Posterior cruciate ligament (PCL) injury happens far less often than does injury to the knee's more vulnerable counterpart, the anterior cruciate ligament (ACL). The posterior cruciate ligament and ACL connect your thighbone (femur) to your shinbone (tibia). If either ligament is torn, it might cause pain, swelling and a feeling of instability.

Ligaments are strong bands of tissue that attach one bone to another. The cruciate (KROO-she-ate) ligaments connect the thighbone (femur) to the shinbone (tibia). The anterior and posterior cruciate ligaments form an "X" in the center of the knee.

Although a posterior cruciate ligament injury generally causes less pain, disability and knee instability than does an ACL tear, it can still sideline you for several weeks or months.

Signs and symptoms of a PCL injury can include:

• Pain. Mild to moderate pain in the knee can cause a slight limp or difficulty walking.
• Swelling. Knee swelling occurs rapidly, within hours of the injury.
• Instability. Your knee might feel loose, as if it's going to give way.

If there are no associated injuries to other parts of your knee, the signs and symptoms of a posterior cruciate ligament injury can be so mild that you might not notice that anything's wrong. Over time, the pain might worsen and your knee might feel more unstable. If other parts of your knee have also been injured, your signs and symptoms will likely be more severe.

The posterior cruciate ligament can tear if your shinbone is hit hard just below the knee or if you fall on a bent knee. These injuries are most common during:

• Motor vehicle accidents. A "dashboard injury" occurs when the driver's or passenger's bent knee slams against the dashboard, pushing in the shinbone just below the knee and causing the posterior cruciate ligament to tear.
• Contact sports. Athletes in sports such as football and soccer can tear their posterior cruciate ligament when they fall on a bent knee with their foot pointed down. The shinbone hits the ground first and it moves backward. Being tackled when your knee is bent also can cause this injury.

Being in a motor vehicle accident and participating in sports such as football and soccer are the most common risk factors for a PCL injury.

In many cases, other structures within the knee — including other ligaments or cartilage — also are damaged when you injure your posterior cruciate ligament. Depending on how many of these structures are damaged, you might have some long-term knee pain and instability. You might also be at higher risk of eventually developing arthritis in your affected knee.

During the physical exam, your doctor might press on your knee to feel for injury, looseness or fluid in the joint from bleeding. He or she may move your knee, leg or foot in different directions and ask you to stand and walk. Your doctor will compare your injured leg with the healthy one to look for any sagging or abnormal movement in the knee or shinbone.

In some cases, your doctor may suggest one or more of the following imaging tests:

• X-ray. While an X-ray can't detect ligament damage, it can reveal bone fractures. People with posterior cruciate ligament injuries sometimes have breaks in which a small chunk of bone, attached to the ligament, pulls away from the main bone (avulsion fracture).
• MRI scan. This painless procedure uses radio waves and a strong magnetic field to create computer images of the soft tissues of your body. An MRI scan can clearly show a posterior cruciate ligament tear and determine if other knee ligaments or cartilage also are injured.
• Arthroscopy. If it's unclear how extensive your knee injury is, your doctor might use a surgical technique called arthroscopy to look inside your knee joint. A tiny video camera is inserted into your knee joint through a small incision. The doctor views images of the inside of the joint on a computer monitor or TV screen.

Treatment depends on the extent of your injury and whether it just happened or if you've had it for a while. In most cases, surgery isn't required.

Medications

Over-the-counter pain relievers, such as ibuprofen (Advil, Motrin IB, others) or naproxen sodium (Aleve), can help relieve pain and reduce swelling.

Therapy

A physical therapist can teach you exercises that will help make your knee stronger and improve its function and stability. You may also need a knee brace or crutches during your rehabilitation.

Surgery

If your injury is severe — especially if it's combined with other torn knee ligaments, cartilage damage or a broken bone — you might need surgery to reconstruct the ligament. Surgery might also be considered if you have persistent episodes of knee instability despite appropriate rehabilitation.

This surgery usually can be performed arthroscopically by inserting a fiber-optic camera and long, slender surgical tools through several small incisions around the knee.

Employing R.I.C.E. — rest, ice, compression and elevation — can help speed recovery of mild to moderate joint injuries.

• Rest. Stay off your injured knee and protect it from further damage. You might need crutches.
• Ice. Apply ice packs to your knee for 20 to 30 minutes every three to four hours for two to three days.
• Compression. Wrap an elastic bandage around your knee.
• Elevation. Lie down and place a pillow under your knee to help reduce swelling.

If your knee injury is severe, you might need emergency medical care. Otherwise, you're likely to consult your primary care doctor. He or she may refer you to a doctor who specializes in knee injuries or sports medicine.

What you can do

You might want to write a list that includes:

• Detailed descriptions of your symptoms
• Information about medical problems you've had in the past, including previous knee injuries
• Information about your parents' or siblings' medical histories
• The medications and dietary supplements you take

What to expect from your doctor

Your doctor might ask you questions, including:

• How and when did you injure your knee?
• What, if anything, seems to relieve your pain?
• What, if anything, seems to worsen your pain?