Injuries to the anterior cruciate ligament (ACL): An overview of rehab and injury management

This article is by no means intended to be the definitive authority on ACL rehab; but will hopefully stimulate further interest in this fascinating topic... 


Injuries to the Anterior Cruciate Ligament (ACL) used to routinely finish the careers of many athletes; but now an ACL injury needn’t be such a big deal provided both the surgery and the rehabilitation are of the required standard. 

The whole subject of ACL rehab has received a lot of publicity and is regularly discussed on medical and physio webs and forums.

As one of the major ligaments providing internal stability to the knee, the ACL is frequently injured in football.  The average rehabilitation period following surgery takes around 9 - 12 months, but that can vary.

The challenge to medical professionals therefore is to ensure that players returning from ACL rehabilitation do so with the minimal risk of injury recurrence. 

Historically, as ACL rehab has developed over the years, so too has our knowledge base increased and techniques have changed, including those used by the surgeons.   

Rehab today is now a lot more structured than it used to be and protocols have been introduced based on emphatic evidence of what has or hasn’t worked in the past.  

In the early days after the concept of ACL surgery was first introduced, it wasn’t unusual to see half a dozen ACL cases in the same gym who had been operated on by different surgeons being rehabbed in as many different ways!

Twenty-five years ago some surgeons used full length immobilisation in plaster (which as we now know only led to serious muscle wastage) while others favoured early movement exercises. 

The success or failure of each method used led to greater clarity being introduced in rehab settings and the standard protocols used today were developed accordingly.

There were various arguments for and against the two main surgical techniques of hamstring graft and patella tendon graft, with supporters in both camps passionately defending their clinical reasoning (before the phrase took on the meaning it has today). 

As we now know, there is no definitive answer as to which technique is the most successful; since each have their own pros and cons.  And as our subject knowledge improved, so too did our understanding of how ACL injuries were sustained in the first place.  
Differences were noted in the aetiology of ACL sprains between male and female athletes and in ACL injuries sustained via contact or non-contact means.

As the years went by, specific surgeons began to make a name for themselves by successfully treating the top athletes; and gaining world-wide reputations to suit.  With the advent of the fitness industry and the increase in people taking part in sport at all levels, the injury rate increased accordingly. 

Suddenly it wasn’t just the superstars who were having ACL injuries; these were occurring at local level and corrective surgery was quickly becoming accessible to the regular sportsperson. 

The success of ACL surgery in general quickly led to this becoming an accepted treatment following what used to be a career-ending injury. 

This also benefitted the non-sporting population for whom a serious knee injury could affect their chances of continuing in specific jobs where the ability to remain physically active was essential. 

Over the years, perhaps more research has been conducted into ACL injuries than any other orthopaedic problem.  Such research has varied between the treatment and management of ACL tears and how these are thought to have occurred in the first place.  This research is continuing. 

Vulnerable groups have been identified where the risk of ACL injury is increased through participation in certain sports such as hockey, football and netball.  Contact sports like soccer and both codes of rugby show high returns of ACL injuries in studies. 

However, recurrent ACL injuries have been shown to be a problem for sportspeople and non-sportspeople alike. 

The high-risk categories of American Football, women’s soccer and netball are known to be three of the most prevalent activities where ACL injury is likely to occur based on the components of the game and participant demographics.  Injury recurrence is frequent; particularly in the older player and in the female athlete.

There are a number of theories as to why this is so, but as Hagglund (2006) pointed out, the biggest single risk factor for any injury is having had a similar injury in the past to the same structure.

Nonetheless, ACL injuries and post-operative rehabilitation remain a huge subject in the rehabilitation world today.  An interest in one aspect invariably leads to discussion about the other. 

It’s almost impossible to isolate ACL rehabilitation from the injury mechanisms normally associated with ACL tears since if you know the risks then you're halfway to preventing them in the future.

So a broad working knowledge of both the injury mechanics of ACL tears together with an understanding of the priorities in rehabilitation are essential if a successful rehabilitation outcome is to be achieved. 

Injuries to the ACL usually occur in one of two different ways

Injuries to the ACL usually occur in one of two different ways; either through direct contact in sport with an opponent or team-mate, or by non-contact means such as jumping and landing awkwardly. 

With the direct contact method, the injury usually occurs in contact sports through the mechanism involved in tackling – or being tackled – when the knee twists or gives way as a result of being forced into a position that it isn’t really meant to go into. 

In these situations it’s usually not only the ACL that sustains the injury, other structures are injured too; such as the menisci (or cartilage as these used to be referred to) and other supporting ligaments of the knee. 

In women’s sports such football and netball, though, non-contact ACL injuries are generally more common and these tend to occur either on landing or by turning sharply to change direction.

Anatomically, the ACL runs within the knee from the medial surface of the tibia and extends upwards, backwards and laterally to insert on the lower aspect of the femur, where it’s major mechanical function is to prevent excessive forward movement of the shin in various degrees of flexion (Liu-Ambrose, 2003).

The ACL is one of two ligamentous structures deep within the knee that connects the femur and tibia with the purpose of preventing excessive knee movement in a backward or forwards direction; the other being the Posterior Cruciate Ligament (PCL).

Basically, the ACL prevents excessive forwards movement of the tibia on the femur while the PCL prevents excessive backwards movement in the same plane.

Torn or stretched ligaments are normally associated with instability; although the ACL as a structure is rarely injured in isolation. Injuries to other ligamentous structures often accompany ACL tears but take less time to heal. 

The PCL can also be injured in sport but is less common.

Injury mechanics

In non-contact ACL injuries the foot usually sticks or twists on landing, and the momentum of the rest of the body results in the knee giving way, resulting in a tear of the ACL. 

