Anterior Cruciate Ligament (ACL) Injury Explained

With the sports season half way through, I have seen both on TV with the professionals, but also with local athletes, a high number of ACL knee injuries occurring. Currently we are treating four athletes that have ACL tears of different degrees, so I decided to write this article to provide education on the process.

Anterior Cruciate Ligament Injury

The Anterior Cruciate Ligament (ACL) is a common knee injury that can occur in athletes and the general population. These injuries occur most frequently in sports that involve pivoting (eg AFL, basketball, soccer, netball, rugby) and can range from mild (strain/tear) to severe (full rupture of the ligament). Both contact and non-contact injuries can occur, although non-contact tears and ruptures are most common. Females have a higher incidence rate of ACL injuries than men, being 2.4 times more likely to become injured performing similar activities.

Anatomy and Mechanism of Injury

The ACL is a band of connective tissue that originates from the posteromedial aspect of the femur to the anterior surface tibia. It is a key structure in the knee joint, which resists anterior tibial translation and rotation loads.

ACL tears or ruptures typically happen with the knee in the ‘position of no return.’ This is where the knee is externally rotated and in 10-30° of flexion. The knee is then placed in a valgus position as the athlete takes off from a planted foot, and internally rotates with the aim of changing direction rapidly, such as a side step.

Patients may report an audible pop or crack, accompanied by severe pain, at the time of the injury. Swelling may be immediate and they can present with an inability to fully extend their knee. Those that may have gone undiagnosed can report episodes of their knee giving way and a general feeling of instability.

Grading of ACL Tears

An ACL injury is classified as a grade I, II, or III sprain.

  • Grade I sprain:

    • The fibres of the ligament are stretched but there is no tear.
    • There is a little tenderness and swelling.
    • The knee does not feel unstable or give way during activity.
    • No increased laxity and there is a firm end feel.
  • Grade II sprain:

    • The fibres of the ligament are partially torn or there’s an incomplete tear with haemorrhage.
    • There is a little tenderness and moderate swelling with some loss of function.
    • The joint may feel unstable or give way during activity.
    • Increased anterior translation yet there is still a firm end point.
    • Painful and pain increasing with Lachman’s and anterior drawer stress tests.
  • Grade III sprain:

    • The fibres of the ligament are completely torn (ruptured). The ligament itself has torn completely into two parts.
    • There is tenderness but not a lot of pain, especially when compared to the seriousness of the injury.
    • There may be a little or a lot of swelling.
    • The ligament cannot control knee movements. The knee feels unstable or gives way at certain times.
    • There is also rotational instability as indicated by a positive pivot shift test.
    • No end point is evident.
    • Haemarthrosis occurs within 1 to 2 hours.

Diagnosis and Treatment

Diagnosis and grading of an ACL injury is given by a Doctor or Physiotherapist through physical examination tests, and is confirmed by radiographs, including X-rays and an MRI. Treatment is determined by the grade and associated injuries, and is directed by an Orthopedic specialist. Most require a full knee reconstruction. However conservative management strategies are also available. The patient always has the final decision on their treatment pathway.

Pre and post-operative conditioning or rehabilitation strategies are performed with a Physiotherapist or Exercise Physiologist. These help regain a full range of motion and strengthen the patient’s knee, with goals to return to work, sport and activities of daily living.

Progressing your rehab from manual physiotherapy into gym-based reconditioning, which addresses postural deficiencies, will result in a stronger knee than before you started. In 2016, the treatment is so effect when you see a professional, that there is no reason why you cannot return better than ever before. Subsequently one of my biggest frustrations is when people don’t commit to the entirety of their rehab, then wonder why their knee is never the same as it once was.

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