A thorough physical examination of the knee, as described in Chapter 46, is the cornerstone of diagnosing an ACL injury. On first inspection, the presence of a sizable effusion can typically be detected in acute injuries. The absence of a large effusion, however, does not preclude the diagnosis of an acute ACL tear and is typical in chronically ACL-deficient knees. Palpation of the periarticular structures such as the collateral ligaments and the medial and lateral joint lines is a critical part of the examination and provides important information regarding potential injury to other intra-/periarticular structures.
Range of motion is often limited in the acute setting secondary to pain and effusion. Limited motion, however, should raise suspicion of a mechanical block resulting from displaced bucket-handle meniscal tears, displaced ACL stump remnants, or osteochondral fragments.
Stability testing of the knee should include a thorough ligamentous examination which includes anterior/posterior, varus/valgus and rotational stability testing. Acute ACL injuries often occur with other combined ligamentous injuries and these should be identified by physical examination. Unidentified associated ligamentous instability is a common cause of failure following reconstruction, and this should be detected prior to surgical planning.5
There are three components of the physical examination that are specific to the diagnosis of an ACL injury: the Lachman, pivot-shift, and anterior drawer tests. The Lachman test is the most sensitive of the three maneuvers6 (Fig. 51-1). It is performed with the knee in neutral rotation at 20 to 30 degrees of flexion. An anterior translation force is imparted to the tibia with one hand while stabilizing the femur with the other hand.
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