ACL Injury

Feb 20, 2023

What is an ACL injury?

The Anterior Cruciate Ligament is one of the two cruciate ligaments found in the middle of the knee joint and runs diagonally from the femur (thigh bone) to the tibia (shin bone). The function of the ACL is to stop the tibia from sliding out in front of the femur as well as providing stability to the knee. An ACL injury is a tear or sprain of the Anterior Cruciate Ligament.

How does an ACL injury happen?

An ACL injury is common in field and contact sports. The most common mechanism of injury that we see presenting to our clinic is a ‘pivot-shift’ mechanism. With this type of injury, it is a combination of rapid deacceleration whilst pivoting the knee. In 70% of cases (Shimoochi et al. 2008), injury to the ACL happens during non-contact movement, e.g. rapidly changing direction, landing from a jump, an abrupt deceleration or twist. Particular sports, e.g. Soccer, Gaelic games, Basketball and Rugby, commonly demand these activities of the knee. Skiing is another common mechanism of cruciate injury and various falling mechanisms have been described.

Direct contact with an opponent can also cause injury to the ACL when the knee is forced into a position that stresses the ligament. Patients often report a “popping” sensation and feel the knee “buckling” or “giving way” at the time of injury. Symptoms often include immediate pain and swelling, unable to continue activity, instability and loss of range of motion.

What are the symptoms of an ACL injury?

ACL injury should be suspected if you have sustained a pivot shift (twisting the knee with your foot planted) injury. Injuries to the cruciate ligaments usually result in immediate swelling. You may feel that the knee is unstable or that you cannot weight bear through it. Your local physiotherapist or GP will be able to perform some tests to check the integrity of the ACL. If an ACL injury is suspected, they will arrange an MRI to confirm this.

What should I do if I have sustained an ACL injury?

Usually young athletes and active adults with a complete ACL rupture looking to return to sporting activity that requires twisting and jumping will require reconstruction.

In order to prepare yourself for surgery it is important that we restore your knee to normal function. You should begin working with your physiotherapist straight away to commence your pre-operative rehabilitation. Your physiotherapist will provide you with a home exercise programme consisting of isometric and range of motion exercises.

It is vital that you have full knee extension and full knee flexion prior to surgery. This ensures the best outcome after surgery. Once a bony injury has been ruled out by your physiotherapist you will be encouraged to mobilise as normal. Crutches may be required to assist a normal gait pattern and to ensure that you are not walking with a limp during the initial days after the injury.

If you have not already done so, please contact our office to set up a consultation with Prof. Moran to discuss your treatment options. We will also require a letter from your GP/Physiotherapist and MRI report. We can arrange an MRI through or office if you have not been able to arrange one locally. You can find out more about other Knee injuries by visiting the knee section of our website.

Shimokochi Y, Shultz SJ. Mechanisms of noncontact anterior cruciate ligament injury.
J Athl Train. 2008 Jul-Aug;43(4):396-408. doi: 10.4085/1062-6050-43.4.396. PMID:
18668173; PMCID: PMC2474820