ACL tears

  • The anterior cruciate ligament is the main ligament at the front part of the middle of the knee that stops the tibia (shin bone) from sliding too far forward. The ACL also helps stabilize the knee from rotating too much.
  • ACL tears most commonly occur from football, netball, squash or skiing injuries, where the knee is twisted in a bent position.
  • When the ACL tears there is often a ‘pop’ felt in the knee. The knee is usually severely painful straight away and swells up rapidly. Most of the time an ACL tear is a fairly severe injury and most people are not able to continue doing whatever sport/activity they were taking part in, and there is often difficultly weight bearing or moving the knee.
  • If there is any suspicion of an ACL tear then you should get yourself an MRI scan ASAP!  If you go to A&E and you’re simply given an X-ray and just told that you’ve only got a ‘soft tissue injury’ in your knee then don’t accept this, because this is trash! If your knee is severely painful and swollen, and if it doesn’t feel ‘right’ then you need an MRI scan!
  • Initial management of an ACL tear involves rest, icing the joint, anti-inflammatories and physiotherapy. If, however, there is other damage inside the knee, such as a meniscal tear, then you may well end up needing a knee arthroscopy to sort this out prior to then having physio rehab.
  • Some patients can do ‘well enough’ without surgical ligament reconstruction through just physio rehab alone, by strengthening the muscles and speeding up the reflexes sufficiently to compensate for the increased laxity in the joint. However, if there is significant functional instability in the knee, with giving way, then you are much better off getting the ligament surgically reconstructed to stabilize the joint, because every time a knee gives way you are potentially causing further damage in the joint and increasing the risk of developing meniscal tears, articular cartilage damage and arthritis.
  • If you’re a professional athlete or a high demand individual (particularly if you take part in impact/pivoting sports such as football, squash, tennis, basketball or netball) and if you’ve torn your ACL then you’re much more likely to need a surgical ACL reconstruction.


The anterior cruciate ligament (ACL) is the main ligament in the middle of the knee that stops the shin bone (tibia) from wobbling to far forwards (anteriorly). The ACL is the ligament that is so often torn by sports people in accidents such as nasty football tackles or skiing falls.

Typically, ACL tears occur when the knee twists externally excessively in a bent loaded position, although some ACL tears can occur from hyperflexion of the knee. When the ACL tears/ruptures, patients often feel a snap/ping in the joint, the knee gives way and there is severe pain followed by marked swelling on the joint, and patients are normally unable to weight bear properly.

When the ACL tears, it is often part of a multi-part injury. First, the medial collateral ligament (MCL) sprains or tears, then the ACL ruptures and finally there is impact on the lateral side of the knee that often causes bone bruising and/or a lateral meniscal cartilage tear. In up to 10% of cases there is also an associated tear of the posterolateral corner structures. In up 50% of ACL tears there is an associated meniscal cartilage tear.


Anytime that an ACL tear is suspected, the first step is for the patient to get an MRI scan ASAP, which normally confirms not only the diagnosis of an ACL tear, but which also shows what other potential damage there might be in the joint.

Early treatment

If an ACL tear is caught very quickly (within the first 48 hours) then it is possible to go straight ahead with surgery to reconstruct the ligament. This is a fair thing to do for very high demand patients such as top athletes. However, for most patients this is just not really appropriate, and it is far better to let the knee settle down, to check everything fully and for the patient to be given sufficient time to research the whole subject of ACL tears, to fully understand the all pros and cons of all the options along with the risks and rehab potentially required, and then make a measured confident decision in the cold light of day after a full, detailed discussion with their knee surgeon and their physiotherapist.

For most people, this is not a relevant discussion anyway, as their injury tends to be more than 48 hours old. After the first 48 hours or so, the knee enters what is referred to as ‘the inflammatory phase’, where the joint stiffens up badly. If the ACL is reconstructed during this phase then there is an increased risk of the knee developing what is called ‘arthrofibrosis’, where the joint fills up with scar tissue and becomes extremely stiff, and this is then something that is extremely difficult to treat. Therefore, once the joint has entered this inflammatory phase then the patient should protect the joint, give things time to settle down, start physio treatments as soon as the knee is comfortable enough and then see how things go. If the patient does decide that they do need/want surgery, then this can be undertaken once the joint inflammation has settled and once the knee has regained a decent range of motion, which often tends to take about 6 weeks or so.

