Extraction of Synovial Fluid from the Non-Effusive Pathologic Knee with Pneumatic Compression

Objectives –Aspiration of synovial fluid from non-effusive joints is undertaken for the diagnosis of crystal-associated arthritis, biomarker analysis, and to confirm intraarticular positioning. We hypothesized that pneumatic compression of the non-effusive knee would mobilize occult synovial fluid and improve arthrocentesis success. Methods – The absence of a knee effusion was determined by physical examination, imaging, and exclusion of confounding disease.  Conventional arthrocentesis was performed in 111 consecutive non-effusive knees and arthrocentesis volume (milliliters) determined. Pneumatic compression was then applied, and arthrocentesis was resumed. Results – Pneumatic compression improved fluid yield: conventional: 0.4±1.0 ml, compression: 1.8±2.5 ml (319% increase, 95% CI  -1.9<-1.4<-0.9; p=0.0001). Pneumatic compression reduced arthrocentesis failure (< 0.1 ml) from 74.8% (83/111) to 41.4% (46/111) (p=0.0001) and improved successful arthrocentesis in terms of adequate synovial fluid yield: 1) ≥ 0.1 ml from 25.2% (28/111) to 58.5% (65/111) (+132%, p=0.0001), 2) ≥ 0.5 ml from 22.5% (25/111) to 57.7% (64/111) (+156%, p =0.0001), 3) ≥ 2.0 ml from 11.7% (13/111) to 47.7% (53/111) (+300%, p =0.0001), and 4) ≥ 3.0 ml from 5.4% (6/111) to 36.0% (40/111) (+319%, p =0.0001). Conclusions: Pneumatic compression of the non-effusive knee improves the extraction of synovial fluid of various requisite volumes for conventional and biomarker analysis.