ACL tears are one of the most recognized injuries in sports and athletics, and not for a good reason. Many are aware of the devastating consequences that come from ACL injuries, from surgery to missed games. Add to that several months of rehabilitation and recovery, and it’s easy to see why these athletes with ACL tears miss entire seasons of competition.
But why does ACL recovery take so long? To answer this question and more, it’s important to delve into the contributing factors to the injury itself. Then, we’ll introduce some interesting theories about ACL injury mechanism, statistics, and gender bias.
There’s a ton of information to cover, so let’s begin with the basics.
What Is An ACL Injury?
The Anterior Cruciate Ligament (ACL) is found inside the knee joint and connects the femur to the tibia. Although it’s incredibly strong, the ligament itself has very little elasticity. As a result, it absorbs large amounts of stress until it stretches or weakens, and then it tears.
An ACL tear usually occurs as a result of:
Cutting or pivoting maneuvers, like when an athlete plants a foot and suddenly shifts direction
Landing on one leg
A direct hit to the knee is hit directly, especially when it is hyper-extended or bent inward
Deceleration from running
Repeated stress to the knee
Falling on a bent or twisted knee
Some of the most common signs and symptoms of an ACL injury are:
Sudden, sharp pain
Immediate swelling and warmth in the knee joint
Deep, aching pain in the joint that worsens with walking or climbing stairs
Feeling as if the knee is “giving out.”
Limited range of motion
Tenderness and bruising around the area
It’s important to realize that, while some signs and symptoms occur immediately after injury to the ACL, others may appear or worsen over the next few days.
Fast Facts About ACL Injury
It is believed that more than 200,000 cases of ACL injuries each year. However, exact estimates are hard to come by since there is no standard method to track the number of ACL tears in a given year.
The ACL is the most commonly injured structure in the knee, accounting for more than 50% of all knee injuries.
A majority, about 60-70%, of ACL tears occur by non-contact, meaning there is no collision with another person or object. Surprisingly, research has found that athletes who ski or play soccer and basketball are at the highest risk for a non-contact ACL tear. Conversely, those who play football are most vulnerable to an ACL tear due to direct contact.
Important Factors that Contribute to an ACL Knee Injury
A delicate balance between your muscles, bones, and ligaments allows your body to move freely without restriction or pain. When muscles are weak or injured, the ligaments and tendons are forced to do more work to support your bones. Over time, the ligaments become overstretched, overstressed, and weak. This, combined with specific sport maneuvers, creates the perfect storm for an ACL tear.
There are two categories of factors that can predispose you to an ACL injury. One category is known as non-modifiable factors and includes things like genetics, a previous history of an ACL injury, and the size of your ACL ligament. Non-modifiable risk factors cannot be changed to lessen your risk of injury.
The second category is referred to as modifiable factors, which means they can be changed or altered in some way. Modifiable factors that might affect one’s risk for an ACL tear include:
Body mass index
Having one, or more than one, risk factor does not necessarily mean that you’ll suffer an ACL injury. However, it does increase the probability that you could have one, especially if you play a sport that requires frequent and sudden deceleration or cutting, pivoting, and jumping on one leg.
The aforementioned modifiable factors are often discussed when it comes to ACL knee injuries, but we want to talk about others you may not be aware of. For example, did you know that mental fatigue can raise your risk of sustaining an ACL tear? Mental fatigue can result from bad sleep habits, lack of recovery time between games, or incomplete physical recovery. It plays a major role in your ability to concentrate, focus, and pay attention which are obvious risk factors for any injury.
Another cause for concern when it comes to ACL injury in children and teens who specialize in one sport at a young age. According to several studies, emphasis on playing one sport, known as sport specialization, leads to overuse injuries, overtraining, and mental burnout. To combat this, the American Academy of Pediatrics suggests delaying sport specialization until after puberty (around 15 or 16 years of age) will minimize such risks.
