Knee
Anterior Cruciate Ligament - Rehab and Prevention
Blog Series - Anterior Cruciate Ligament (ACL) No. 2
Rehab and Prevention
Incidence
As mentioned in our first blog about cruciate ligament and knee injuries , injuries to this joint and its associated structures are very common, especially to the anterior cruciate ligament. We also see this regularly in our practice BodyLab osteopathy and Physiotherapy in Zurich, where we continually treat patients with knee injuries. According to the Swiss accident statistics, between 2012 and 2016 there was an annual average of around 50,000 occupational and non-occupational accidents involving a knee injury in the form of a dislocation, sprain, or strain. The costs for these knee injuries averaged more than 500 million Swiss francs over the same period [1]. In a ten-year study, Majewski, Habelt, and Steinbrück classified all sports-related knee injuries registered with them into different categories [2]. In total, 7,769 knee injuries were recorded during this period, of which 3,482 involved either the cruciate ligaments, collateral ligaments, or the menisci; these were grouped together as internal knee injuries. Almost half of all internal knee injuries involved the anterior cruciate ligament (ACL) alone [2].
Costs and Consequences of an Anterior Cruciate Ligament Tear
Not only do these injuries cost the healthcare system millions of francs each year, but acute knee injuries can also lead to degenerative diseases such as chondropathy or osteoarthritis due to biochemical processes within the joint. As you get older, these secondary issues can lead to increased limitations in daily life and sports, as well as significantly higher costs than those of the initial injury alone [3]. Myklebust and Bahr even demonstrated that 50–100% of women who suffered an ACL rupture will show radiological signs of knee osteoarthritis in the subsequent 10–20 years [4]. In their review, the expert panel of the German Knee Society (DKG) also highlights the fact that 7–24% of patients with an operated ACL subsequently suffer an acl tear in the uninjured knee [5]. Among young patients (<26) who participate in high-risk sports (e.g., soccer, volleyball, handball), almost one in four athletes injures their ACL a second time after returning to their high-risk sport. This happens most often during the early Return-to-Play (RTP) phase, once rehabilitation is completed [6]. Compared to uninjured healthy adolescents, the risk of an ACL injury in patients with a reconstruction increases by 30- to 40-fold [6].
Furthermore, post-pubescent women playing the same sports as men already face a 2- to 10-fold higher risk of primary ACL injury due to various factors such as hormone levels or neuromuscular control [7].
You can find more about the anatomy and function of the cruciate ligaments in our first blog.
Risk Factors
The literature describes various risk factors that can increase the likelihood of an ACL tear. These risk factors are divided into two categories. On one hand, there are extrinsic risk factors such as weather conditions, clothing, equipment, or playing surfaces. On the other hand, there are intrinsic risk factors. Intrinsic risk factors can include anatomical, physiological, neuromuscular, genetic, or biomechanical aspects, among others [12].
Anatomical risk factors primarily refer to the length, width, and volume of the cruciate ligaments. Additionally, differences in the angle of the cruciate ligaments can also influence your risk of an ACL injury.
According to the study by Quatman et al., the combination of anterior tibial translation and internal tibial rotation, as well as abduction and anterior tibial translation, led to a 3.9-fold and 4.6-fold increase in load on the ACL compared to normal landing conditions [18].
Landing in knee valgus further increases the load on the ACL because the ground reaction force is heightened in this position. This leads to an increased risk of ACL tears, especially in women. In "non-contact" ACL tears, your body's center of gravity is often behind the affected knee. Contraction of the quadriceps femoris muscle pulls the tibia forward (anterior translation). This places tension on the ACL. To prevent losing balance, the hip flexes, causing the quadriceps femoris to contract even further. Due to an unfavorable lever arm, the hamstrings can no longer adequately support the ACL posteriorly. Consequently, the ACL is subjected to excessive load, and the risk of a tear rises significantly in this position [11, 18].
As neuromuscular risk factors, Myers et al. describe reduced strength of the hamstring muscles compared to the strength of the quadriceps muscle [19]. Pfeifer et al. also found that the hamstring muscles fatigue more quickly, which increases the imbalance between the quadriceps and hamstring muscles [12]. This likewise leads to an elevated risk of ACL tears.
Additionally, it has been shown that biomechanical risk factors—such as poor landing technique and knee positioning—can be modified through neuromuscular training programs, making them a crucial strategy for injury prevention (Hewett, Myer, and Ford [17]).
Nessler, Denney, and Sampley concluded from their study that a valgus position combined with limited neuromuscular control of the knee poses the greatest threat for an ACL injury [13]. These risk factors can be addressed preventatively through targeted training. To date, neuromuscular training is considered the only effective method to reduce the incidence of ACL tears [7].
Injury Mechanisms
To examine ACL lesions more specifically, they are categorized into different injury mechanisms. A "non-contact injury" refers to an injury mechanism where no external impact from another person or opposing player caused the injury. Non-contact injuries account for approximately 72–95% of all ACL injuries [14, 15]. Conversely, a "contact injury" refers to when a direct force acts on the knee, leading to the injury [16]. ACL injuries involving external contact but without direct force applied to the knee are described by authors as "non-contact injuries with perturbation" [17]. In team handball, according to a study by Olsen et al., two movement patterns are primarily responsible for non-contact ACL injuries [16]. Both situations—single-leg landing after a jump shot and rapid sidestepping (cutting)—result in a valgus position of the knee in slight flexion combined with tibial rotation.
We discuss other common injury mechanisms, such as in skiing accidents or soccer, in more detail here in our first blog.
Surgery vs. Conservative Treatment
Although there is intensive research into optimal treatment options for an ACL tear, there is still a lack of high-quality studies on the long-term management of this injury. Currently, surgical interventions for athletes are often favored over conservative therapy—especially for patients who have accompanying injuries to the meniscus or medial collateral ligament, or who experience pronounced joint instability [8, 9]. The rehabilitation following an ACL rupture with subsequent surgical treatment lasts several months. The literature cites varying timelines for different sports, ranging from about 6 to 13 months. Currently, however, there is not yet enough data to determine whether athletes from different sports require different lengths of rehabilitation before they can safely return to their sport. Despite this, 83% of elite athletes return to their sport following an ACL reconstruction [10].
Conclusion
Knee injuries, and anterior cruciate ligament injuries in particular (with or without involvement of other joint structures), are among the most common everyday and athletic injuries of the musculoskeletal system.
It remains unclear whether surgery is strictly necessary, and the choice must be carefully weighed in every individual case.
Neuromuscular training remains the only proven, effective method to decrease the incidence of ACL ruptures.
A return to everyday activities and sports is achievable in the vast majority of cases. However, the greatest risks lie in the Return-to-Play (RTP) phase, where many athletes suffer a secondary injury.
In our next blog about cruciate ligaments, we will take a closer look at the available treatment options.
Whenever you need us, we are here for you!
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Find out more on our page about acl tear.
References
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Image Credits
Mak-Ham Lam, Daniel TP Fong, Patrick SH Yung, Eric PY Ho, Wood-Yee Chan and Kai-Ming Chan, ACLI 18, CC BY-SA 2.0
