Intra‐articular pressure, elastance and range of motion in healthy and injured racehorse metacarpophalangeal joints
Authors: STRAND E. , MARTIN G. S. , CRAWFORD M. P. , KAMERLING S. G. , BURBA D. J. 
Published: April 2010

The objective of this study was to determine if intraarticular pressure, elastance of the soft tissue forming the dorsal pouch, and range of motion in flexion measurements are significantly different in Thoroughbred metacarpophalangeal joints with clinical evidence of idiopathic synovitis, primary synovitis, synovitis/capsulitis, or osteoarthritis relative to clinically normal joints. Forty‐two metacarpophalangeal joints, in 25 active or retired Thoroughbred racehorses, were categorised 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 from 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 ml 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 detected by the pressure transducer placed in that region. A lateral radiographic view was taken of each metacarpophalangeal joint in maximal flexion. The maximum angle of flexion was measured from the radiograph, and this angle was subtracted from 180° to acquire the range of motion in flexion.

In this study, all Thoroughbreds with clinical evidence of lameness and/or sensitivity to flexion, referable to the metacarpophalangeal joint region, had fluid distention of the palmar pouch (grade 2 or 3distention). 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 intraarticular pressures (mean +51.00 mmHg),‐ however, joints with idiopathic synovitis (mean +15.71 mmHg), primary synovitis (mean +28.33 mmHg) and osteoarthritis (mean +26.20 mmHg) also had significantly elevated intraarticular pressures relative to the clinically normal group. Thoroughbred metacarpophalangeal joints diagnosed with synovitis/capsulitis, or 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 significant immediate effect on elastance of the dorsal pouch and range of motion in flexion. The 16 Thoroughbred metacarpophalangeal joints assessed as having no clinical abnormalities had a mean range of motion in flexion of 60.81°. The mean range of motion in flexion of Thoroughbred metacarpophalangeal joints with a clinical diagnosis of primary synovitis was 53.67°; idiopathic synovitis 52.14°; synovitis/capsulitis 44.20°; and those with radiographic evidence of moderate to marked osteoarthritis 30.80°. This study demonstrated that, as the severity of the clinical evidence of metacarpophalangeal joint injury/disease increased, the range of motion in flexion decreased.