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The Anterior Cruciate Ligament ACL

The Anterior Cruciate Ligament ACL

A patients guide to Anterior Cruciate Ligament Injuries. Anatomy, causes, symptoms, diagnosis, treatments, surgery and rehabilitation.

The anterior cruciate ligament is one of the most commonly injured ligaments in the knee joint. In most cases, an injured or torn ACL is result of trauma experienced when participating in sporting activity.

Over the past few decades, sports have increasingly become an important part of education and day-to-day life. This has led to a steady rise in the number of ACL injuries.

Injuries to the ligaments or cartilage in the knee can be extremely painful and over the last 15 years orthopedic surgeons have paid a great deal of attention to ACL injuries. There are now very successful operations that have been developed to help reconstruct a torn ACL.


The Anterior Cruciate Ligament of the Knee

The anterior (meaning ‘front’) cruciate ligament is responsible for controlling how far forward the tibia (shinbone) moves under the femur (thighbone). This front to back motion of the knee joint is known as the anterior translation of the tibia.

The ACL runs through a notch in the middle of the femur called the intercondylar notch, it then attaches to the tibia in an area called the tibial spine.

If the tibia moves to far, there is a good chance the ACL can rupture. The ACL is the first ligament to tighten when the knee is straightened, if the knee is forced past this point, or hyperextended, the ACL can also be torn.

Due to the nature of how most knee injuries occur, it is common that damage to ACL may be coupled with other knee injuries such as a tear of the medial collateral ligament.


Common Cause Of Anterior Cruciate Ligament Injuries

Most ACL injuries occur from a sudden deceleration (slowing or stopping), hyperextension, or pivoting in place, usually as a result of participating in sporting activities.

The types of sports associated with this injury are numerous. They include any sport which requires the foot to be planted on the ground while the body rapidly changes direction.

In this way, most ACL injuries are considered noncontact; however, contact-related injuries can result in ACL tears.

For example, a blow to the knee when the foot is firmly planted on the ground is likely to damage the ACL.

Football carries a high risk of damaging the ACL, combining the activity of planting and pivoting the body with the threat of bodily contact.

Downhill skiing is another frequent source of injury, especially since ski-boots come high up the calf. This moves the impact of a fall to from the ankle to the knee.

The number of women suffering ACL injuries has dramatically increased. Studies have shown that female athletes are two to four times more likely to suffer ACL tears than male athletes in the same sports.

Research has shown several factors that may explain why women are at a higher risk of ACL tears.

Women athletes appear less able to tighten their thigh muscles. This means a women’s knee does not hold as steady as a man’s.

Tests also show that women’s quadriceps and hamstring muscles work differently than men’s. Women’s quadriceps muscles (on the front of the thigh) must work extra hard during activities. This pulls the tibia forward, placing the ACL at a higher risk of tearing.

Meanwhile, women’s hamstring muscles (on the back of the thigh) respond more slowly than in men. The hamstring muscles help stop the tibia from sliding too far forward. Women’s slower hamstring response may allow the tibia to slip forward, straining the ACL.

Other studies suggest that women’s ACL’s may be weakened by the effects of the female hormone estrogen.


Symptoms following a tear of the ACL can vary between cases, however most people who experience sudden trauma to the knee report hearing and feeling a pop as the ACL tears.

The knee will suddenly swell due to the bleeding from the torn blood vessels in the damaged ligament. This causes significant pain in the knee.

After one or two weeks the pain and swelling from the initial injury will slowly reduce. This usually disappears after two to four weeks however, the knee may still feel very unstable.

You will find walking downhill or on ice especially difficult. The knee may feel like it wants to slip backwards and you may have trouble coming to quick stop.

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 on the knee.

The continuous symptoms of instability and the inability to trust the knee for support are what require treatment.

Also important in the decision about treatment is the growing realization by orthopedic surgeons that long-term instability leads to early arthritis of the knee.


There are several techniques used in the diagnosis of a ruptured or deficient ACL. What you were doing at the time of your injury and physical examination are perhaps the most important ways to diagnose the injury.

Swelling of the knee is a good indicator, especially if it occurs suddenly as the result of trauma to the knee. Orthopedic surgeons generally suggest that any tense swelling that occurs within two hours of a knee injury represents a hemarthrosis or swelling in the joint. Swelling which occurs the next day is usually from the inflammatory response.

A technique known as aspirating – Placing a needle in the swollen joint and draining as much fluid as possible – gives sufficient relief from the swelling and provides useful information for your surgeon.

