Differences in Knee Kinematics Between Awake and Anesthetized Patients During the Lachman and Pivot-Shift Tests for Anterior Cruciate Ligament Deficiency

BACKGROUND: The Lachman and pivot-shift tests have been widely used for detecting anterior cruciate ligament (ACL) deficiency. However, it still remains unclear whether these manual tests can be quantified accurately while patients are awake. PURPOSE: To assess the differences in knee kinematics of awake and anesthetized patients. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: A total of 50 patients with unilateral ACL rupture were examined. Anteroposterior tibial translation was assessed using a KT-1000 arthrometer at maximal manual power. Anterior tibial translations during the manual Lachman test and the acceleration of tibial posterior translation (APT) during the pivot-shift test were also measured using an electromagnetic measurement system (EMS). All 3 measurements were performed on the day previous to surgery while the patients were awake and on the operative day before the surgery while the patients were under general anesthesia. RESULTS: The mean side-to-side difference in anteroposterior tibial translation was 5.6 ± 2.6 mm in the awake state and 5.9 ± 3.5 mm under anesthesia, indicating a nonsignificant difference. According to the EMS, the mean side-to-side difference in anteroposterior tibial translation during the Lachman test was 4.6 ± 3.6 mm in the awake state and 6.9 ± 4.3 mm under anesthesia, indicating a significant difference (P < .01). The mean APT during the pivot-shift test was −0.8 ± 0.3 m/s(2) in intact knees and −1.1 ± 0.4 m/s(2) in ACL-deficient knees when the patients were awake and was −0.7 ± 0.2 m/s(2) and −1.7 ± 1.0 m/s(2), respectively, when the patients were under anesthesia. In ACL-deficient knees, the APT pivot-shift test result was significantly higher when the patients were under anesthesia than when they were awake (P < .01). CONCLUSION: In ACL-deficient knees, the knee kinematics during the Lachman and pivot-shift tests is significantly affected by patient consciousness, and caution is needed in quantifying anterior knee laxity during these tests when the patients are awake.