The knee is the second most common location for injuries sustained during football (soccer) after the thigh. An ACL injury is not as common as other knee injuries and only accounts for 1% of all football (soccer) injuries but the impact on players is significant due to the long recovery time.


The anterior cruciate ligament is one of two ligaments inside the knee joint. Its purpose is to stop the tibia (shin bone) from moving forward on the femur (thigh bone) and it also helps externally rotate (twist) the tibia at full extension, prevents hyperextension of the knee and plays a part in neurosensory control.


70% of ACL tears are non-contact injuries – there is a twisting or deceleration injury, often when the athlete tries to change direction when running and they may report hearing a pop or feeling a popping sensation. The other 30% are traumatic injuries occurring during contact.

Risk factors

The biggest risk factor for a non-contact ACL injury is having had a previous ACL injury. Females have a bigger risk of ACL injury than males for multiple reasons including their bony anatomy, strength imbalances between muscle groups and possibly their hormonal profiles.


Some people who have injured their ACL describe a sense of something going out of place during the injury and there is usually swelling in the knee joint afterwards. Some athletes experience significant pain during the injury and are unable to walk off the field due to pain, while others don’t feel much pain at all.


Examination on the field straight after the injury can be helpful to rule in or out an ACL injury but after the swelling, muscle spasm and stiffness kicks in, which can be in the first 10 minutes after injury, the initial clinical examination becomes less accurate.

Diagnosis is made based on a combination of clinical examination and imaging techniques. MRI is the best imaging modality for visualizing a tear in the ligament and it can also determine if there have been other associated injuries such as an MCL sprain and/or a meniscal tear.


ACL injuries can be managed surgically or non-surgically but the ACL rarely heals after a full thickness injury. Surgical decision is based on the level of activity required by the athlete, functionaldemands on the knee and other associated injuries. Other factors to consider are the age and occupation of the player, their desire to return to football or other jumping and pivoting sports and if there is instability present. ACL injuries with associated meniscal and/or MCL injuries usually need surgical management due to increased instability in the knee, which is a risk factor for future arthritis.


Surgical reconstruction is appropriate in players who want to return to football or other change of direction sports and also for those who experience significant functional instability (ie giving way during climbing stairs). The ACL can’t be repaired because it usually tears within the substance of the ligament, so surgical techniques involve reconstruction with another tissue as a substitute for the ligament. The two most common grafts used are either one of the hamstring tendons with the gracilis tendon or part of the patella tendon taken from the same leg. There are other options for grafts including donor grafts and synthetic versions but the results generally aren’t as good.

A large study by Adern et al in 2014 showed that in 7556 athletes who had an ACL reconstruction, 81% returned to some level of athletic activity, 65% returned to pre-injury level of sport and 55% of high-level athletes returned to competition. Despite these lower rates, 90% had normal or near normal knee function after surgery. A more recent systematic review by Lai et al in 2017 showed that in1272 elite athletes, 83% returned to sport and the average time taken was between 6 to 13 months.

Non-operative management

A comprehensive and progressive rehabilitation program is needed for all athletes with an ACL injury regardless of whether operative management is used or not. Returning to sport too quickly before appropriate strength and neuromuscular control is regained is a big risk factor for re-injury. If non-surgical management is chosen, the rehabilitation and return to sport can be accelerated if the athlete meets functional outcomes and does not show any instability, as there is no extra time needed for tissue healing.


An athlete undergoing rehabilitation after surgical reconstruction needs to meet functional outcomes for both recovery from the ACL injury as well as the harvesting of the graft and also consider time frames for incorporation of the reconstructed tendon into the native tissues in the knee. In some cases, the athlete may meet all functional outcomes for return to play at 6 months post surgery, but this coincides with the time that the new graft is at its weakest and studies have shown that every month of delay of return to sport up to 9 months post surgery results in considerably less re-tears on return.

Return to sport

Initial stages of rehabilitation involve regaining full pain-free range of motion in the knee and at least 90% strength compared to the non-injured side in the muscles that work across the knee joint. A return to run program is usually started somewhere between 3 – 6 months after surgery depending on how quickly the athlete regains their range of motion and strength. In order to be able to return to sport, the athlete needs strength, proprioception and function equal to theuninjured knee, equal single leg balance on both legs with eyes open and closed, equal dynamic movements on both legs such as hop and land and 3 hop distance and sports specific movements at full pace without pain or instability. This usually occurs somewhere between 9-12 months after surgery.

Re-injury risk

Unfortunately, despite good surgical management and a comprehensive rehabilitation program, re-injury is still a recognised complication of return to sport. There is also an increased risk of an injury to the other ACL in people who have already had one ACL tear. The total rate of graft re-rupture up to10 years after surgery is approximately 6% and the risk is highestwithin the first12 months after surgery. From one year after surgery, the risk of injury is still higher compared to people who have never injured their ACL but the risk is now the same for both legs. The risk of re-injury is significantly higher for younger people, especially those under 20.


Given the long term implications of an ACL injury and the significant time away from sport required during recovery, prevention programs are essential to try to reduce rates of initial injury. Injury prevention training programs such as the FIFA 11+ have been shown to have a 50% reduction in overall ACL injury rates (including contact and non contact injuries) and 67% reduction in non-contact injuries in female athletes who are at the highest risk. Athletes must participate in these prevention programs at least twice weekly for 6 weeks for any benefit to occur.

If you have sustained a knee injury that has resulted in significant joint swelling, pain or a limp, a consultation at Shire Sports Medicine can be beneficial for you to get an accurate diagnosis, to help guide management of your condition and to ensure the prevention of further complications.