The Anterior Cruciate Ligament (ACL) is one of two ligaments that cross in the middle of the knee. The ACL stabilizes the knee by preventing forward motion of your lower leg. It is a very strong ligament but also the most commonly injured ligament in the knee. ACL injuries are often higher in those who participate in high-risk sports, such as basketball, football, skiing, and soccer. It is estimated that 100,000 -200,000 ACL tears occur each year in the US, and ACL reconstruction is one of the most common surgeries performed by orthopedic physicians.
ACL Anatomy & Biomechanics:
The ACL is a band of dense connective tissue that connects the femur (thigh bone) to your lower leg. Two cruciate ligaments are in the knee, the anterior(ACL) and the posterior cruciate ligament (PCL). Cruciate means “cross” and signifies the x shape the ACL and PCL make as they cross over each other. The primary function of the ACL is to stop forward movement and rotation of the shin bone on the thigh bone, and the secondary role is proprioception or providing position awareness.
What causes ACL injuries?
Athletes and weekend warriors who participate in sports that involve a lot of knee cutting, sudden stops, or a change in direction have a higher risk of ACL injury. Most injuries are not by contact or colliding with another player.
Instead, non-contact injury of the ACL is the most frequent, involving a combination of knee valgus and internal rotation or dropping your knee and foot arch down and in.
Approximately 50% of ACL tears are accompanied by other knee damage, including injury to the medial collateral ligament (MCL), a tear in the meniscus, and a bone bruise. Because most ACL tears are non-contact, avoiding stress in the problematic position of knee valgus with internal rotation will reduce ACL tears and other overuse injuries, including Achilles tendonitis, ITB Friction Syndrome, Infrapatellar tendonitis, and Plantar Fasciitis.
What are the types of ACL tears?
Injury to your ACL ligament does not always mean a complete tear. Similar to an ankle sprain, you can have varying degrees of involvement.
- Grade 1: Your ligament is strained but intact. Your knee is sore, but there is no disruption in the stability of your knee.
- Grade 2: There is a partial tear in your ligament. There may or may not be a feeling of instability or your knee “giving way”.
- Grade 3: Your ligament is completely torn. There is a feeling of “giving way”, but this feeling of instability may improve as the swelling reduces (2 weeks) or after the body compensates, usually after two+ months.
What are the risk factors for ACL injuries?
Injury to the ACL ligament is caused by high-pressure loading of the knee in a valgus and internal rotated position (inward knee with a flat foot). This stress can occur when stopping suddenly, cutting, or turning quickly, especially during sports participation.
An ACL tear can happen to anyone at any age, but the most common age is between 19-25 in males and 14-18 in females. Females have another peak in their forties and some research report that they are four times more likely than males to sustain a tear. Experts disagree on why girls have higher rates, but if we look at the positional cause – knee valgus and internal rotation is a common running form found in females and should be addressed with education and biomechanical changes to reduce the stress on the knee and other overuse injuries.
Factors associated with an increased risk include:
- *Poor running mechanics* – knee valgus, pronation, heel inward during swing
- Participation in sports activities that requires cutting and pivoting
- Age 14 -25
- Decreased physical condition.
- Fatigue – causes poor mechanics
- Wearing ill-fitted footwear or improper equipment
- Playing on artificial turf
What are the symptoms of an ACL injury?
A loud pop is usually the first thing one feels/hears, followed by severe pain and a feeling that your knee is unstable or “giving out”. Within a few hours, there is immediate swelling. (Only a fracture and ACL tear cause immediate swelling. A meniscal tear usually takes 24 hrs. for swelling to appear.)
- Feel or hear a pop in your knee
- Feeling of the knee “giving way”
- Swelling starts immediately or a few hours later and lasts up to four weeks.
- Loss of range of motion in your knee, especially extension
- Discomfort and. difficulty with walking
Do ACL tears hurt?
Yes. You will hear or feel a pop when the injury happens and then pain. Trauma triggers a complex healing process, starting with inflammation or releasing chemicals to clean and repair the injury. Inflammation also triggers pain to caution you, let you know that you have an injury, and to be mindful of the injured joint.
Can you walk with a torn ACL?
