The anterior cruciate ligament (ACL) is one of four major ligaments that stabilizes the knee joint. A ligament is a tough band of fibrous tissue, similar to a rope, which connects the bones together at a joint. There are two ligaments on the sides of the knee (collateral ligaments) that give stability to sideways motions: the medial collateral ligament (MCL) on the inner side and the lateral collateral ligament (LCL) on the outer side of the knee. Two ligaments cross each other (therefore, called cruciate) in the center of the knee joint: The crossed ligament toward the front (anterior) is the ACL and the one toward the back of the knee (posterior) is the posterior cruciate ligament (PCL). The ACL prevents the lower bone (tibia) from sliding forward oo much and stabilizes the knee to allow cutting, twisting and jumping sports. The PCL stops the tibia from moving backwards.
The most common mechanism that tears the ACL is the combination of a sudden stopping motion on the leg while quickly twisting on the knee. This can happen in a sport such as basketball, for example, when a player lands on the leg when coming down from a rebound or is running down the court and makes an abrupt stop to pivot. In football, soccer, or lacrosse, the cleats on the shoes do not allow the foot to slip when excess force is applied. In skiing, the ACL is commonly injured when the skier sits back while falling. The modem ski boot is stiff, high, and is tilted forward. The boot thus holds the tibia forward and the weight of the body quickly shifts backwards too much force is suddenly applied to the knee. The excess force causes the ACL to pop. A contact injury, such as when the player is clipped in football, forces the knee into an abnormal position. This may tear the ACL, MCL and other structures.
When the ACL tears, the person feels the knee go out of joint and often hears or feels a “pop”. If he or she tries to stand on the leg, the knee may feel unstable and give out. The knee usually swells a great deal immediately (within two hours
The meniscus is a crescent shaped cartilage that acts as a shock absorber between the femur and tibia. Each knee has two menisci: medial (inner) and lateral (outer). The menisci are attached to the tibia. When the tibia suddenly moves forward and the ACL tears, the meniscus can become compressed between the femur and tibia tearing the meniscus. The abnormal motion of the joint can also bruise the bones. There is a second type of cartilage in the knee joint called articular cartilage. This is a smooth, white glistening surface that covers the ends of the bones. The articular cartilage provides lubrication and as a result, there is very little friction when the joint moves. This joint cartilage can get damaged when the ACL tears and the joint is compressed in an abnormal way. If this articular cartilage is injured, the joint no longer moves smoothly. Stiffness, pain, swelling and grinding can occur. Eventually, arthritis can develop. The MCL and other ligaments in the joint can also be disrupted when the ACL tears. This is more common if an external blow to the knee caused the injury (such as if the knee was clipped while playing football) or when skiing.
The initial treatment of the injured joint is to apply ice and gentle compression to control swelling. A knee splint and crutches are used. The knee should be evaluated by a doctor to see which ligaments are torn and to be sure other structures such as tendons, arteries, nerves, etc. have not been injured. X-rays are taken to rule out a fracture. Sometimes an MRI is needed, but usually the diagnosis can be made by physical examination.
If no structure other than the ACL is injured, the knee usually regains it range of motion and is painless after six or eight weeks. The knee will typically feel completely normal. However, it can be a “trick knee”. If a knee does not have an ACL it can give way or be unstable when the person pivots or changes direction. The athlete can usually run straight ahead without a problem but when he or she makes a quick turning motion such as when pivoting, the knee tends to give way and collapse. This abnormal motion can damage the menisci or articular cartilage and cause further knee problems. If a person does not do sports and is relatively inactive, the knee can feel quite normal even if the ACL is torn. Thus, many patients especially over the age of thirty may not need to have the ACL reconstructed, especially if they do not participate in sports that require quick changes in direction. In young, athletic patients, however, the knee will tend to reinjure frequently and give way during activities in which the person quickly changes direction. Therefore, it is usually best to reconstruct the torn ACL.
It is best to wait for the pain and swelling to subside and to allow associated injuries to heal before performing surgery for the ACL. If surgery is done soon after injury, rehabilitation is difficult; the knee may get stiff and have permanent loss of motion. The athlete will usually get back to sports much more quickly if the knee is allowed to recover from initial injury and to regain its full painless range of motion (usually at least six weeks) before performing surgery.
If surgery is delayed until the joint has full painless range of motion, then an accelerated rehabilitation program can be used after surgery. With accelerated rehabilitation, continuous passive range of motion (CPM) is used for the first week following surgery. The knee heals much more quickly and better joint function results.
The best treatment following acute ACL injury is to usually protect the joint and apply ice and use crutches for several weeks. As the swelling and pain subside, and the patient can put weight on the leg; then the immobilizer and crutches are discontinued. The emphasis is on regaining knee motion. Resistive exercises to build up strength should not be done during this time to prevent damaging the knee cap and causing chondromalacia patella.
If the knee also has an injured medial collateral ligament (MCL), it is best to allow the MCL to heal completely (usually six to eight weeks) before reconstructing the ACL. Then an arthroscopic procedure can be performed to reconstruct the ACL. The torn MCL usually does not need to be repaired surgically.
