What is an ACL?
The anterior cruciate ligament (ACL) is one of several ligaments that are involved in stabilizing your knee. Ligaments are like thick pieces of string that connect two separate bones and help to keep them in place. The specific purpose of the ACL is to prevent your lower leg from moving forward with respect to your thigh.
How do you injure it?
Because the ACL is meant to prevent your lower leg (tibia) from moving too far forward with respect to the thigh (femur), movements taking that motion to its limit can injure your ACL. Some of the common movements that injure the ACL are non-contact twisting and pivoting motions of the knee, especially in conjunction with a valgus, (or knocked knee), movement. ACL injuries are more common in female and adolescent athletes, often due to a higher amount of dynamic valgus forces. In other words, female and rapidly growing athletes are more likely to have their knees go into a valgus position during sports. This patient population is a key place for intervention because if we can find the athletes that are predisposed to these injuries due to their knocked knee motions, we can strengthen the corresponding musculature to prevent them from putting themselves in these precarious positions.
What is a partial tear?
A partial tear is just what it sounds like, the ligament is only partially torn. There are varying degrees to a partial tear. 75% of the ACL is still intact with a minimal tear, whereas a severe partial tear would have only 25% of the ACL still intact.
What is a full tear?
A full tear is again just what it sounds like, a tear all the way through the ACL, which leaves it in two distinct separate pieces. This is a more severe injury and will usually require a more intense treatment, which can often include surgery.
How do you treat ACL tears?
Treating ACL injuries depends on a number of variables including your age, severity of injury, sport, and level of function you plan to have in the future.
Lets look at age first. Generally you don’t often injure your ACL when you are younger (pre-pubescent), since at that young age your ACL is actually stronger than the bones its attached to. In these cases your bones usually break before your ACL tears, resulting in avulsion fractures. However, there are cases in which a younger athlete tears an ACL. If the tear is partial, treatment usually involves conservative measures such as rest, bracing, physical therapy, and functional knee rehabilitation. If the tear is full thickness it becomes a little more complicated. The problem is that full tears often require surgical repair but in young athletes that have open growth plates in their bones, surgery can damage growth plates and cause a stunt in bone growth. Because of this there are some people who would suggest conservative measures with physical therapy, bracing, and activity modifications to see if this can postpone surgery until growth plates are fully ossified. Some people find that with appropriate physical therapy they don’t even need surgery. The problem with this option is that if you continue to have pain and instability of the knee you have a higher chance of having arthritis later in life due to damage to knee cartilage and meniscus.
Partial or full thickness tears?
Ok, now lets look at partial versus full thickness treatment options. As we said before if there is some part of the ACL that is still functional conservative measures of physical therapy and activity modification can allow for strengthening of the stabilizing muscles around the knee and core to prevent further damage to the ACL. Appropriate bracing and activity modification (sports restrictions) can allow for some healing and regeneration of the existing ACL. However, if the ACL is completely torn it will often require surgical correction to fix. Even after surgery you will still need to have physical therapy, but if the ACL is completely torn there will not be regeneration of the ligament. In this case, the best one can hope for is strengthening compensatory structures to stabilize the knee the way the ACL once did.
The final aspect that plays a role in treatment choice is your future goals of activity. For example if you are trying to be a collegiate level pivoting and cutting athlete you will probably want to surgically repair your ACL. However, if you do not plan on putting your knee through that level of activity you may be fully functional with physical therapy and activity modification. The important point here is that if you can rehabilitate your knee while strengthening stabilizing musculature for the knee you may not need surgery. As long as you are able to perform all the movements that you desire and are not having pain or instability with these movements you may find that you don’t even need an ACL. There are a number of anecdotal examples of professional level athletes who tore their ACL’s at a young age (or never had one) and went on to high level sports without an ACL. The presumed theory is that the surrounding structures and kinematic chain have the capacity to compensate for the ACL’s role.
In the end the decision of how to treat an ACL injury usually comes down to personal issues related to what your future needs from your knee will be, but there is no one size fits all treatment for ACLs. Like the great Dr. Osler said, its not enough to understand the condition, or even the patient with the condition… but we must understand the patient in his or her world.
By Brett Dusenberry and Mo Mortazavi MD