[Association between arthritis, functional disability and quality of life using a structural equation]

To establish a conceptual model that links arthritis, functional disability in activities of daily living, and quality of life (QoL).

A multicentre, cross-sectional, observation study was performed. The location of the arthritis (presence/absence) was recorded. Disability was measured using the Health Assessment Questionnaire Disability Index and the QoL determined using the EQ-5D-3 Level questionnaire. The relationship between the arthritis, disability, and the QoL was evaluated using the structural equation model (SEM).

965 patients with arthritis (mean age=64 years, with 75% females). Arthritis: mean areas affected: 2.8. Areas most frequently affected: knees (67%); lumbar spine (60%) and cervical spine (45%). QoL: The majority of patients did not mention serious problems in the five domains assessed. Disability: «other activities» (mean=1.2); «reach» (mean=1.1) and «walking» (mean=1.0) were the categories that demonstrated greater disability. The SEM showed arthritis, disability and QoL as associated latent variables. Although 92% of the QoL explained the disability, only 5% of the disability was due to the presence/absence of arthritis. The global model that describes arthritis as a cause of disability, and disability was affecting the QoL, had a reasonable goodness of fit (CMIN/DF=5.42; RMR=0.026; RMSEA=0.069).

Functional disability can explain the decrease in QoL. In theory, arthritis is closely related with disability and QoL, but the model did not mange to fully explain this link. As statistical techniques required good measurement models to correctly determine relationships, conventional medical records seem to be insufficient for this purpose. Other valid measurements of arthritis are needed to provide tests of its direct effect on disability and QoL.