RELATION BETWEEN FLEXION ANGLE AND INTRAARTICULAR PRESSURE DURING ACTIVE AND PASSIVE MOVEMENT OF THE NORMAL KNEE

Objective. To determine the effect of full active and passive flexion and extension at physiological rates of movement on intraarticular pre ssure of the normal knee. Methods. A 22 gauge Intracath catheter was i ntroduced into 7 clinically normal knees and one abnormal knee in 4 su bjects. Pressures were recorded via a pressure transducer and correlat ed with simultaneous recordings of flexion angle from an electronic go niometer while the subject's knees were traversed through active and p assive horizontal flexion at a rate of 1 cycle/2 s. Results. The techn ique produced 6 satisfactory records over mean active and passive flex ion ranges of 135 degrees and 148 degrees. On passive movement, pressu res remained negative through most of the cycle, rising to mean maximu m pressures of 10 mm Hg after about 110 degrees of flexion. On active movement, the most common result was a U shaped curve rising from nega tive in midflexion to positive on full flexion and extension. The mean maximum pressures recorded on active movement were 38 mm Hg on flexio n and 18 mm Hg on extension. Conclusion. There is no linear correlatio n between flexion angle and pressure. Under dynamic conditions at zero gravity intraarticular pressure shows a moderate rise on full passive flexion and in most subjects a substantial rise on active flexion and extension. These differences are significant. The factor governing pr essure is not the flexion angle but the accompanying soft tissue chang es. Failure to use the full movement range could reduce the efficiency of trans-synovial flux.