There are two sets of ligaments that give the knee stability: the cruciate and the collateral ligaments. Injuries to either set of ligaments can result in pain, stiffness, swelling and a sense of instability.

The cruciate ligaments are located inside the knee joint and connect the thighbone (femur) to the shinbone (tibia). They crisscross each other to form an "x," and are made up of many strands that function like short ropes holding the knee joint tightly in place when the leg is bent or straight. This stability is needed for proper knee joint movement. The cruciate ligament located toward the front of the knee is called the anterior cruciate ligament (ACL), and the one located toward the rear of the knee is called the posterior cruciate ligament (PCL). Damage to either ligament can occur in varying degrees.

Causes of ACL Injuries
The ACL prevents the shinbone from sliding forwards beneath the thighbone. The ACL can be injured in several ways, such as changing direction rapidly; slowing down when running; landing from a jump; and direct contact, such as in a football tackle. If you walk or run on an injured ACL, you can damage the cushioning cartilage in the knee. For example, you may plant the foot and turn the body to pivot, only to have the shinbone stay in place as the thighbone above it moves with the body.

Symptoms of ACL Injuries
If you injure your ACL, you may not feel any pain immediately. However, you might hear a popping noise and feel your knee give out from under you. Between 2 and 12 hours later, the knee will swell and you will feel pain when you try to stand. Apply ice to control the swelling and elevate your knee until you can see an orthopedic surgeon.

Treating ACL Injuries
Both nonoperative and operative treatment choices are available. Nonoperative treatment may be recommended if the overall stability of the knee seems good, or because of a patient's age or overall low activity level. It usually involves a treatment program of muscle strengthening, often with the use of a brace to provide stability.

Surgical Options
Operative treatment (either arthroscopic or open surgery) uses a strip of tendon, usually taken from the patient's knee (patellar tendon) or hamstring muscle, that is passed through the inside of the joint and secured to the thighbone and shinbone. It is followed by an exercise and rehabilitation program to strengthen the muscles and restore full joint mobility.

Causes of PCL Injuries
The posterior cruciate ligament, or PCL, is not injured as frequently as the ACL. Sprains of the PCL can occur when the ligament is pulled or stretched too far through a blow to the front of the knee, or a simple misstep. PCL injuries disrupt knee joint stability because the shinbone can sag backwards. The ends of the thighbone and shinbone rub directly against each other, causing wear and tear to the thin, smooth articular cartilage. This abrasion may lead to arthritis in the knee.

Symptoms of PCL Injuries
The symptoms of an injury to the PCL may vary from person to person. Some people have more problems than others, such as when other ligaments compensate for the stability lost when the PCL is torn. The instability caused by the torn ligament leads to a feeling of insecurity and giving way of the knee, especially when trying to change direction on the knee. While the pain and swelling from the initial injury will usually diminish after 2 to 4 weeks, the instability remains. The symptom of instability, and the inability for the patient to trust the knee for support, is what requires treatment.

Treating PCL injuries
Patients with PCL tears often do not have the symptom of instability in their knees, so surgery is not always needed. Many athletes return to activity without significant impairment after completing a prescribed rehabilitation program. However, if the PCL injury pulls a piece of bone out of the top of the shinbone, surgery is needed to reattach the ligament. Knee function after this surgery is often quite good.

Collateral ligaments
The collateral ligaments are located on the inner and outer side of the knee joint. The medial collateral ligament (MCL) connects the thighbone to the shinbone and provides stability to the inner side of the knee. The lateral collateral ligament (LCL) connects the thighbone to the other bone in the lower portion of your leg (fibula) and stabilizes the outer side.

Causes of Collateral Ligament Injuries
Injury occurs when the lower leg is forced sideways -- either towards the other knee (medially) or away from the other leg (laterally). Injuries to the MCL are usually caused by contact on the outside of the knee and are accompanied by sharp pain on the inside of the knee. The LCL is rarely injured.

Symptoms of Collateral Ligament Injuries
If you have injured your MCL, the knee will be stiff and painful. As the initial pain and stiffness lessen, there may be a feeling of instability in the knee joint or the knee may give away and not support your body weight.

Treatment of Collateral Ligament Injuries
If the medial collateral ligament (MCL) has a small partial tear, conservative treatment usually works. Remember the acronym RICE: Rest, Ice, Compression, Elevation.

• Rest the knee to give the ligament time to heal.
• Ice can be applied two or three times a day for 15 to 20 minutes each time.
• Compress the injury to limit swelling. You may have to wear a bandage or brace for a while.
• Elevate the knee whenever possible.

Your physician may also recommend a course of rehabilitation exercises for optimal healing.

Surgical Options
If the collateral ligament is completely torn or damaged in a way that prevents ligament fibers from healing, you may need surgery. Surgical repair usually brings satisfactory results, with a return to good knee stability. After rehabilitation, many people resume their previous levels of activity. Most rehabilitation plans include passive range-of-motion exercises designed to restore flexibility; braces to control joint movement; and exercises to strengthen the quadriceps muscles in the front of the thigh.