Intraarticular pressure during continuous passive motion of the human knee.

Intraarticular pressure (IAP) was continuously monitored during continuous passive motion (CPM) of five normal and 11 abnormal human knees using a new fiberoptic, transducer-tipped Camino catheter. IAP varied in a consistent hysteresis pattern in the normal knees, with subatmospheric pressures recorded at intermediate angles of joint flexion. A similar pattern was recorded in the abnormal knees without cruciate ligament pathology, whereas considerable variability was noted in the knees with cruciate ligament abnormality. IAP was lower in the extension to flexion than in the flexion to extension portion of the CPM cycle, providing evidence of intraarticular fluid flow during portions of the CPM cycle. IAP changes were consistent with "physiologic compartmentation" within the knee at extremes of joint position. Capsular viscoelastic changes and/or synovial fluid volume changes were observed during CPM. The therapeutic mechanism of continuous passive motion may be related to cyclic variation of the intraarticular pressure.