During the early post-injury period, standard treatment to help the knee settle down as quickly as possible includes:-

  • relative rest and taking things easy, but not total general immobility
  • painkillers and anti-inflammatories
  • icing the knee (but not allowing direct contact of ice with the skin, and taking care to avoid ice burns)
  • the GAME READY system, for effective icing and intermittent compression, to reduce pain and swelling
  • crutches, if necessary
  • a knee brace, if the knee is very painful, if the joint feels unstable or if there is a multi-ligament injury or a severe MCL injury as well as the ACL tear
  • PHYSIOTHERAPY – it is essential to find yourself a decent physio, as effective physiotherapy and rehab treatments are essential for a good outcome.

The rule of thirds

As a generalization, about 1/3 of patients with an isolated ACL tear can actually do very well by giving their knee time, having regular physiotherapy rehab treatments and building up the strength in their muscles (particularly the hamstrings) and speeding up their reflexes (proprioception) to compensate for the increased laxity in the joint. In this group of patients, they may actually be able to achieve a good outcome and return to normal activities without the need for any surgery.

The middle 1/3 of patients might do reasonably well with initial rehab treatments, and they might be able to return to some level of exercise or gentle sport but they do not get back to full sport or full function. In this group, the decision as to whether or not to have surgery to reconstruct the ACL is very much down to just how happy the patient actually is with their knee and what their functional aspirations might be.

With the final 1/3 of patients, the knee is wobbly and unstable and the joint gives way intermittently (particularly with any twisting type manoeuvre), and their function is significantly restricted. Each time the knee gives way there is the propensity for further damage in the joint, quite apart from the fact that the patient might generally hurt themselves if they fall badly. In this group, the patient really should go ahead and get the ACL reconstructed.

ACL tears with a meniscal tear

If there is other, concomitant, associated damage in the knee at the same time as an ACL rupture, then this certainly changes things significantly. If there is a meniscal tear, then the patient is likely to need a knee arthroscopy to confirm the diagnosis, to tidy up the joint (and trim the torn ACL stump) and to deal with the meniscal tear (either trim or repair, as appropriate). Whether or not to go ahead and just get on and reconstruct the ACL at the same time as the arthroscopy or whether to just have the arthroscopy and then follow this with physio rehab and give things time to see how things go with respect to the ACL is a difficult argument and something that requires careful discussion and consideration.

ACL tears with other ligament injuries

If the injury is a multi-ligament injury such as a combined ACL/PCL tear or an ACL tear + posterolateral corner injury, then the joint is far more likely to have more severe instability and to end up needing a reconstruction of all the relevant torn structures.

Concomitant tears of the medical collateral ligament (MCL) are different. The MCL is extra-synovial / extra-articular, and sits outside the capsule of the knee and is therefore not surrounded by synovial joint fluid. Also, the MCL is a broad ligament (and not like a narrow bungee rope, like the ACL). Therefore, most MCL tears or sprains (partial tears) actually heal up very well on their own and don’t need any kind of surgical treatment. More minor partial tears can often simply be ‘ignored’, as they settle down very quickly. If there is a more severe partial tear or a complete tear of the MCL then the knee may need to be protected with a hinged brace for 6 weeks to protect the MCL and to allow it to heal up successfully without stretching out.

The ACL tibial avulsion fracture

There is one special kind of ACL injury that is different from a standard ACL rupture. This is where the ligament actually pulls off from its attachment to the top of the tibia, fracturing off either a large chunk or a number of smaller chunks of bone off the tibia, from what is called the tibial spines (or the tibial intercondylar eminence). However, the fibres of the ligament are actually intact and in continuity (even though they might also have been sprained and slightly stretched). This injury is not very common, but it tends to occur predominantly in children or in younger women, where the ligament may actually be stronger than the bone to which it is attached.

The reasons that this is a special case are that:-

  • the ACL is actually intact
  • the bone fragments and the ACL attachment to the tibia can often be fixed back in place surgically, with either a screw, wires or strong sutures
  • if left alone, the ACL will retract and become non-functional, and any displaced bone fragments may catch at the front of the knee and prevent full straightening (extension) – a fixed flexion deformity
  • if there is an ACL tibial avulsion fracture then this should not be left, and the appropriate treatment is usually for this to be managed surgically, with early reduction and surgical fixation as soon as possible
  • with successful early surgical treatment, most patients do very well and manage to achieve a good, functional, stable knee, avoiding the need for an ACL reconstruction.


Whether an ACL rupture is treated conservatively with physio rehab alone, or surgically with an ACL reconstruction, either way the patient is definitely going to need a lot of time and help from their physiotherapist, and this is going to be key to the success of their outcome. The importance of physiotherapy and of the quality of the individual physiotherapist really should not be underestimated.

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