Proprioception in the nearly extended knee. Measurements of position and movement in healthy individuals and in symptomatic anterior cruciate ligament injured patients.

Proprioception of the knee was measured in 19 healthy individuals to evaluate whether there were any differences between extension and flexion movements from two different starting positions. The threshold before detecting a passive movement, visual estimation on a protractor of a passive change in position (30 degrees angular change) and active reproduction of the same angular change were registered. The reference population was tested twice to study normal variation and reproducibility, followed by the evaluation of 20 patients with chronic, symptomatic and unilateral anterior cruciate ligament (ACL)-deficient knees. In the normal population no differences were found between the right and the left leg, men and women, or measurements made at the first and at the second test occasion. The thresholds from a starting position of 20 degrees were lower for extension than for flexion. When comparing the thresholds for extension between the 20 degrees and the 40 degrees starting position, lower values were found in the more extended position. The thresholds for flexion were lower from the 40 degrees starting position than from the 20 degrees starting position. The active reproduction of an angular change of 30 degrees was more accurate during flexion (30 degrees-60 degrees) than during extension (60 degrees-30 degrees). There were no differences in the reproduction tests or in thresholds from the 40 degrees starting position between the patients and the normal group, but the patients had higher thresholds from the 20 degrees starting position, in movements towards both extension 1.0 degree (range 0.5 degree-12.0 degrees) and flexion 1.5 degrees (range 0.5 degree-10.0 degrees) than the normal group 0.75 degree (range 0.5 degree-2.25 degrees) (P = 0.01) and 1.0 degree (range 0.5 degree-3.0 degrees) (P = 0.06), respectively. Thus, information of passive movements in the nearly extended knee position was more sensitive towards extension than towards flexion in threshold tests and the sensitivity improved closer to full extension, which implies a logical joint protective purpose. In this nearly extended knee position, which is the basis for most weight-bearing activities, patients with symptomatic ACL-deficient knees had an impaired awareness in detecting a passive movement. There were no differences in the more flexed position or in the reproduction tests between the patients and the normal group, and reproduction tests in the present form seem less appropriate to use in the evaluation of ACL injuries.