Significant swelling in the knee causes neural inhibition of the quadriceps muscle. The quad can suddenly shut off when walking, causing the knee to “give way”. As long as swelling is in the knee, the quad may be shut down, leading to loss of strength over time. Marked weakness is typically observed following any injury, surgery, or pathology affecting the knee joint, and “giving way” is a common complaint. For those that have recently torn their ACL, the instability can be from swelling, quad inhibition, and lack of ligamentous support.
Some people feel stable enough to walk as long as they do it slowly and carefully. Others use crutches and/or a knee brace with lateral bars for more support). As the swelling subsides. quadricep strength returns and the body compensates for the ligament loss; the stability in the knee often also improves, and this usually starts to occur by the second month after injury.
How is an ACL injury diagnosed?
Your healthcare professional will take a medical history and ask specific questions about the cause of your knee pain. History of turning on your knee, hearing a “pop” and immediate swelling are usually indicative of ACL involvement. A physical exam is performed, including a Lochman’s test for knee stability (stabilizing your thigh and moving your tibia forward), range of motion, test for swelling, and palpation for abnormalities and tenderness.
An x-ray or MRI will probably be ordered to rule out fractures and potential ACL tears. An MRI may not be necessary because a physical exam may reveal that the ligament is torn.
What is the immediate treatment for an ACL injury?
As soon as you sustain an acute injury to your knee, use RICE therapy:
- R: Rest.
- I: Ice.
- C: Compression.
- E: Elevation.
What is the BEST long-term treatment? Surgery or Conservative Care?
While surgery is the most common treatment and advice for athletes or anyone who would like to continue with a higher activity level, surgical outcomes are not as great as they preach. Surgery is painful, and rehab after surgery is long and grueling. The rate of returning to sports activity after surgery is only 55%, and you are 15x more likely to get a second ACL tear within 12 months of ACL surgery compared to healthy subjects (contralateral knee higher rate).
The rate of ACL spontaneous healing is at least 56% and as much as 85%! Yes, ACLs can heal! Contrary to popular belief, internet searches, and many physicians, full ACL tears can heal.
(Our next blog will review and compare ACL surgery versus conservative care.)
What is conservative care for an ACL tear?
Conservative care consists of:
- Reducing stress on the healing knee:
- Crutches initially as needed (2 weeks)
- Caution with twisting, turning
- Option of a knee brace with metal hinges until knee feels stable. Wear the hinged brace with all weight-bearing activity while the knee is unstable. Start to wean at 2 months, but if the knee still feels unstable, use a brace for up to 10 months.
- Regain full AROM
- Regain full strength
- Progress to balance and proprioception exercises
- Finally, progress to high-level proprioception and sport-related activity
Should I have surgery or conservative care if I want to go back to sports activity?
The type of treatment you receive is up to you. The most important thing is to allow and give your knee time to heal. You should consider surgery only after you have completed conservative care for at least 5 months and your knee is still unstable. Do your own research, and weigh the options that are best for you.
Can I live a normal life with an ACL tear?
Absolutely, but it may take some time before you’re completely back to how you were before the injury. . ACL tears are quite common, with 70 occurring in every 100,000 persons or 100,000-200,000 each year. Almost all are able to return to full daily activity. Returning to high-level sports activity is much lower, but there are factors that can improve return to sport, and these will be discussed in our next article. Whether you choose to have surgery or not, with proper exercise, you will eventually be back to normal and able to live your life.
Can I play sports with a torn ACL?
Yes, many athletes have returned to sports and even professional sports after ACL reconstructive surgery and after no surgery at all.
After surgery, it takes about six to nine months of physical therapy to regain full range of motion, balance, strength, endurance, and proprioception. Returning too early significantly increases your risk of tearing your ACL again. There is also a high risk of tearing the opposite (contralateral) ACL within two years of returning to athletics, with females being much higher than males. But proper rehabilitation includes not only regaining full range of motion and leg strength but also proprioception and biomechanical correction of knee valgus and pronation while running and pivoting. Proprioception is your awareness of your body in space. Exercises to improve proprioception include balance with eyes open and closed, lunges, quick turns, jumping, etc..
What questions should I ask my healthcare provider?
