Anterior Cruciate Ligament (ACL) injury | Testing & Diagnosis

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If you suspect your child has an ACL injury, you want to find the best care available. Boston Children’s ACL specialists offer unsurpassed expertise in ACL surgery, recovery and injury prevention. Our mission is to provide innovative and age-specific ACL treatment and guide patients toward a safe return to play. We are here for your family.

How are ACL tears diagnosed?

Diagnosis begins with a patient history and physical exam. Your child may feel her knee shift or hear a popping sound when the injury occurs. There is usually a twisting injury to the knee that occurs at the time of injury. The knee often appears swollen with an ACL tear. It may be difficult to walk on the leg after the injury.

The doctor (or sometimes a trainer at the scene of the injury) examines the knee and often uses specific tests to stress the knee to identify the injured ligaments.

An x-ray may be ordered to check for any fractures in the bones of the knee. However, since x-rays only produce images of the bone, they can’t detect soft tissues such as ligaments and tendons.

An MRI is often necessary to confirm the diagnosis. This diagnostic imaging exam can show the severity of the injury to the ACL and check for damage to other ligaments and tendons.

Is an ACL tear an emergency?

An ACL tear is not an emergency. Doctors prefer to see patients as early as possible, so they can begin therapy to reduce swelling and return motion and strength. Orthopedic surgeons typically wait a minimum of three weeks from the date of the injury to perform surgical reconstruction. That’s because the risk of stiffness is higher if surgery is performed too soon after injury. However, if surgery is postponed too long, the patient runs the risk of additional injury to other ligaments or cartilage in the knee. Postponing surgery also may lead to progressive damage to the meniscus or knee cartilage.

What other injuries may occur with an ACL tear?

About half of children and teens with a torn ACL present with an additional injury to the knee.

A common second injury is a torn meniscus; this cartilage acts as a shock absorber in the knee. Boston Children's orthopedic surgeons recommend very close management of meniscal tears. If the meniscus is injured, it can be repaired at the time of surgery for ACL reconstruction.

Patients also may injure the articular cartilage or other ligaments in the knee. These injuries are usually noted on the MRI and can be repaired at the time of surgery.

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