ACL Tear

Located in the center of the knee, the ACL is a strong band of tissue that prevents the shin bone (tibia) from extending excessively beyond the thigh bone (femur). ACL injuries are common and usually sports-related—especially associated with basketball, football and skiing.

The four primary stabilizers of the knee are the ACL, the PCL (Posterior Cruciate Ligament), the MCL (Medial Collateral Ligament) and the LCL (Lateral Collateral Ligament). These ligaments function in concert with the muscles and cartilage of the knee to help control motion. Proprioceptive (nerve) fibers in these ligaments and the capsule of the knee joint augment this control via reflex feedback

Patients with ACL tears usually describe a twisting or hyperextension of the knee. The patient may also feel a "popping" in the knee that is associated with immediate swelling. Typically, there is a significant effusion (excess fluid inside the knee) when the patient is first evaluated. A complete examination of the knee should be done to rule out associated injuries such as a fracture or a meniscus tear. The Lachman test is the best way to assess a knee for an acute ACL rupture. Range of motion should also be documented. Usually, the patient has difficulty fully straightening the knee immediately after the injury. This may be due to swelling or entrapment of the ACL stump in the intracondylar notch. Occasionally, a displaced bucket handle tear of the meniscus or a sprain of the medial collateral may present in conjunction with an ACL tear and lead to frank locking of the knee.