Lindee Abe, APRN
Knee injuries are common in urgent care centers and emergency departments across the country. There are various mechanisms of injury that include everything from direct trauma to twisting. There are also patient that experience knee pain with an insidious onset.
The knee is a complex joint that can have different etiologies of pain, to include bone, bursa, tendons, meniscus, and ligaments. Most facilities have limited testing available for acute injuries, so the reliance on a good history and physical exam is essential to evaluate these patients.
The first step in the evaluation is walking the patient walk to the room. Can they walk? Are they walking with a limp? Are they using a cane or walker? This is important in the overall assessment and helps the provider to initially evaluate the severity of the knee injury with the caveat that some patients are still ambulatory despite a significant derangement of the knee. The provider must evaluate the history of the injury: was there a direct impact to the knee, did they pivot and twist wrong, etc. and how long has it been going on? The duration of symptoms (acute versus chronic) can help guide the provider to the appropriate work up and referral if indicated.
Range of motion is important as well as noting any swelling or color changes to the area. Most clinics and ERs have limited imagining capability for acute injuries. MRI will be the most informative test, but is rarely available in an acute setting. Xray is the normal test available, but tells us more about fractures than soft tissue injury. Most knee injuries seen in the acute setting are injuries to the soft tissue. This requires the provider to perform a thorough physical exam to determine possible underlying structure damage. The provider should examine both knees. These tests are most effective when performed by an experienced provider. The only way to get experience is by doing these test routinely.
Anterior Cruciate Ligament
There are three primary tests to assess the anterior cruciate ligament.
The first test is the Lachman test. This will test for anterior instability, i.e. ACL injury. The patient starts by lying on the exam table on their back with knee flexed to about 20 degrees of flexion. The provider places one hand above the knee to stabilize femur and another below knee pulling the knee anteriorly. A normal knee should not move. The knee should not move during this test. Any movement is abnormal and rated on a scale from 1 to 3. Grade 1 being the least amount of laxity and 3 being the greatest and a positive test noted with 5mm of anterior translation. The Lachman test is 87% sensitive and 93% specific for ACL disruption.
Anterior Drawer Test
The second test is the anterior drawer test. To perform this test the patient should lie on their back with knee bent and foot resting on table. The provider again anchors the foot, most often by sitting on the foot, while placing a hand on either side of the knee with thumbs anterior on either side of the patella. Next, apply gentle pressure anteriorly to the knee while pulling the knee towards the operator. Findings are also graded 1-3, with a positive test showing greater than 5mm of anterior translation. The anterior drawer test has a sensitivity of 48% and a specificity of 93%.
Pivot Shift Test
The last test for ACL injury is the pivot shift test. This starts with the patient laying supine with their legs straight. The provider grabs the patient’s heel and the lateral aspect of the leg just below the knee. Flex the knee and apply gentle inward pressure. Findings are also graded 1-3 and 5mm of anterior translation defines a positive test. The sensitivity of the test is 61% and specificity is 97%.
Posterior Cruciate Ligament
There is one primary test for posterior cruciate ligament injury, as it is less common than
ACL injuries, the posterior drawer test.
Posterior Drawer Test
This test Is similar to the anterior drawer test, but with posterior stress applied to the tibia. Findings are also graded 1-3. Greater than 5mm of posterior translation is a positive test. The posterior drawer test has a sensitivity of 90% and specificity of 99%
Tests for Medial and Lateral Stability
The next group of tests check the medial and lateral stability of the knee. The two primary causes of medial and knee pain are meniscus injury and MCL tear. The patient’s symptoms can help to differentiate the type of injury. MCL and LCL injuries are associated with a popping or giving way at the time of injury. Meniscal injuries involve locking of the knee.
Valgus Stress Test
Injury to the medial cruciate ligament can be evaluated by the valgus stress test. This is also performed with the patient laying on their back. The knee should be slightly bent. The provider places one hand on the lateral aspect of the knee and one hand on the medial aspect of the ankle. Valgus pressure should be applied with the knee held at zero degrees and thirty degrees. Pain or gapping defines a positive test.
Varus Stress Test
The Varus stress test evaluates the Lateral cruciate ligament. This is similar to the valgus stress test. The difference is that one hand is placed on the medial knee and the other on the lateral ankle. Apply varus pressure at both zero and thirty degrees. Pain or gapping defines a positive test.
The McMurray test looks for medial and lateral meniscus injury. This test also starts with the patient laying on the exam table on their back with knee bent to approximately ninety degrees. The provider grasps the heel with one hand and while placing the other hand over the knee, palpates the medial joint line. Stress is applied through internal rotation while moving the knee through flexion and extension. This isolates the medial meniscus and external rotation isolates the lateral meniscus. The test is positive if a click is felt or heard over the meniscus during extension. The McMurray test has a sensitivity of 79% and a specificity of 78%.
Hopefully this quick review of several of the most commonly utilized tests to evaluate knee injuries helps you feel more comfortable with a knee exam for the next knee injury patient. These tests guide the appropriate treatment. They can also help to determine the need for referral. Just remember, practice makes perfect so consistently using these tests is essential to having better sensitivity and specificity for these tests.
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