The anterior cruciate ligament (ACL) is one of the four ligaments that holds the knee (hinge joint) together and connects the thigh bone (femur) and the top of the shin bone (tibia) together. It provides stability and helps control the motion of the joint. During activity, the ACL ensures that the shinbone does not slide out too much from the femur, preventing too much forward movement.

An ACL tear or injury is common, especially among athletes, whereby there are sudden pivoting or cutting movements during sports, more so in sports such as football or basketball. An ACL tear can be divided into different grades.

• Grade I (Mild Sprain): The ligament is stretched but not torn. There may be some mild pain and swelling, but joint stability is usually maintained. Functional activities may be possible with minimal discomfort.
  
  
• Grade II (Moderate Sprain): The ligament is partially torn, resulting in increased pain and swelling. There is a noticeable loss of stability in the knee, and it may feel unstable during certain movements. Functional activities may be more difficult, and the knee may give way occasionally.
  
  
• Grade III (Complete Tear): The ligament is completely torn, leading to significant swelling, pain, and instability. The knee may feel very unstable, making it difficult to perform weight-bearing activities. Surgical intervention is often required to restore stability and function.