Sensitive tests for ACL injury
What physical examination tests are most sensitive and specific for the diagnosis of an anterior cruciate ligament injury (ACL)?
The ACL is a crucial ligamentous stabilizer of the knee. A tear results from a twisting (valgus) or hyperextension injury. Greater than 50% of ACL ruptures are accompanied by a meniscal tear. Overall, female athletes are 2 to 10 times more likely to sustain an ACL injury than male athletes depending on the sport. This may be due to multiple factors including anatomy, hormones, and neuromuscular imbalance.
The best-known test for ACL deficiency is the anterior drawer sign. It is performed with the patient supine and the knee flexed to 90 degrees. With the hamstrings relaxed, the examiner grasps the proximal tibia with both hands and attempts to slide the tibia anteriorly while simultaneously stabilizing the patient’s leg (can be accomplished by sitting on the foot). The degree of tibial translation is compared with the uninjured knee. This is a subjective test with the least sensitivity of all the tests for an ACL tear.
The most sensitive test is the Lachman test. With the thigh supported, muscles relaxed, and femur stabilized by one of the examiner’s hands, the knee is placed in 20 to 30 degrees of flexion, and the proximal tibia is then translated anteriorly by the examiner’s other hand. ACL-deficient knees exhibit increased translation and a soft or absent endpoint as compared with the opposite, uninjured knee.
The most specific test is the pivot shift test. It is performed by applying a valgus and internal rotation force on the tibia with the knee in full extension and hip abducted 10 to 20 degrees. The knee is then gently flexed. A clunk of tibial rotation is appreciated as the knee passes 20 to 40 degrees of flexion. This must be compared with the opposite side. The appreciable clunk occurs when the tibia, which is abnormally subluxated (anterior and internally rotated), is pulled back into its normal position by the secondary restraints.