ACL Injury Risk Reduction

Tears of the anterior cruciate ligament, or ACL, are a prevalent sports-related injury. 250,000 ACL tears occur on an annual basis, and athletes that participate in sports such as soccer that involve cutting, jumping, and pivoting are at an especially high risk¹. The ACL prevents anterior tibial translation (the tibia sliding forward relative to the femur), and prevents the knee from hyperextending. It is also a stabilizer against knee valgus (it prevents the knee from collapsing inwards).

Recently, more and more data has emerged that suggests that performing a dynamic warm-up before practices and games can be effective at reducing the risk of ACL injury¹¹. However, a consensus regarding the most effective components of a prevention program has not been reached. Despite the lack of an evidence-based consensus on the optimal warm-up, there is ample evidence that certain knee movements, muscle activation patterns, and movement strategies predispose the ACL to excessive strain, and therefore potential injury. Therefore, we at MOTUS Specialists Physical Therapy Orange County have proposed some foundational concepts of a soccer warm-up that primes the body to activate and move in a way that protects the ACL.

While mobility is an important aspect of ACL injury prevention, it is important to consider how that mobility is gained during warm-up. Static stretching is performed by taking a limb or joint to it’s end-range and staying there for 30-60 seconds. Static stretching has been shown to increase the amount of anterior tibial translation available at the knee⁴, and such laxity has been shown to be a risk factor for ACL injuries⁸. Additionally, static stretching actually seems to decrease athletic performance, likely as a result of the inhibitory effect it has on muscle activity². To the contrary, dynamic stretching, or active movements that take an athlete through his/ her full range of motion, has been shown to increase performance. Furthermore, dynamic stretching is favorable because it allows an athlete to practice actively moving through his/ her full range of motion. Therefore, dynamic stretching should be favored over static stretching for pre-activity warm-ups.

Mobility in certain movements are especially important to reduce ACL injury risk. Specifically, decreased range of motion at the ankle and hip joint can necessitate more motion at the knee, resulting in increased ACL strain. Decreased ankle dorsiflexion (toes/ foot pointing up) and hip external rotation (toes pointing out) can lead to increased knee valgus, a position that directly strains the ACL¹². Additionally, athletes with decreased hip internal rotation (toes pointing in) has been found to have an increased risk of ACL tears⁵. Therefore, active movements into ankle dorsiflexion and hip internal/ external rotation are important components of an effective warm-up.

Movement patterns are another important component of an effective prevention program. While retraining of movement patterns can take extensive training outside of a warm-up routine, it is important to incorporate ideal movement patterns in a warm-up to prime the body to move in a safe and efficient manner. Specifically, training a “hip strategy” with lunging, jumping, and landing is an effective way to reduce strain through the ACL. A hip strategy refers to increased hip flexion/ forward trunk lean during loading and landing tasks. By leaning forward and increasing hip flexion you tension and stretch the hamstring muscles, which prevents anterior tibial translation and reduces load through the ACL¹⁴. Additionally, you put the gluteal muscles in a better position to create force to stabilize and support the hip and knee. It has also been shown that increased knee and hip flexion (bending) with landing tasks put an athlete at decreased risk for ACL injury¹². It is important that this is controlled hip and knee flexion, as increased quadriceps stiffness during landing has been shown to decrease strain on the ACL⁹. By increasing the depth of controlled hip and knee movement, you put more demand on the active structures (muscles) and less on the passive structures (ligaments, like the ACL).

Lastly, it is important to perform some light muscle activation exercises that will prime key muscles to activate during activity. It is important to dose this portion of the warm-up appropriately, as you do not want to fatigue the muscles heading into a game or practice. Two important muscles are the hamstrings and the gluteus maximus. The hamstrings work as an ACL agonist (they work together with the ACL to prevent anterior tibial translation), and stronger hamstrings have been correlated with decreased ACL injury risk¹⁰. Additionally, it has been demonstrated that the ability of the gluteus maximus to produce force quickly, or generate power, is an important protector against valgus knee movements that predispose the ACL to injury⁶. Therefore, exercises that strengthen the hamstrings and gluteus maximus outside of warm-up should be coupled with a relatively small volume of activation exercises in the pre-game warm-up to facilitate ideal muscle activation patterns.

As with any warm-up, it is important to ensure that the warm-up increases heart rate/ body temperature and recreates sports-specific skills and movements. However, if the goal of the warm-up is to reduce ACL injury risk, the following components should be included:

• Mobility: ankle dorsiflexion, hip internal and external rotation
• Movement patterns: controlled knee and hip flexion with landing, hip strategy
• Muscular strength: hamstring strength, gluteus maximus power

So get out there, incorporate these specifics into your warm-up routine (and ideally your training routine), and keep yourself on the field!

