History and exam
Key diagnostic factors
common
audible pop
Reported in up to 70% of anterior cruciate ligament (ACL) tears. If positive, greatly heightens suspicion, but lack of pop does not rule out ACL injury.[64]
rapid knee swelling/effusion
Patients usually present acutely, within a few hours of injury and typically report rapid development of marked knee swelling.
inability to return to the ongoing sporting activity
Patients may be able to hobble or jog a little but are rarely able to return to the ongoing sporting activity.
sensation of knee instability or buckling
Patients often describe a sensation of the femur and tibia twisting apart from each other or the knee feeling loose.
pain
Varies greatly. Some describe minimal pain, others describe severe pain. Not a very useful discriminator.
positive anterior drawer test
This test involves placing the patient in a supine position, flexing the hips to 45 degrees, with the knees at 90 degrees and the patient's feet on the table.[Figure caption and citation for the preceding image starts]: Anterior and posterior drawer test starting positionFrom the personal collection of Philip H. Cohen [Citation ends].
Sitting on the patient's feet, the clinician takes hold of the tibia and pulls it anteriorly. If the tibia moves more than usual, the test is positive. Testing will often be positive, but is less sensitive and specific.[54]
positive Lachman test
The most accurate maneuver for detecting an acute anterior cruciate ligament (ACL) tear.[52][53]
The Lachman test is performed with the patient in a supine position. The patient’s knee is positioned at 20 to 30 degrees of flexion. One hand is placed on the patient’s thigh and the other behind the tibia, with the clinician's thumb on the tibial tuberosity and the femur held in a stable position. The tibia is then pulled anteriorly. If the ACL is intact, a firm endpoint is felt. If this does not occur, and there is an increase in laxity compared with the uninjured knee, the test is positive, suggesting a torn ACL. [Figure caption and citation for the preceding image starts]: Lachman maneuverFrom the personal collection of Philip H. Cohen [Citation ends].
positive pivot shift maneuver
The pivot shift maneuver evaluates rotatory instability that may accompany acute anterior cruciate ligament (ACL) injuries. It may be difficult to perform and to elicit a positive test after an acute injury secondary to patient guarding from the knee injury. It is easier to perform after the acute injury pain has subsided or in the operating room under anesthesia when patients are fully relaxed. The test is performed with the hip slightly abducted, knee fully extended, and tibia internally rotated. This would sublux the lateral tibial plateau anteriorly in an ACL deficient knee. An axial load is then applied to the knee as the knee is flexed. A palpable shift may occur when the lateral tibial plateau relocates posteriorly as the knee is flexed past 30 degrees.[Figure caption and citation for the preceding image starts]: Pivot startFrom the personal collection of Philip H. Cohen [Citation ends].
[Figure caption and citation for the preceding image starts]: Pivot finishFrom the personal collection of Philip H. Cohen [Citation ends].
Other diagnostic factors
common
tenderness at lateral femoral condyle, lateral tibial plateau
Often due to kissing bone bruises that occur when femur and tibia bang against each other when the anterior cruciate ligament tears.[Figure caption and citation for the preceding image starts]: T1-weighted MRI showing ACL tearFrom the personal collection of Philip H. Cohen [Citation ends].
Tenderness at the tibiofemoral joint line may also indicate a meniscal tear, but is difficult to distinguish on initial exam.
Risk factors
strong
acute trauma
Contact injuries, especially with hyperextension and/or valgus stress, are a classic cause of anterior cruciate ligament (ACL) tears.[24]
Noncontact injuries, especially involving sudden deceleration, pivoting, change in direction, landing from a jump, or excessive rotation and extension, are responsible for the majority of ACL tears.[25][26][27][28]
female sex (after puberty)
Studies have shown a significantly increased risk of anterior cruciate ligament tears among female athletes compared with their male counterparts.[11][12][13][14][15] Theories to explain this disparity are centered around anatomic, hormonal, neuromuscular, and biomechanical differences between males and females.[29]
biomechanics
Lower levels of core stability, weak hip abduction strength, increased knee valgus, and landing with heel strike, have all been attributed to an increased risk of anterior cruciate ligament injury among athletes.[30]
history of previous anterior cruciate ligament injury
May be ipsilateral or contralateral.[31]
use of cleats or spikes
Cleats and spikes used during sports on grassy surfaces increase the likelihood of planting a foot and twisting the body without release, consequently twisting upon the knee joint.[32]
rough or uneven playing surface
ground condition/weather
fatigue
adolescent, young adults, and middle-aged athletes
Increased risk in adolescents and young adults, but also middle-aged athletes/skiers. The 15-45 years age group is at highest risk. Skeletally immature athletes are more likely than adults to avulse the anterior cruciate ligament insertion rather than have an intrasubstance tear.
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