Health Sciences

    

Weber State University Health Sciences

EXAMINATION OF THE
ANTERIOR CRUCIATE LIGAMENT

  • What is the function of the anterior cruciate ligament?

The function of the anterior cruciate ligament is to prevent the tibia from sliding forward on the femur.

  • Name three ways of assessing whether the anterior cruciate ligament is torn.

Three ways of assessing the anterior cruciate ligament are:

Anterior drawer test for a ruptured
anterior cruciate ligament.

Have the supine patient flex his hips to about 45 degrees
so his knees are at about a 90 degrees angle when his
feet are flat on the examining table.
Sit on the patient's feet and place your hands around
the upper part of the calf of the limb to be examined.
Apply an increasingly firm pull on the calf.

Figure 181



Lachman's test for a ruptured
anterior cruciate ligament.

Passively flex the knee of the supine patient to
between 20 degrees and 30 degrees
Hold the lower part of the patient's thigh in one
hand and the upper part of the patient's calf in
the other.
Pull the tibia forward as you would in doing the
anterior drawer test.
If the patient's thigh is too big to be held by one
hand, stabilize the thigh by resting it on a pillow,
or have an assistant hold the thigh with two hands
while you use your hand or hands to pull on the tibia.

Figure 182



Pivot shift test for a rupture
anterior cruciate ligament.

Have the patient lying in the lateral decubitus
position, with the affected knee extended and
the tibia internally rotated.
Apply a valgus stress to the knee as you flex it.
A clunk at about 30 degrees of flexion indicates
a positive test.

Figure 183


  • How do you perform the anterior drawer test?

See (fig 181).

    1. Have the supine patient flex his hips to about 45 degrees so his knees are at about a 90 degrees angle when his feet are flat on the examining table.

    2. Sit on the patient's feet and place your hands around the upper part of the calf of the limb to be examined.

    3. Instruct the patient to relax the muscles of his legs (tight hamstrings can mask a positive sign).

    4. Apply an increasingly firm pull on the upper calf.

    5. Observe whether the tibia pulls forward like a drawer opening up. Always compare with the unaffected side; some normal individuals have up to half a cm. of play in the ligaments.

If you think the patient has an anterior drawer sign, check the knee for a sag sign. If the posterior cruciate is torn, you could be fooled into thinking that the anterior drawer sign was present when all you were doing was pulling the posteriorly displaced tibia back into its normal anatomical position.

  • How do you perform Lachman's test?

    1. Passively flex the knee of the supine patient to between 20 degrees and 30 degrees. Hold the lower part of the patient's thigh in one hand and the upper part of the patient's calf in the other.

    2. Gently pull the tibia forward as you would in doing the drawer test (fig. 182).
      If you get movement, test the unaffected limb as a control.

It is often impossible to hold the thigh and calf as described above because the patient's thigh is too big for your hand. One way around this dilemma is to support the thigh on pillows, and then use one or two hands to move the upper tibia. Alternatively, you can get an assistant to stabilize the lower thigh with both his hands while you use your hand or hands to hold and pull on the upper portion of the lower leg.

  • Why bother with Lachman's test when you already know
    how to perform the drawer test?

Lachman's test is more sensitive than is the anterior drawer sign. One reason may be that it is difficult for the patient to contract his hamstrings and thus prevent forward sliding of the tibia when the knee is in only 20 degrees - 30 degrees of flexion. This is particularly so if the examiner lifts the whole of the lower leg off the examining table while performing the test.

The other situation where Lachman's test is used is during the examination of the acutely injured knee. Often there is a hemarthrosis and a great deal of pain. One simply can not flex the knee more than 20 degrees or 30 degrees.

  • How do you perform the pivot shift test (MacIntosh test)?

    1. Have the patient lie in the lateral decubitus position with the affected leg uppermost. Place the leg in full extension.

    2. With one hand, apply a valgus stress to the knee and with the other holding the ankle or heel, internally rotate the tibia. In this position, the tibia will be displaced forward if the anterior cruciate ligament is torn.

    3. Next, while maintaining the valgus stress and internal rotation, flex the knee. If the anterior cruciate is torn, the tibia will reduce with a clunk at about 30 degrees of flexion.
      This is a positive pivot shift test (fig. 183).

  • Are there any other tests for ligamentous injuries?

There are undoubtedly many, but I know of only one other that family physicians should probably know about.

This is the Apley distraction test.

    1. Have the patient lie prone on the examining table with the knees flexed 90 degrees so the soles of the feet are facing the ceiling.

    2. Holding the thigh on the examining table, pull firmly upwards on the ankle or foot thus applying a distraction force to the knee and its ligaments, and, while doing this, internally and externally rotate the tibia.

The idea is that such a maneuver should cause pain if the ligaments are injured. Note that the opposite of the Apley distraction test is the Apley compression test. The patient assumes the same position, but the examiner applies a downward compressive and back and forth rotary force to the knee. The idea is that this grinding pressure will cause pain if the patient has a torn meniscus.