Non-invasive electroarthrography measures cartilage in live horses and correlates to direct measurements of cartilage streaming potentials in weight bearing regions of equine metacarpophalangeal joints

To perform non-invasive Electroarthrography (EAG) on live horses and establish relationships between EAG and direct measurements of cartilage streaming potentials in weight bearing areas of the equine metacarpophalangeal joint.

EAG was performed bilaterally on the metacarpophalangeal joints of live horses (n = 3). Separate experiments used metacarpophalangeal joint explants (n = 11) to measure EAG obtained during simulated loading followed by direct measurements of cartilage streaming potentials on joint surfaces using the Arthro-BST probe. Joints were assigned to relatively normal (n = 5) and mildly degraded (n = 6) groups based on histological scoring of Safranin-O/Fast Green stained sections.

EAG, involving application of electrodes to skin surrounding the joint and repeated weight shifting, was well-tolerated in live horses. One pair of distal forelimbs were available for analogous ex vivo EAG testing and measurements were strongly correlated to in vivo EAG measurements obtained on the same joints (r = 0.804, p = 0.016, n = 8). Both indirect (EAG) and direct (Arthro-BST) measurements of cartilage streaming potentials distinguished between normal and mildly degraded cartilage with statistically significant differences at 5 of 6 and 4 of 6 electrodes during simulated standing and walking, respectively. Strong and moderate correlations for weight bearing regions on the dorsal phalanx and central metacarpus were detected during both standing and walking. At the metacarpus/sesamoid interface a moderate correlation occurred during walking.

Non-invasive EAG was used successfully in a clinical scenario and correlated to direct measurements of streaming potentials in weight bearing cartilage. These data support the potential of EAG to contribute to the diagnosis and treatment of degenerative joint diseases.

EAG measurements were captured from each forelimb during simulated loading as described above. Joints were then disarticulated and cartilage appearance assessed with India ink. (Super Black, 100% Carbon Pigment, Speedball LLC). Direct measurements of cartilage streaming potentials were made with the Arthro-BST (Biomomentum Inc., Laval, Canada), a hand held probe that non-destructively measures streaming potentials by compressing cartilage with a hemispherical indenter (D = 6.35 mm) containing an array of 37 microelectrodes (5 microelectrodes/mm2). Joint surfaces were mapped using a virtual high density grid resulting in measurements at 106 ± 9 (n = 11) sites and 138 ± 4 (n = 11) sites on the phalanx and metacarpus, respectively. The Arthro-BST calculates a quantitative parameter (QP) corresponding to the number of microelectrodes in contact with cartilage when the sum of streaming potentials reaches 100 mV. QP reflects cartilage function, structure and composition and is inversely proportional to cartilage stiffness. Average QP for weight bearing regions were calculated from all sites measured in the respective region. Weight bearing regions were labeled medial (MAP) and lateral (LAP) dorsal phalanx, medial (MCC) and lateral (LCC) central metacarpus, and medial (MSI) and lateral (LSI) sesamoid-metacarpus interface.

Keywords:

Electroarthrography; Streaming potential; Osteoarthritis; Cartilage degeneration.