The ACL is one of four main ligaments (or fibrous tissues) that connect the thigh bone (femur) to the shin bone (tibia) in the leg. It helps stabilise the knee joint when you are twisting it, for example when pivoting or landing from a jump. The ACL works with the Posterior Cruciate Ligament (PCL) to stop the tibia moving forwards or backwards from underneath the femur. These two ligaments are vitally important to the stability of the knee so that it doesn’t give way.
Injury to the ACL ligament may be sudden and acute (short term), or long-lasting and recurrent (chronic) when it is known as ACL deficiency or ACL insufficiency. An acute injury may develop into a chronic problem (but not in every case). If this happens there is a risk of osteoarthritis as the bones rub excessively and your doctor may advise ACL surgery.
These include a ‘popping’ sound at the time of the injury, a wobbly knee (or a feeling that the knee is about to give out), pain, swelling and limited leg movement. The pain may not be too intense immediately, although it may grow worse, particularly without treatment. However, similar symptoms may also indicate other types of knee ligament injury including to the cartilage, knee cushions (menisci), other ligaments, or a bone fracture. It is therefore particularly important that you see a doctor quickly to make sure you have a full diagnosis of the injury.
It is likely that your GP will refer you to a specialist orthopaedic surgeon who will take a full medical history and conduct a physical examination of the joint to check for stability and strength, movement and tenderness.
If you have gone straight to an A&E department you are likely to be sent for an x-ray, although CT or MRI scans may also be used. The x-ray will determine if you have broken a bone and whether the ACL has been torn (avulsion) or if there’s blood in the knee (effusion).
Other procedures are also used to diagnose ACL injury including arthrocentesis (where fluid is removed from the knee to check for the presence of blood) and arthroscopy (involving small incisions and careful examination of the bone and ACL).
ACL injury can result from both contact and non-contact sports, as well as from ordinary, everyday activities including walking and coming down stairs. The injury occurs when the knee has been hyperextended (ie, straightened beyond its normal range), or twisted, or bent to one side. Some sports players (including footballers, skiers and gymnasts) are more vulnerable to this type of injury than others and women are generally more susceptible than men.
Although there is no guaranteed way of avoiding injury, proper stretching and warm up exercises may help, as will strengthening the quadriceps, hamstrings and inner and outer thigh muscles in the legs. It’s unlikely that wearing strapping on your leg will make a difference to the risk of injuring yourself and sometimes this can give you a false sense of security. The best way to avoid injury is to ask your coach or physiotherapist to show you the proper technique for your sport to avoid placing strain on your ACL.
Although there is no guaranteed way of avoiding injury, proper stretching and warm up exercises may help, as will strengthening the quadriceps, hamstrings and inner and outer thigh muscles in the legs. It’s unlikely that wearing strapping on your leg will make a difference to the risk of injuring yourself and sometimes this can give you a false sense of security. The best way to avoid injury is to ask your coach or physiotherapist to show you the proper technique for your sport to avoid placing strain on your ACL.
The London Knee Unit offers advice and treatment for conditions that affect all parts of the knee. If you would like to find out more about the treatments we provide for orthopaedic conditions please visit our other musculoskeletal sites:
Musculoskeletal Foot and Ankle injuries Nerve injuries Shoulder injuries