The posterior cruciate ligament is located in the back of the knee. It is one of several ligaments that connect the femur (thighbone) to the tibia (shinbone). The posterior cruciate ligament keeps the tibia from moving backwards too far.
An injury to the posterior cruciate ligament requires a powerful force. A common cause of injury is a bent knee hitting a dashboard in a car accident or a football player falling on a knee that is bent.
Two bones meet to form your knee joint: your thighbone (femur) and shinbone (tibia). Your kneecap sits in front of the joint to provide some protection.
Bones are connected to other bones by ligaments. There are four primary ligaments in your knee. They act like strong ropes to hold the bones together and keep your knee stable.
Collateral ligaments. These are found on the sides of your knee. The medial collateral ligament is on the inside and the lateral collateral ligament is on the outside. They control the sideways motion of your knee and brace it against unusual movement.
Cruciate ligaments. These are found inside your knee joint. They cross each other to form an “X” with the anterior cruciate ligament in front and the posterior cruciate ligament in back. The cruciate ligaments control the back and forth motion of your knee.
The posterior cruciate ligament keeps the shinbone from moving backwards too far. It is stronger than the anterior cruciate ligament and is injured less often. The posterior cruciate ligament has two parts that blend into one structure that is about the size of a person’s little finger.
Injuries to the posterior cruciate ligament are not as common as other knee ligament injuries. In fact, they are often subtle and more difficult to evaluate than other ligament injuries in the knee.
Many times a posterior cruciate ligament injury occurs along with injuries to other structures in the knee such as cartilage, other ligaments, and bone.
Injured ligaments are considered “sprains” and are graded on a severity scale.
Grade 1 Sprains. The ligament is mildly damaged in a Grade 1 Sprain. It has been slightly stretched, but is still able to help keep the knee joint stable.
Grade 2 Sprains. A Grade 2 Sprain stretches the ligament to the point where it becomes loose. This is often referred to as a partial tear of the ligament.
Grade 3 Sprains. This type of sprain is most commonly referred to as a complete tear of the ligament. The ligament has been split into two pieces, and the knee joint is unstable.
Posterior cruciate ligament tears tend to be partial tears with the potential to heal on their own. People who have injured just their posterior cruciate ligaments are usually able to return to sports without knee stability problems.
An injury to the posterior cruciate ligament can happen many ways. It typically requires a powerful force.
- A direct blow to the front of the knee (such as a bent knee hitting a dashboard in a car crash, or a fall onto a bent knee in sports)
- Pulling or stretching the ligament (such as in a twisting or hyperextension injury)
- Simple misstep
The typical symptoms of a posterior cruciate ligament injury are:
- Pain with swelling that occurs steadily and quickly after the injury
- Swelling that makes the knee stiff and may cause a limp
- Difficulty walking
- The knee feels unstable, like it may “give out”
During your first visit, your doctor will talk to you about your symptoms and medical history.
During the physical examination, your doctor will check all the structures of your injured knee, and compare them to your non-injured knee. Your injured knee may appear to sag backwards when bent. It might slide backwards too far, particularly when it is bent beyond a 90° angle. Other tests which may help your doctor confirm your diagnosis include X-rays and magnetic resonance imaging (MRI). It is possible, however, for these pictures to appear normal, especially if the injury occurred more than 3 months before the tests.
X-rays. Although they will not show any injury to your posterior cruciate ligament, X-rays can show whether the ligament tore off a piece of bone when it was injured. This is called an avulsion fracture.
MRI. This study creates better images of soft tissues like the posterior cruciate ligament.