A physician or other health professional can usually diagnose a posterior cruciate ligament (PCL) tear through a patient interview, physical exam, and medical imaging.

Patient Interview

A person should be prepared to answer questions about his or her medical history, and details surrounding the injury, such as:

  • How did the injury occur?
  • When did the injury occur?
  • Has the knee been injured before?
  • Where is the location of the pain?
  • Was there a “popping” sound at the time of the suspected injury?
  • Does the knee feel weak or unstable, as if it is about to give out?

Knee instability can be a sign of a recent, severe PCL tear or an undiagnosed PCL tear that occurred months or even years earlier.

In addition to a patient interview, the doctor will perform a series of physical exams to help confirm the diagnosis of a PCL tear.

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Physical Exam

During a physical examination the doctor will check for any signs of trauma, such as bruising, swelling, and lacerations that may be present around the knee area. The doctor may perform specific physical tests, such as the posterior drawer test and posterior sag test.

Posterior drawer test

  • The test is performed with the person lying on his or her back.
  • The examiner will ask the person to bend their hip to 45º with foot flat) and knee to 90º.
  • He or she will lean lightly on the person’s foot to stabilize the leg.
  • The examiner will wrap both hands around the joint line of the knee and attempt to move the tibia (shin bone) backwards.
  • This movement may be done several times to confirm the diagnosis.

By putting pressure on the shin bone, the doctor will be able to gauge resistance from the PCL; an injured PCL will have less resistance than an uninjured ligament, causing the tibia to move backwards.

Posterior sag sign test

  • This test is performed with the person laying on his or her back.
  • The doctor will bend the affected knee so that it and the hip are each at a 90º angle, with the foot in the air, and hold the heel for support.
  • If there is an increased posterior sag in the affected knee (due to gravity), a PCL tear is likely present.

A doctor may also perform physical tests to determine if any other structures in the knee have been damaged. In addition to a physical exam, the doctor may order an x-ray or other medical imaging.

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Medical Imaging

In order to confirm the diagnosis of a PCL tear and determine the severity, the doctor will likely call for one or more diagnostic medical imaging tests.

  • Magnetic resonance imaging (MRI). This type of diagnostic imaging shows a detailed view of the soft tissue surrounding the knee joint. An MRI of the knee is utilized to confirm the diagnosis and evaluate for other injuries to the knee.
  • X-ray. An x-ray cannot show a PCL tear, however, it can help rule out other causes of knee pain, such as a bone fracture.

Once an accurate diagnosis has been made, the doctor can move forward with treatment options.

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