There may be instances when immediate surgery is indicated following injury. Examples are knee dislocation when multiple ligaments are torn. Tears of the outer knee ligaments (lateral collateral ligament) often do require surgical repair. Individual decisions need to be made on whether or not to reconstruct the ACL soon after injury in these instances where immediate surgery may be required.
No — some knees function almost normally despite having a torn ACL. Good knee function is more common in patients who are over thirty years old who are relatively inactive in sports. Patients who are less than twenty-five years old, regardless of activity level, tend to have problems with instability and frequent episodes of giving way. Therefore, surgical reconstruction of a torn ACL is usually recommended for patients who are less than age twenty-five years. However, surgery should be delayed until after the acute injury has subsided (usually at least six weeks following injury).
Some patients can function well even if the ACL is torn. However, it may be necessary to modify activities and avoid high-risk sports (such as basketball, soccer and football). The key to prevent the knee that has a torn ACL from giving out is to avoid quick pivoting motions. Wearing a knee brace can help reinjury. The main effect of a knee brace is to be a constant reminder to be careful.
However, a brace will not completely stabilize a knee that has a torn ACL. Exercises that restore the muscle strength, power, coordination, and endurance will also improve knee function and help stabilize the knee. However, a fully rehabilitated knee that has a torn ACL can still give way if a quick change in direction is unexpected.
Many knees in which the ACL is torn have additional injuries such as torn memsci or fragments of articular cartilage that are knocked loose (creating a loose body and a defect in the articular cartilage). These associated injuries can cause symptoms of pain, swelling, and locking (in addition to symptoms of giving way due to a torn ACL). Arthroscopic surgery to remove torn memsci or to remove loose bodies can improve pain and eliminate locking. However, it would usually not eliminate symptoms of instability, i.e. giving way. Thus, correcting can improve the knee symptoms but not restore stability to the knee.
Surgical reconstruction of a torn ACL involves replacing the torn ACL with a tendon (called a graft) from another part of the knee and putting it into a position to take the place of the torn ACL. The most commonly used graft is taken from the middle third of the patellar tendon (the tendon connecting the knee cap to the tibial bone). Hamstring tendon grafts taken from the inner thigh to the back of the knee are also used. Occasionally, tendon grafts are taken from cadavers (referred to as allograft). For most of these procedures, the operation is done arthroscopically instead of making big incisions. The knee is examined arthroscopically and associated injuries such as torn menisci, loose bodies, etc are treated. If the middle third of the patellar tendon is used, a small incision is made on the inner side of the leg just below the knee to take the graft (this results in numbness on the front of the knee). While viewing the inside of the joint through the arthroscope, guides are used to create bone tunnels in the exact positions to allow proper placement of the graft. The graft is then pulled into the bony tunnels. Absorbable screws are placed in the tunnels to wedge the bone graft against the wall of the tunnel to give immediate stability and allow healing of the bone graft. Thus, the bone plug on one end of the graft is secured to the tunnel in the femur and the bone plug on the other end of the graft is secured to the tunnel in the tibia. The piece of patellar tendon graft between the two bone plugs becomes the new ACL.
Postoperatively, an accelerated rehabilitation program allows the quickest return of function. This necessitates using a continuous passive motion (CPM) machine for approximately 10 hours a day for the first week following surgery. The patient can get up whenever he or she wishes for short periods of time using crutches and a knee immobilizer. The CPM can be rented and it is a small device that sits on the bed and very slowly moves the knee continuously. The knee actually has less pain and regains its function much more quickly if CPM is used continuously. If the knee is taken out of the CPM for periods of time, it becomes stiff and more painful. Therefore, it is best to devote the first week following surgery to continuous use of the CPM at home. One week after surgery, the sutures are removed and the patient can walk bearing full weight on the leg. A knee immobilizer and/or crutches are used for the first week or two until the leg regains enough strength to allow unaided walking.
Within two or three weeks after surgery, the patient is usually walking on level surfaces without a brace or crutches. At about five or six weeks, he or she can usually go up and down stairs without support. For the next several months, exercises are done to regain motion in the knee. When the knee has full range of motion (usually at six to eight weeks), muscle-strengthening exercises are done. At six months, the patient is usually running and at nine months, participating in sports.
Most people can get back to desk work or sedentary activity one or two weeks after surgery. If the right knee has been operated, it may be four to six weeks before the knee is strong enough to hit the brakes to drive safely. For heavy work, it may take 3 to six months before the leg is strong enough to allow working.
Sedentary/Desk - 1 to 2 weeks
General Office - 2 to 3 weeks
Light - 6 to 8 weeks
Medium - 3 months
Heavy - 4 to 5 months
Normal walking/stairs - 1 to 2 months
Light individual sports - 3 to 4 months
Running and jumping - 6 months
Contact/high performance - 9 months
• Repetitive injuries may cause further permanent damage and eventually lead to arthritis.
