When a person suddenly slows down during running, twisting, or pivoting with valgus force applying on the knee, the anterior cruciate ligament can rupture.
[1] Physical examination of the knee begins by observing the person's gait to assess for any abnormalities seen while walking.
Radiographic imaging should be done if the examination findings fulfills the Ottawa rules: age 55 years and older, pain at the head of fibula, patellar pain, unable to flex the knee to 90 degrees, and inability to stand and walk at least four steps.
If anterior cruciate ligament injury is suspected, radiographic imaging should also be ordered because it is frequently associated with lateral tibial plateau fracture.
If there is a painful, reddish, and warm swelling in front of the patella, acute prepatellar bursitis should be considered which may require aspiration or drainage.
[1] Valgus stress test can be performed with the examined knee in 25 degrees flexion to determine the integrity of the medial collateral ligament.
Similarly, varus stress test can be performed to access the integrity of the lateral collateral ligament.
In a third degree tear, there will be 10 mm laxity with no definite resistance either with knee with full extension or flexion.
In the anterior drawer test, the person being examined should lie down on their back (supine position) with the knee in 90 degrees flexion.
For the Lachman test, the person lies down in supine position with the knee flexed at 20 degrees and the heel touching the bed.
If there is 6 to 8 millimeters of laxity, with no definitive resistance when the knee is pulled, then the test is positive thus raising concern for a torn anterior cruciate ligament.
A large collection of blood in the knee can be associated with bony fractures and cruciate ligament tear.
Similar to anterior drawer test, the knee should be flexed 90 degrees and the tibia is pushed backwards.
In tibial sag test, both knees are flexed at 90 degrees with the person in supine position and bilateral feet touching the bed.
In McMurray test, the person should lie down in supine position with the knee should in 90 degrees flexion.
the examiner put one hand with the thumb and the index finger on the medial and lateral joint lines respectively.
To test the medial meniscus, the hand at the heel applies a valgus force and external rotates the leg while extending the knee.
To test for the lateral meniscus, the varus force, internal rotation are applied to the leg while extending the knee.
[1] In Apley compression test, the person lie down in prone position with the knee flexed at 90 degrees.