ACL and Knee Ligament Injuries

When one or more of the four ligaments in the knee are overstretched or torn, a knee ligament injury has occurred.

Ligaments connect bones to other bones. The four ligaments in the knee hold the bones together and keep the knee stable.

  • The anterior and posterior cruciate ligaments (ACL and PCL) are found inside the knee joint. They control the forward and backward motion of the knee.
  • The medial and lateral collateral ligaments (MCL and LCL) are on the sides of the knee. They control the sideways motion of the knee.

Direct contact to the knee or changing direction rapidly while running can cause a knee ligament to stretch or tear. These injuries are called sprains and have different severity levels:

  • A Grade 1 Sprain is when the ligament has been slightly stretched but is still able to help keep the knee joint stable.
  • A Grade 2 Sprain is when the ligament stretches to the point where it becomes loose. This is often referred to as a partial tear of the ligament.
  • A Grade 3 Sprain is most commonly referred to as a complete tear of the ligament. The ligament has been split into two pieces and the knee joint becomes unstable.

Risk Factors

A knee ligament injury can occur if you:

  • Get hit very hard on the side or front of your knee, such as during a football tackle
  • Overextend your knee joint
  • Quickly stop moving and change direction while running, landing from a jump, or turning

Basketball, football, soccer, and skiing are common sports linked to knee ligament injuries.


If you have suffered a knee ligament injury, you are likely to experience some or all of these symptoms:

  • Hearing a popping sound when the injury occurs
  • Swelling within six hours of the injury
  • Pain that gets worse over time, especially when you try to put weight on the injured leg
  • Instability in your knee, or a feeling that your knee is going to give way
  • Knee stiffness due to swelling
  • Difficulty walking and going down stairs

Detection and Diagnosis

Orthopedic surgeons at South Texas Health System Clinics can diagnose a knee ligament injury by performing a physical exam and comparing your injured knee to your healthy one. If needed, the doctor may also order imaging tests such as an MRI or X-ray to measure the extent of the injury and determine whether the ligament was torn or simply overstretched.

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See your healthcare provider if you think you have suffered a knee ligament injury. Do not play sports or other activities until you have been examined.

First aid for a knee ligament injury may include:

  • Raising your leg above your heart
  • Putting ice on the knee
  • Taking pain relievers such as ibuprofen

Your doctor may also recommend:

  • Using crutches to walk until the swelling and pain subside
  • Wearing a brace to prevent the knee from moving and causing more damage
  • Physical therapy to help improve joint motion and leg strength

If the ligament is torn or other treatment methods don’t work, you may need surgery to repair it. This is done by rebuilding the ligament. The torn ligament is replaced with a tissue graft taken from another part of your body or from another human donor. Arthroscopic surgery is performed with an arthroscope using small incisions. This type of surgery is less invasive and normally results in less pain from surgery, less time spent in the hospital and quicker recovery times.