What is an anterior cruciate ligament (ACL) Injury?

injury to the anterior cruciate ligament (ACL), medial collateral ligament (MCL) and meniscus.  Research in the 1990s revealed that this unhappy triad is a peculiar clinical entity involving athletes with knee injuries.  The research shows that lateral meniscus tears are more common than medial meniscus tears in conjunction with ACL sprains.

The unhappy triad which is also referred to a a ‘blown knee’ occurs as a result of a lateral blow to the knee which causes a rupture in the anterior cruciate ligament, medial collateral ligament and the meniscus.  The injury usually happens when a lateral (outside) force impacts the knee and while the foot is on the ground.  The rotary force to the knee tears the ACL, MCL and meniscus all at the same time.  This particular injury often occurs in contact sports such as rugby, motocross and football.  

An ACL tear often requires surgery to repair the torn ligament and many patients are given a knee brace to wear post-surgery.  There is also a great deal of debate regarding just how effective a knee brace can be during the post-surgery healing process.  Yet, much depends on the preference of the surgeon as well as the attitude of the patient.  Often, it is thought that once an ACL tear occurs, a sportsman may never regain his former level of prowess.  Yet, there is a great deal of evidence to the contrary.  Recovery time is anything from two to six months on average but can take up to nine months in certain cases.

What are the symptoms of an ACL injury to the affected knee?

  • Pain 
  • Swelling and stiffness 
  • Catching or locking of the knee
  • Instability of the knee
  • Inability to move the knee in terms of full range of motion

How do ACL injuries occur?

ACL injuries occur when:

  • Sudden stopping and changing direction
  • Direct contact to the knee from other opponents on the field
  • Landing onto a bent knee from a jump and twisting and/or landing on the over-extended knee

Sporting examples

Injured soccer players who are keen to get back into their game as quickly as possible might choose to wear an ACL knee brace post-surgery to aid recovery.  

Fear of being away from the soccer field for too long ensures determined player stays in the game

In 2017, veteran Manchester United striker Zlatan Ibrahimovic suffered injuries that resulted in meniscus and cruciate ligament damage and was told that he would be laid off for at least 9 to 12 months.  However, despite his own fears that his injuries were more severe than first diagnosed, his determination saw him back on the field much sooner than that.  

Over the years, many soccer players who have suffered ACL injuries have defied the odds and returned to sporting victory such as Tottenham England striker Paul Gascoigne, Manchester United/The Netherlands striker Ruud van Nistelrooy and Arsenal/England Winger Theo Walcott.

How does an ACL knee brace work?

Once an ACL tear or injury has occurred, wearing an ACL knee brace can help to prevent injury to the anterior cruciate ligament and help support the knee.  An ACL knee brace stabilises the knee while allowing movement of the knee within the confines of the brace and reduces the amount of time the anterior cruciate ligament is at risk from tearing.  The knee brace helps to relieve discomfort and provide support and the best devices have compression to support the knee without interfering with mobility, which also helps to increase blood flow thereby reducing pain.

Those who sustain injuries when riding off-road motorcycles use a knee brace to help prevent further injuries.  Wearing a sports brace after injury or surgery allows the restoration of good blood flow which would otherwise take longer without the aid of the brace.

Figure 1:  ACL Knee Brace

What are the advantages and disadvantages of wearing an ACL knee brace?

Let us examine the advantages and disadvantages of wearing an ACL knee brace.


  • Enables the knee to rest
  • Affords protection in the event of falling
  • Assists in maintaining the extension of the leg
  • Makes the limb stronger 
  • Allows for proper vascularization to take place
  • Can prevent further injuries


  • May be uncomfortable
  • Some braces tend to slip

Important considerations

Some patients often ask Roger whether a brace can make the knee weaker since certain sources often report that this is the case.  However, in answer to this question Roger states that if a patient is in too much pain and the brace provides pain relief and enables the patient to walk then the knee will become stronger through walking.  When the patient is lying down and not moving the limb the knee cannot be strengthened.  

Once an injury is sustained, as far as the healing process is concerned not even a doctor will know how long it will take for the tiny blood vessels to fully heal.  However, wearing a brace during the healing process offers support to the knee as it heals.   

The importance of choosing the right knee brace

When choosing to wear a knee brace it is vital that the brace is prescribed by a qualified practitioner such as an orthotics specialist.  In the case of ACL injuries, it is not sufficient to merely opt for off-the-shelf products. 

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Reference sources:  Williamsterett.com, Wikipedia, Verywellhealth.com