Principal component and cluster analysis of functional parameters in rheumatic patients: Identifying the most...

Rheumatic diseases significantly impact hand function, leading to disability and reduced quality of life. Various tools assess upper limb function, including the DASH questionnaire, grip strength measurement, and range of motion (ROM) evaluation. However, the most efficient parameters for assessing functional impairment remain unclear.

To determine the most relevant anthropometric and functional measurements for evaluating hand function impairment in patients with rheumatic diseases, using principal component analysis (PCA) and cluster analysis.

We conducted a cross-sectional study in 36 patients with inflammatory arthritis, primarily rheumatoid arthritis (RA). Hand function was assessed using the DASH questionnaire, grip and pinch strength tests (Jamar dynamometer and Mathiowetz protocol), and ROM measurements. PCA was applied to identify the most relevant functional variables, and K-means clustering was used to classify patients into functional subgroups.

Grip and pinch strength were the dominant factors, explaining 33.5% of total variance, while ROM contributed less to functional impairment assessment. Cluster analysis identified four functional subgroups, differentiating patients based on grip strength and disability levels (DASH score). Patients with higher grip strength exhibited lower disability, while those with severe disability had significantly weaker grip strength, reinforcing its importance as a functional marker.

Grip strength is a key indicator of upper limb function impairment in RA and other rheumatic diseases. Given its strong association with disability and its dominance in variance explanation, grip strength measurement alone may serve as a time-efficient and reliable assessment tool, especially in resource-limited settings. Further research should validate grip strength as a primary clinical indicator and optimize assessment protocols for rheumatic patients.