THE RELATIONSHIP BETWEEN INTRAARTICULAR AND JUXTAARTICULAR INTRAOSSEOUS PRESSURES IN THE METATARSOPHALANGEAL REGION OF THE PONY

Eight metatarsophalangeal (fetlock) joints were studied in anaesthetiz ed young ponies. Pressure measurements were made in the joint and at v arious sites in the marrow cavity of the third metatarsal bone with si multaneous measurement of systemic arterial and venous blood pressures . Fetlock joint flexion was always associated with a statistically sig nificant initial decrease in intra-articular pressure (p<0.05) followe d by a marked increase in pressure (p<0.05). Subsequent extension was accompanied by a similar pressure pattern, although there appeared to be a hysteretic relationship. Fetlock joint distension induced by incr emental injection of saline caused a stepwise increase in the intra-ar ticular pressure. Both joint flexion and effusion were associated with an increased intraosseous pressure within the third metatarsal bone. This effect was most pronounced at the distal end of the bone, probabl y through partial obstruction of the vessels draining the epiphysis an d metaphysis.