When this happens, an audible ‘pop’ or ‘cracking’ sound is often heard at the time; followed by immediate swelling and an inability to weight-bear without the knee giving way. 

These are known to be the “classic signs” of ACL injury. 

Diagnosis of ACL sprain or rupture is normally made by clinical examination with the history of the incident together with the mechanics of injury making evaluation a relatively simple process. 

An MRI scan may be taken in order to examine the potential for injury to associated structures such as the meniscus cartilage and / or collateral ligaments. 

However, the knee will feel unstable in the examiner’s hands and will demonstrate movements well in excess of the normal ranges if such a major structure as the ACL is torn, ruptured, or stretched. 

During the surgical repair process, some tidying up of minor injuries such as damage to the menisci is often required.

It’s normally the medial collateral ligament (MCL) which is the most frequent of the knee injuries sustained that accompanies ACL sprains. 

The MCL is the structure that prevents excessive sideward movement in an inwards or medial direction and is normally the first part of the knee to give in a block tackle in football since the impact will often ‘open the joint’. 

This action, known as a valgus force, stresses the ligament; resulting in a sprain or tearing of the tissue. 

This often happens when contact is made with the inside of the foot, resulting in the knee ligaments being stretched or torn as the joint opens as a result. 

MCLs are injured in exactly the same way if the player in possession of the ball is tackled on the lateral side of the body. 

The knee is forced to buckle inwards –medially – stressing the MCL in the same way as in the block tackle but from the opposite direction.

Meniscal injuries – or cartilage tears as they used to be called - are caused by excessive rotatory movements.  The most common of these mechanisms are if the knee is twisted and / or folded underneath the body when tackling or being tackled in football.

Another injury method is by ‘spinning’ around the fixed lower leg such as when taking a swipe at the ball and failing to make proper contact. 

This can cause a tear in the actual meniscus which often requires surgery.  But sometimes the foot just sticks in the ground and the knee twists; this simple movement can result in damage to any or all of the structures mentioned. 

In all cases above, there is a risk of ACL injury in conjunction with other ligamentous or cartilaginous structures.  If all three structures are injured together   - ACL, MCL and medial meniscus –this is known as O’Donoghue’s Triad and the recovery period for this is lengthy. 

O’Donoghue’s Triad usually occurs as a result of a tackle and the rehab period can often reach twelve months on average although variables exist on either side of this time-frame. 

In football, basketball, or netball, jumping and landing awkwardly on a fixed foot can have the same effect on the ACL as on the meniscus.  If you jump and land and the foot sticks, the momentum of the rest of the body can result in the knee giving way, resulting in a tear of the ACL. 

When this happens, an audible ‘pop’ or ‘cracking’ sound is often heard at the time; followed by immediate swelling and an inability to weight-bear without the knee giving way.  These are said to be the “classic signs” of ACL injury.

The rehabilitation period post-ACL surgery

Like most long-term injuries, perhaps the most difficult aspect of the whole process lies in coming to terms with the fact that rehabilitation is likely to take anything from six to nine months up to a year. 

ACL rehab is a slow and steady process and despite aggressive marketing techniques it’s just not possible to cut corners. 

From the early importance of being able to get the knee 100% straight within the first ten days after surgery, through to the functional stages where balance and proprioception are essential, a progressive approach is required.

Rehab work is designed to challenge the body’s senses and stimulate the natural neuromuscular reactions, so from beginning a run – walk programme to returning to full training, everything needs to be done at the correct stages and at the right time. 

Players who have had ACL repair or reconstruction virtually live in the gym or rehab centre where progressive strength work underpins all the rehab principles specific to knee surgery. 

ACL reconstruction needs to be combined with detailed post-operative rehabilitation in order for patients to return to their pre-injury levels (Saka, 2014), and getting fit after ACL surgery can literally be a full-time job. 

During the first few weeks post-operatively, pain and swelling tend to be the main difficulties that can hinder rehab.  At that stage, specific goals are simply to be able to achieve and maintain a full range of movement in the knee and begin to specifically strengthen the leg through a controlled exercise routine. 

Later, as the programme becomes more functionally -orientated, the whole rehab routine has the emphasis placed on developing neuromuscular control, proprioception and balance; all of which are essential for the functional stability of any joint (Lephart et al, 1997). 

Developing this aspect of rehabilitation takes time; and no matter how optimistic you are, there is no getting away from the fact that an ACL repair means an average of four to six months before any kind of realistic, high-level, sport-specific work can even be considered. 

As football goalkeeper, for example, needs to have the ability to be able to throw himself around, jump and catch, take high balls and of course be able to land safely on the knee without it giving way. 

Similarly, outfield players have to be able to twist, turn, run and jump at high speed in addition to being strong enough to challenge for the ball in competitive situations.

So the target for any player recovering from knee surgery is to build up to this stage through steady progressions, and by integrating the sport-specific work into training routines. 

However, these rehab targets are only going to be achieved by intensive interventions to improve strength, proprioception and reaction time; and by repeated functional practice in specific training activities relative to football (Jamshidi et al, 2005). 

It can be a long job; and patience is often the key.  There will inevitably be setbacks along the way.  Persistent swelling can be an issue, particularly in early stages and the initial objective of regaining full knee extension can be a common problem. 

With correct management however, and allowing for adequate recovery time in the event of any adverse reactions to rehab such as the presence of swelling for example, ACL rehabilitation today is generally successful. 

Most players who have undergone ACL surgery generally make a full and complete recovery.


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​Explaining injuries in a way that's easy to understand!!


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