The anterior cruciate ligament (ACL) is the most commonly injured ligament of the knee. In most cases, the ligament is injured by people participating in athletic activity.
As sports have become an increasingly important part of day-to-day life over the past few decades, the number of ACL injuries has steadily increased.
This injury has received a great deal of attention from orthopedic surgeons over the past 15 years, and very successful operations to reconstruct the torn ACL have been invented.
Where is the ACL, and what does it do?
Ligaments are tough bands of tissue that connect the ends of bones together. The ACL is located in the center of the knee joint where it runs from the backside of the femur (thighbone) to connect to the front of the tibia (shinbone).
The ACL runs through a special notch in the femur called the intercondylar notch and attaches to a special area of the tibia called the tibial spine.
The ACL is the main controller of how far forward the tibia moves under the femur. This is called anterior translation of the tibia. If the tibia moves too far, the ACL can rupture. The ACL is also the first ligament that becomes tight when the knee is straightened. If the knee is forced past this point, or hyperextended, the ACL can also be torn. The ACL also plays an important role in resisting rotation of the tibia.
Other parts of the knee may be injured when the knee is twisted violently, as in a clipping injury in football. It is not uncommon to also see a tear of the medial collateral ligament (MCL) on the inside edge of the knee, and the lateral meniscus, which is the U-shaped cushion between the outer half of the tibia and femur.
How do ACL injuries or tears occur?
The mechanism of injury for many ACL ruptures is a sudden deceleration (slowing down or stop), hyperextension, or pivoting in place. Sports-related injuries are the most common.
The types of sports that have been associated with ACL tears are numerous. Those sports requiring the foot to be planted and the body to change direction rapidly (such as basketball) carry a high incidence of injury. In this way, most ACL injuries are considered noncontact. However, contact-related injuries can result in ACL tears. For example, a blow to the outside of the knee when the foot is planted is the most likely contact-related injury.
An ACL injury usually occurs when the knee is forcefully twisted or hyperextended while the foot remains in contact with the ground. Many patients recall hearing a loud pop when the ligament is torn, and they feel the knee give way.
What does a torn ACL feel like?
The symptoms following a tear of the ACL can vary. Some patients report hearing and/or feeling a pop. Usually, the knee joint swells within a short time following the injury. The instability caused by the torn ligament leads to a feeling of insecurity and giving way of the knee, especially when trying to change direction. The knee may feel like it wants to slip backwards and there may be activity-related pain and/or swelling. Walking downhill is especially difficult and you may have trouble coming to a quick stop.
The pain and swelling from the initial injury will usually be gone after two to four weeks, but the knee may still feel unstable. The symptom of instability and the inability to trust the knee for support are what require treatment. long-term instability leads to early arthritis of the knee and a very high chance of meniscal tears.
How do doctors identify ACL injuries?
The history and physical examination are probably the most important ways to diagnose a ruptured or deficient ACL.
During the physical examination, special stress tests are performed on the knee. Three of the most commonly used tests are the Lachman test, the pivot-shift test, and the anterior drawer test. The doctor will place your knee and leg in various positions and then apply a load or force to the joint. Any excess motion or unexpected movement of the tibia relative to the femur may be a sign of ligament damage and insufficiency. These exam findings are very good at predicting an ACL injury.
The results of these tests will help your doctor determine how badly the ACL was injured. Other tests may be combined with tests of ACL integrity to determine whether other knee ligaments, joint capsule, or joint cartilage have also been injured.
X-rays of the knee are very important and are used to rule out a fracture. Ligaments and tendons do not show up on X-rays, but bleeding into the joint can result from a fracture of the knee joint, or when portions of the joint surface are chipped off.
Magnetic resonance imaging (MRI) is probably the most accurate test for diagnosing a torn ACL without actually looking into the knee.
In some cases, arthroscopy may be used to make the definitive diagnosis if there is a question about what is causing your knee problem.
How do doctors treat an ACL injury?
Initial treatment for an ACL injury focuses on decreasing pain and swelling in the knee. Rest and mild pain medications can help decrease these symptoms. Most patients are instructed to try and walk normally. The knee joint may need to be drained with a needle to remove any blood in the joint.
Most patients receive physical therapy after having an ACL injury. Therapists treat swelling and pain with the use of ice, electrical stimulation, and rest periods with your leg supported in elevation. Preoperative physical therapy is one of the most important factors in preventing injury to the ACL after it has been reconstructed.
Exercises are used to help you regain normal movement of joints and muscles. Range-of-motion exercises should be started right away with the goal of helping you swiftly regain full movement in your knee. This includes the use of a stationary bike, gentle stretching, and careful pressure applied to the knee by the therapist. Exercises are also given to improve the strength of the hamstring and quadriceps muscles. As your symptoms ease and strength improves, you will be guided in specialized exercises to improve knee stability.
An ACL brace may be suggested. An ACL brace is often recommended when the knee is unstable and surgery is not planned. As mentioned, a torn ACL that isn’t corrected often leads to early knee arthritis. In addition, there is no evidence that an ACL brace will prevent further damage to the knee if it is not reconstructed. The ACL brace may help keep the knee from giving way during moderate activity. However, it can give a false sense of security and won’t always protect the knee during sports that require heavy cutting, jumping, or pivoting.
