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Anterior Cruciate Ligament (ACL) Injury

Anterior Cruciate Ligament (ACL) Injury

ACL Injury of the knee. Anterior cruciate ligament injury.The anterior cruciate ligament or ACL is a vital ligament that provides stability to the knee joint. The ACL is an intra-articular knee ligament, meaning it is found within the knee joint. The ACL is vulnerable to injury as the knee often supports the body’s full weight and is subjected to extreme stresses during running and twisting movements. Ligaments, which are tough fibrous bands of tissue, connect two bones together. If the knee is twisted in an abnormal fashion or subjected to trauma, these ligaments in your knee can be overstretched, resulting in ligament tears and instability of your knee joint.

The ACL is one of most well known knee ligaments as it commonly injured. It has two bundles of ligament fibres that provide stability in different ways. The anteromedial (AM) fibres of the ACL provides stability to your knee when you run in a straight line while the posterolateral (PL) fibres of the ACL provide stability to your knee when perform cutting or twisting movements.

How does an ACL injury occur?

Like all ligament injuries, the ACL is injured when it is overstretched. The ACL can be injured from a:

  • Non-contact injury: 80% of ACL injuries occur when there is a sudden decrease in pace followed by a rapid change in direction while the foot is planted on the ground (pivot). This frequently occurs in sports such as soccer, basketball, hockey, netball, dance and skiing. An ACL injury can also result when landing with a straightened knee (hyperextension).
  • Contact injury: 20% of ACL injuries occur when your knee is placed under force. This usually occurs as a result of a tackle in sports such as martial arts or football.

What are the risk factors of ACL injuries?

 Research has shown that the following factors increase the risk of sustaining an ACL injury:

  • A previous history of an ACL injury (up to 15x greater risk)
  • Females
  • Generalised joint laxity (hypermobility)
  • Poor trunk control (core strength)
  • Abnormal biomechanics
  • Strength differences between your thigh muscles

What are the signs and symptoms of an ACL injury?

  • An abnormal feeling of movement at the knee
  • A “pop”, “snap” or “crack” may be heard at the time of injury
  • You may need to be carried or helped off field
  • Swelling in your knee
  • Pain when moving your knee
  • Difficulty walking due to pain
  • Night pain
  • Instability when walking, running or turning/twisting

How is an ACL injury diagnosed?

A thorough subjective and physical examination by a physiotherapist is usually sufficient to diagnose an ACL injury. An MRI may be ordered to assess the extent of the injury, confirm the diagnosis and exclude other injuries to the knee.

What are your treatment options?

ACL injuries can be managed conservatively (non-surgical) or surgically. Surgical management is the most popular option, which involves reconstructing the anterior cruciate ligament. Some new research suggests that conservative management may be as effective while most report better outcomes with surgery. It is best to discuss this with your healthcare professional as they can guide your decision based on your needs. You optimal treatment option may be influenced by the following factors:

  • Age
  • Severity of injury
  • Activity level
  • Participation in sporting activities

Conservative management

Conservative management for ACL injuries involves significant rehabilitation, consisting of strengthening, motor control, flexibility, proprioception and specific sports skills. Conservative management may be suitable for an individual with a functionally stable knee who is looking to avoid surgery and does not regularly participate in high level sporting activities.


  • Cheaper
  • Rehab can commence early
  • Good long term functional outcomes


  • Knee joint is less stable
  • Development of secondary meniscus (cartilage) tears is more likely
  • Higher likelihood of developing osteoarthritis
  • May require surgical reconstruction in the future

Surgical management

Surgical management in the way of an ACL reconstruction may be suitable for an individual who is participates in high level sport, especially if it involves cutting or twisting.


  • Increased stability of the knee joint
  • Decreased risk of secondary meniscal tears


  • Surgical risks
  • Usually 6-9 months of rehabilitation before returning to sport

Is there a risk of re-injury to the ACL?

Unfortunately, there is a risk of re-injury to the ACL. Surgery restores normal stability of the knee, however it does not prevent injury to the reconstructed ACL or the ACL on the opposite knee. Research has shown:

  • 30% of young athletes suffered a second ACL injury within 2 years of returning to sport (21% injured the opposite knee while 9% injured the same knee after ACL reconstruction)
  • 17% of professional athletes had a second ACL injury to the same knee after reconstruction within 4 months of returning to sport

Is rehabilitation for an ACL injury necessary? 

A supervised rehabilitation program for at least 1 year by a physiotherapist is essential for successful return to sport following an ACL injury. A study found that athletes were 4 times more likely to sustain a second ACL injury if they did not meet the discharge criteria or if they had strength differences between their thigh muscles. In contrast, individuals who completed a supervised rehabilitation program achieved symmetrical strength in thigh muscles.

My Physio Perth will develop a personalised rehabilitation program that will ensure you will be able to participate in your favourite activities and sports safely and to the best of your ability.


Image credits:


  • Paterno MV, Rauh MJ, Schmitt LC, Ford KR, Hewett TE. Incidence of Second ACL Injuries 2 Years After Primary ACL Reconstruction and Return to Sport. American Journal of Sports Medicine. 2014; 42(7):1567-1573.
  • Kyritsis P, Bahr R, Landreau P, Miladi R, Witvrouw E. Likelihood of ACL graft rupture: not meeting six clinical discharge criteria before return to sport is associated with a four times greater risk of rupture. British Journal of Sports Medicine. 2016; 50(15).
  • Kostogiannis I, Ageberg E, Neuman P, Dahlberg L, Friden T, Roos H. Activity level and subjective knee function 15 years after anterior cruciate ligament injury: a prospective, longitudinal study of nonreconstructed patients. Am J Sports Med. 2007; 35:1135–1143.
  • Strehl A, Eggli S. The value of conservative treatment in ruptures of the anterior cruciate ligament (ACL). J Trauma. 2007;62:1159–1162
  • Kessler MA, Behrend H, Henz S, Stutz G, Rukavina A, Kuster MS. Function, osteoarthritis and activity after ACL-rupture: 11 years follow-up results of conservative versus reconstructive treatment. Knee Surg Sports Traumatol Arthrosc. 2008 May;16(5):442-8.
  • Louboutin H, Debarge R, Richou J, Selmi TA, Donell ST, Neyret P, Dubrana F. Osteoarthritis in patients with anterior cruciate ligament rupture: a review of risk factors. Knee. 2009 Aug;16(4):239-44.
  • Monk AP, Davie s LJ, Hopewell S, Harris K, Beard DJ, Price AJ. Surgical versus conservative inter ventions for treat-ing anterior cruciate ligament injuries. Cochrane Database of Systematic Reviews 2016, Issue 4. Art. No.: CD011166.

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