An update on the study of synovial fluid in the geriatric patient

Background

The characteristics of synovial fluid (SF) in geriatric patients differ from those in younger patients. In Mexico, epidemiologic data on the incidence of different rheumatic diseases in geriatric patients are scarce.

Objective

To describe the physical characteristics of geriatric SF and the prevalence of crystals in knee and other joint aspirates from patients with previously diagnosed joint disease.

Materials and methods

A retrospective study was performed with a baseline of 517 SF samples between 2011 and 2023. White blood cell count was performed by Neubauer chamber and crystals were identified by polarized light microscopy. Descriptive statistical analysis was performed and prevalence was reported as a percentage.

Results

The mean age of the adults was 73.5 ± 5.0 years, 54.4% were women and 45.6% were men. The mean SF volume was 6.3 ± 9.5 mL in older adults and 15.3 ± 24.9 mL in those younger than 65 years. The mean viscosity in older adults was 9.5 ± 4.5 mm and the mean leukocyte count was 7352 ± 16,402 leukocytes/mm³. Seventy percent of the older adults’ SFs were referred to the laboratory for osteoarthritis (OA), with lower proportions for rheumatoid arthritis (RA) (14.6%) and gout (5.1%). Of the crystals observed in the geriatric population, 14.6% corresponded to monosodium urate crystals (CUM) and 18.9% to calcium pyrophosphate crystals (CPP).

Conclusions

The characteristics of LS in older adults were smaller volume, increased viscosity, and non-inflammatory. The main diagnoses were OA, RA, and gout. The crystal content of the SF of the geriatric population corresponded mainly to CPP.