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Anterior Cruciate Ligament

One of the most common knee injuries is partial or complete tear the anterior cruciate ligament also known commonly as the ACL. At the knee joint there are three bones, the femur (thigh bone) the tibia (shin bone) and the kneecap (patella).  The bones of the knee are held together by ligaments that act as scaffolding around the knee to limit potentially dangerous movements and help keep the knee stable. The ligaments of the knee are categorized into two groups collateral ligaments and cruciate ligaments.

Collateral ligaments

These types of ligaments are found on both on the inside of the knee MCL medial collateral ligament and the outside of the knee LCL (lateral collateral ligament).

Cruciate ligaments

The Cruciate ligaments are found inside the knee joint itself where they crossover each other to form a X with anterior cruciate ligament in front and the posterior cruciate ligament in the back, these ligaments control forward and backwards movements of the knee.

Grades of ligament damage

Grade 1 – Mild damage: a small amount of fibres torn, ligament is still able to ,provide some stability.

Grade 2- Grade two tears consist of increased damage to fibres to the point where there is growing laxity in the joint often referred to as partial tear.

Grade 3 – the most common grade of ACL injury, the ligament has been torn into two pieces and is no longer providing stability at the joint. A partial ACL tear is considered rare as the majority of injuries involved a complete tear.

Causes of ACL injury

The most common causes of ACL injuries are listed below:

  • Direct collision e.g. football/rugby tackle
  • Slowing down from high speed
  • Stopping suddenly
  • Changing direction rapidly

Most of these mechanisms come into the same category and research suggests that ACL is typically damage during any plant and twist motion of the leg. Both the thigh and shin bones move at different times or in different directions.


Often at the time of injury with an ACL tear you may here a pop or crack sound associated with you knee giving way. Shortly after other symptoms may consist of:

  • Loss of full range of motion
  • Tenderness around the knee
  • Discomfort when weight bearing/walking
  • Rapid onset of pain with swelling within 24hours of your injury
  • Feeling of pain deep inside the knee with instability or feeling of the knee giving way

When to get it checked out?

If you have any signs of an ACL injury you need to seek medical attention as soon as possible. Delaying this may cause you to damage other structures in the knee as in this state is it unstable. It is important to get an accurate diagnosis as fast as possible to minimise the recovery time.

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