KT-1000 arthrometer: conscious and unconscious test results using 15, 20, and 30 pounds of force

A recent published report indicated that the reliability and validity of anterior laxity measurements obtained by using the KT-1000 arthrometer were questionable. The purpose of our study was to examine the diagnostic validity of anterior laxity measurements testing patients in conscious and unconscious states using the KT-1000 arthrometer at 15, 20, and 30 pounds of force. The sample included 68 patients with confirmed anterior cruciate ligament disruption. They were given anterior-posterior drawer tests at 20 degrees in both unconscious and conscious states; measurements were recorded at 15, 20, and 30 pounds of force. The results indicated that the measurements in the unconscious state were significantly higher (P less than 0.01) than the values obtained in the conscious state. The anterior cruciate ligament-disrupted knees produced significantly higher (P less than 0.01) anterior laxity. The difference between anterior cruciate ligament-disrupted knees and normal knees grew significantly larger (P less than 0.01) as force increased. More patients demonstrated a difference greater than 2 mm between anterior cruciate ligament-disrupted knees and normal knees at 30 pounds (81% to 83%) than at 20 pounds (64% to 72%) of force. Seventy-nine percent of the patients demonstrated a compliance index difference greater than 1 mm using 15 and 30 pounds between the normal and anterior cruciate ligament-disrupted knee. These data provide statistical validity for the compliance index and support for the use of anterior laxity measurements at 30 pounds of force. However, approximately 20% of these patients did not demonstrate an anterior cruciate ligament-disrupted-normal knee difference greater than 2 mm or a compliance index difference of greater than 1 mm.