The Anterior Cruciate Ligament (ACL) is the most commonly injured ligament of the knee and accounts for over 60% of all knee injuries. The major cause of ACL injury is sports where the foot is planted so the body can change directions. An ACL injury occurs when the knee is forcefully twisted or hyperextended. Many patients hear a loud pop when the ligament tears, and feel the knee give away. More ACL injuries are now seen in women, as women’s sports have become more competitive.
Remember from knee anatomy that the ACL controls how far forward the tibia (shinbone) moves in relation to the femur (thighbone). If the tibia is forced to move too far forward, as when hit in the knee from behind, the ACL can tear. This tearing of the ACL results in the loud pop and the feeling of instability in the knee. When the knee is twisted violently, such as in a clipping injury in football, the ACL may not be the only ligament injured. It is not uncommon to see both the Medial Collateral Ligament and the ACL injured.
Knee Anatomy
The knee is the largest joint in the body. The kneecap protects the knee and gives the leg it’s power. The muscles, tendons and ligaments give your knee stability. When the ACL is torn the knee is no longer stable. Understanding the anatomy of your knee can help you with rehab, healing of your ACL and surgery if you need it.
Symptoms of ACL Tear
The symptoms following a tear of the ACL vary. Usually there’s swelling of the knee a short time after the injury due to bleeding into the knee joint from torn blood vessels in the ligament. The instability caused by the torn ligament causes the knee giving way, especially when changing directions and you will have trouble walking.
The pain and swelling after the initial injury will usually go away after 2 to 4 weeks, but the instability remains. The symptom of instability, and the inability to trust the knee to support you is what requires treatment. Also important in the decisions about treatment is the growing realization that long term instability leads to early arthritis in the knee.
Diagnosis of ACL Tear
A history—your story as to what happened to your knee, and how long the problem has been going on—and physical exam are important in diagnosing a ruptured or strained ACL. In sudden injuries, swelling in the knee is a helpful indicator. A rule most orthopedic surgeons use is that any intense swelling that occurs within 2 hours of a knee injury usually means blood in the joint, called hemarthrosis. If the swelling occurs the day after the injury, the fluid is most likely an inflammatory response. Draining as much fluid as possible using needle aspiration from the swollen joint relieves swelling and provides diagnostic information. If blood is found in the fluid drained from the knee, there’s a very good chance the ACL is torn.
X-Rays of the knee may be taken to rule out bone fracture. Ligaments and tendons—soft tissues—don’t show up on regular xrays, but bleeding into the joint also occurs with a fracture through the knee joint, or when portions of the surfaces of the bones in the joint are “chipped off”.
The most accurate test, without actually looking into the knee with arthroscopy, is the MRI Scan (Magnetic Resonance Imaging). The MRI is magnetic waves rather than xrays, that shows soft tissues like ligaments, muscles, and tendons. The MRI makes “slice” images through the injured area and shows the extent of the injury very clearly. The MRI is painless and does not require needles or special dyes.
In some cases, arthroscopy is used to make the definitive diagnosis if there is some question about the cause of your knee problem. Arthroscopy is an operation where a small fiberoptic camera is placed into the knee joint, allowing the surgeon to actually see the structures inside the knee joint. Most ACL tears are diagnosed without surgery. However, arthroscopy is also used to treat knee problems after a diagnosis.
Treatment of ACL Tear
The initial treatment for an ACL injury includes ice packs, crutches, and rest until the swelling goes down. (See R.I.C.E. Therapy) Blood and fluid may be removed from the knee joint using needle aspiration. Anti-inflammatory medicine and physical therapy are often tried to avoid having surgery.
Once, the pain and swelling begins to resolve, physical therapy can be started to get back as much of the normal range of motion as possible. One problem a torn ACL causes is the small nerve endings in the ligament are also torn. These “proprioceptive” nerves give the brain information about where the body is in 3D space. For example, proprioceptive nerves make it possible for you close your eyes and still touch your nose. Joints rely on proprioceptive nerves to fine tune muscle actions that allow the joint to function properly. A good physical therapy program will help retrain proprioceptive nerves as they repair themselves as well as strengthen other muscles that will take over stabilizing the knee joint now that the ACL can’t.
An ACL brace may be used to help replace stability in the knee. ACL braces are fairly effective at preventing the knee from “giving way” during strenuous activity. These braces are usually fitted by a therapist or doctor. They are NOT the same as braces you buy off the shelf at the pharmacy. Most orthopedists recommend wearing an ACL brace for at least a year after ACL reconstruction.
If your instability is not controlled using a brace and doing rehab exercises and you are not able to do the activities you want to do, then surgery may be needed. Most surgeons reconstruct (fix the structure so it can function as it should) the ACL using a harvested piece of tendon or ligament to replace the torn ACL. Today, this surgery is most often done using the arthroscope. Small incisions are required around the knee, but the joint itself is not opened. The arthroscope is used to perform the repair inside of the knee joint. Expect at least an overnight stay in the hospital, although more and more surgeries are done as an outpatient and you go home the same day.