Anterior Cruciate Ligament (ACL) Injury
1. Introduction
The anterior cruciate ligament is one of four important stabilising ligaments in the knee. The role of the anterior cruciate ligament is to resist the combined motions of your tibia (shin bone) moving forwards on your femur (thigh bone) and internal rotation of your tibia (2). It originates from the bottom of your femur and attaches to the top of your tibia.
Anterior cruciate ligament injuries are often talked about in the media linked to football and other sports, with many high-profile athletes having suffered such injuries. Our understanding of the best approaches in the management of such injuries has developed a lot over the past 20 years. Improving general knee stability, balance and strength have been shown to reduce the risk of knee ligament injury. When recovering from anterior cruciate ligament injuries, regaining the same stability is a key goal to achieve the best possible rehabilitation outcome.
Frequently Asked Questions
- An anterior cruciate ligament injury is typically when you tear one of the two major ligaments of the knee. It normally occurs in high-speed sports such as football or rugby or following a significant twisting injury to the knee.
- An injury to the anterior cruciate ligament is rare in the general population.
- The annual incidence of anterior cruciate ligament tears is less than 0.1% of the population per year (1).
- Anterior cruciate ligament injuries are more common in sports such as football.
- No.
- Anterior cruciate ligament injuries are serious but, with the right rehabilitation, returning to a previous level of sport is achievable.
- It is common for this injury to require surgery.
- Anterior cruciate ligament injuries are not linked to serious pathology.
- People who participate in multi-directional sports.
- Females are at a slightly higher risk of anterior cruciate ligament injury than males (6).
- Much more common in the sporting population.
- Most common in men 19-25 years old.
- Most common in women 14-18 years old (1).
- Pain and rapid swelling after an injury.
- Hearing a ‘pop’ during the mechanism of injury.
- Instability after injury.
- Reduced weight-bearing after injury.
- Initially, after injury, the main goal is swelling management through ice, elevation and compression.
- Regain knee extension as soon as possible after injury (4).
- In athletes, anterior cruciate ligament injuries are frequently managed with keyhole surgery, however, anterior cruciate ligament injuries are sometimes managed conservatively without surgical input (5).
- Pre-operative rehabilitation is important as research shows better function after 2 years when pre-operative rehabilitation is performed (4).
- Recovery time is dictated by your pre-injury function and your post-injury goals.
- Returning to sport safely after an anterior cruciate ligament reconstruction normally takes between 9 and 18 months.
We recommend consulting a musculoskeletal physiotherapist to ensure exercises are best suited to your recovery. If you are carrying out an exercise regime without consulting a healthcare professional, you do so at your own risk.
2. Signs and Symptoms
- You may hear a ‘pop’ in your knee.
- Significant, rapid swelling and pain in your knee soon after the initial injury.
- A feeling of instability.
- Inability to fully weight-bear (3).
3. Causes
The anterior cruciate ligament normally tears during a sudden injury. The most common mechanism of injury is when the foot is planted and the rotational forces applied to the anterior cruciate ligament are greater than the ligament’s capacity. 75% of anterior cruciate ligament injuries occur during non-contact or minimal contact (7).
4. Risk Factors
This is not an exhaustive list. These factors could increase the likelihood of someone developing an anterior cruciate ligament injury. It does not mean everyone with these risk factors will develop symptoms.
- People with certain bony architecture and geometry are at higher risk, such as decreased intercondylar femoral notch size, decreased depth of concavity of the medial tibial plateau, increased slope of the tibial plateaus and increased anterior-posterior knee laxity.
- Increased BMI is thought to be a risk factor however, this is disputed.
- The presence of knee hyperextension (over straightened knee position).
- Hamstring/quadricep strength imbalance – weakness greatly increases the risk.
- Females are at a slightly higher risk than males of anterior cruciate ligament injuries due to pelvic/leg positions (6).
5. Prevalence
In the general population, the incidents of developing an anterior cruciate ligament injury are less than 1%. However, this is higher in individuals who participate in sports that involve multidirectional movements. It is more common in women than men and it is more common in people under the age of 25 years old.
6. Assessment & Diagnosis
Musculoskeletal physiotherapists and other appropriately qualified healthcare professionals can provide you with a diagnosis by obtaining a detailed history of your symptoms. A series of physical tests might be performed as part of your assessment to rule out other potentially involved structures and gain a greater understanding of your physical abilities to help facilitate an accurate working diagnosis.
