INTRAARTICULAR PRESSURE, ELASTANCE AND RANGE OF MOTION IN HEALTHY ANDINJURED RACEHORSE METACARPOPHALANGEAL JOINTS

The objective of this study was to determine if intra-articular pressu re, elastance of the soft tissue forming the dorsal pouch, and range o f motion in flexion measurements are significantly different in Thorou ghbred metacarpophalangeal joints with clinical evidence of idiopathic synovitis, primary synovitis, synovitis/capsulitis, or osteoarthritis relative to clinically normal joints. Forty-two metacarpophalangeal j oints, in 25 active or retired Thoroughbred racehorses, were categoris ed by palpation and visual inspection of the palmar pouch into one of 4 increasing grades of distention. Intra-articular pressures were then measured using 2 pressure transducers attached to 22-gauge needles fr om both the dorsal and palmar pouches simultaneously while the horses stood squarely under mild sedation. After obtaining baseline pressure measurements, a third needle was inserted into the dorsal pouch, and 0 .5 mi increments of saline solution were added every 10 s to perform a pressure/volume (elastance) study of the dorsal pouch. The elastance study for each joint ended when leakage into the palmar pouch was dete cted by the pressure transducer placed in that region. A lateral radio graphic view was taken of each metacarpophalangeal joint in maximal fl exion. The maximum angle of flexion was measured from the radiograph, and this angle was subtracted from 180 degrees to acquire the range of motion in flexion. In this study, all Thoroughbreds with clinical evi dence of lameness and/or sensitivity to flexion, referable to the meta carpophalangeal joint region, had fluid distention of the palmar pouch (grade 2 or 3 distention). The 16 metacarpophalangeal joints with no clinical abnormalities had a mean palmar pouch pressure of -1.25 mmHg. Joints afflicted with synovitis/capsulitis had the highest intra-arti cular pressures (mean +51.00 mmHg); however, joints with idiopathic sy novitis (mean +15.71 mmHg), primary synovitis (mean +28.33 mmHg) and o steoarthritis (mean +26.20 mmHg) also had significantly elevated intra -articular pressures relative to the clinically normal group. Thorough bred metacarpophalangeal joints diagnosed with synovitis/capsulitis, o r osteoarthritis, had significantly increased elastance (stiffness) of the soft tissue forming the dorsal pouch relative to the normal group and, probably, as a result significantly decreased range of motion in flexion. The presence of primary synovitis alone did not have a signi ficant immediate effect on elastance of the dorsal pouch and range of motion in flexion. The 16 Thoroughbred metacarpophalangeal joints asse ssed as having no clinical abnormalities had a mean range of motion in flexion of 60.81 degrees. The mean range of motion in flexion of Thor oughbred metacarpophalangeal joints with a clinical diagnosis of prima ry synovitis was 53.67 degrees; idiopathic synovitis 52.14 degrees; sy novitis/capsulitis 44.20 degrees; and those with radiographic evidence of moderate to marked osteoarthritis 30.80 degrees. This study demons trated that, as the severity of the clinical evidence of metacarpophal angeal joint injury/disease increased, the range of motion in flexion decreased.