Definition: The posterior cruciate ligament (PCL) is one of the four main stabilizing ligaments in the knee. It attaches at its upper end to the bottom of the femur (thighbone), crosses diagonally through the joint, and attaches at its lower end to the top of the tibia (shinbone). Together with the anterior cruciate ligament (ACL), which lies in front of the PCL, it forms an ‘X’ shape within the joint, hence the name cruciate. Its purpose is to limit the backwards motion of the tibia, thereby keeping the knee joint stable. It is a strong ligament and is consequently injured less often than the ACL, although it is thought that many PCL injuries remain undiagnosed.
Causes: An injury to the posterior cruciate ligament is usually the result of the tibia being subjected to a powerful force, which drives it up and behind the femur. Such injuries are often known as ‘dashboard’ injuries as they commonly occur in car collisions when the shin has struck the dashboard. An athlete can injure the PCL by falling onto the front of the knee when the knee is fully bent backwards and the foot is pointing down. Twisting or overextending the knee can also damage the PCL, although this is a less common cause of injury. PCL injuries often occur in conjunction with injuries to other structures of the knee.
Symptoms: Sometimes an isolated PCL injury (one that does not involve other parts of the knee) may simply produce some swelling that goes down after a few days. Patients may therefore not visit their doctor. If untreated, however, a PCL injury can lead to problems such as abnormal movement of the joint and eventual degenerative arthritis.
Some commonly experienced symptoms may include:
Swelling that begins within three hours of the injury
Decreased range of motion of the knee and difficulty walking
Instability of the joint
A feeling that the knee might give way
Diagnosis: Injuries to the PCL can be quite difficult to diagnose. Your doctor will ask you questions about your medical history and any previous injuries to the knee. You will be asked about the circumstances of the injury, for example, how and when it happened and the position that your leg was in at the time.
You will have a physical examination, during which your doctor will look at and feel the structures of the knee. A comparison will be made with the uninjured leg. A test called the posterior drawer test will probably be used to assess the viability of the PCL. Your injured knee will be bent, and then the doctor will gently push backwards on the tibia. If the tibia moves too far backwards, it is an indication that the PCL has been damaged.
You may have an X-ray to determine if a piece of bone has torn away with the ligament. MRI (magnetic resonance imaging) scans provide clear pictures of soft tissues, so one may be used to help with a diagnosis and to detect any damage to other parts of the knee.
PCL injuries are termed sprains, and are graded according to the severity of the damage. Grade I indicates that the ligament has been stretched and that there are microscopic tears, but the joint is still stable. Grade II is termed a partial tear. The ligament has been stretched to the point of looseness. Grade III means that the ligament has been completely torn into two pieces and the joint is unstable.
Most PCL sprains are partial tears and can heal with conservative treatment and time. The prognosis for a return to full, pre-injury activities and sports is good.
Treatment: Initial treatment of a partial tear to the posterior cruciate ligament includes:
Rest: You may find it helpful to avoid putting any weight on the knee by using crutches when walking.
Ice: Apply ice, crushed in a bag and covered with a towel, to the knee for as long as is comfortable, several times a day.
Compression: Wrapping the knee in an ace bandage to reduce pain.
Elevation: Raise the leg above the level of your heart, whenever possible, to reduce swelling.
Take NSAIDs (non-steroidal anti-inflammatory drugs) to relieve pain and reduce inflammation.
Following the acute stage of the injury and when the swelling has gone down, you might be able to begin rehabilitation exercises. Follow the advice of your doctor or physiotherapist. Such exercises are designed to restore mobility to the knee and to strengthen the leg muscles that support the joint, particularly the quadriceps muscle of the thigh.
Sewing a torn PCL back together is not successful, so surgery, if required, would be to reconstruct the ligament using a tissue graft taken either from another part of your body, or from a donor. Due to the position of the PCL in the knee, surgery can be difficult and over time grafts can stretch and lose function. Surgery therefore tends to be restricted to cases where there is significant damage to other major knee ligaments. Arthroscopy, using small incisions around the knee, is the preferred surgical technique as it minimizes trauma and enables swifter healing. You would have to use crutches for a time, and wear a knee brace to temporarily immobilize the knee.
Exercises: Follow professional advice as to when to begin exercising. Do not rush: recovering from a PCL sprain will take time. Try to do these exercises twice a day. Quad contraction: Tighten the quadriceps muscles at the front of the thigh. Hold for 10 seconds. Repeat10 times. Straight leg raise: Lie on the floor with one leg bent and the other straight out in front of you. Lift the straight leg up about 5 inches off the floor, keeping the knee straight. Hold for 10 seconds. Repeat 10 times. Switch legs and repeat exercise. Quad stretch: Hold the right foot with your right hand and gently pull the foot up and behind you towards the buttocks, stopping when you feel a stretch. Keep your knees together. Hold the stretch for 10 seconds then relax. Switch legs and repeat exercise. Hamstring stretch: Sit on the floor with one leg bent and the other straight out in front of you. Keep your toes pointing to the ceiling and lean forward from the hips until a stretch is felt under the outstretched thigh. Hold 10 seconds. Repeat 10 times. Switch legs and repeat exercise. Half-knee bends: Stand with your feet about shoulder width apart. Slowly bend your knees as though you were about to sit on a chair. Stop halfway, or earlier if you feel any pain, and then stand up straight again. Repeat 10 times.
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