Parents of young children should also keep in mind that a lack of expertise and guidance when it comes to physical conditioning is a significant risk factor for sports injuries. Without proper guidance to develop motor skills, children are predisposed to poor movement patterns that alter their ability to run, jump, or turn and in turn increase the risk for ACL injury.
ACL Injury Rate in Females
It may come as no surprise that females are more prone to ACL injuries than males.
When comparing high school athletes, females are 1.6x more likely to sustain an ACL tear than males, especially in high-risk sports like soccer, basketball, and lacrosse. However, that doesn’t discount the fact that any high school athlete who plays those sports, as well as football, is more likely to be injured than other sports. One study found that injury rates are significantly higher during games than practice, with female soccer having the highest injury rate followed by male football.
There are a number of reasons why females may have an increased risk of ACL injury. First of all, male and female bodies are not built the same. Because their hips are wider for childbearing, women may have more stress on the soft tissues surrounding the knee joint. One difference that is commonly seen in women is known as knee valgus, which refers to the angle between the knee joint. Knee valgus places more stress on the ACL, thus increasing the risk for an ACL tear.
Secondly, most females are smaller in size than males, and that includes the amount of muscle around the knee joint. This, combined with the fact that females tend to rely more upon the quadriceps during deceleration, places huge amounts of stress on the ACL that can lead to instability and a higher chance of tearing if it is overstretched. The quadriceps are significantly less effective than the hamstrings are at controlling the knee joint.
Lastly, some experts think that hormones may have something to do with the differences between male and female ACL injury rates. Females have less testosterone, a key hormone for increasing muscle density, and much more estrogen than men. Estrogen may be responsible for looseness in tendons and ligaments, another area of concern when it comes to an ACL tear.
Surgery for an ACL Tear
Although ACL injuries can be treated conservatively, surgery for an ACL tear is sometimes necessary. Overall, about 77% of ACL injuries require surgery.
Surgery for ACL tear involves rebuilding the torn ligament using something called a graft. Most times, the torn fragments of the ACL are beyond repair. Therefore, a graft is used from a different tendon in the body (autograft) or a donor graft from another source (allograft).
The material in the graft acts as the foundation for the new ligament to grow on. Below are the most common autografts used in surgery for an ACL tear.
1. Patellar tendon. Your patellar tendon is used to replace the torn ACL. Recovery is usually uncomplicated, and its strength makes the patellar tendon a popular choice for elite athletes.
2. Hamstring tendon. Becoming more common, hamstring tendon autographs have been shown to decrease knee pain and recovery time compared to patellar tendon grafts.
3. Quadriceps tendon. Quadriceps tendon autografts are often used for ACL revision surgery.
The graft selection is determined by your surgeon. However, you should know that no specific graft type has been proven to be superior to the others.
There have been documented statistics on ACL re-injury after surgery, especially in children. Females are most at risk for repeat ACL tears in both the operated and non-operated knee.
What To Expect After Surgery for ACL Tear
You may be surprised to hear that most people can move the knee immediately following surgery for an ACL tear. Rehabilitation begins almost immediately after surgery to achieve these goals:
Improving range of motion
Restoring balance and proprioception
Some surgeons may recommend the use of knee braces; however, there is no evidence to link them with decreased recovery time or better outcomes.
Achieving specific goals after surgery may make the difference between a full and incomplete recovery from an ACL tear. Regaining full motion, especially leg extension, on both sides of the body is critical for recovery and will affect future episodes of knee pain. Research has found that the critical window for regaining that full leg extension is within the first two weeks after ACL surgery.
At Myokinetix, we are fully equipped to handle your ACL recovery from start to finish. Our ACL Rehabilitation program includes a 1-on-1 session with your doctor of physical therapy in a state-of-the-art facility designed for active individuals and athletes. Rest assured that each session lasts 60 minutes with the highest level of care in Essex and Morris County areas. But don’t just take our word for it. Come in for your initial evaluation and let us show you why we are the providers to trust. Give us a call at 973-281-4853 today.
