How Are Knee Ligament Injuries Diagnosed?

As the body's most complex joints, knees comprise several bones and cartilaginous structures, which are held together tightly by ligaments and tendons. Ligaments are durable strands of fibrous tissue that connect the joint's bones and provide stability.

The knee has 4 primary ligaments that connect the thighbone (femur), shinbone (tibia), and fibula (calf bone):

  • Cruciate Ligaments – The anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) cross one another inside the knee in an "X" shape, with the ACL crossing forward and the PCL backward.
  • Collateral Ligaments – The lateral collateral ligament (LCL) is located on the knee's exterior, and the medial collateral ligament (MCL) is situated on the inside, both controlling side-to-side movement and limiting the joint's range of motion.

Damage to the ligaments can occur as a result of vehicle accidents, sports injuries, or falling and landing improperly, with the most common symptoms including:

  • Sudden and severe pain
  • Excessive swelling in the first 24 hours
  • Popping/snapping sound
  • Joint looseness and instability
  • Inability to place weight on the knee

When diagnosing injured ligaments, physicians will ask patients about any prior joint issues and analyze the ligament damage in a thorough physical examination. They may order X-rays to see if any bones have sustained damage, and MRI imaging is used to observe damage to softer tissues internally. Arthroscopic diagnosis may be performed to confirm imaging test results.

Knee ligament injuries differ for every individual and are classified based on their extent and severity:

  • Grade 1 – The damage is minimal and treatable non-operatively
  • Grade 2 – Ligaments may be partially torn or stretched but remain intact overall
  • Grade 3 – One or more ligaments are entirely torn

Grade 1 injuries usually respond to conservative treatment and don't require surgery. In contrast, grade 2 and 3 knee ligament injuries are more extensive and need surgery to repair or replace the damaged structures.