Central Sensitization and Functional Outcomes in Chronic Shoulder Pain

Chronic shoulder pain is one of the most common musculoskeletal disorders and is associated with pain, functional limitations, reduced quality of life, and work disability. Although structural abnormalities are often identified in clinical evaluation and imaging findings, the relationship between tissue pathology and symptom severity is not always clear. Therefore, factors beyond peripheral tissue damage may contribute to persistent shoulder pain and rehabilitation outcomes.

In recent years, central sensitization has become an important concept in chronic musculoskeletal pain conditions. Central sensitization refers to increased responsiveness of the central nervous system to sensory input, resulting in pain hypersensitivity and amplification of pain perception. Previous studies have demonstrated that individuals with chronic shoulder pain may present with symptoms related to central sensitization, which can negatively affect pain severity, disability, and treatment response.

Psychological factors such as pain catastrophizing, fear of movement, anxiety, and depression are also known to influence chronic pain experiences and rehabilitation outcomes. Higher levels of maladaptive psychological responses may contribute to increased pain perception, reduced treatment adherence, and poorer functional recovery. However, prospective studies evaluating the combined influence of central sensitization and psychological factors on rehabilitation outcomes in chronic shoulder pain remain limited.

This study is designed as a prospective observational cohort study. Individuals with chronic shoulder pain attending physiotherapy rehabilitation clinics will be recruited. Participants will undergo baseline assessments before treatment and follow-up assessments after a standardized 6-week rehabilitation program routinely applied in clinical practice.

The primary objective is to determine whether baseline central sensitization and psychological factors predict functional improvement following rehabilitation. The findings may contribute to a better understanding of the biopsychosocial mechanisms underlying treatment response and support the development of more individualized rehabilitation strategies for chronic shoulder pain management.

• Physiotherapy Rehabilitation Program (Other): A standardized 6-week exercise-based physiotherapy and rehabilitation program routinely applied in clinical practice, including patient education, scapular stabilization exercises, strengthening exercises, range of motion exercises, functional training, and home exercise recommendations for individuals with chronic shoulder pain.

Primary outcomes

• Shoulder Pain and Disability Index (SPADI) [Baseline and 6 weeks after rehabilitation]: The Shoulder Pain and Disability Index (SPADI) is a validated questionnaire used to assess shoulder pain and disability. Total scores range from 0 to 100, with higher scores indicating greater pain and disability.

Secondary outcomes

• Central Sensitization Inventory (CSI) [Baseline and 6 weeks after rehabilitation]: The Central Sensitization Inventory is a self-reported questionnaire assessing symptoms related to central sensitization. Scores range from 0 to 100, with higher scores indicating greater central sensitization symptoms.
• Pain Catastrophizing Scale (PCS) [Baseline and 6 weeks after rehabilitation]: The Pain Catastrophizing Scale (PCS) assesses exaggerated negative thoughts and emotional responses related to pain. Total scores range from 0 to 52, with higher scores indicating greater pain catastrophizing.
• Pain Intensity (Visual Analog Scale) [Baseline and 6 weeks after rehabilitation]: Pain intensity will be assessed using a Visual Analog Scale (VAS) ranging from 0 to 10, where 0 indicates no pain and 10 indicates the worst imaginable pain. Higher scores indicate greater pain intensity.
• Shoulder Range of Motion [Baseline and 6 weeks after rehabilitation]: Shoulder range of motion will be assessed using standard goniometric measurements. Higher values indicate greater shoulder joint mobility.
• Shoulder Muscle Strength [Baseline and 6 weeks after rehabilitation]: Shoulder muscle strength will be evaluated using standardized clinical strength assessment procedures. Higher values indicate greater muscle strength.

Sex: All, ages: 18 Years to any

Inclusion Criteria:

* Adults aged 18 years and older
* Presence of chronic shoulder pain lasting at least 3 months
* Clinical findings consistent with shoulder-related pain
* Willingness to participate in a 6-week physiotherapy rehabilitation program
* Ability to complete study assessments and questionnaires
* Provision of written informed consent

Exclusion Criteria:

* History of shoulder surgery within the previous 6 months
* Major shoulder trauma within the previous 6 months
* Serious pathology affecting the shoulder (e.g., infection, tumor, systemic inflammatory disease)
* Neurological disorders affecting the upper extremity (e.g., cervical radiculopathy, myelopathy, peripheral nerve injury)
* Severe cognitive impairment
* Communication problems preventing participation
* Shoulder injection within the previous 4 weeks
* Pregnancy