Streaming Potential-Based Arthroscopic Device Can Detect Changes Immediately Following Localized Impact in an Equine Impact Model of Osteoarthritis

Early Post-traumatic Osteoarthritis (PTOA) can be asymptomatic but represents a possible window of opportunity for therapeutic intervention before disease progression. Impact models are ideal for studying these strategies because the location and severity of impact can be controlled. Streaming potentials generated during cartilage compression are a sensitive measure of degeneration, which may be valuable in detecting early PTOA. An arthroscopic device, the Arthro-BST (Fig. 1) permits non-destructive electromechanical measurements and computes a Streaming Potential Integral (SPI) that reflects cartilage function, structure and composition. A custom-built Impactor device, consisting of a spring loaded shaft and a sterilizable, 6.5 mm diameter plane-ended tip with rounded edges, was developed to facilitate the delivery of local impact stresses to the articular surface in both in vitro and in vivo studies. Consistent impacts were successfully delivered with the custom-built Impactor device at two levels: low impact, 15.0 ± 1.4 MPa (n=6) and high impact, 41.3 ± 5.3 MPa (n=8). India ink revealed surface cracking and diffuse staining at high impact sites compared with faint or no staining at low impact sites (Fig. 4C). SPI decreased at all high impact sites (p<0.0001) and a nominal increase was observed due to low impact (p=0.002). Small increases in SPI may indicate alterations to the extracellular matrix but is unlikely to influence tissue function (Fig. 5). High impact caused a reduction in Ef (p=0.04), which reflects collagen network stiffness, an increase in k (p=0.03), but no change in Em (p=0.21), which reflects proteoglycan matrix stiffness. This suggests immediate damage to the collagen network but insufficient time for proteoglycan depletion to occur10 (Fig. 6). Detrimental changes to both electromechanical (SPI) and biomechanical properties of articular cartilage were detected immediately following impact injury.