending on individual treatment progress. The number of measurements per phase was determined based on the discriminative power required to detect changes in outcome trajectories. Replication across 11 cases is achieved by delivering the intervention through different physiotherapists working in different geographic regions, all applying identical eligibility criteria.

Researcher blinding is not applied, as outcome measures are self-reported and the researcher is not involved in intervention delivery.

Study setting and therapist training The study will be conducted in nine primary care physiotherapy practices participating in the project consortium, purposefully selected to ensure variation in demographic characteristics, specialization, and practice size. Prior to study commencement, all participating physiotherapists complete a structured training programme targeting knowledge transfer, skill development, professional identity, and behavior change in practice. The programme consists of four sequential components: preparatory video modules with personal reflection, an online interactive case-based session, a live training session including role-play with a trained actor and guided reflection, and structured peer supervision sessions during the active treatment phase of the study to support implementation.