Anterior Cruciate Ligament Injuries
Introduction
The Anterior Cruciate Ligament (ACL) is the most commonly injured ligament of the knee, most commonly during sports. A ligament is a tough, non-stretchable rope-like tissue that connects bone to bone. The injury occurs at a higher percentage in women than in men, although no one knows why. Because of the increase in the number of ACL injuries, a great deal of attention has been given to the treatment of the ACL deficient knee.
Anatomy
The ACL runs inside the knee from the tibia (shinbone) to the femur (thighbone). The ACL’s main role is to keep the tibia from moving too far forward in relation to the femur. If the tibia does move too far, the ACL can rupture (tear or stretch). The ACL is also the first ligament that becomes tight when the knee is straight. If the knee is forced past its normal amount of straight (hyperextended), the ACL can be torn. When the ACL is injured it is not uncommon (80%) to have an injury to another structure in the knee also. This could be another ligament, bone, articular cartilage, and/or a meniscus. Also, the ligament has blood vessels in it and when the ligament tears, so due the blood vessels causing swelling in the knee (an effusion).
Symptoms
The symptoms following an injury to the ACL vary greatly from one person to another. Most commonly, there is swelling of the knee within a short time following the injury. This is due to bleeding into the knee joint from torn blood vessels in the ACL. There is pain, which can be caused from the tearing of the ligament, the swelling of the knee, and/or an injury to another structure in the knee. And, there is instability, which may be caused by any one or combination of the following: swelling, pain, lose of strength, and/or lose of the ACL and/or another structure.
The pain and swelling will subside with time. The instability may remain. The symptoms of instability usually are the inability for the patient to trust the knee for support and the feeling that the knee is moving in an abnormal way. (“It feels funny.”) It is the instability that leads patients to surgery.
Through the years, the orthopedic surgery community has come to realize that long term instability leads to early arthritis of the knee. (This may take 20-30 years.) There is no way to know when arthritis may have occurred in a knee even without an ACL injury. Studies have actually shown that patients who have injured their ACL are still at higher risk of developing arthritis than patients that have never injured their ACL.
Diagnosis
The history (H) and physical examination (PE) are probably the most important tools. Some important questions in the history will include;
What activity were you participating in at the time of the injury?
What did you feel or hear at the time of the injury?
When did the knee swell after the injury?
Were and are you able to put weight on the knee?
Does the knee feel unstable?
How much pain did and do you have?
The PE will test for areas of pain, evidence of instability, and check the knee for other possible injured structures.
X-rays of the knee may be taken to rule out a fracture (a broken bone) and any arthritis that may already be present. A Magnetic Resonance Imaging (MRI) study may be ordered also.
Treatment
Initial treatment for a recent ACL injury is focused of reducing the swelling and pain. Rest, ice, crutches, and elevation (RICE) best accomplish this. Rest is done by reducing your activities. Ice helps to minimize the swelling and inflammation. Crutches help to take weight off the injured knee. Elevation helps to reduce or minimize the swelling. In addition to RICE, Tylenol or an over-the-counter anti-inflammatory such as ibuprofen or Aleve will help reduce the pain and swelling. A brace or knee wrap may also help make the knee feel more comfortable.
Once the initial pain and swelling have begun to improve, therapy to regain normal range of motion (ROM) is begun. As ROM improves, you will be started on an exercise program. The exercise program is essential to your recovery. First, the exercise program will focus on strengthening and proprioceptive training. The muscles around the knee get weak very fast after an injury, but will take quite a lot of time to return to normal (many months). Proprioception is the body’s ability to tell where it is in 3-dimensional (3D) space. It is lost in the knee by a combination of nerve endings in the ACL being torn and the nerve endings around the knee being stretched by swelling. Second, as your strength and proprioception improve, the exercise program will start to focus on functional activities and return to sports.
To help the stability of the knee, a brace may be ordered. There are two levels of braces. First, the neoprene brace. It is a simple wrap and helps with proprioception. Second, is an ACL brace either custom or off-the-shelf. They are not the kind of braces sold in a drugstore. These braces will not replace your ACL, but they can help control some of the abnormal motion that can occur with an ACL injury.
If the symptoms of instability are not controlled by the exercises and bracing or if you are a young very active individual, surgery may be suggested. The surgery is a replacement of the torn ACL. In the US, more than 50,000 ACL ligament reconstructions are done each year. The arthroscope is used to perform the work needed on the inside of the knee.
The replacement material is either a tendon graft or a bone-tendon-bone graft. The surgery is successful 85%-92%.
The graft material can either come from your own knee (an autograft) or it can come from someone else (an allograft). The advantage of the autograft is you know where it came from. The disadvantage is more pain and possible problems from the disturbing or removal of normal tissue. The advantage of allograft is less pain and no concern of creating other problems in the knee. The disadvantage is the possible transmission of disease (this is very small, < 1 in 4,000,000).
After surgery, a rehabilitation program will be started. A physical therapist will help guide you through your recovery. How fast you progress though your recovery will depend on a number of factors, but most significant of those will be how hard you can and do push yourself. The minimum recovery time will be 3 months, the average recovery time is 6 months, but recovery can take as long as 12 months. A brace may still be needed for some sports.
We hope this brief information is helpful in improving your understanding of ACL injuries and their treatment. For more information or to answer any additional questions, please contact our office at 262-656-3150.
Written by James A. Shapiro, MD