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Evans J, Nielson Jl. Anterior Cruciate Ligament Knee Injuries. [Updated 2021 Feb 19]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK499848/
Shelbourne, K. & Benner, Rodney & Gray, Tinker. (2017). Results of Anterior Cruciate Ligament Reconstruction With Patellar Tendon Autografts: Objective Factors Associated With the Development of Osteoarthritis at 20 to 33 Years After Surgery. The American Journal of Sports Medicine. 45. 10.1177/0363546517718827.
Kane, Patrick & Wascher, Jocelyn & Dodson, Christopher & Hammoud, Sommer & Cohen, Steven & Ciccotti, Michael. (2016). Anterior cruciate ligament reconstruction with bone-patellar tendon-bone autograft versus allograft in skeletally mature patients aged 25 years or younger. Knee Surgery, Sports Traumatology, Arthroscopy. 24. 10.1007/s00167-016-4213-z.
Maletis, Gregory & Chen, Jason & Inacio, Maria & Love, Rebecca & Funahashi, Tadashi. (2017). Increased Risk of Revision After Anterior Cruciate Ligament Reconstruction With Bone–Patellar Tendon–Bone Allografts Compared With Autografts. The American Journal of Sports Medicine. 45. 036354651769038. 10.1177/0363546517690386.
Beischer, S., Gustavsson, L., Senorski, E. H., Karlsson, J., Thomeé, C., Samuelsson, K., & Thomeé, R. (2020). Young Athletes Who Return to Sport Before 9 Months After Anterior Cruciate Ligament Reconstruction Have a Rate of New Injury 7 Times That of Those Who Delay Return. Journal of Orthopaedic & Sports Physical Therapy, 50(2), 83–90. doi: 10.2519/jospt.2020.9071
Gans, I., Retzky, J. S., Jones, L. C., & Tanaka, M. J. (2018). Epidemiology of Recurrent Anterior Cruciate Ligament Injuries in National Collegiate Athletic Association Sports: The Injury Surveillance Program, 2004-2014. Orthopaedic Journal of Sports Medicine, 6(6), 232596711877782. doi: 10.1177/2325967118777823
Joseph, A. M., Collins, C. L., Henke, N. M., Yard, E. E., Fields, S. K., & Comstock, R. D. (2013). A Multisport Epidemiologic Comparison of Anterior Cruciate Ligament Injuries in High School Athletics. Journal of Athletic Training, 48(6), 810–817. doi: 10.4085/1062-6050-48.6.03
Joseph AM, Collins CL, Henke NM, Yard EE, Fields SK, Comstock RD. A multisport epidemiologic comparison of anterior cruciate ligament injuries in high school athletics. J Athl Train. 2013;48(6):810-817. doi:10.4085/1062-6050-48.6.03
Gornitzky AL, Lott A, Yellin JL, Fabricant PD, Lawrence JT, Ganley TJ. Sport-Specific Yearly Risk and Incidence of Anterior Cruciate Ligament Tears in High School Athletes: A Systematic Review and Meta-analysis. Am J Sports Med. 2016;44(10):2716-2723. doi:10.1177/0363546515617742
American Academy of Orthopedic Surgeons website, Ortho Info. Anterior Cruciate Ligament (ACL) Injuries. Accessed May 16 2021.
Perrone GS, Proffen BL, Kiapour AM, Sieker JT, Fleming BC, Murray MM. Bench-to-bedside: Bridge-enhanced anterior cruciate ligament repair. J Orthop Res. 2017 Dec;35(12):2606-2612. doi: 10.1002/jor.23632. Epub 2017 Jul 9. Review. PubMed PMID: 28608618; PubMed Central PMCID: PMC5729057.
McGuine TA, Post EG, Hetzel SJ, Brooks MA, Trigsted S, Bell DR. A Prospective Study on the Effect of Sport Specialization on Lower Extremity Injury Rates in High School Athletes. The American Journal of Sports Medicine. 2017;45(12):2706-2712. doi:10.1177/0363546517710213