This study aims to evaluate the reliability and convergent validity of the Vietnamese version of the Pain Self-Efficacy Questionnaire (VIET-PSEQ) in patients with knee osteoarthritis (KOA). Pain self-efficacy refers to a person's confidence in managing their pain and maintaining daily activities despite it.

A total of 173 patients with KOA will be recruited at Gia Dinh People's Hospital using a convenient sampling method. Eligible participants are 50 years or older, diagnosed with KOA, and experiencing chronic knee pain. They will complete the VIET-PSEQ and other health-related questionnaires during an in-person interview.

The study will assess internal consistency (using Cronbach's alpha), test-retest reliability (by re-assessing a subgroup after 72 hours), and convergent validity by correlating VIET-PSEQ scores with EQ-5D-5L utility index. Additionally, linear regression analysis will examine how age, sex, pain severity, and education level influence pain self-efficacy.

The goal is to determine whether VIET-PSEQ is a reliable and valid tool for measuring pain self-efficacy in Vietnamese patients with KOA.

Inclusion Criteria:

Participants will be eligible for inclusion if they meet all of the following conditions:

• Age ≥ 50 years.

• Diagnosis of knee osteoarthritis (OA) according to the criteria of the American College of Rheumatology (ACR), confirmed by:

  1. application of ACR criteria by the investigator at the time of enrollment; or
  2. a prior diagnosis documented in medical records by a rheumatologist or musculoskeletal specialist.

• Presence of chronic pain related to knee OA, with current pain intensity ≥ 1 on the Visual Analog Scale (VAS).

• No acute flare of knee pain within the past 2 weeks.

• Ability to perform activities of daily living (with or without assistance).

• Ability to read, understand, and complete questionnaires in Vietnamese.

• Willingness to participate and provide informed consent.

Exclusion Criteria:

Participants will be excluded if they meet any of the following conditions:

• Diagnosis of severe psychiatric disorders (e.g., schizophrenia, severe anxiety disorders).
• Presence of cognitive impairment that interferes with the ability to comprehend or answer the questionnaire.
• Diagnosed with systemic inflammatory diseases such as rheumatoid arthritis, systemic lupus erythematosus, or gout.
• Presence of other chronic pain conditions (unrelated to knee OA) that are predominant and significantly affect mobility and daily functioning.
• History of intra-articular injection or knee surgery within the past 3 months.
• Questionnaire (PSEQ) with ≥ 20% of items missing or invalid.

The study population will consist of adults aged 50 years and older diagnosed with knee osteoarthritis, either newly confirmed at the time of enrollment using the American College of Rheumatology (ACR) criteria or previously diagnosed and documented in the medical records by a specialist. Participants will be recruited from outpatient departments in urban hospitals in Vietnam. The population includes patients with chronic knee pain related to osteoarthritis who are able to perform daily activities and comprehend written Vietnamese.

Individual participant data (IPD) underlying the results of this study will be shared with other researchers upon reasonable request. The data will be de-identified to protect participant privacy and used solely for academic and non-commercial research purposes.

IPD and supporting documents will be available beginning 6 months after publication of the primary results. Data will remain accessible for a period of 5 years following this initial release.

Qualified researchers affiliated with academic institutions or research organizations may access the data by submitting a data use request, including a brief proposal outlining research objectives, methodology, and intended outcomes. Data access is conditional upon signing a data-sharing agreement to ensure ethical use and data protection compliance.