Functional Index Questionnaire: structural validity study in Brazilian patients with anterior knee pain

Area of Science:

• Orthopedics
• Rheumatology
• Physical Medicine and Rehabilitation

Background:

• Anterior knee pain is a common condition affecting various patient populations.
• The Functional Index Questionnaire (FIQ) is used to assess functional status in patients with knee pain.
• Validating assessment tools is crucial for accurate clinical evaluation and research.

Purpose of the Study:

• To evaluate the psychometric properties of the Functional Index Questionnaire (FIQ) in a Brazilian cohort with anterior knee pain.
• To assess the structural validity of the FIQ using confirmatory factor analysis (CFA).

Main Methods:

• A cohort of 100 Brazilian patients (≥18 years) with anterior knee pain for at least 3 months participated.
• Confirmatory factor analysis (CFA) was employed to evaluate the FIQ's structure.
• Standard fit indices including CFI, TLI, RMSEA, and SRMR were used to assess model fit.

Main Results:

• The initial one-dimensional FIQ model showed a poor fit (RMSEA = 0.104), indicating substantial residual error.
• Correlations between similar items (e.g., stair climbing, squatting/kneeling) were identified as sources of redundancy.
• After accounting for item correlations, the model fit improved significantly (RMSEA = 0.072).

Conclusions:

• The current version of the FIQ, when applied to Brazilian patients with anterior knee pain, demonstrates structural limitations.
• Item redundancy within the FIQ contributes to model misfit.
• Clinicians and researchers should use the FIQ with caution in this population, considering potential biases due to item overlap.