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Sports Injury Prevention

ACL Injury


The anterior cruciate ligament (ACL) is a very important ligament inside of the knee joint. Ligaments are tough bands of tissue that connect bones to bones. The ACL connects the femur (thighbone) to the tibia (lower leg bone). The ligament is deep inside the knee joint and cannot be felt. It is called “anterior” because it is in front of another important ligament, the posterior cruciate ligament or PCL. The ligaments cross, thus the name “cruciate” which comes from the Latin word for crossing. The ACL is required for knee stability, especially in activities or sports that require cutting or pivoting.

ACL Injuries

There are around 200,000 ACL injuries every year in the United States. Most ACL tears in children and teenagers occur during sports. Many injuries occur when a player twists the knee. For example, they may change direction suddenly or land awkwardly after a jump. This is called a “non-contact” injury. About 3 out of 4 ACL tears occur this way. The ACL can also be torn if the player is hit directly on the side of the knee. This often happens in football and rugby players and is called a “contact” injury.   

The highest risk of ACL injury is in male football and female soccer players. One study found that the chances a high school football or soccer player would tear their ACL was about 1% per year. Other “high-risk” sports include gymnastics, basketball, and lacrosse.

Women are at higher risk for injuring their ACL. A large study in college soccer players found that women had three times more injuries than men. There are many reasons for this difference. Women have a different shape of their knee joint. They also tend to jump and land in a position that puts the ACL at risk (straight knees rather than bent knees) and may have differences in knee muscle strength.


It is very common for the player to feel or hear a pop and feel the knee give way. However, you can still have an ACL tear even if you didn’t feel a pop. The knee usually gets very swollen within a few hours. It is often difficult to move the knee fully and walking can be very painful.

It is common for the swelling and loss of motion to improve over the next week or two. Some athletes may think the injury is not very severe because the pain improves dramatically with the improvement in swelling. However, if the athlete attempts to return to sports the knee will be unstable and can give way. Players may sense that they “can’t trust” their knee or can’t pivot off of that side. 


The orthopedic surgeon will first talk about your injury, the symptoms you are feeling, and what type of treatment you have had since the injury. They will also ask about your sport, previous knee injuries or symptoms, and your medical history. 

The physical examination is very important. Often, the orthopedic surgeon can diagnose an ACL tear during the exam. The ACL is important for stabilizing the leg bone and preventing it from “sliding” forward on the thigh bone. One of the most common exam tests is performed by pulling forward on the tibia with the knee flexed. The surgeon will also examine the other structure around the knee. It is common for there to be injuries to other structures like the meniscus or collateral ligaments. Anywhere from 50-70% of patients with ACL tears will have a meniscus injury. 

X-rays and Tests

Your doctor will initially order x-rays. Even though the x-rays do not show things like the ligaments or meniscus, they are very important. The x-rays will show the swelling that goes along with an ACL tear. They can also show fracture (breaks) around the knee. Younger children can have a fracture of the bone where the ACL attaches on the tibia. This type of injury is treated differently that an ACL tear. The surgeon will also check whether the bone is still growing; they will decide if the growth plates are still open. This may also affect what type of surgery needs to be done. 

If there is concern for an ACL tear, an MRI will be ordered. The MRI will show injuries to the ACL and other ligaments as well as the meniscus and the cartilage (the soft cushioning material that covers the end of the femur and tibia).

Initial Treatment

After the initial injury, it is important to reduce the swelling and control the pain. A great way to think about the initial treatment is RICE. This stands for Rest, Ice, Compression (with an ACE wrap or elastic bandage), and Elevation (raising the knee). Icing is very important. You can use ice packs, but packs of frozen peas or corn also work very well. Place the ice packs on the front and back of the knee. You should make sure there is a sock or thin towel between the ice and skin to avoid frostbite. You can use an ACE wrap or plastic wrap to keep the ice packs in place. Keep the ice pack in place for 15 to 20 minutes and repeat every one to two hours for the first 5-7 days.

Your surgeon may also recommend you take Acetaminophen (Tylenol) or an anti-inflammatory like Ibuprofen (Motrin or Advil) or Naproxen (Aleve). Your doctor may keep you on crutches until the MRI. 

Once the swelling starts to come down, you should begin moving the knee. It is very important to try to regain motion (especially extension or straightening) before surgery. 

Surgical Treatment

A completely torn ACL will not heal without surgery. However, a small number of ACL tears may be partial tears, meaning a part of the ACL is still intact. In these injuries, patients may be treated without surgery. A brace is usually worn, and the patient is treated with physical therapy to regain motion and strength.

The majority of ACL injuries require surgery. This surgery is usually performed as an outpatient. The surgery is performed using an arthroscope (small camera) and small instruments placed in the knee through small incisions or “portals”. The surgeon will evaluate the other structures inside the knee. If there is a meniscus tear, this may need to be repaired or “cleaned up” by trimming the damaged portion.

The torn ACL is “reconstructed” or replaced. The surgeon will reconstruct the torn ligament with a graft. This graft is usually obtained from somewhere else in the knee. There are pros and cons to each graft option. You should discuss graft choices with your orthopedic surgeon to determine which is best based upon your age, sport, and other injuries. The most common grafts are:

  • Patellar tendon or “BTB” (bone-tendon-bone): This is taken from the middle of the patellar tendon which runs from the kneecap to the patella.
  • Hamstring tendon: Usually two of the hamstring tendons that run on the inside of the thigh are used.
  • Quadriceps tendon: This is taken from the tendon that runs from the top of the kneecap.  

