The knee has four primary ligaments. Ligaments are strong fibrous bands that attach one bone to another. In the case of the knee these ligaments attach the femur or thigh bone to the tibia or shin bone. There are two ligaments, the collateral ligaments, which stabilize the side to side movement of the knee. The medial collateral ligament is on the inner aspect of the knee while the lateral collateral is on the outer aspect of the knee. Within the center of the knee are the anterior and posterior cruciate ligaments. These two ligaments stabilize the front to back motion of the knee.
Anterior Cruciate Ligament (ACL) tears are relatively common. Almost everyone either knows someone who has sustained a torn ACL or they have heard of this injury in athletes. It is estimated that more than 200,000 persons in the United States will tear their ACL each year. There is a distinctly higher rate of ACL tears in female athletes than male athletes with females being somewhere between 3 and 9 times more likely to tear their ACL per hour of sports participation. ACL tears typically occur in one of two ways. The first is simple non-contact twisting where the patients slips, missteps, or pivots forcefully during sports and the ligament tears. With contact injuries the knee is struck, usually by another athlete on the field, while the foot is planted firmly on the ground.
Most patients will report that they recollect feeling, and often even hearing, a distinct “pop” at the time of injury. Almost always they report a sensation that the knee “slipped out of place”. Usually, if they are playing sports at the time of injury, they report that they were unable to continue their activity. Frequently they had inability to bear weight on the leg because of pain, swelling, and sense of instability. Because bleeding occurs within the knee joint when the ligament tears swelling is usually prompt and significant.
Many tissues within the body will heal given some time and protection. Skin, bone, and organs like the liver would be good examples of this healing capacity. Some knee ligaments, particularly the medial collateral ligament, fall into this category. Experience has shown us, however, that anterior cruciate ligament tears don’t heal once torn. That being said, torn anterior cruciate ligaments may or may not cause patients ongoing or long term symptoms. The initial symptoms from an acute anterior cruciate ligament tear are pain and swelling. These two symptoms will resolve with time and early rehabilitation. Torn anterior cruciate ligaments are not the cause of ongoing knee pain. Torn anterior cruciate ligaments can cause patients an ongoing sense of instability.
As with most things there are operative and non-operative choices. Many things must be considered when evaluating the treatment options including patient’s expected activity level and associated other knee injuries. As noted above, torn anterior cruciate ligaments do not cause patients ongoing pain. It is an unequivocal fact that many patients with torn anterior cruciate ligaments do not experience ongoing instability or giving way complaints and it is specifically instability that is the reason for surgical intervention. It is not possible to predict with absolute certainty who will have ongoing instability complaints and who will not. However, it is possible through thorough discussion with the patient to establish their risk for ongoing instability.
In general the older the patient at the time of injury the less likely it is they will be bothered by instability complaints. To some extent this relates to activity levels and to some extent it may relate to willingness or desire to modify activities and avoid “at risk” activities rather than undergo surgery. It is activity level and not age that is the important factor.
When anterior cruciate ligament tears are associated with instability symptoms those symptoms occur with pivoting and twisting. Straight ahead activities such as walking and even jogging are not usually a problem. A 50 year old who plays competitive singles tennis will likely have more trouble with return to that level of activity than a 50 year old whose primary activities are a non-manual laboring job and exercise on a treadmill or elliptical glider. An 18 year old, almost irrespective of sports participation will be at high risk for instability complaints because of their age activity level. For patients like competitive athletes and persons likely to be regularly involved in pivoting and twisting activities early surgical intervention is often indicated in order to restore desired lifestyle activities and prevent further injury to the knee. It is true that recurrent instability episodes are damaging to the knee joint and can tear the meniscus cartilages and lead to premature arthritis.
If after a period of therapy a patient who was an acceptable candidate for attempted non-operative treatment can accomplish activities that are important to their life then there is no need to proceed with surgery. As long as patients are not having recurrent instability or giving way episodes there is no evidence that the anterior cruciate ligament tear itself will lead to worse outcome for the knee than one that is treated surgically. Since in most situations the operative procedure is the same whether the procedure is done shortly after injury or at some point in the future, and success rates are similar, there frequently is little risk in delaying surgical treatment for a period of rehabilitation.
For patients that have failed non-operative treatment and have persistent instability, for those determined initially to be at high risk for ongoing instability due to age or lifestyle, and for those who have other injuries like certain meniscus tears needing treatment, surgical reconstruction is the initial treatment of choice. The option for surgery is specifically ligament “reconstruction” and not “repair”. When your skin has a cut the cut it is sewn together or repaired. Experience and science have taught us that simply stitching a torn ACL back together is not a reliable procedure to restore stability to the knee. Since the anterior cruciate ligament cannot be reliably repaired the preferred option is to “reconstruct” or replace the ligament. This reconstruction requires something be available to replace the ligament. Potential options would include a prosthesis, in other words a manufactured product, or a biologic tissue graft. To date all attempts at creating a well-functioning prosthesis have failed so no such option currently exists. That leaves the need for human tissue and the options are “autograft” or tissue taken from the patient and “allograft” or tissue taken from another person; typically a deceased tissue donor.
There a many autogenous tissue options available to surgeons but the most common are a portion of the patient’s patellar tendon or several of their hamstring tendons. The advantages of these autogenous sources are that there is no risk of disease transmission from a donor and there is no risk of tissue incompatibility or rejection. The downside is that the actual size of the graft available for reconstruction is not known until the time of surgery and there is pain and maybe some disability associated with removal of normal tissue from the patient. Allografts are meticulously prescreened and tested to make the risk of disease transmission remote and a predetermined product size and quality is known before surgery. There is overall less pain from the surgical procedure for the patient because no graft harvest is necessary. Also there is no “donor site morbidity” or risk of problems from removing or taking a portion of an otherwise normal structure from the patient. There are other considerations that are specific to certain patient specific situations. We will discuss those that relate to your specific situation during your office visit or visits.
I look forward to helping you manage your knee injury. I hope that you have found this information helpful. Please see the resources below for additional information including a video animation demonstrating the basics of how the surgical procedure is accomplished as well as some general and specific information about allograft tissue that I frequently use.