Effect of flexion angle on the pressure-volume of the human knee.

The objective of this study was to determine pressure-volume relationships in the human knee. Eight normal knees in eight patients undergoing elective arthroscopic surgery were studied to develop pressure-volume curves at 0 degrees, 15 degrees, 30 degrees, 60 degrees, and 80 degrees of flexion, and measure capsular volume at 0 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees, and 80 degrees of flexion. The results showed that capsular volume decreases with flexion, whereas capsular stiffness increases. This suggests that during arthroscopy, flexion with obstructed outflow may cause significant intraarticular pressure and potential rupture of synovial membranes. Our results support the concept of flow rates with low distension pressures for maximum safety.