CASE An athletic 25-year-old woman presents to her family physician complaining of a painful and swollen knee. She says that she injured the knee the day before during a judo match. The injury occurred when her upper body suddenly changed direction while her foot remained planted and her knee rotated medially. A cruciate ligament injury immediately comes to mind, but other potential diagnoses include meniscal injury, collateral ligament injury, and patellar instability. The first step in determining an accurate diagnosis is to evaluate the stability of the knee by physical examination—often a difficult task immediately following an injury.
How would you proceed?
Rupture of the anterior cruciate ligament (ACL), partial or complete, is a common injury, especially in athletes who hurt their knee in a pivoting movement.1 The number of patients who present with ACL injury is estimated at 252,000 per year.2 Cruciate ligament injury may lead to complaints of instability with subsequent inability to engage in sports activities. Cruciate ligament injury is also associated with premature development of osteoarthritis later in life.3 Operative treatment seems to be superior to conservative treatment in improving both subjective and objective measures of knee instability and in helping athletes return to their former level of activity.4
Because early detection is key to achieving the best clinical outcome, it is essential that the most accurate physical examination tests are performed during the acute phase. Primary care physicians, emergency room doctors, physical therapists, and athletic trainers are the ones who most often see these patients immediately following the injury, and they often have only the physical examination with which to assess ACL injury. Their task is to identify the patient with potential ACL injury and to refer the patient swiftly.
Three physical examination tests are most commonly used to evaluate cruciate ligament injury. The best known and most frequently used technique is the anterior drawer test. The other 2 tests, the Lachman test and the pivot shift test, are more difficult to perform and are used less often, especially by physicians untrained in their use. In addition, there is a relatively new diagnostic test: the lever sign test. The aim of our article is to provide a short, clinically relevant overview of the literature and to assess the diagnostic value of physical examination for the primary care physician.
Anterior drawer test
How it’s done. In this test, the patient lies supine on the examination table with hips flexed to 45 degrees and knees flexed to 90 degrees (FIGURE 1).5 The examiner sits on the table with a leg resting on the patient's foot, grasps the tibia of the injured leg just below the knee, and draws the tibia forward. If the tibia, compared with the tibia of the uninjured leg, moves farther anteriorly, or if the endpoint feels softened or is absent, the result is positive for an ACL injury.
The literature. Nine systematic reviews conclude that the anterior drawer test is inferior to the Lachman test,6-14 which we’ll describe in a moment. This is due, in part, to the anterior drawer test’s unacceptably low sensitivity and specificity in the clinical setting—especially during the acute phase.10 The most recent meta-analysis on the anterior drawer test reports a sensitivity of 38% and a specificity of 81%.9 In other words, out of 100 ruptured ligaments, only 38 will test positive with the anterior drawer test.
The literature offers possible explanations for findings on the test’s validity. First, rupture of the ACL is often accompanied by swelling of the knee caused by hemarthrosis and reactive synovitis that can prevent the patient from flexing the knee to 90 degrees. Second, the joint pain may induce a protective muscle action, also called guarding of the hamstrings, that creates a vector opposing the passive anterior translation.15
Apart from the matter of a test’s validity, it's also important to consider the test’s inter- and intra-rater reliability.16 Compared with the Lachman test, the anterior drawer test is inferior in reliability.7
How it’s done. The Lachman test is performed with the patient supine on the table and the injured knee flexed at 20 to 30 degrees (FIGURE 2).5 The examiner holds the patient’s thigh with one hand and places the other hand beneath the tibia with the thumb of that hand on the tibial joint line. As the tibia is pulled forward, firm resistance suggests an uninjured ACL. Free movement without a hard endpoint, compared with the uninjured knee, indicates ACL injury.
The literature. The Lachman test is the most accurate of the 3 diagnostic physical procedures. The most recent meta-analysis reports a sensitivity of 68% for partial ruptures and 96% for complete ACL ruptures.6 According to a recently published overview of systematic reviews, the Lachman test has high diagnostic value in confirming or ruling out an ACL injury.17
Two factors are important when assessing results of the Lachman test. The quantity of anterior translation of the tibia relative to the femur is as important as the quality of the endpoint of the anterior translation. Quantity of translation must always be compared with the unaffected knee. Quality of the endpoint in passive anterior translation should be assessed as “firm” or “sudden,” indicating an intact ACL, or as “absent, ill-defined, or softened,” indicating ACL pathology (TABLE).18
A drawback of the Lachman test is that it is challenging to perform correctly.19 The patient’s ability to relax the upper leg musculature is critically important. It is also essential to stabilize the distal femur, which can be problematic if the examiner has small hands relative to the size of the patient's leg musculature.10 These difficulties might be resolved by conducting the Lachman test with the patient in the prone position, known as the Prone Lachman.19 However, good evidence is not yet available to support this proposed solution. One systematic review, though, reports that the Prone Lachman test has the highest inter-rater reliability of all commonly used physical examination tests.7
The Lachman test is known as the test with highest validity on physical examination. When the outcome of a correctly performed Lachman test is negative, a rupture of the ACL is very unlikely.