06 Jun ARE YOU OR YOUR ATHLETES AT RISK OF AN ACL INJURY?
Attention soccer players, coaches and trainers. Are you or your athletes at risk of an ACL injury?
In this 3 part series, I will discuss the Anterior Cruciate Ligament (ACL) and it’s relation to soccer performance.
The ACL is one of the most common yet highly PREVENTABLE knee ligament injuries that occurs in soccer. I will cover the following topics:
- ACL background information and injury statistics in soccer
- Common ACL injury mechanism in soccer
- Specific athletic screening / testing protocol for the ACL you can and SHOULD use in soccer
- ACL injury prevention exercises to add into your gym routine and soccer training sessions
By the end of the article I hope you can take away some practical relevance to your own sporting or coaching situations.
Background and Statistics
The knee joint requires an enormous amount of stability from passive structures such as ligaments but also requires incredible amounts of dynamic stability from surrounding musculature (e.g. quads). In soccer, the knee is subject to rotational and pivoting movements and as such is placed under a lot of stress. One of the passive structures that is vital for knee stability is the ACL. In short, its primary role is to prevent excessive forward translation and rotation of the tibia relative to the femur. The ACL is essential for control of the tibial movement and rotation during pivoting, jumping, or quick change of direction or deceleration movements. (Brukner and Khan, 2006)
The annual incidence of ACL injuries in professional soccer is reported to range between 0.15-3.7% per person per year and between in 0.03-1.7% per person per year in amateur soccer (Moses et al., 2012). Unfortunately for females the incidence is a lot higher compared to men, with research reporting that female soccer players are 2 to 3 times more likely to suffer ACL injuries (Walden et al., 2010). Remarkably, most ACL injuries are NON-CONTACT in soccer.
Common ACL injury mechanism in soccer
Soccer is a multidirectional and fast-paced sport involving numerous jumping, twisting, cutting and deceleration movements. A study by Walden et al., 2015 analysed videos of 39 fully torn ACL injuries in professional male soccer players. From this video analysis they found that 64% (25) of these ACL injuries were the result of 3 separate NON-CONTACT mechanisms. These mechanisms are summarised below:
PRESSING / SIDESTEPPING / CUTTING
In every case this involved a defending player running at a high speed who would make a cutting / sidestep movement in an attempt to get the ball / tackle the other player. This requires a fast deceleration (slowing down) combined with a change of direction placing the position of the hip, knee and ankle in a vulnerable position. Look at the right leg of the blue player in the bottom right of the photo where you can see that the entire weight of his body is on his right leg in outstretched position.
RE-GAINING BALANCE AFTER KICKING
This mostly occurred when a player was clearing a ball. During this action the player was moving forward at a fast speed while being off balance. Again, look at the position of the right leg of the yellow player in this photo: the right leg and outstretched with minimal knee bend and the ankle and rotating outwards (eversion).
LANDING AFTER HEADING
During this situation, the individual jumps and competes with the opponent for the ball. Both players make contact in the air. Focus on the red and blue player in this instance. As he comes back to the ground he is out of balance (both backwards and sideways) and lands on an outstretched leg at a fast speed with minimal knee bend. This shifts the entire load of the body onto this leg forcing the knee to give way.
In all situations, the injured leg was always in a vulnerable position (e.g. outstretched leg, hip externally rotated – turned outwards – and the ankle in either a rolled in / out position). All of these situations shift the entire load of the body onto one leg in the described positions and consequently result in a full ACL tear. Zlatan Ibrahimovic and Kurt Zouma (both professional footballers) both tore their ACLs landing after heading the ball. What you will notice is how unnatural the position of their legs were.
Following on from Part 1, I will take you through a few examples of tests that you can use in your athletic screening process. Note that these tests reflect the injury mechanisms for an ACL injury seen in part 1 (e.g. drop vertical jump [double & single leg] reflect landing after heading a ball), hence the relevance of these tests to athletic performance and injury prevention. The first one is the single leg hop and land for distance which reflects the ability to land effectively on one leg when moving in a forward direction.
Test #1 – Single leg hop and land for distance test
To perform the single leg hop and land for distance test, stand on one leg and find your balance. Once ready, hop as far as you can forward and land on that same leg. Repeat 3 times each side and take the best of the 3 measures for each side. This will give you some objective data to work with when you reassess. However, for the purpose of this series, we are more concerned with the movement quality (e.g. kinematics) of the LANDING. What we are looking for in this test is the coordination between the trunk, hip, knee and ankle when the athlete lands (Rowland, 2016). This means we want to see a soft landing with a 2 to 3 second hold/stick, good alignment of the knee (over the toes) and an upright trunk position. Below is a video of one of my soccer athletes performing this test in his pre-season this year:
As you can see in the single leg hop and land for distance video the athlete displays a stiff landing, knee collapses inwards, and the trunk bends to the side – all signs indicating an increased risk of non-contact knee injury due to undesirable kinematics.
Test #2 – Drop Vertical Jump Test
To perform this test, set up and stand on a 30cm height. You can use a box, steps + risers or weight plates, depending on what you have in your current facility. Drop off this height with a jump, hit the ground and straight away jump as high as you can and then land on two legs. For the single leg variant of this, the procedure is exactly the same however it all done on one leg.
VIDEO: Drop Vertical Jump Test (double)
Test #3 – Crossover Hop and Land Test
This test assesses the cutting /sidestepping movement capability of the individual. To perform the crossover hop test stand on one side of a 15cm wide line on one leg and find your balance. Once ready, perform 3 consecutive hops as far as you can while crossing the line between each hop. Repeat 3 times each side and take the best of the 3 measures for each side. “The distance from the start line to the toe of the test leg following the third hop was measured” (Hopper et al., 2002). Again, this will give you some objective data for when you reassess. As mentioned in the single leg hop and land for distance, the purpose of these tests are to look at movement quality of the landings. Below is a schematic diagram of hour this test would be performed and a video of how you do this in practice:
VIDEO: Crossover Hop and Land Test
There are many other screening tests that you should use with soccer players. I have only focussed on the 3 that best replicate the injury mechanisms that I discussed in part 1. Other testing should involve range of motion, strength and endurance of the lower limbs.
This wraps up part 2 of this series. Part 3 will take you some of the best exercises used to prevent knee injuries in soccer.
If you struggled to land properly and displayed poor movement quality on any of the screening tests from part 2 it is not the end of the world. Luckily for you I have provided exercises which I believe are some of the best for preventing non-contact ACL injury in soccer. Please note that I am solely focussing on landing exercises and these won’t make up the bulk of your strength and conditioning program.
The following 6 exercises can be implemented into your own soccer training sessions, for example during the warm-up, or before and between sets of your main strength exercises in the gym. The aim is to build a robust and resilient knee to reduce your risk of non-contact ACL injury (or any non-contact knee injury for that matter!). The big focus is on the movement quality of the landing, specifically the link between the trunk, hip, knee and ankle. Perform 2-3 sets of 4-8 repetitions and aim to stick/hold the landings for about two to three seconds. Don’t get left behind this soccer season and miss out because your knee was not prepared for the rigours of a soccer match.
- VIDEO 1: Forward Hop (single leg)
- VIDEO 2: Diagonal Hop and Stick
- VIDEO 3: Lateral Hop and Stick
- VIDEO 4: Single Leg Drop and Stick
- VIDEO 5: Jump and Land with Perturbation
- VIDEO 6: Rotational Hop and Stick (double)
An Accredited Exercise Physiologist can take you through an ACL preventative program that is structured and individualised to give you and your players the best chance of staying injury-free this soccer season.