- Do I have a partial or complete ACL? (MRI picture may be misleading)
- Is there any other damage to my knee? (MCL, meniscus, bone bruise)
- Do I need to see a specialist?
- Can you provide a good orthopedic surgeon and physical therapist that focus on conservative care?
- What should I be doing now to protect my knee and allow healing?
- When can I return to work/school?
- When can I drive?
- How long do you predict it will take me to recover?
- If I want to return to sports, what are the measurable signs of an excellent outcome from conservative care?
- Since this is a non-contact injury, how can I reduce my chances of tearing the opposite side and/or re-injury my involved knee?
- What are the signs of a poor conservative outcome and the need for surgery?
- What are the pros and cons of surgical repair of my ACL tear?
- What kind of graft is best for me?
- What are the milestones that I need to hit to have a successful outcome and return to sport?
How soon after treatment will I feel better? What’s the recovery time?
Six to nine months is typically how long it takes to recover from both conservative care and ACL surgery.
Can ACL injuries be prevented?
It is not possible to completely eliminate ACL injuries, but various training techniques can minimize the risk of tearing the ACL. Most ACL injuries are again non-contact, meaning that the ACL tore because of the position of the knee when pivoting, stopping suddenly, and landing from a jump. Planting incorrectly overwhelms the ACL’s integrity leading to a tear. Reducing the stress on the knee when performing pivoting, jumping, etc., will reduce stress on the ACL and make it less likely to tear.
1. The number one position of the knee when the ACL tears is valgus and internal rotation (inward with foot pronated). Athletes should be evaluated and learn about this faulty mechanic when they are young, especially females.
Sports physicals should include a simple assessment to assess knee valgus and internal rotation with squatting, running, and pivoting, and athletes should be given educational material and a referral for biomechanical assessment when found.
2. Fatigue as a factor in ACL injuries
Tired athletes are more likely to use poor mechanics, especially when they are making a split-second decision to execute an unexpected move.
3. Proper training can help prevent injuries.
Studies show that specific training programs can improve athletes’ running form, leg strength, and jump-landing techniques. The techniques that improve ACL safety can also enhance performance and increase vertical jump height, acceleration, and the ability to change direction, as well as reduce overuse injuries.
4. Proper footwear and equipment
Footwear or equipment that is ill-fitted or compromised can cause altered biomechanics and lead to unusual tweaking of the knee, causing undo stress on the ACL. Be sure to check cleats and equipment for any malfunctions prior to playing.
5. Avoiding artificial turf:
It has been shown that artificial turf does not give as much as natural grass and has been correlated to increased injury and ACL tears.
Nothing can prevent ACL injuries altogether. But exploring their potential causes and maximizing prevention strategies can stop the “pop” and its frustrating consequences.
Can ACL tears be cured?
With time, dedication, hard work, and proper physical therapy, you can regain full use of your knee within six to nine months.
Some ACL tears do not heal, but stability in the knee is regained after the swelling has subsided, quadricep strength is regained, and the body compensates for the ligament. The ACL may not be intact, but when balance and proprioception are regained, these individuals are able to return to play.
Some individuals with ACL tears (stable and not stable) choose not to return to higher-level activity because of fear or other circumstances.
Some ACL tears do not spontaneously heal, strength, balance, and proprioception are NOT regained, and the knee remains very unstable. Surgery may be an option, but first, a discussion must be on regaining ROM, strength, and proprioception, for surgery will also be a failure if not.
Will an ACL tear ever happen again?
Yes, you can retear your ACL, both post-surgical and one that has spontaneously healed. There is also a high incidence of having a tear in one and, within two years, tearing the ACL in the opposite knee. Being female, poor conditioning and improper biomechanics of knee valgus with internal rotation significantly increase your risk of retearing and tearing of the opposite knee.
The most important thing is to prevent the mechanism that caused the ACL tear – knee valgus and foot pronation. A biomechanical assessment only takes 30 minutes. Retraining your mechanics is valuable in not only reducing your chance of an ACL injury, but improvements in your biomechanics can also improve your performance and reduces your chances of overuse injuries! Schedule with one of our biomechanical experts now and learn simple exercises to improve your form!
(Our next blog will review and compare ACL surgery versus conservative care.)