Anterior Cruciate Ligament (ACL) Injury

An anterior cruciate ligament (ACL) injury, are most often a result of low-velocity, noncontact, deceleration injuries and contact injuries with a rotational component. Contact sports also may produce injury to the ACL secondary to twisting, valgus stress, or hyperextension all directly related to contact or collision. 

Athletes who participate in high demand sports like soccer, football, and basketball are more likely to injure their anterior cruciate ligaments.

If you have sustained an injury to your knee during a pivoting, or twisting incident,  you felt a pop and then noted the inability to walk as well as significant swelling within your knee, there is a significant chance that you have injured your anterior cruciate ligament. The anterior cruciate ligament or ACL is the most commonly injured of the four major ligaments that exist within our knee. Most patients who have sustained an injury to their ACL will have enough discomfort and enough of a disability that they will seek attention either in an emergency room or in orthopedists’ office fairly rapidly. Many of those patients will be indicated for an MRI to better ascertain whether or not an ACL tear exists. Even though the literature is fairly clear that a physical exam is as good if not better at predicting the integrity of the ACL, many surgeon still rely on the imaging studies to arrive at a final diagnosis.


ACL injuries occur when an individual stops suddenly or plants his/her foot hard into the ground (cutting). ACL failure has also been linked to heavy or stiff-legged landing; the knee rotating while landing, especially when the knee is in an unnatural position.

Women in sports such as association football, basketball, and tennis are significantly more prone to ACL injuries than men. The discrepancy has been attributed to gender differences in anatomy, general muscular strength, reaction time of muscle contraction and coordination, and training techniques. Women also have a relatively wider pelvis, requiring the femur to angle toward the knees. The role of genetics is currently speculative.

Significantly many ACL injuries occur in athletes landing flat on their heels. The latter directs the forces directly up the tibia into the knee, while the straight-knee position places the anterior femoral condyle on the back-slanted portion of the tibia. The resultant forward slide of the tibia relative to the femur is restrained primarily by the now-vulnerable ACL.


When you injure your anterior cruciate ligament, you might hear a “popping” noise and you may feel your knee give out from under you. Other typical symptoms include:

  • Pain with swelling. Within 24 hours, your knee will swell. If ignored, the swelling and pain may resolve on its own. However, if you attempt to return to sports, your knee will probably be unstable and you risk causing further damage to the cushioning cartilage (meniscus) of your knee.
  • Loss of full range of motion
  • Tenderness along the joint line
  • Discomfort while walking


People who experience an ACL injury are at higher risk of developing knee osteoarthritis, in which joint cartilage deteriorates and its smooth surface roughens. Arthritis may occur even if you have surgery to reconstruct the ligament.


During the physical exam, your doctor will check your knee for swelling and tenderness comparing your injured knee to your uninjured knee. He or she also may move your knee into a variety of positions, to help determine if your ACL is torn.

Often the diagnosis can be made on the basis of the physical exam alone, but you may need tests to rule out other causes and to determine the severity of the injury. These tests may include:

  • X-rays. X-rays may be needed to rule out a bone fracture. However, X-rays can’t visualize soft tissues such as ligaments and tendons.
  • Magnetic resonance imaging (MRI). An MRI uses radio waves and a strong magnetic field to create images of both hard and soft tissues within your body. An MRI can show the extent of an ACL injury and whether other knee ligaments or joint cartilage also are injured.
  • Ultrasound. Using sound waves to visualize internal structures, ultrasound may be used to check for injuries in the ligaments, tendons and muscles of the knee.

Initial treatment for an ACL injury aims to reduce pain and swelling in your knee, regain normal joint movement and strengthen the muscles around your knee.

You and your doctor will then decide if you need surgery plus rehabilitation, or rehabilitation alone. The choice depends on several factors, including the extent of damage to your knee and your willingness to modify your activities.

Athletes who wish to return to sports involving cutting, pivoting or jumping usually pursue surgical reconstruction to prevent episodes of instability. More-sedentary people without significant injury to the cartilage or other ligaments usually can maintain knee stability with rehabilitation alone.


Whether or not you have surgery on your knee, you’ll need rehabilitation. Therapy will include:

  • The use of crutches and, possibly, a knee brace
  • Range-of-motion exercises to regain your full knee motion
  • Muscle-strengthening and stability exercises


A torn ACL can’t be successfully sewn back together, so the ligament is usually replaced with a piece of tendon from another part of your knee or leg. A tendon graft from a deceased donor also may be an option. This surgery is usually performed through small incisions around your knee joint. A narrow, fiber-optic viewing scope is used to guide the placement of the ACL graft.

  • Do NOT move your knee if you have had a serious injury.
  • Use a splint to keep the knee straight until you see a doctor.
  • Do NOT return to play or other activities until you have been treated.
Home Remedies
If you choose nonsurgical treatment for your ACL injury, you should avoid future participation in sports activities that involve a lot of cutting, pivoting or jumping.
Self-care treatments you can do at home include:
  • Rest. Use crutches to avoid full weight bearing on your knee after your ACL injury.
  • Ice. When you’re awake, try to ice your knee at least every two hours for 20 minutes at a time.
  • Compression. Wrap an elastic bandage or compression wrap around your knee.
  • Elevation. Lie down with your knee propped up on pillows.

Use proper techniques when playing sports or exercising. Some college sports programs teach athletes how to reduce stress placed on the ACL.

The use of knee braces during aggressive athletic activity (such as football) is controversial, and has not been shown to reduce the number of knee injuries.