PRESSURES IN NORMAL AND ACUTELY DISTENDED HUMAN KNEE JOINTS AND EFFECTS ON QUADRICEPS MAXIMAL VOLUNTARY CONTRACTIONS

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Abstract
Pressures were recorded in ten knees from five subjects with informed consent. Resting intra‐articular pressures were found to be sub‐atmospheric with a mean value of ‐5±1·5 mmHg (S.E. of mean). There was little variation in intra‐articular pressure with changing joint angle in the normal joint. Infusion of as small a volume as 5 ml of sterile saline into the joint cavity caused the intra‐articular pressure to increase to supra‐atmospheric levels. Changing joint angle now produced clear modulations in intra‐articular pressure. Pressure increased as the limb was moved out to extension and back to flexion with a minimum occurring in the mid‐range. These modulations were more pronounced with active positioning of the joint than with passive positioning. Successive increases in intra‐articular volume produced increases in intra‐articular pressure as well as the degree of modulation of intra‐articular pressure with joint angle. Cyclical flexion‐extension movements caused a progressive decrease in the maximum pressure observed in extension. Non‐noxious distension of the knee joint caused substantial reductions in the magnitude of isometric and isokinetic maximal voluntary contractions of quadriceps due to a reflex inhibition from joint mechanoreceptor afferents.