We introduced an automatic knee arthrometer (AKA) and aimed to evaluate the repeatability and effectiveness thereof in diagnosing ACL rupture compared with the KT-2000.

The AKA was compared to the KT-2000 at 134 N in this study, the anterior displacement and difference of both knees of every subject were measured. The first protocol was designed to evaluate examiner effect (level of experience) and contralateral-side effect (left or right knee) in a single healthy subject, ten times, on ten consecutive days. The second was to compare the stability in 20 healthy subjects, with a single experienced examiner. Third, we recruited 200 ACL rupture and 200 healthy subjects as contrast to compare the accuracy of the devices in diagnosing ACL rupture.

Inclusion Criteria:

• patients with ACL rupture from our institution were included. All patients were diagnosed by sports medicine specialists based on clinical manifestation, combined with imaging examinations, and hospitalized for further surgery.

Exclusion Criteria:

• Patients aged <18 or >45 years, with combined multiple knee ligament injury combinations, and/or limited range of motion of the knee (unable to flex to 20-30°)

one healthy subject was tested with both devices for ten consecutive days to estimate examiner effect； 20 healthy subjects were tested with both devices to determine the method effect； 200 medicine students volunteered as healthy subjects; each with pain-free knees in the last three months, and without a history of knee injury； 200 patients with ACL rupture from our institution were also included.