The main goal of surgery is to keep the tibia from moving too far forward under the femur bone and to also control the increased rotation seen with an ACL deficient knee. Also, reconstructing your ACL with significantly decrease your risk of further damaging your articular cartilage and meniscus.
It is very important to obtain full knee motion prior to surgery. This practice also reduces the chances of scarring inside the joint and can speed recovery after surgery.
Most surgeons now favor reconstruction of the ACL using a piece of tendon or ligament to replace the torn ACL. This surgery is most often done with the aid of the arthroscope. Incisions are usually still required around the knee, but the surgery doesn’t require the surgeon to open the joint. The arthroscope is used to view the inside of the knee joint as the surgeon performs the work.
One type of graft used to replace the torn ACL is the patellar tendon. This tendon connects the kneecap (patella) to the tibia. It involves a strip from the center of the patellar ligament with bone attached to each end and uses this graft as a replacement for the torn ACL.
This graft is taken from the hamstring tendons that attach to the tibia just below the knee joint. The hamstring muscles run down the back of the thigh. Their tendons cross the knee joint and connect on each side of the tibia. The graft used in ACL reconstruction is taken from the semitendinosus and gracilis tendons along the inside portion of the knee.
What happens during the operation?
This surgery is performed using an arthroscope, a small fiber-optic TV camera that is used to see and operate inside the joint. Only small incisions are needed during arthroscopy for this procedure. The surgery doesn’t require to open the knee joint.
Before surgery you will be placed under either general anesthesia or a type of spinal anesthesia.
An incision is also made along the inside edge of the knee, just over where the hamstring tendons attach to the tibia. Working through this incision, we take out the semitendinosis and gracilis tendons.
The tendons are arranged into three or four strips, which increases the strength of the graft.
Next, we prepare the knee to place the graft. The remnants of the original ligament are removed and the anatomic insertions of the ACL on the tibia and femur are marked.
Once this is done, holes are drilled in the tibia and the femur to place the graft. These holes are placed so that the graft will run between the tibia and femur in the same direction as the original ACL.
The graft is then pulled into position through the drill holes. Screws or special suspensory devices are used to hold the graft inside the drill holes.
The portals and skin incisions are then stitched together, completing the surgery.
What can go wrong?
As with all major surgical procedures, complications can occur. This document doesn’t provide a complete list of the possible complications, but it does highlight some of the most common problems. Some of the most common complications following hamstring tendon graft reconstruction of the ACL are
Most surgical procedures require that some type of anesthesia be done before surgery. A very small number of patients have problems with anesthesia. These problems can be reactions to the drugs used, problems related to other medical complications, and problems due to the anesthesia. Be sure to discuss the risks and your concerns with your anesthesiologist.
Thrombophlebitis, sometimes called deep venous thrombosis (DVT), can occur after any operation, but is more likely to occur following surgery on the hip, pelvis, or knee. DVT occurs when blood clots form in the large veins of the leg. This may cause the leg to swell and become warm to the touch and painful. If the blood clots in the veins break apart, they can travel to the lung, where they lodge in the capillaries and cut off the blood supply to a portion of the lung. This is called a pulmonary embolism. (Pulmonary means lung, and embolism refers to a fragment of something traveling through the vascular system.)
Following surgery, it is possible that the surgical incision can become infected. This will require antibiotics and possibly another surgical procedure to drain the infection.
After surgery, the body attempts to develop a network of blood vessels in the new graft. This process, called revascularization, takes about 12 weeks. The graft is weakest during this time, which means it has a greater chance of stretching or rupturing. A stretched or torn graft can occur if you push yourself too hard during this period of recovery. When revascularization is complete, strength in the graft gradually builds. A second surgery may be needed to replace the graft if it is stretched or torn.
Problems can occur at the donor site (the area behind the leg where the hamstring graft was taken from the thigh). A potential drawback of taking out a piece of the hamstring tendon is a loss of hamstring muscle strength.
The main function of the hamstrings is to bend the knee (knee flexion). This motion may be slightly weaker in people who have had a hamstring tendon graft to reconstruct a torn ACL.
The body attempts to heal the donor site by forming scar tissue. This new tissue is not as strong as the original hamstring tendon. Because of this, there is a small chance of tearing the healing tendon, especially if the hamstrings are worked too hard in the early weeks of rehabilitation following surgery.
What should I expect after treatment?
Nonsurgical rehabilitation for a torn ACL will typically last six to eight weeks. Therapists apply treatments such as electrical stimulation and ice to reduce pain and swelling. Exercises to improve knee range of motion and strength are added gradually.
You can return to your sporting activities when your quadriceps and hamstring muscles are back to nearly their full strength and control, you are not having swelling that comes and goes, and you aren’t having problems with the knee giving way. It is important to understand that patients with ACL deficient knees that return to cutting athletics have a significant chance of causing further damage to their knee.
Patients will take part in formal physical therapy after ACL reconstruction. You will probably be involved in a progressive rehabilitation program for four to six months after surgery to ensure the best result from your ACL reconstruction. At first, expect to see the physical therapist two to three times a week. If your surgery and rehabilitation go as planned during the first six weeks, you may only need to do a home program and see your therapist every few weeks over the four to six month period. You will be required to complete a return to athletics evaluation to be sure you are able to safely return to your sport.