A knee arthrometer for measuring varus, valgus, and rotation

Due to the characteristics of cruciate ligaments, knee ligament tears are not suitable to heal by remedy. Anterior cruciate ligament (ACL) reconstruction is one of the most common and reliable surgeries to handle knee ligament injuries. To date, most knee ligament reconstructions can be done by using endoscopic surgery. Although single bundle ACL reconstructions could improve the recovery of knee function, yet it was still not enough for the stability of the knee joint. In some cases instability might even develop to be osteoarthritis. Via some vitro tests, such as varus, valgus and rotation tests, the test results showed that the ligament after single bundle ACL reconstruction was not able to bear the rotational, and varus/valgus torque at the knee joint. That means using conventional arthrometer such as KT-1000 could lead to misdiagnosis in the above mentioned situation. We developed a new instrument to measure the extent of tibia's varus, valgus and rotation relative to the femur. Via the test data, the instrument could quantify the knee laxity and help surgeon to diagnose the injured knee more accurately and verify whether an ACL reconstruction was successful. The main function of the instrument is to test knee ligament laxity by measuring the varus/valgus angulation, and internal/external rotation with high sensitivity and data reproducibility. We verified the instrument's performance via experiments. The results of the experiments demonstrated the usability of the arthrometer.