References

1. Acevedo, R. J., Rivera-Vega, A., Miranda, G., & Micheo, W. (2014). Anterior Cruciate Ligament Injury. Current Sports Medicine Reports,13(3), 186-191. doi:10.1249/jsr.0000000000000053
2. Behm, D. G., Blazevich, A. J., Kay, A. D., & Mchugh, M. (2016). Acute effects of muscle stretching on physical performance, range of motion, and injury incidence in healthy active individuals: A systematic review. Applied Physiology, Nutrition, and Metabolism,41(1), 1-11. doi:10.1139/apnm-2015-0235
3. Barengo, N., Meneses-Echávez, J., Ramírez-Vélez, R., Cohen, D., Tovar, G., & Bautista, J. (2014). The Impact of the FIFA 11 Training Program on Injury Prevention in Football Players: A Systematic Review. International Journal of Environmental Research and Public Health,11(11), 11986-12000. doi:10.3390/ijerph111111986
4. Baumgart, C., Gokeler, A., Donath, L., Hoppe, M. W., & Freiwald, J. (2015). Effects of Static Stretching and Playing Soccer on Knee Laxity. Clinical Journal of Sport Medicine,1. doi:10.1097/jsm.0000000000000174
5. Boutris, N., Byrne, R. A., Delgado, D. A., Hewett, T. E., Mcculloch, P. C., Lintner, D. M., & Harris, J. D. (2018). Is There an Association Between Noncontact Anterior Cruciate Ligament Injuries and Decreased Hip Internal Rotation or Radiographic Femoroacetabular Impingement? A Systematic Review. Arthroscopy: The Journal of Arthroscopic & Related Surgery,34(3), 943-950. doi:10.1016/j.arthro.2017.08.302
6. Cronin, B., Johnson, S. T., Chang, E., Pollard, C. D., & Norcross, M. F. (2016). Greater Hip Extension but Not Hip Abduction Explosive Strength Is Associated With Lesser Hip Adduction and Knee Valgus Motion During a Single-Leg Jump-Cut. Orthopaedic Journal of Sports Medicine,4(4), 232596711663957. doi:10.1177/2325967116639578
7. Dallinga, J. M., Benjaminse, A., & Lemmink, K. A. (2012). Which Screening Tools Can Predict Injury to the Lower Extremities in Team Sports? Sports Medicine,42(9), 791-815. doi:10.2165/11632730-000000000-00000
8. Homan, K. J., Norcross, M. F., Goerger, B. M., Prentice, W. E., & Blackburn, J. (2013). The influence of hip strength on gluteal activity and lower extremity kinematics. Journal of Electromyography and Kinesiology,23(2), 411-415. doi:10.1016/j.jelekin.2012.11.009
9. Lipps, D. B., Oh, Y. K., Ashton-Miller, J. A., & Wojtys, E. M. (2013). Effect of increased quadriceps tensile stiffness on peak anterior cruciate ligament strain during a simulated pivot landing. Journal of Orthopaedic Research,32(3), 423-430. doi:10.1002/jor.22531
10. Myer, G. D., Ford, K. R., Foss, K. D., Liu, C., Nick, T. G., & Hewett, T. E. (2009). The Relationship of Hamstrings and Quadriceps Strength to Anterior Cruciate Ligament Injury in Female Athletes. Clinical Journal of Sport Medicine,19(1), 3-8. doi:10.1097/jsm.0b013e318190bddb
11. Michaelidis, M., & Koumantakis, G. A. (2014). Effects of knee injury primary prevention programs on anterior cruciate ligament injury rates in female athletes in different sports: A systematic review. Physical Therapy in Sport,15(3), 200-210. doi:10.1016/j.ptsp.2013.12.002
12. Pollard, C. D., Sigward, S. M., & Powers, C. M. (2010). Limited hip and knee flexion during landing is associated with increased frontal plane knee motion and moments. Clinical Biomechanics,25(2), 142-146. doi:10.1016/j.clinbiomech.2009.10.005
13. Sigward, S. M., Ota, S., & Powers, C. M. (2008). Predictors of Frontal Plane Knee Excursion During a Drop Land in Young Female Soccer Players. Journal of Orthopaedic & Sports Physical Therapy,38(11), 661-667. doi:10.2519/jospt.2008.2695
14. Withrow, T. J., Huston, L. J., Wojtys, E. M., & Ashton-Miller, J. A. (2008). Effect of Varying Hamstring Tension on Anterior Cruciate Ligament Strain During in Vitro Impulsive Knee Flexion and Compression Loading. The Journal of Bone and Joint Surgery-American Volume,90(4), 815-823. doi:10.2106/jbjs.f.01352