Non-invasive Electroarthrography Measures Load-Induced Cartilage Streaming Potentials via Electrodes Placed on Skin Surrounding an Articular Joint.

Objective: We aimed to demonstrate that electroarthrography (EAG) measures streaming potentials originating in the cartilage extracellular matrix during load bearing through electrodes adhered to skin surrounding an articular joint.

Design: Equine metacarpophalangeal joints were subjected to simulated physiological loads while (1) replacing synovial fluid with immersion buffers of different electrolyte concentrations and (2) directly degrading cartilage with trypsin.

Results: An inverse relationship between ionic strength and EAG coefficient was detected. Compared to native synovial fluid, EAG coefficients increased ( < 0.05) for 5 of 6 electrodes immersed in 0.1X phosphate-buffered saline (PBS) (0.014 M NaCl), decreased ( < 0.05) for 4 of 6 electrodes in 1X PBS (0.14 M NaCl), and decreased ( < 0.05) for all 6 electrodes in 10X PBS (1.4 M NaCl). This relationship corresponds to similar studies where streaming potentials were directly measured on cartilage. EAG coefficients, obtained after trypsin degradation, were reduced ( < 0.05) in 6 of 8, and 7 of 8 electrodes, during simulated standing and walking, respectively. Trypsin degradation was confirmed by direct cartilage assessments. Streaming potentials, measured by directly contacting cartilage, indicated lower cartilage stiffness ( < 10). Unconfined compression data revealed reduced Em, representing proteoglycan matrix stiffness ( = 0.005), no change in Ef, representing collagen network stiffness ( = 0.15), and no change in permeability ( = 0.24). Trypsin depleted proteoglycan as observed by both dimethylmethylene blue assay ( = 0.0005) and safranin-O stained histological sections.

Conclusion: These data show that non-invasive EAG detects streaming potentials produced by cartilage during joint compression and has potential to become a diagnostic tool capable of detecting early cartilage degeneration.