History
Obtain as much information as possible directly from the patient. The important facts can be clarified by asking questions about the following:
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Mechanism of injury
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Pain
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Feeling/hearing a pop
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Feeling knee give out
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Ability to continue playing sport
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Swelling
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Loss of knee motion
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History of previous knee injury
Physical
Up to 50% of patients with acute knee injuries who report feeling or hearing a snapping or popping sound are found to have an anterior cruciate ligament (ACL) injury. A hemarthrosis almost always is present because of the vascular supply to the ACL. When a complete ligamentous tear occurs, pain may begin immediately, followed by resolution. Immediately following injury, minimal effusion or spasm is present, so ACL injury usually can be identified easily. Several hours after injury, effusion and spasm make diagnosis of an ACL tear more difficult.
To determine the patient's normal amount of laxity, examine the uninjured knee first.
Many diagnostic tests exist (eg, Slocum test, pivot-shift test), but the Lachman and anterior drawer tests are used most commonly.
Lachman test
The Lachman test is performed with the knee in 30° of flexion, with the patient lying supine.
Using one hand on the anterior aspect of the distal femur and a second hand behind the proximal tibia, attempt to displace the tibia forward from the femur.
A positive Lachman occurs when no endpoint is encountered. The degree of excursion may also indicate an ACL tear.
Anterior drawer test
Another test to detect ACL tears is the anterior drawer.
Perform this test with the knee at 90° of flexion, with the patient lying supine.
Place both hands behind the proximal tibia and attempt to displace the tibia forward from the femur.
If there is more than 6 mm of tibial displacement, an ACL tear is suggested.
The anterior drawer test is not very sensitive and has been found to be positive in only 77% of patients with complete ACL rupture.
Causes
Anterior cruciate ligament (ACL) injuries have no single cause. ACL injuries can be related to extrinsic factors and intrinsic factors. Numerous studies document the fact that poor levels of conditioning correlate directly with increased levels of injury. Research also has demonstrated that improved conditioning results in reduced numbers of injuries.
Body and movement factors
The first 2 factors, body movement and positioning, play a big role in ACL injuries. [8]
Noyes and colleagues demonstrated that most ACL injuries (ie, 78%) occur without contact. [9] Most of these injuries occur upon landing after a jump. The Noyes study involved only female basketball players, but the capacity of the knee to plant and turn or to absorb the shock of a jump is relevant to men and women in all sports.
Muscle strength
Muscle strength is the last of the extrinsic factors that affect the ACL. The hamstring is an ACL agonist working in concert with the ACL to prevent anterior tibial translation. Conversely, the quadriceps acts as an antagonist to the ACL, generating force that promotes anterior tibial translation. Ideally, a balance exists between these opposing forces to protect the knee; however, the quadriceps averages 50-100% greater muscle strength than does the hamstring.
Strength coaches often emphasize quadriceps strengthening and ignore hamstring strengthening, further exacerbating the inequality.
Other factors
Several intrinsic factors can contribute to ACL injuries.
Joint laxity is one such factor. Significant controversy surrounds this topic, because published studies are contradictory about whether or not increased laxity contributes to ACL injuries. Acasuso-Diaz and colleagues concurred with Kibler and coauthors that a strong relationship exists [10, 11] ; however, reports by Godshall and by Jackson and colleagues maintained that ACL laxity does not predispose to ACL injury. [12, 13]
The Q angle is the acute angle between the line connecting the anterior superior iliac spine, the midpoint of the patella, and the line connecting the tibial tubercle with the same reference point on the patella. Theoretically, larger Q angles signal increases in the lateral pull of the quadriceps muscle on the patella and put medial stress on the knee. Shambaugh and colleagues studied 45 athletes and found that the average Q angles of athletes sustaining knee injuries were significantly larger than were the average Q angles for players who were not injured. [14] Because lower extremity alignment cannot be altered, no recommendation can help to minimize the athlete's risk of ACL rupture; however, the dynamic position of the tibia can be improved with internal rotation exercises for the tibia (eg, medial hamstrings).
A narrow intercondylar notch may be a predictive factor for ACL rupture. According to various reports, athletes who sustain ACL injuries often have narrow notch widths compared with fellow athletes with uninjured knees. The notch width index (NWI), defined by Souryal and colleagues, is "the ratio of the width of the intercondylar notch to the width of the distal femur at the level of the popliteal groove on a tunnel view radiograph."
Another study by Souryal and coauthors established that NWI measurements fall along a Gaussian curve, indicating that measurement is reproducible. [15, 16] Results showed that athletes sustaining noncontact ACL injuries had the lowest NWIs. The critical NWIs were calculated as being 1 standard deviation below the gender-dependent mean. Athletes falling into this critical range, according to reported data, are 26 times more susceptible to ACL injuries than are other athletes.
