ACL tears occur from a significant injury to the knee. This is a relatively common athletic injury that can occur from several different mechanisms. There are a number for factors that go into the appropriate treatment for ACL tears, so it is important that you get an evaluation by an orthopedic doctor to determine the best treatment options for you.
The knee joint is made up of three bones: the thighbone (femur), shinbone (tibia) and kneecap (patella). The femur and tibia are held together by 4 major ligaments. The collateral ligaments are on the sides of the knee. The MCL or medial collateral ligament is on the inner side and the LCL or lateral collateral ligament is on the outer side. The two cruciate ligaments are strong structures that cross over each other inside the middle of the knee joint. The ACL or anterior cruciate ligament prevents the tibia from shifting forward whereas the PCL or posterior cruciate ligament prevents the tibia from shifting back. The combination of all four of these ligaments and other secondary stabilizers allow the knee to withstand various stresses and maintain normal motion and function. Damage to any of these ligaments can disrupt the normal function of the knee. Whereas injury to the other ligaments can usually be treated non-operatively, in many cases, a sprain or tear of the ACL may require surgery.
Ligaments tears are classified as Grade I-III sprains. Grade I sprains are slight stretch injuries of the ligaments where the fibers stay intact but are slightly elongated. These injuries do not cause the knee to be unstable and usually resolve with a period of rest and brief rehab. Grade II sprains are partial tear where there has been disruption of some of the fibers, or enough of a stretch where the ligament becomes loose. Grade III sprains are complete tears of the ligaments where all the fibers are disrupted and the knee becomes unstable. Partial tears of the ACL are uncommon. Usually significant injuries to the knee cause either complete tears or high-grade partial tears that cause the knee to become unstable.
Many ACL tears occur in athletes. There are several different mechanisms that can lead to tears and include both noncontact and contact injuries. Non-contact mechanism include cutting or pivoting with the foot planted, a sudden stop or deceleration and landing awkwardly from a jump. Contact injuries in collision sports included getting hit from the side like a clip in football or from the front causing the knee to bend backwards or hyperextend. Twisting or rotational forces from skiing injuries are also common causes of ACL tears. Injuries can also occur from non-athletic causes such as jumping down from a height or slipping on snow or ice. There are factors that make some females more prone to ACL tears, such as differences in pelvic anatomy and leg alignment, structure of the end of the femur, differences in strength and conditioning, and effects of estrogen on ligaments. Training programs have been developed specifically for female athletes to try to decrease the risk factors that lead to ACL tears.
Most of the time, it takes a significant injury to tear the ACL as it is a strong ligament. Commonly a “pop” or “crack “ is heard and/or felt by the athlete and sometime by bystanders as well. There is often significant swelling that results quickly inside the knee called an effusion. This is blood from the torn ligament at fills up the joint space in the knee. This leads to pain and stiffness and difficulty bending and straightening the knee. Sometimes it is too painful to put any weight on the knee initially. There can be feeling of “giving way” when trying to walk afterwards as the knee may be unstable. Less commonly there is no significant pop and the swelling is less obvious. In these cases people don’t always get an evaluation right away and it’s only after the knee continues to feel unstable that they seek medical attention.
It is important to have your knee evaluated by an orthopedic doctor after any significant injury to determine the extent of the damage and what treatment is required. The doctor will want to know about how the injury occurred and any previous problems with the knee along with your medical history. After that, your knee will be examined including looking for swelling, palpating for tender areas, checking for range of motion and testing the ligaments. When there is a lot of swelling and pain, the exam is usually limited and it can be difficulty to determine the extent of the injury.
In addition to examining the knee, your doctor will order tests for further evaluation.
Although x-rays do not show the ligaments or other soft tissues, they show fractures, which can occur with ACL tears and also determine if there are any underlying abnormalities in the joint such as osteoarthritis. Xrays are usually the first step in imaging the knee.
Magnetic resonance imaging (MRI)
This test shows both the bones and all the soft tissues, including the meniscus, cartilage and ligaments. A mri is important in visualizing the ACL in addition to other structures that might be injured such as meniscal tears or cartilage injuries (chondral defects). Even if the exam determines the ACL is torn, a mri will usually be obtained to confirm this and look for other damage.
Not everyone that tears their ACL will require surgery. Your orthopedic doctor considers multiple factors before recommending treatment and also involves you in the decision process. Things like your age and activity level, type of work, previous problems with the knee and how unstable your knee feels are all part of the decision. Sometimes the decision is for nonoperative treatment that may involve using crutches and a brace initially. Physical therapy is an important part of regaining range of motion and strength and restoring function to the knee.
Getting the knee ready If your doctor recommends surgery for your knee, the timing of surgery depends on how long it takes the swelling and stiffness to resolve. It is important that the knee has some time to recover from the initial injury prior to surgery to avoid the potential of getting very stiff afterwards. You likely will be instructed on “prehab” or preoperative rehab for the knee to do either on your own or with help from a physical therapist.
The torn ACL cannot be “repaired” or sewed together. The torn ligament has to be removed and replaced with a graft. There are several choices for a graft including “autograft” which is tissue from your own body and includes hamstrings, patellar tendon or quadriceps tendon. The other option is an “allograft” which is a tendon from a cadaver. There are pros and cons to each of the graft types, which your surgeon will discuss with you to help make the best choice for you.
The current technique for ACL reconstruction is “arthroscopic assisted” meaning that a small camera and instruments are introduced through very small incisions in the knee. The first step is to examine the knee to determine what other damage is done and to address cartilage or meniscus injuries. A slightly larger incision is used to obtain the graft and pass it through “tunnels” in the bone to create the new ACL. A critical part of the surgery is placing the bone tunnels in the correct positions so that the new graft matches the anatomy of the original ACL to recreate the normal motion and function of the knee. There are many different implants or devices used to secure the graft to the bone.
The postoperative recovery and rehab are as important as the surgery itself in restoring the function of the knee. You will be on crutches for several weeks afterwards and likely in a brace to support the knee while it is regaining motion and strength. Physical therapy is an important part of the recovery process. After the first month you likely will be able to do many of your normal daily activities, but it may be at least 6 months before you are able to return to full activities and sports. Your surgeon may recommend that you wear a sports brace when you initially return to high risk activities.