Prevention and Rehabilitation of ACL injuries

An anterior cruciate ligament (ACL) injury is one of the most serious injuries for an athlete, with major consequences on both a sporting and social level. An anterior cruciate ligament (ACL) injury is common in athletes, especially football players. Why is this? What’s important during rehabilitation, and more importantly, how can you prevent it?

An anterior cruciate ligament (ACL) injury is one of the most serious injuries for an athlete, with significant consequences for both sporting and social well-being. During the 2023 Women’s World Cup, this topic received a great deal of attention because more than a full team of players were absent due to an ACL injury. Besides football, skiing is another sport with a high risk of such injuries.

Women at Higher Risk
Possible causes of ACL injuries include a strength imbalance between the quadriceps and hamstrings, instability in the knee joint, incorrect movements, knee valgus, playing on artificial turf, poor footwear, and fatigue. Research in Australia shows that the number of ACL injuries has increased by approximately 7 percent per year over the past twenty years. In girls up to 14 years old, this was even 10.4 percent per year, and in women over 45 years old, 8.6 percent. It is striking that the number of other knee injuries remained virtually the same or even decreased during the same period. Women are at greater risk of an ACL injury than men, possibly due to differences in anatomy, a greater knee valgus (inward knee position), and the influence of the hormone cycle. The increase in the number of female soccer players may also contribute to this trend.

Large-scale studies
To measure the progress of rehabilitation after an ACL injury, in addition to passive tests, primarily isokinetic tests (focusing on the knee joint), balance, and hop tests are performed. Determining the right time to return a player to full weight-bearing remains difficult, as evidenced by the high number of recurrences. In a large-scale German study among professional, semi-professional, and amateur teams, 958 ACL injuries were recorded. Of these players, 23.3 percent had previously sustained an ACL injury and 19.3 percent had suffered another knee injury to the same leg. Most injuries were non-contact injuries, involving no contact with other players. In this group, the risk of a second ACL injury appeared to be significantly higher, regardless of whether they were amateurs or professionals. It is striking that the second ACL injury occurred almost as often in the previously injured leg as in the other leg, suggesting a possible coordinative cause.

Many factors
To better understand the causes of ACL injuries, it is essential to examine as many factors as possible in conjunction and improve them. Daily movement is a complex activity that is partly controlled by innate programs in the body. This is clearly visible in animals, such as a foal that can stand and walk on their first day. Humans also develop such programs that control the body largely unconsciously. Every person has a unique anatomy and is exposed to unique stimuli, which leads to a unique way of moving. Sometimes these movement programs are limited or disrupted, for example, by pain, uncertainty, an injury, or surgery. The body then compensates by loading other body parts differently. For example, pain can cause someone to walk crookedly, with one leg being loaded extra to protect the other. Forces in the body are partly dampened and partly transmitted to other body parts, meaning that movements in one body part can influence other parts. For example, the force exerted on the foot can extend to the hand. This means that a measurement with a force platform, such as a vertical jump, can provide insight into the risk of injuries, even to body parts such as the elbow. This interdependence and influence between body parts emphasizes the importance of test methods and training stimuli that simultaneously measure and improve multiple aspects of the body in a functional setting.

Gold Standard
A force platform is a measuring device on which you can stand and perform various actions, such as balancing on one leg, squatting, or jumping. The platform continuously measures the ground reaction force, allowing the development of these forces to be analyzed. With systems with two separate platforms, the forces from the left and right sides can be recorded and compared separately. The force platform is considered the ‘gold standard’ in science and is increasingly used in sports and rehabilitation practice. The device provides accurate and highly reproducible data during a functional activity, making it ideal for assessing both performance capacity and injury risk. The platform can be used effectively to compare with other people and to determine the progress and management of rehabilitation processes.

