Anterior cruciate ligament (ACL) is a ligament in the center of the knee joint where is from the end of femur (thigh bone) down to tibia (shin bone). This ligament is one of the main structure in the knee joint due to it prevents tibia slide out in front of the femur (anterior tibial translation) and rotational loads. Moreover, ACL also plays an important role to stabilize the knee joint from the rotational loads. ACL is easily injured from the high impact or sport activities such as football, basketball and volleyball. ACL injury may happens from some activities such as jumping, running and kicking.

Causes of injury

ACL injury is happen when the ligament is torn or stretched beyond their normal range. There are three causes of an ACL injury, which is direct contact, indirect contact and non-contact.
  1. Direct contact is a directly force from the outside to the knee joint.
  2. Indirect contact is a force from the outside to the other parts of the body such as lower leg but it is not direct to the knee joint.
  3. Non-contact occurs when changing the sudden direction of movement such as running, pivoting or landing from the jump. Non-contact is the most causes of ACL injury with 70%.

Grade of injury

ACL injury grade 1: The ligament is stretched but it is not tear.

  1. Little tenderness and swelling on the knee joint
  2. Still feel stable in the knee joint
  3. Can feel a firm end feel
  4. No increased laxity

ACL injury grade 2: Partially torn

  1. Some part of ligament fibers are torn or incomplete tears
  2. Pain, little tenderness and moderate swelling on the knee
  3. Feel unstable in the knee joint or give out when doing some activity
  4. Have an anterior translation but still have a firm end feel

ACL injury grade 3: Completely torn

  1. The ligament of ACL are completely torn into two parts
  2. Pain, tenderness and swelling on the knee
  3. Feel unstable of the knee or give out (ligament cannot control the knee movement)
  4. No end point



  1. Pain
  2. Swelling
  3. Tenderness
  4. Hearing a audible pop or crack sound during the injury
  5. Instability in the knee joint
  6. Loss range of motion
Goals of ACL injury treatment
  • Gain good functional stability
  • Regain muscle strength
  • Reach the best possible functional level
  • Decrease the risk for re-injury
Treatment without surgery
Goal – improve range of motion, increase strength, decrease pain and swelling

PRICE (P = Protection, R = Rest, I = ICE, C = Compression, E = Elevation) for reducing pain and swelling in the knee

Exercise for strengthening muscle and regaining range of motions:

  • 1. Straight leg raise (SLR): raise the straight leg up and hold for 10 secs 10 times 2 sets
  • 2. Static quads: tighten quadriceps muscle (front of the thigh) by pushing down without lifting the heel up for 10 secs 10 times 3 sets
  • 3. Heel slide: bend the knee by sliding the heel to the buttock, try to bend until feel uncomfortable and then stop by holding in that position for 10 secs 10 times 3 sets
  • 4. Knee extensions: place an roller towel under the heel on the injured leg, try to relax and straight the leg to maintain the normal range of motions by holding 5-10 mins 2-3 times
  • 5. Stationary bicycle: 10-15 mins for strengthening muscle and maintain range of motion
Chavisa Wasinchutchwal (PT)
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