How is a PCL tear diagnosed?

The examination

With the knee bent, the front of the shin normally sits a little ahead of the thigh bone. When the PCL is torn, gravity lets the shin sag backwards, which can be seen from the side. In the posterior drawer test, Dr. Gelber gently pushes the shin backwards and compares the movement with the other knee.

He also tests the outer corner of the knee with the dial test and checks the collateral ligaments and ACL, because PCL tears are often combined with other injuries and that changes the treatment.

Grading the injury

• Grade I: a partial tear with a small increase in backward movement
• Grade II: a larger partial tear, with the shin moving back level with the thigh bone
• Grade III: a complete tear, with the shin moving behind the thigh bone, often with other ligament damage

The grade, combined with whether other structures are injured, is the main factor in deciding between rehabilitation and surgery.

Imaging

MRI shows the PCL well in a recent injury and also shows the meniscus, cartilage, bone bruising and the other ligaments. X-rays look for a small fragment of bone pulled off where the PCL attaches, called an avulsion, which is often treated by fixing the fragment back. In chronic cases, stress X-rays that measure backward movement under a set load can help, because an old PCL tear can heal in a lengthened position and look continuous on MRI.

When to book

Book an assessment if you have had a blow to the front of the shin or a fall onto a bent knee and the knee still aches or feels unsteady after a week or two. Bring any emergency X-rays or scans. Seek urgent care for a cold or numb foot, severe calf pain or a deformed knee.