Proprioception in the nearly extended knee

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 (30o 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 20o were lower for extension than for flexion. When comparing the thresholds for extension between the 20o and the 40o starting position, lower values were lower from the 40o starting position. than from the 20o starting position. The active reproduction of an angular change of 30o was more accurate during flexion (30o–60o) than during extension (60o-30o). There were no differences in the reproduction tests or in thresholds from the 40o starting position between the patients and the normal group, but the patients had higher thresholds from the 20o starting position, in movements towards both extension 1.0o (range 0.5o–12.0o) and flexion 1.5o (range 0.5o–10.0o) than the normal group 0.75o (range 0.5o–2.25o) (P=0.01) and 1.0o (range 0.5o–3.0o) (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.