ACL Tear and Injury Symptoms and Diagnosis

Your knee joint has three bones — the:

  • Femur (thigh bone)
  • Tibia (shin bone)
  • Kneecap

Four ligaments hold the bones in place. The anterior cruciate ligament (ACL) crosses the middle of the knee diagonally, providing stability.

An ACL tear or sprain is a common knee injury and happens most often to athletes. Weekend warriors and non-athletes can also sustain an ACL injury.

ACL Injury Causes

You can injure your ACL during a stop/start motion, pivot, or quick direction change that causes the knee joint to:

  • Bend backward
  • Twist
  • Bend side to side

The chance of injury is higher if more than one of these movements occurs at the same time.

ACL tears from sports

An ACL tear or sprain often occurs during sports when you:

  • Firmly plant your foot on the ground, and a sudden force hits your knee while your leg is straight or slightly bent.
  • Quickly change direction.
  • Slow down when running.
  • Land from a jump.

This type of injury is common in sports with lots of stop-and-go movements, jumping, or weaving like:

  • Soccer
  • Skiing
  • Football
  • Basketball

Other causes of ACL injuries

Falling off a ladder or missing a step on a staircase can also cause an ACL sprain or tear.

Like any other body part, the ACL gets weaker with age. A tear happens more easily in people older than age 40.

ACL Injury Symptoms and Signs

Many people who injure their ACL hear a popping noise in the knee.

Other common symptoms of ACL sprains or tears include:

  • Swelling
  • Tenderness
  • Less range of motion
  • Trouble walking
  • Pain

ACL injury symptoms can vary widely among people.

Some people have a lot of pain, while others can walk around for a few hours after the injury. But, as the swelling in your knee increases, it's harder to walk and you lose range of motion.

Diagnosing an ACL Injury

Your UPMC Sports Medicine knee doctor can tell if you have an ACL injury. He or she will ask about your health history and examine your knees.

During the exam, your doctor will check both the injured and uninjured knee for:

  • Stability
  • Movement
  • Tenderness

Tests to help diagnose ACL tears

Your doctor may use the Lachman test and pivot shift test to assess:

  • Your range of motion.
  • The instability of your knee.
  • The grade of your injury.

You also may need:

  • X-rays to check for damage to the knee bones.
  • An MRI to see any damage to ligaments, tendons, muscles, and knee cartilage.

Types of ACL Injuries

Doctors use a grade to diagnose how severe your ACL tear is.

  • Grade 1least severe ACL injury. Means you stretched but didn't quite tear, the ACL. The ligament can still keep the knee joint stable.
  • Grade 2a partial tear. Means you stretched the ACL, making it loose. The ligament can't provide full stability to the joint.
  • Grade 3most severe ACL injury. Means a complete or near complete tear. The ligament has split into two pieces. Grade 3 is the most common type of ACL injury.

Learn More About ACL Injury Symptoms and Treatment

Contact the UPMC Sports Medicine ACL Program today to learn more or make an appointment.