Anterior cruciate ligament (ACL) sprains and tears are among the most common knee injuries and can occur during childhood, adolescence and adulthood.
Athletes who participate in sports such as football, soccer and basketball — where they do a lot of running, jumping and quickly switch directions — are more likely to sustain serious ACL injuries. Some of these injuries will require surgical treatment.
About half of all ACL injuries occur in combination with other knee injuries, such as meniscus tears, anterior knee pain or damage to other structures of the knee such as articular cartilage and other ligaments.
Understanding the anatomy of the knee
Your child’s knee joint is at the intersection of three bones:
- Femur (thighbone)
- Tibia (shinbone)
- Patella (kneecap)
The kneecap is positioned in front of the knee joint to provide some protection for the four ligaments that connect the thighbone and shinbone, and keep your child’s knee stable.
Collateral ligaments are on the side of the knee — the medial ligament is on the inside of your child’s knee; the lateral ligament is on the exterior. These ligaments control the sideways motion of the knee.
Cruciate ligaments run diagonally inside the middle of the knee, forming an “X”, with the anterior cruciate ligament in the front part of the knee, and the posterior cruciate ligament in the back. These ligaments control the back and forth motion of the knee. Additionally, the ACL provides stability to the knee and prevents the tibia from moving in front of the femur.
Types of ACL injuries
ACL injuries are considered sprains and vary in severity.
- Grade 1: The ligament has sustained mild damage and been slightly stretched but can still keep the knee joint stable.
- Grade 2: The ACL is stretched and becomes loose. This type of ACL injury is often referred to as a partial tear of the ligament. It is rare.
- Grade 3: Commonly referred to as a complete ligament tear, the ACL is split into two pieces and the knee is unstable.
ACL injuries can be caused by:
- Stopping suddenly while running
- Slowing down while running
- Changing directions rapidly while running
- Jumping or landing incorrectly
- Contact injuries, such as a football tackle
- Overuse of the leg from repetitive impact activity — such as jumping, running, twisting or pivoting
If your child injuries his ACL, he may:
- Hear a popping sound
- Feel as if his knee has given out from under him
- Feel immediate pain
- Experience swelling, especially for the first 24 hours after the injury
- Be unable to continue playing immediately after the injury
- Lose full range of motion
- Experience joint tenderness
- Feel discomfort while walking
If you suspect your child or teen has sustained an ACL injury, he should be evaluated by an experienced orthopaedic physician.
At Children's Hospital of Philadelphia, ACL injuries are treated by physicians from the Division of Orthopaedics and the Sports Medicine and Performance Center who specialize in diagnosing and treating bone and muscle injuries in children, teens and young adults.
Our expert doctors will perform a physical exam of your child, specifically addressing all structures of the injured knee, and comparing them to the non-injured knee.
We will assess your child’s pain, learn about your child's medical history and may perform diagnostic imaging — such as X-rays and MRIs — to help diagnose your child’s condition and the severity of the injury.
Then, we will work with you and your child to develop an individualized treatment plan.
Treatment for your child’s ACL injury will depend on a number of factors, including your child’s age and development, the severity of the injury, and lifestyle goals long-term.
For example, an elite young athlete will likely require surgery to return to sports safely; while non-surgical treatment may be recommended for patients who are still growing and have been less seriously injured.
If the overall stability of your child’s knee is intact (i.e. grade 1 injury) and your child still has open growth plates, orthopaedic physicians at CHOP will likely recommend non-surgical treatment.
- Activity modification, which includes avoiding sports such as soccer and football, which involve "cutting" — running with jumping, pivoting, and twisting
- Immobilization with a brace may be recommended to help protect the knee from instability
- Physical therapy and rehabilitation may be started after swelling has decreased; specific exercises will strengthen the quadriceps and hamstring muscles and help restore knee function
A torn ACL will not heal without surgery, but it is not appropriate for everyone.
ACL reconstruction surgery is recommended for:
- Older adolescents, young adults and adults who have finished growing and no longer have open growth plates
- Individuals who have sustained a grade 2 (partial tear) or grade 3 (complete tear) ACL injury
- Individuals who want to continue to be involved in competitive sports that require cutting and twisting (i.e. football, soccer, basketball)
ACL reconstruction is typically performed with surgical arthroscopy, which is less invasive than open surgery and allows patients to recover more quickly. During this procedure, a skilled orthopaedic surgeon will make small incisions that create minimal trauma to the knee.
Because most ACL tears cannot simply be stitched back together, orthopaedic surgeons must recreate the ligament using a tissue graft to act as “scaffolding” for the new ligament to grow onto.
Tissue grafts to create a new ACL may be obtained from:
- The patient’s patellar tendon (between the kneecap and shinbone)
- The patient’s hamstring tendon (on the back of the thigh)
- The patient’s quadriceps tendon (between the kneecap and thigh)
- An allograft tissue transplant
Each graft source has advantages and disadvantages. Talk to your child’s orthopaedic surgeon to determine which option is best for your child.
Most ACL reconstruction procedures are not done right away after injury. Instead, surgeons prefer to wait until swelling has decreased and joint motion has returned. If an ACL reconstruction is performed too early, there is a significantly increased risk of arthrofibrosis (scar tissue forming in the joint) which could lead to loss of knee motion.
Rehabilitation is vital for recovery after an ACL injury — even if your child did not have surgery. Physical therapy will help your child regain strength and motion in his knee and leg.
If your child had surgery, rehabilitation will initially focus on returning motion to the knee and leg muscles. Then, your child will participate in a strengthening program designed to protect the new ligament by gradually increasing stress on the ligament. Finally, your child will participate in a customized program designed to optimize his return to his chosen sport.
Regrowth of the ACL takes time. It’s important to help your child have realistic expectations about his recovery. It may be six months or more – depending on strength and agility training — before an athlete can return to sports after surgery.