Functionality
When moving, the entire limb chain must communicate optimally. The body functions as an engine that initiates movement and as a spring that provides cushioning, increases efficiency and conserves energy, while transferring forces across all body parts produces the final result. By stiffening the body, movement becomes more explosive and stability increases. But the muscles must also relax. The timing of contraction and relaxation between the involved muscles and the course of force output per body part partly determines performance, while stabilization of a joint must also occur at the right time. Each person has a specific technique and individual characteristics, but there are several conditions for optimal performance and injury prevention, such as jumping and movement technique.

Movement Technique
There are different techniques in movement, including a vertical jump. The peak forces around the knee, particularly eccentric ones, can vary significantly depending on the technique. An incorrect force distribution around the knee appears to be a very good predictor of general knee complaints and ACL injuries. Good posture, sufficient flexibility and mobility, and correct timing of muscle activation are not only essential for optimal acceleration, sprinting, braking and changing direction, but also for maintaining stability at the right moment. The muscles must already be contracting, building stiffness and stability around the joints before large forces are exerted on them. For example, during running, the muscles in the chain, and especially the muscles around the ankle, are already contracting before the foot hits the ground. The timing of muscle activation is automatic and affects the entire chain, similar to reflexes. Furthermore, specific attention is needed for the posture of the torso, pelvis, and feet. These function as steering wheels and provide cushioning. Biarticular muscles, those that cross two joints, such as the gastrocnemius and hamstring muscles, also play an important role in stabilizing the knee and thus in preventing ACL injuries.

Hypergravity Training
Certain training methods can also contribute to knee stabilization and thus to the prevention and rehabilitation of ACL injuries. One example is Hypergravity Training, a form of stimulation that increases acceleration rather than mass. Force is mass times acceleration. You can apply external force with a barbell, which is mass. However, the resistance of a barbell is not constant due to mass inertia, but depends on the acceleration. So, when you move more explosively, the resistance is greater than when you move slowly. With hypergravity resistance, the additional mass remains the same and the body is accelerated more, making the eccentric movement faster and forcing the body to build up preload earlier, thus increasing functional stability. Hypergravity Training primarily stimulates the functioning of the spring system and the cooperation within the chain, while the function of the muscles as motors is particularly stimulated at higher speeds. This training method is therefore particularly effective for everyday movements that frequently involve rapid pre-stretching, such as quick squats, descending stairs, jumping, braking, and changing direction, but also throwing a ball.

Vector Training
A specific form of Hypergravity Training is Vector Training. In this training, there is resistance on both the left and right sides of the body that constantly changes direction. The person walks forward and backward through the axis, causing the pulling force to come alternately from the front and from behind. This exercise can be performed at any pace, for example, walking, running, or jumping. The person is forced to stabilize the chain and simultaneously improves their posture. The pulling force is always present and therefore requires overcoming the extra resistance while walking away and braking more quickly when approaching the power source. The person experiences the resistance as an additional load and simultaneously as an aid that provides guidance and control in the movement.

Conclusion
The ACL injury is a rapidly increasing and serious injury. Despite extensive research and preventive and rehabilitation programs, the risk of this injury and recurrence is still relatively high. Innovations in testing based on performing daily activities provide more insight into the actual injury risk. Innovations in training used for both prevention and rehabilitation improve functionality and reduce the injury risk. A major advantage here is that the person has control over the movement while simultaneously being forced to perform this movement more effectively and does so automatically. Implementing these innovations offers a new dimension in assessment and training that at first glance seems drastic and complicated, but with little experience on the part of the patient and therapist, can be easily implemented within the existing program.

Article translated from
https://www.kngf.nl/magazine/artikelen/preventie-en-revalidatie-van-voorste-kruisband-blessures/ The KNGF is the professional association of physiotherapists in the Netherlands and has existed since 1889.

On the author:
Drs. Martin Huizing is an exercise scientist and trainer. He has been working with and researching innovations in sports and rehabilitation for 25 years, with a special focus on ACL injuries.