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ACL Tear

The Anterior Cruciate Ligament (ACL) is considered one of the most important ligaments for stability of the knee, and probably the best-known knee injury. ACL tears most commonly occur during athletic activity but can happen any time there is a sudden stop or change in direction of the knee. Keep reading to learn what should you know.

The knee consists of four bones: femur(thigh), tibia (leg), fibula (leg), and patella (kneecap), and four major ligaments: ACL, PCL, MCL and LCL. The two ligaments in the middle of the knee cross each other and are therefore known as the cruciates. On the inner, or medial side is the Medial Collateral Ligament (MCL) and on the outer, or lateral side, the Lateral Collateral Ligament (LCL). Between the femur and tibia are the meniscal cartilages, medial meniscus on the inner side, and lateral meniscus on the outer side. The quadriceps muscle, in front, attaches, by the quadriceps tendon, to the patella, which, in turn attaches by the patella tendon, to the tibia. When working properly, the quadriceps mechanism can straighten the knee and provide kicking power. The hamstring muscles attach to the fibula and the back of the tibia to help to power bending the knee.

Ligaments of the Knee

The cruciate ligaments are found deep within the knee joint, knee between the medial femoral condyle, and lateral femoral condyle.

The Anterior Cruciate (ACL) is a thick, very strong fibrous tissue that connects from the back of the femur, crossing in front of the PCL, to the front of the tibia, and prevents uncontrolled translation of the tibia on the femur, and more importantly, the pivoting, or sense of giving out, when injured.

The Posterior Cruciate Ligament (PCL) connects from the front of the femur to the back of the tibia, thereby preventing the tibia from shifting backward on the femur.

The Medial Collateral Ligament (MCL) and Lateral Collateral Ligament (LCL) attach the femur to the tibia on the medial and fibula on the lateral side of the knee respectively.  These provided side to side, or lateral stability.

When healthy, these four ligaments allow for controlled rolling and gliding of the femur on the tibia, or what we all see as normal flexion (bending) and extension (straightening) of the knee.

The ACL normally is a strong band of tissue that connects the femur to the tibia and helps stabilize the knee joint. An ACL tear often occurs during sports or fitness activities that place high amounts of stress on the knee. When the ACL is damaged, there is typically a pop felt, and immediate pain and instability, followed by rapid swelling, as the torn ligament bleeds into the knee joint. ACL injuries are most commonly complete tears, but partial tears also occur.  The ligament most commonly tears from the femur, but can also tear in the mid-substance, and occasionally at the attachment to the tibia.

There are many activities that can result in injury to the ACL, most often in athletic pursuits. However, even non-athletes can tear the ACL if there is enough force and the right mechanism. Hyperextension and twisting injuries are most common. They can occur frequently with contact sports, when the knee and leg are struck, but often occur when an individual cuts, or makes a sudden change in direction while running. Sports include skiing and snowboarding, football, soccer, volleyball, and even tennis and pickleball.

The most common and immediate symptom of an ACL tear is a painful pop in the knee. Other symptoms include:

  • A feeling of instability
  • Giving way” when bearing weight on the injured extremity
  • Ongoing pain in the knee, from mild to severe.
  • Inability to continue athletic activity.
  • Swelling, usually developing within an hour.
  • Loss of range of motion, sense of stiffness.

When acute knee injuries occur on the athletic field, where a skilled examiner such as an Orthopaedic surgeon is present, the knee can usually be examined before it becomes very swollen, painful, and stiff. In these cases, careful physical examination can determine if the ACL has ruptured, as well as the other major ligaments. Most people who are injured, however, aren’t professional athletes, and will go to an emergency room or Urgent care, where a preliminary evaluation can be done until they can be seen and fully evaluated by an Orthopaedic Surgeon. X-rays are needed to determine if there is any obvious bone injury.

When going to the Orthopaedic office, the first thing a good physician will do is take a history to learn how the injury occurred, and what are the usual activities and demands on the knee.

Then, as able, a physical examination of both knees is performed. The injured knee will be checked for tenderness and swelling in comparison to the uninjured knee. There are a variety of tests that can be performed, if someone is comfortable enough, to determine the extent of injury. These include range of motion measurements, strength testing, and maneuvers to assess the status of the major ligaments.


High quality, Orthopaedic X-Ray views of the knee are usually needed, and done at the initial office visit to evaluate for fractures and other bone abnormalities.


In general, if a severe injury is suspected, a high-quality MRI is appropriate, and the MD will order one, which usually requires insurance approval.

MRI stands for Magnetic Resonance Imaging and is a very large magnet with a sophisticated computer and software, that will generate images of the soft tissues, including ligaments, joint cartilage, meniscus cartilage, and subtle details of the bone. For this reason, MRI is the most common imaging test after X-Ray.

CT scans, and ultrasound have a limited value in evaluating an acutely injured knee.

Any acutely injured knee will require basic treatment to reduce swelling and pain and regain range of motion. The best-known mnemonic for initial treatment is:


As soon as possible, the injured knee should be treated with:

  • Rest – Relative rest is necessary until the knee recovers, this usually involves no athletic activity, and limited weight bearing on the knee, often with crutches.
  • Ice – Ice the knee frequently, but never directly on the skin, and no more than 15 minutes on followed by at least 15 off. This reduces pain and helps minimize swelling and bleeding into the knee.
  • Compression – A compression knee sleeve or wrap will help minimize bleeding and promote the body’s resorption of fluid from the knee.
  • Elevation – Raising the affected area, ideally above the level of the heart, helps reduce swelling.

Definitive Treatment

At the Center for Orthopaedic Specialists, our physicians will review the options for treatment of an ACL tear, and tailor treatment based on the extent of injury, and patient needs and athletic demands. In general, the goal for everyone is a knee that is stable enough to return to normal activities. This can sometimes be accomplished by activity modification, with or without bracing. Most healthy, physically active individuals, however, will chose surgery.


ACL Reconstruction has advanced greatly from the early days when large incisions were needed. With the advances in arthroscopic techniques, a skilled arthroscopic surgeon can reconstruct the ligament, and treat any other associated injuries with minimal, arthroscopic incisions, as an outpatient. During surgery, the ruptured ligament is removed and replaced with a suitable substitute tendon. This can be obtained from the patient, (autograft), or more commonly these days, from a donor (allograft).


Initially, your doctor will recommend physical therapy, and exercises, that will be done under direct supervision at first. As you progress, you will be able to do much of the exercises at home and in a gym setting, with guidance, and ultimately independently. Crutches are usually used for a short time, until adequate muscle strength returns to the knee.

Consult With A Professional

The physicians at Center for Orthopaedic Specialists have been treating patients who have ACL tears with state-of-the-art treatment since the first arthroscopic ACL surgeries. They have the expertise and understanding to guide you and treat your injuries so that you can return to an active lifestyle. If you are currently experiencing any symptoms of an ACL tear, or require treatment, contact the Center for Orthopaedic Specialists today!

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