The Anterior Cruciate Ligament, or ACL, is an important stabilising ligament in the knee, and injuries to it are a widespread concern among athletes and fitness enthusiasts. The fear surrounding ACL injuries stems not only from their frequency but also from the extensive and challenging recovery process they often necessitate. But are these injuries merely a stroke of bad luck, or are there proactive measures that can be taken to prevent them? In this blog post, we discuss the mechanics of how and why ACL injuries occur, and more importantly, we explore whether effective strategies exist to avoid these debilitating injuries.
Understanding the ACL: Anatomy and Function
The ACL is one of the key ligaments that help stabilise the knee joint. It connects the thigh bone (femur) to the shin bone (tibia), playing a pivotal role in controlling the back-and-forth and rotational motion of your knee. The ACL is instrumental in providing the knee with the stability needed for activities like running, jumping, and changing direction quickly. This ligament's importance becomes evident in high-demand sports where agility and knee stability are paramount. Understanding its function is the first step in recognising why injuries to the ACL can be so impactful and why their prevention is a topic of significant interest.
How does an ACL injury occur?
It doesn’t seem like much, but analysing the pictures below reveal two typical scenarios leading to an ACL injury- the knee buckling inwards when landing from a jump or during a change-of-direction movement. This buckling movement puts a large amount of force through the ACL which can lead to a tear (as was the outcome in the two athletes seen below). Unfortunately, the ACL very rarely heals itself. For high-level athletes, this means surgery to reconstruct this important ligament and 10-12 months of rehabilitation!
Why do ACL injuries happen?
Some studies have been able to identify clear factors which may increase the risk of an ACL injury. These include:
The size and shape of the intercondylar femoral notch (The size and shape of a specific notch at the end of your thigh bone).
The depth of the medial tibial plateau's concavity (How deep the inward curve is on the top of your shinbone, specifically on the inner side).
The slope of the tibial plateaus (The angle or incline of the top surfaces of your shinbone).
Knee joint hypermobility (The ability of the knee joint to move beyond its normal range of motion, often referred to as having "loose" or "extra flexible" knees).
Seperate risk factors for repeat injury following an ACL reconstruction should also be considered, given the high rate of re-rupture following surgery. These include:
Improper graft placement: This can happen during surgery when the graft is not aligned correctly with the natural orientation of the original ACL. Proper alignment is crucial for the graft to function like the original ligament, allowing for normal knee movement and stability. If the graft is placed too vertically or horizontally, or if it's not anchored securely, it can lead to complications such as limited knee function, instability, or even re-tearing of the graft.
Inadequate/incomplete rehabilitation before returning to sport, most commonly involving:
Impaired quadriceps strength: this remains a significant risk factor for repeat ACL injuries. The quadriceps are key muscles in supporting and stabilising the knee joint. After an ACL injury or reconstruction surgery, these muscles often weaken due to disuse or protective inhibition — a natural response of the body to pain and injury.
Impaired neuromuscular control: Neuromuscular control of the knee refers to its ability to perceive its position in space, which is essential for preventing awkward movements that can lead to re-injury. Following an ACL injury, neuromuscular control is impaired and needs to be worked on through specific rehabilitation exercises.
Lack of sport-specific training: It's crucial for athletes to undergo adequate, tailored training that aligns with the specific demands of their sport before engaging in competition. This type of training ensures that athletes are not only physically prepared — with the necessary skills, strength, and agility — but also mentally confident to safely compete.
The level of an athlete's preparedness for their specific sport might influence their risk of a first-time ACL injury, though the exact relationship is not definitively clear. Theoretically, certain factors that increase strain on the ACL during sports activities should be considered. These include:
Poor Jumping and Landing Techniques: For instance, knees collapsing inward (valgus collapse) when landing from a jump. This improper technique increases the stress on the ACL.
Increased Body Mass Index (BMI): A higher BMI may contribute to greater stress on the knee joints during physical activities, potentially increasing the risk of ACL injuries.
Lack of Sport-Specific Training: Insufficient training and exposure to the specific demands of a sport prior to competition can leave the athlete unprepared for certain movements, leading to a higher risk of injury.
Increased Q-angle: This is particularly relevant for women. The Q-angle is the angle formed by the quadriceps muscles and the patella tendon. A larger Q-angle is thought to put more strain on the knee, possibly increasing the risk of ACL injuries in women.
Research has indicated that these factors, among others, may contribute to the likelihood of sustaining an ACL injury. Therefore, tailored training and conditioning programs that target the potentially modifiable risk factors (e.g. risk factors 1-3 above) should be considered, particularly in sports with high demands on knee stability and strength.
Can ACL injuries be prevented?
Research indicates that implementing an injury prevention program, particularly one that emphasises neuromuscular control of the knee and hip, may modestly reduce the risk of first-time ACL injuries. These programs typically focus on improving the coordination and strength of muscles around the knee and hip joints to enhance stability and correct movement patterns. However, the exact details and most effective components of such programs are not yet fully established. While the broad principles are understood — like strengthening, balance training, and agility exercises — the specifics regarding the most effective exercises, their intensity, duration, and frequency are still subjects of ongoing research.
Ultimately, each athlete's risk is determined by the interplay between the above mentioned risk factors and more. The best you or any athlete can do to prevent such an injury is focus on correcting any modifiable risk factors with the guidance of your physiotherapist. Tailoring a program to individual needs and sport-specific demands could potentially enhance their effectiveness in reducing ACL injury risk.
If you have had a previous ACL injury or would like to implement an injury prevention program to reduce your future risk of injury, get in touch with us for an appointment (book online or call us on 0415 889 903). If you'd just like some more info, send us an email kris@prosportphysio.com.au and we can direct you to some great resources!
