Injury typified by sudden, painful, audible pop noise. Patient typically presents with inability to return to activity, joint instability, and rapid development of effusion (hemarthrosis).
Often tender at lateral femoral condyle, lateral tibial plateau, and tibiofemoral joint lines.
A positive Lachman test is most accurate right after the injury and the pivot shift test is more useful in subacute or chronic cases.
History and physical usually provide accurate diagnosis.
X-rays obtained to rule out avulsion fractures or other related conditions, but do not directly identify ACL injury. MRI delineates ACL tears nicely, along with associated injury to menisci and other structures.
Initial treatment for most patients consists of protection, rest, ice, compression, elevation, and analgesia (as appropriate). Subsequent treatment varies by an individual patient's health and fitness status and goals. Treatment may range from minimal or no additional intervention to bracing, physical therapy, and activity modification, and to surgical reconstruction (either early or delayed).
A torn anterior cruciate ligament (ACL) usually occurs as the result of an acute noncontact deceleration injury, forceful hyperextension, or excessive rotational forces about the knee.   The ligament may be completely torn, partially torn, or avulsed from its origin or insertion. The ACL is the primary restraint to excessive anterior translation and rotation of the tibia on the femur; therefore, complete ACL disruption typically results in dynamic knee instability or the inability to respond to quick changes in position. 
Clinical Assistant Professor of Medicine
Robert Wood Johnson Medical School
University of Medicine and Dentistry of New Jersey
PHC declares that he has no competing interests.
University of Kentucky School of Medicine
President and Chief Executive Officer
American Board of Family Medicine
JCP declares that he has no competing interests.
Department of Orthopedic Surgery
Seoul Veterans Hospital
JRY declares that she has no competing interests.
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