Tunnels or sockets are drilled into the bone where the ACL normally runs. The graft is placed into the tunnels and then “fixed” with a screw or button. In young patients with open growth plates (bone is still growing), special techniques are used to avoid damage to the growth plate.


Your surgeon may recommend crutches or a brace immediately after surgery, especially if a meniscus is repaired at the same time. Physical therapy (PT) is very important. The goals of PT are to reduce swelling, regain range of motion and flexibility, regain strength in the muscles around the knee, improve balance, and ultimately prevent further injuries. The final phase of rehabilitation is often tailored around the patient’s sport and includes exercises that simulate playing. 

It usually takes between 8 and 12 months to return to sports. Before being cleared to return, your surgeon and therapist may have you complete a series of tests. These tests are designed to check your balance, strength, and range of motion. 


ACL reconstruction is generally successful in restoring knee stability. Eighty to 90% of patients will return to sports. Re-rupture of the graft can happen. Large studies have shown that the risk of tearing the reconstructed ACL is between 5 and 20%. Younger patients participating in cutting or pivoting sports are at especially high risk. For that reason, it is very important to not return to sports until cleared by your doctor.

Q: I’ve heard that women are at higher risk for ACL injury. Why is this? 

Women are definitely at higher risk of tearing their ACL. There are multiple factors that may cause women to be more prone to ACL tears. There are important differences in the anatomy (structure) of the knee between men and women. The intercondylar notch, or the space where the ACL is located, is narrower in women than in men. Female athletes also put greater stress on their ACL during athletics. Their knees are more “turned in” and frequently less bent when jumping and landing. Female athletes often land on their heels with the knees “locked out”. This places more stress on the ACL than if they land with bent knees and a wider stance. 

Q: I didn’t feel a pop when I hurt my knee. Could my ACL still be torn?

Yes. While many athletes who tear an ACL feel a pop, the ligament can still be injured even if you didn’t. In fact, only about 70% of patients with a torn ACL feel a pop during their injury.

Q: Do I need an MRI?

If your doctor is concerned about an ACL tear, they will usually recommend an MRI. Ligaments, like the ACL or MCL, cannot be seen on x-rays. Many orthopedic doctors can diagnose an ACL tear with physical examination. The MRI can confirm the diagnose and also evaluate other structures that may be injured like the meniscus or the cartilage.

Q: I tore my ACL, but my knee feels much better after a few weeks. The swelling has gone, and I can walk and bend it without any problems. Why do I still need surgery?

It is very common for patients to feel much better once the swelling goes down. This usually occurs in 2 to 3 weeks. Patients will usually be able to walk without much difficulty and their range of motion also improves. Often, their knee will feel “fine” until they try to run or pivot or return to sports. It is important to follow the advice of your doctor. When the ACL is completely torn, the knee is “unstable.” If your child returns to sports and twists the knee again, they could tear the meniscus or cartilage or damage other structures.

Q: I’m worried my child injured their ACL. What can we do while we are waiting for the appointment with the surgeon or for the MRI?

First and foremost, it is important not to injure the knee further. If your child has a large amount of swelling, they should not return to sports until evaluated by a doctor. It is also important to reduce the swelling and control the pain with RICE. This stands Rest, Ice, Compression (with an ACE wrap or elastic bandage), and Elevation (raising the knee). 

Q: My son is 13 years old. How is his surgery different from the surgery an adult would need?

The growth plates (where the bone is growing) are most likely still open. This means he still has potential for more growth. Special techniques are needed in patients with open growth plates. For example, some types of grafts that include pieces of bone or “bone blocks” are not good options when the bone is still growing. Your surgeon may recommend a soft tissue type graft such as the hamstring tendon or iliotibial band. Also, your surgeon may use special techniques to avoid injuring the growth plate.

Q: What “graft” should my child have for the ACL reconstruction?

There are three main graft choices in young athletes – patellar tendon, hamstring tendon, and quadriceps tendon. There are pros and cons to each option. It is important to talk to your child’s surgeon about their sport and previous knee problems. For example, your surgeon may not recommend patellar tendon graft if your child has a history of pain at the front of the knee since this graft has a higher risk of anterior knee pain. Patellar tendon may be a great option for older teenage football or soccer players, and some studies have shown a lower failure rate with this graft.

Q: How long will my child need crutches after surgery?

Many surgeons only recommend crutches for a few days to a couple of weeks after an ACL reconstruction. They may, however, recommend crutches for 6 to 8 weeks if they have to repair a meniscus tear.

Q: How long is the surgery? Will my child need to stay in the hospital?

Surgery is usually between an hour and a half and two hours. Most ACL reconstructions are performed as outpatient surgery (no overnight stay).

Q: Does my son or daughter have to do physical therapy after surgery?

Yes! Physical therapy is incredibly important. The goals of PT are to reduce swelling, regain range of motion and flexibility, regain strength in the muscles around the knee, improve balance, and ultimately prevent further injuries.

Q: When can my child return to sports?

This can vary based upon the sport, the ACL technique used, and the recommendations of the individual surgeon. Most children return to sports between 8 and 12 months.