The anterior cruciate ligament (ACL) is one of the four ligaments in the knee that connects the femur to the tibia.

In essence, the knee is a hinged joint held together by the lateral collateral ligament (LCL), anterior cruciate ligament (ACL), medial collateral ligament (MCL), and the posterior cruciate ligament (PCL).

When there is a tear in the ACL, an ACL injury occurs.

An ACL injury can range from mild (small tears) to severe (complete ligament tears).

Left untreated, the ACL will not be able to control knee movements as much and the bones can end up rubbing against each other. This can result to a condition known as chronic ACL deficiency.

The erratic bone movement can also cause damage to the tissues (cartilage) that covers the bone end and can also tear the pads (menisci) that cushions the joints of the knee. This can sometimes lead to osteoarthritis.


What are some of the causes of ACL injuries?

An ACL injury oftentimes occurs while playing sports. When the knee joint is bent side to side, twisted, or bent backward, an ACL injury is likely to take place.

During sports, an ACL injury can occur when the foot is planted firmly on the ground and a force hits the knee while the leg is slightly bent or straight. This can happen when doing rapid direction changes, slowing down from a run, or when one lands from a jump.

ACL injuries are very prevalent in sports like skiing, football, soccer, and other sports that involve a lot of weaving, jumping, and lots of stop-and-go movements.

Missing a step while climbing or going down the stairs and falling off a ladder may also cause ACL injuries.

What are some of the symptoms of ACL injuries?

  • Hearing or feeling a “pop” in the knee
  • Severe pain outside and at the back of the knee
  • Swelling in the knee within the first few hours after the injury (this may indicate bleeding in the knee joint)
  • Knee movement becomes limited (this can be because of the swelling or pain or both).
  • Feeling of instability, giving out, or buckling in the knee.

When is seeing a doctor necessary?

Immediate medical attention is needed when:

  • Severe Knee Pain Treatment is experienced.
  • There is noticeable deformity of the knee.
  • Signs of damage to the blood vessels or nerves manifest—tingling, numbness, inability to move the affected leg, coldness in the leg, bluish skin, and “pins-and-needles” sensation are felt below the injured area.
  • There is severe swelling in the affected knee (often within 2 hours after the injury).
  • A “pop” is heard or felt during the injury.
  • Straightening the knee becomes challenging.
  • The knee gives out, buckles, or becomes unstable.
  • The knee “locks” in one position.

How are ACL injuries treated?

The goals of ACL treatment include:

  • Restoring knee stability
  • Restoring the knee’s level of function prior to the injury
  • Limiting loss of knee function
  • Preventing damage or injury to other knee structures
  • Reducing pain
  • Preventing osteoarthritis

Treatment approach will depend on:

  • Severity of the tear
  • Stability of the knee
  • When the injury occurred
  • Whether you have previous knee problems or injuries
  • Age
  • Overall health
  • Willingness to commit to months of rigorous rehab

First aid treatment for ACL injuries will often include applying ice, resting the knee, elevating the affected leg, taking pain medications (nonsteroidal anti-inflammatory drugs and acetaminophen), and resting the knee.


Using splints/crutches the first few days may also be suggested. However, long-term use is prohibited as it can make knee movements restricted and stiff.

While not all ACL tears will require surgery, it is imperative to seek medical attention so the doctor can assess if months of rehabilitation would suffice or surgery (ACL reconstruction or repair) with rehabilitation is necessary.