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 pressure of the normal knee. Methods. A 22 gauge Intracath catheter was introduced into 7 clinically normal knees and one abnormal knee in 4 subjects. Pressures were recorded via a pressure transducer and correlated with simultaneous recordings of flexion angle from an electronic goniometer while the subject's knees were traversed through active and passive horizontal flexion at a rate of I cycle/2 s. Results. The technique produced 6 satisfactory records over mean active and passive flexion ranges of 135° and 148°. On passive movement, pressures remained negative through most of the cycle, rising to mean maximum pressures of 10 mm Hg after about 110° of flexion. On active movement, the most common result was a U shaped curve rising from negative in midflexion to positive on full flexion and extension. The mean maximum pressures recorded on active movement were 38 mm Hg on flexion and 18 mm Hg on extension. Conclusion. There is no linear correlation 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 pressure is not the flexion angle but the accompanying soft tissue changes. Failure to use the full movement range could reduce the efficiency of trans-synovial flux.