Ligament Injuries of the Knee

Anatomy
A ligament injury to the knee involves partial or complete damage to one of the major supporting ligaments. It can be as simple or minor as a stretching of the ligament resulting in some inflammation or as severe as a complete rupture causing instability of the knee. The ligaments are essential to proper knee function. There are four primary ligaments of the knee, two on the side: the lateral collateral ligament and the medial collateral ligament, and two in the center: the anterior cruciate ligament and the posterior cruciate ligament. They attach the femur or thigh bone to the tibia or leg bone. They are the primary stabilizers of the knee preventing abnormal motion of the femur relative to the tibia.

How the injury occurs
When the knee sustains a twisting-type injury, the force is sometimes greater than the ligaments can tolerate and a partial or complete tear results. Depending on which ligament is damaged, there are various consequences of such an injury. If the ligament becomes attenuated or lengthened, it will no longer hold the tibia in correct relationship to the femur. There may be an associated injury to the meniscus or shock absorber of the knee or damage to the cartilage covering the bones. Ligaments have small blood vessels in them and when torn these may bleed, causing swelling. This may be within the knee joint itself or outside the joint into the tissues.

Symptoms
Many patients feel the ligament tear or pop at the time of the injury. If it is one of the inside ligaments (the cruciate ligaments), there is usually an accumulation of blood within the knee joint causing swelling. There is approximately a 60 to 70 percent chance of an associated meniscal injury with this type of ligament rupture. After the swelling starts to diminish and the knee becomes less painful, the patient usually notices a giving way sensation or an abnormal looseness. This may be particularly true when trying to pivot or turn but depends on which ligament was injured.

Physical Examination
Within the first few days to weeks after an injury, it may be difficult to demonstrate the ligamentous instability by physical exam due to swelling of the knee and the patient's inability to relax because of pain. Eventually, when compared to the opposite knee, there will be a demonstrable difference in the physical exam. Depending on which ligament is involved, the instability may slowly increase over time as a result of stretching of the other ligaments and tissues known as the secondary restraints. This is one argument for not allowing certain ligament injuries to become chronic.

Treatment
Treatment depends on which ligament is torn and the severity of the injury. The medial collateral ligament, even when completely torn, will often heal relatively well with nonoperative treatment in a brace. Unfortunately, the other ligaments do not fair so well. Most patients who are active in pivoting-type sports and activities will find it difficult to function well with a major ligament injury. The giving way of the knee which they experience can lead to further injury, particularly to the meniscus. With time, if the other restraining ligaments and tissues become stretched, the instability may increase.

Some patients, however, do tolerate ligament insufficiency. Those whose activities do not require strenuous knee use or those who give up this type of activity can sometimes function adequately without one of their ligaments. Muscle strengthening and occasionally, bracing can assist in tolerating a ligament injury. The bottom line is that one must avoid meniscal damage as this is important for the longevity of the knee. If this cannot be done with an unstable knee, then consideration should be made for stabilization.

Once a diagnosis has been made and the severity of the ligament injury has been established, the treatment options can be considered. A partially injured ligament, and usually even a completely injured medial collateral ligament, can be treated conservatively with bracing and rehabilitation while it heals. The patient is then progressed back to full activity gradually. Those with complete ligament injuries--the anterior cruciate ligament rupture being the most common--can try a course of conservative treatment and see how they do. This, of course, is assuming that they do not have an accompanying meniscal injury. They may decide to give up certain activities and try muscle strengthening and perhaps bracing, although bracing has been recently shown to offer little, if any, benefit to the athlete with an anterior cruciate deficient knee.

If the patient is young, very active -- especially in pivoting-type sports, or has an associated meniscal tear, consideration should be made for stabilization. There are various ways to stabilize or reconstruct a ruptured ligament. A healthy tissue graft is usually used to replace the injured ligament. The source of this graft depends on which ligament is being reconstructed and, given various options, the patient's choice.

Surgery
The ligament reconstruction procedure is performed with the assistance of an arthroscope. All meniscal surgery and other indicated surgery is performed at the same time. Usually the procedure can be done as an outpatient, not requiring hospitalization. Small incisions are made about the knee to assist in placing the graft. The graft is secured using screws or staples.

Risks
The risks of ligament reconstruction are the same as those for general arthroscopy with a few additions. If the graft is harvested from around the patient's own knee, risks of harvest site morbidity exist (e.g. weakness to donor tissue, longer rehabilitation, etc.). If a donor graft (allograft) is used, the potential for disease transmission (e.g. AIDS) is present. These grafts are very carefully selected from donors who are not at risk and who test negative for the AIDS virus. However, at present there is no test that can insure absolutely that the graft is disease-free. When the patient decides to use his or her own tissue for the graft, the risk of weakening the donor site and the possibility of donor site pain must be considered. If a donor graft is obtained from a bone bank (allograft), the risk of disease transmission must be considered. In addition, the risk of the graft breaking or stretching is present, as is the fact that not all reconstructed ligaments function as well as the original equipment.

After Surgery
A brace is worn after surgery to protect the graft fixation as it becomes secure. An important part of the process is the postoperative rehabilitation and physical therapy. The muscles must be strengthened and motion regained without disrupting the graft. This process varies depending on which ligament is reconstructed and what other surgery is necessary (such as meniscal repair or excision).

The long-term outlook for patients with reconstructed ligaments is generally good. The majority return to pre-injury activities, although some have to modify them somewhat. Many say that they can tell the difference between their reconstructed knee and their normal knee but that it does not keep them from participating in most of their activities. Much of the prognosis depends on the accompanying knee injuries such as meniscal or cartilage injuries that occurred at the same time or as a result of the ligament injury.