• Inability to participate in sports that require pivoting.
• Some people manage well without surgery.
Permanent numbness in the front of the knee near the incision - 100%
Other nerve injury - 0.5%
Patello-femoral pain (kneecap) - 5%
Flexion contracture (stiffness/reduced motion of the knee) - 10%
Reinjury (knee becomes unstable again) - 5% to 10%
Swelling - 10%
Superficial infection - 1%
Deep infection - 0.5%
Deep vein thrombosis (blood clots) - 0.5%
Delay in regaining motion - 5%
Vascular (damage to blood vessels) - 0.01%
Death - 0.0%
• Return to sports with a stable knee
Here are guidelines that will help you in preparing for surgery to reconstruct your torn anterior cruciate ligament.
Your doctor will see you in the office. He will do a preoperative history and physical examination and complete the necessary paperwork. He will write preoperative hospital orders and schedule an appointment with the pre-operative test center. You will have an opportunity to speak with anesthesia and physical therapy. It is recommended that you utilize a stationary cycle to maintain your knee range of motion and improve the overall function of the knee prior to surgery.
Wash the knee several times a day to get it as clean as you can. This decreases the risk of infection. Be careful not to get any scratches, cuts, sunburn, poison ivy, etc. The skin has to be in very good shape to prevent problems. You do not need to shave.
Please be in touch with your doctor’s office to confirm the exact time that you should report to the hospital for surgery. You can have nothing to eat or drink after midnight on the day before surgery. It is very important to have a completely empty stomach prior to surgery for anesthesia safety reasons. If you have to take medication, you can do so with a sip of water early in the morning prior to surgery (but later tell the anesthesiologist you have done so).
Surgery is performed in the Wang building at MGH and at the Orthopedic Ambulatory Surgery Center at Mass General West in Waltham.
• For surgery at MGH main campus in Boston: Report directly to the Surgical Day Care Unit on the third floor of the Wang Ambulatory Care Building at Massachusetts General Hospital two hours prior to surgery.
• For surgery at the surgery center at MGH West in Waltham: Report directly to the Ambulatory Surgery Center on the second floor of Mass General West.
The operation to replace the torn anterior cruciate ligament will be done arthroscopically. A small incision will be made on the inner side of the knee to take the graft from the middle of the patellar tendon together with a small piece of bone from the bottom of the kneecap to the upper part of the leg bone (mid-third patellar tendon graft, bone-tendon-bone). The incision leaves a small area of numbness on the outer side of the upper leg. Most of this numbness clears but it takes a year or two and is not usually bothersome. In certain circumstances, the graft is a hamstring tendon or a donor graft from a cadaver (allograft).
Prior to surgery, a continuous passive motion (CPM) machine will be delivered to your home. This is a small apparatus that sits on the bed onto which your knee rests. The CPM very slowly bends and straightens out the knee. Once you get used to the machine, it actually hurts much less and your rehabilitation is much quicker if you use a CPM. If you do not use a CPM and the knee is put into a splint, it gets stiff and is more painful and your recovery is delayed (although the end result would still be about the same). You will be able to adjust the CPM with a hand-controlled unit. The most important part of using the CPM in your postoperative rehabilitation is to get the knee out straight (extension). The machine is set to pause for five seconds in extension to allow you to stretch the knee fully. How much flexion (bending) you gain is not as important; how quickly the machine moves also is not important. For the first several days, just allow the machine to bend the knee as much as is comfortable and gradually work on gaining more flexion as the week progresses.
• After four days, try to have the CPM at least 90 degrees of flexion.
• The most important aspect is to get the knee out straight.
• You will be able to adjust the speed: at night have the machine move as slowly as possible and you will be able to sleep better.
• During the day, you can speed up the machine and also gain more flexion.
You will be given a prescription for pain medication to take home with you. In addition to this medication, you should take one aspirin a day to help prevent blood clots (phlebitis) for 10 days. The pain medication has a tendency to make you constipated. The dressing should be changed the day following surgery and can be removed at two days. The wound is sealed with steri-strips (small pieces of tape on the skin). You can shower on the second day following surgery, but be careful standing in the shower so that you do not fall. It is better to have a small stool to be able to sit on. However, you can get the leg wet and wash it. Do not submerge the knee under water in a bath, hot tub or swimming pool. To help control swelling in the lower leg, you should wear the white stockings after surgery until your first post-operative visit. If you develop calf pain or excessive swelling in the leg, call your doctor. The cryocuff is a blue wrap that is put on the knee to keep it cold. You can use this as often as you want to cool down the knee to reduce swelling and pain. Check your skin every time that you remove the wrap to make sure that it is intact. For one week following surgery, it is best to be in the CPM at least 10 hours a day. You can get up whenever you want to but it is best to get up more frequently for short periods of time. If you are out of the CPM for a long period of time, the knee tends to become stiff and painful. This is not really a problem, but it takes a while to get the knee loosened up again and moving in the CPM. Thus, getting up more frequently for short periods of time is better than being out for a long period of time.
