Saline-assisted aspirations for collecting synovial fluid from noneffused knees: technique and validation

To better understand why a knee develops osteoarthritis after joint trauma we need to assess the local biochemical changes. Unfortunately, it is challenging to obtain synovial fluid from a knee with no effusion.

To describe the authors' protocol for aspirating synovial fluid from noneffused knees. Second, they demonstrate the validity of this method by evaluating the relationships between normalized and raw biomarker concentrations among knees with effusion (undergoing a traditional aspiration) and without effusion (requiring a saline-assisted aspiration).

Validation study based on secondary analyses from 2 cohort studies.

Outpatient orthopedic clinic and basic-science laboratory.

Participants had moderate to severe radiographic knee osteoarthritis (n = 15 with and 11 without effusion) and no osteoarthritis or effusion (n = 4).

The same orthopedic surgeon performed all synovial-fluid joint aspirations, including saline-assisted aspirations.

The authors used multiplex enzyme-linked immunosorbent assays to determine 7 synovial-fluid biomarker concentrations. They then calculated correlations between raw and normalized (to total synovial-fluid protein content) biomarker concentrations.

The authors excluded 1 sample collected with a saline-assisted aspiration because it contained blood. Normalized biomarker concentrations had positive associations with raw biomarker concentrations (r = .77-.99), with the exception of interleukin-13 and interleukin-1β among knees that underwent a saline-assisted aspiration. Excluding interleukin-1β, associations between normalized and raw biomarker concentrations were consistent between knees that had a saline-assisted or traditional aspiration.

Saline-assisted aspiration is a valid technique for assessing the local biochemical changes in knees without effusion.