When the fluids drained from the knee contain blood, there is about a 70 percent chance it represents a torn ACL. The fluid can also show if the cartilage on the surface of the knee joint was injured.

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.

Another way to check for anterior tibial translation is with the KT-1000 and KT-2000 arthrometers. These devices measure the anterior tibial translation by applying increasing force against the tibia.

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.

Your doctor may order X-rays of the knee 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 surgery. Although they are costly, MRI scans produce detailed images of the anatomy and any injuries.

In some cases, the minimal invasive surgery known as arthroscopy may be used to make the definitive diagnosis, especially if there is a question about what is causing your knee problem.

Arthroscopy is an operation that involves inserting a small fiber-optic TV camera into the knee joint, allowing the orthopedic surgeon to look at the structures inside the joint directly. The vast majority of ACL tears are diagnosed without resorting to this type of surgery, though arthroscopy is sometimes used to repair a torn ACL.

Nonsurgical Treatment

Initial treatment for an ACL injury focuses on decreasing pain and swelling in the knee.

Rest medications and mild pain killers like Tylenol, can help decrease these symptoms. You may also need to use crutches until you can walk without a limp

The knee joint may need to be drained with a needle (mentioned earlier) 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.

Exercises are used to help you regain normal movement of joints and muscles. 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.

An ACL brace may be suggested. This type of brace is usually custom-made and not the type you can buy at the drugstore. It is designed to improve knee stability when the ACL doesn’t function properly

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.


Surgery is usually suggested if symptoms of instability are not controlled by a rehabilitation program and brace.

The main goal of surgery is to keep the tibia from moving too far forward under the femur bone and to get the knee functioning normally again.

Prior to surgery you may be asked to attend physical therapy. This is done to make sure you can straighten your leg as well as to help reduce swelling

This practice reduces the chances of scarring inside the joint and can also speed up recovery time.

Arthroscopic Method

Most surgeons now favor reconstruction of the ACL using a piece of tendon or ligament to replace the torn ACL.

This surgery is often done using a procedure known as arthroscopy. This procedure involves making incisions around the knee into which the arthroscope and other surgical tools are inserted. The surgeon can then view and repair the damaged the ligament.

Due to the minimally invasive nature of this procedure, most ACL surgeries are carried out in an outpatients ward and many patients return home the same day.

Patellar Tendon Graft

One type of graft used to replace the torn ACL is the patellar tendon. This tendon connects the kneecap (patella) to the tibia. The surgeon removes a strip from the center of the ligament to use as a replacement for the torn ACL.

Hamstring Tendon Graft

It is common procedure to use a hamstring graft to reconstruct a torn ACL. This graft is taken from one of the hamstring tendons, the semitendinosus, which runs along the inside part of the thigh and knee

Surgeons also commonly include as part of the hamstring graft a tendon just next to the semitendinosus, called the gracilis. When arranged into three or four strips, the hamstring graft has nearly the same strength as a patellar tendon graft.

Allograft Reconstruction

In some cases an allograft may be used to replace the torn ACL. An allograft is tissue that is harvested from tissue and organ donors at the time of death. These tissues are sent to a tissue bank and stored for future use.

The allograft (your surgeon’s choice of graft) can be from the tibial tendon, patellar tendon, hamstring tendon, or Achilles tendon (the tendon that connects the calf muscles to the heel).

Many surgeons use patellar tendon allograft tissue because the tendon comes with the original bone still attached on each end of the graft (from the patella and from the tibia). This makes it easier to fix the allograft in place.

The advantage of using an allograft is that the surgeon does not have to disturb or remove any of the normal tissue from your knee to use as a graft. The operation also usually takes less time because the graft does not need to be harvested from your knee.

Nonsurgical Rehabilitation

Nonsurgical rehabilitation for a torn ACL typically lasts six to eight weeks. During this time therapists apply treatments like as electrical stimulation and ice to reduce pain and swelling.

Exercises to help improve knee’s range of motion and strength will gradually be added to your physical therapy.

If your doctor prescribes a brace, your therapist will work with you to obtain and use the brace.

You will be able to return to your sporting activities when your quadriceps and hamstring muscles are:

  • Almost back to their full strength and control
  • You are not having swelling that comes and goes
  • You aren’t having problems with the knee giving way

After Surgery

Knee Brace For Anterior Cruciate Ligament Injuries

Most doctors have their patients 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.

Visit our site if you would like to find out more about knee injuries, knee replacement surgery or other types of orthopedic surgery

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