by Dr Anthony Theodorides, Consultant Trauma and Orthopaedic Knee Surgeon Athens, Greece
The burden of ACL injuries
Approximately 350,000 ACL reconstructions are carried out annually in the USA with the financial impact estimated to be around $2 billion. When the ACL tear is accompanied by meniscal or cartilage injury there is increased risk of developing subsequent osteoarthritis. Despite ACL reconstruction having excellent results, 20% of patients will suffer re-injury within 2 years. Individuals at greatest risk of reinjury are men aged 20-24 years and women 15-19 years. Revision ACL reconstructions can be performed following a reinjury of the operated ACL however the results are not as good as the first time around. That is why it is imperative to get things right the first time. Not only in choosing the right surgeon to perform the operation optimally but to also be dedicated to the postoperative rehabilitation programme. No matter how well the operation is performed if the patient cannot commit to the rehabilitation programme they will have an increased risk of ongoing problems with their knee including increased risk of retearing of their reconstructed ACL. There is an increasing focus on ACL injury prevention programmes which can reduce by half the risk of tearing the ACL.
Mechanism of ACL injury
ACL is one of the four major ligaments in the knee. It helps prevent the tibia (shin bone) going too far forwards in relation to the femur (thigh bone) and provides rotational stability. It occurs most commonly due to a non-contact injury whilst rapidly changing direction, pivoting or landing after a jump. 70% of ACL injuries are due to a non-contact injury (i.e. due to a wrong movement rather than a collision). Only 30% of ACL injuries are due to contact injury with either another player or an object. Rapid change in direction and speed (particularly deceleration) pose an increased risk to ACL injury.
Who is at risk of an ACL injury?
ACL injury has an incidence of about 1 in 3000 in general population and 1 in 1750 in people aged 16-45 years. Individuals at greatest risk of injury are men aged 20-24 years and women 15-19 years. It is most commonly seen in sports involving pivoting such as football, basketball, netball (highest risk), volleyball, down-hill skiing and gymnastics. Netball carries the highest risk of any sport for ACL injury because it involves rapid deceleration and is played by women who have additional inherent risks of ACL injury. It can occur at any age but typically adolescents to middle age are affected. ACL injuries are increasingly seen in children due to increased competition of youth sports with intense drive to succeed and obtain scholarships and future financial benefits.
Why women have a higher risk of ACL Injury
Female athletes are 2-10 times more likely to injure their ACL than males playing the same sport. In football, females are 3-5 times more likely to injure their ACL than males and in basketball this increases to 2-7 times more likely to injure their ACL than males.
There are numerous reasons why women have higher risk of injuring their ACL. These vary from anatomical reasons such as having a higher BMI (Body Mass Index which is a measure of obesity), more elastic ligaments leading to hypermobility, to a wider pelvis putting the knee in a suboptimal position. Biomechanical and neuromuscular causes have been found to be a worse landing technique due to weaker core musculature and reduced bending at the hip and knee. The knees in women tend to come together on landing and this is mainly due to weaker gluteal (buttock) muscles and this too puts the ACL at risk. Women’s menstrual cycle has a direct impact on the risk of ACL injury. The hormonal fluctuations that occur during the menstrual cycle result in certain times of the month being of greater risk. Women have 2.4 times greater risk of ACL injury in the pre-ovulatory (first half of menstrual cycle) than post-ovulatory phase (second half of menstrual cycle).
Symptoms of ACL tear
ACL injuries cause immediate and intense pain. The patient may hear and feel a pop inside their knee which rapidly becomes very swollen. Typically, they are unable to carry on playing during a game and if they do, they feel the knee relatively stable when moving in a straight line but give way when they change direction. If there is a displaced meniscal tear, the knee can lock (inability to straighten out the knee) and this requires prompt medical assessment and potentially an operation to regain knee mobility and sort out the meniscal tear. If the patient tries to play sports after the ACL is torn, they will have a feeling of instability with the knee buckling under them. In particular they will be unable to reliably jump and land on the knee, accelerate and decelerate and rapidly change directions.
How is ACL injury diagnosed?
A thorough history and examination of the knee can detect an ACL tear in more than 80% of cases. MRI scan is the gold standard investigation for diagnosing ACL injury by being able to detect over 95% of cases but it is not quite 100%. More importantly though MRI scan detect additional injuries which can affect the management plan for the patient, to better plan what will be needed during the operation as well as to know how urgently to proceed with an operation. Meniscal tears occur in 50-75% of ACL injuries and additional ligament injuries (most commonly the inner side ligament – also called medial collateral ligament) in around 40% of cases.
Does every ACL injury need an operation?
Not every ACL injury needs to be operated. Conservative management would be suitable for older patients, less physically demanding patients, those who do not have a feeling of instability during everyday activities, those who are happy to restrict their activities to exercises that put less rotational stresses to the knee such as straight-line jogging on level ground, cycling, and rowing, and the presence of moderate to severe knee osteoarthritis. ACL reconstruction can be carried out at a later date if the patient despite a good course of physiotherapy is still having instability episodes and they wish to go back to competitive and rotationally demanding sports.
The disadvantage of conservative management is that rehabilitation can be more painful due to lack of protection of an intact ACL. There is a higher risk of meniscal injury when the knee gives way which then increases the risk of developing osteoarthritis. The incidence of meniscal tear (especially the inner/medial meniscus) in the presence of chronic ACL instability is 75-90%. ACL reconstruction permits return to competitive sports by stabilising the knee and preventing instability episodes in the knee which would cause further damage to the cartilage and meniscus.
What is an ACL reconstruction?
The primary goal of ACL reconstruction is to restore knee stability, enabling return to sport and reduce risk of subsequent arthritis. The procedure typically involves a general anaesthetic and a regional block around the knee to provide extra pain relief. Most commonly a tendon graft is used from the same patient usually two hamstring tendons. Tunnels are drilled into the femur and tibia accurately as their position greatly affects how stable the knee will be. The graft is then passed through the tunnels and secured both on the femur and the tibia. Other soft tissue injuries such as meniscus, chondral and ligament injuries should also be addressed in the same operation where appropriate.
Who should have an ACL reconstruction?
Active individuals who wish to get back to competitive sport especially pivoting sports such as football, basketball and tennis, would benefit from having an ACL reconstruction as this would provide them a rotationally stable knee so that they can do their sport without their knee giving way and causing further injury. Patients who continue to have ongoing instability despite trying conservative measures and carrying out an ACL rehabilitation programme should consider proceeding with surgery. Patients who have additional injuries such as meniscal, cartilage and other ligaments as they have the highest risk of osteoarthritis without operative intervention are prime candidates for surgery. Children and adolescents should have their ACL reconstructed promptly to prevent further injury inside the knee. It is difficult for this age group to abstain from sporting activities and without an ACL, as recurrent instability episodes occur that put cartilage and menisci at risk of injury with disastrous consequences for early onset osteoarthritis. Surgery should not be delayed by more than 5 months as this doubles the risk of requiring medial meniscal surgery and the risk increases to 6 times if delayed by more than a year.
What should you expect from an ACL reconstruction
ACL reconstruction is the gold standard for surgical treatment. 90% of patients are able to return to sport at the same level of competition as before the injury. 98% of patients would undergo surgery again. 85% of patients who have undergone ACL reconstruction are satisfied with their outcome.
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