Hemiplegic Shoulder Pain (HSP) is a common and disabling complication after stroke, negatively affecting upper limb function, participation in rehabilitation, and quality of life. Despite the widespread use of conservative and physical therapies, evidence supporting the efficacy of specific non-invasive neuromodulation techniques remains limited.

Focal Vibration Therapy (FVT) is a non-invasive physical modality that delivers localized mechanical vibration to targeted muscles or tendons and may modulate pain, muscle tone, and proprioception through frequency-dependent mechanisms.

This randomized controlled trial aims to evaluate the efficacy of a multimodal FVT protocol, in addition to standard rehabilitation, compared with a sham intervention plus standard rehabilitation, in reducing pain in patients with chronic post-stroke Hemiplegic Shoulder Pain.

Hemiplegic Shoulder Pain (HSP) is a frequent and disabling sequela of stroke, with reported incidence rates ranging from 30% to 65% within the first six months after stroke onset. This variability reflects differences in diagnostic definitions and heterogeneity among studied populations. The underlying pathophysiology of HSP is multifactorial, involving musculoskeletal alterations (e.g., glenohumeral subluxation), abnormal nociceptive processing and central sensitization, and spasticity-related impairments, particularly affecting shoulder adductor and internal rotator muscles.

HSP significantly interferes with post-stroke recovery by reducing upper limb motor performance and functional use, impairing participation in rehabilitation programs, and worsening quality of life. Although early and multidisciplinary management is recommended, available therapeutic approaches remain heterogeneous and include positioning strategies, manual therapy, pharmacological treatments, nerve blocks, botulinum toxin injections, dry needling, robotic-assisted therapy, and neuromodulation techniques.

Physical therapeutic modalities are commonly used in rehabilitation settings due to their non-invasive nature and potential analgesic and functional benefits. However, evidence regarding their specific effectiveness in the treatment of HSP is inconsistent, and existing reviews often include heterogeneous interventions or focus on invasive approaches, leaving uncertainty about the role of targeted physical neuromodulation.

Focal Vibration Therapy (FVT) is an emerging physical modality that applies localized mechano-sonic stimulation to muscle bellies or tendon insertions. Its effects are frequency-dependent and include modulation of nociceptive input through spinal gate control mechanisms at low-to-medium frequencies (approximately 35-50 Hz), modulation of muscle tone and proprioception through stimulation of Ia afferent fibers and induction of the tonic vibration reflex at intermediate frequencies (around 100 Hz), and modulation of deep pain perception through activation of Pacinian corpuscles at higher frequencies (approximately 200 Hz).

Given the multifactorial nature of HSP and the limitations of current conservative treatments, there is a need to investigate structured intervention protocols integrating advanced physical modalities with standard rehabilitation. This randomized controlled trial will compare a multimodal FVT protocol, delivered in addition to standard rehabilitation, with a sham intervention plus standard rehabilitation in patients with chronic post-stroke HSP. The study will assess changes in pain intensity as the primary outcome, along with secondary outcomes related to shoulder function, range of motion, spasticity, quality of life, persistence of treatment effects, and safety of the intervention.

Inclusion Criteria:

• Age ≥ 18 years
• Ischemic or hemorrhagic stroke confirmed by CT or MRI
• Chronic post-stroke phase (≥ 6 months from event)
• Presence of hemiplegic shoulder pain (NRS ≥ 4)
• Preserved cognitive function sufficient to provide informed consent

Exclusion Criteria:

• Severe cognitive impairment or language deficits (e.g., severe aphasia) that prevent understanding of study procedures or reliable reporting of pain (e.g., inability to complete NRS or questionnaires).
• Severe neglect, apraxia, or disorders of consciousness that interfere with participation in rehabilitation or outcome assessments.
• Pre-existing shoulder pathology of the affected side unrelated to stroke (e.g., full-thickness rotator cuff tear, advanced glenohumeral osteoarthritis, inflammatory arthritis, prior shoulder surgery).
• Fixed shoulder contractures or severe joint deformities limiting passive range of motion and preventing standardized assessment.
• Botulinum toxin injections to shoulder upper limb muscles within the last 3-4 months prior to enrollment .
• Current treatment with other experimental or non-conventional physical therapies for shoulder pain during the study period.

Participants and outcome assessors will be blinded to group allocation. Participants in both groups will undergo identical treatment sessions in terms of duration, setting, therapist interaction, and device application procedures. In the control group, the focal vibration device will be connected to inactive outputs while maintaining identical transducer placement and operational noise. To preserve participant blinding, an additional active transducer delivering perceptible vibration will be applied to a distant and clinically irrelevant site. Participants will be informed that the device operates through a systemic reflex stimulation mechanism, ensuring credibility of the sham procedure. Outcome assessors responsible for pain, functional, and biomechanical evaluations will not be involved in treatment administration and will remain unaware of group assignment throughout the study.

Treating therapists administering the intervention will not be blinded.