Your treating clinician will want to know how your condition affects you day-to-day so that treatment can be tailored to your needs and personalised goals can be established. Intermittent reassessment will ascertain if you are making progress towards your goals and will allow appropriate adjustments to your treatment to be made.
7. Self-Management
As part of your treatment, your musculoskeletal physiotherapist will help you to understand the condition and what needs to be implemented to effectively rehabilitate after an anterior cruciate ligament injury. This will include a detailed progressive strength programme and rehabilitation programme that should be performed under a physiotherapist’s guidance.
Compliance with rehabilitation after an anterior cruciate ligament injury is key to preventing reinjury and returning to sport safely, allowing you to perform at a pre-injury level.
8. Rehabilitation
Pre-operative Rehabilitation:
Your physiotherapist will have a conversation with you providing education around anterior cruciate ligament rehabilitation and expectations. The primary goal after an anterior cruciate ligament injury is to reduce swelling and pain, then regaining knee extension. This is vital as a pre-operative deficit in knee extension range of movement is a significant risk factor for post-operative knee extension deficit (9). Additionally, regaining quadriceps strength pre-operatively to <20% deficit of the uninjured side provides a better outcome post-operatively so compliance with a pre-operative rehabilitation is important (9). Your physiotherapist will take you through strength, neuromuscular and cardiovascular training at an appropriate level to ensure the best outcomes post-operatively. Prehabilitation creates better outcomes 2 years after anterior cruciate ligament reconstruction (11).
Post-operative Rehabilitation:
Post-operative rehabilitation should be criteria-based rather than time-based (10). As you progress through rehabilitation, regular outcome measures will be taken to advise yourself and the physiotherapist when you should progress through the different stages of rehabilitation.
Concomitant surgery will influence rehabilitation timeframes and demands, particularly important with regards to early-stage weight-bearing, however, your physiotherapist will discuss this with you.
9. Anterior Cruciate Ligament (ACL) Injury
Rehabilitation Plans
Our team of expert musculoskeletal physiotherapist have created rehabilitation plans to enable people to manage their condition. If you have any questions or concerns about a condition, we recommend you book an consultation with one of our clinicians.
What Is the Pain Scale?
The pain scale or what some physios would call the Visual Analogue Scale (VAS), is a scale that is used to try and understand the level of pain that someone is in. The scale is intended as something that you would rate yourself on a scale of 0-10 with 0 = no pain, 10 = worst pain imaginable. You can learn more about what is pain and the pain scale here.
The primary goals post-operatively are the reduction of swelling and pain, and to normalise your walking pattern and patella mobility as soon as possible. The physiotherapist will prescribe exercises to regain knee extension and flexion within the first few days post-operatively. Full knee extension should be retained as early as possible, ideally within the first few weeks, and knee flexion should be regained fully within the first 6 weeks.
Quadricep activation exercises should start within the first few days post-operatively, progressing onto closed kinetic chain exercises at the knee between 0-60º. It is important that we do not solely focus on the knee joint and look to strengthen the entire lower limb including the glute, calf and hamstring with exercises focusing on muscle hypertrophy.
Cardiovascular training on a static bike can begin when 100º of knee flexion is achieved and neuromuscular training should begin in the first few weeks (8,9). Pain should not exceed 3/10 on your perceived pain scale whilst completing this exercise programme.
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When certain criteria have been met, you can then progress to the next stage of rehabilitation. During this stage, you will start to complete more dynamic exercises, including progressing onto single leg open and closed chain exercises and low-level plyometric exercises. Focus in the early phase of this stage will continue to be increasing load capacity, muscle hypertrophy and eventually returning to running (9,11). Pain should not exceed 4/10 whilst completing this exercise programme.
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In the later stages of rehabilitation, you will start to develop your single-leg multi plantar and multisegmental movements. This is important to develop as the role of your injured anterior cruciate ligament is to prevent multi-planar movements. Sports-specific rehabilitation should begin involving visual-motor training (15). Strength and power work must continue through the intermediate and advanced stages of rehabilitation, making sure there is the incorporation of exercises addressing the limb’s rate of force development. It is important to be strong and powerful but, as peak anterior cruciate ligament strain can be seen very early on in a movement (within less than a second), it is important that our muscles are not only strong but are able to react quickly to protect the ligaments from excessive pressures (14). Pain should not exceed 4/10 whilst completing this exercise programme.
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- 910
10. Return to Sport / Normal life
Return to sport can be expected between 6-12 months post-operatively. If return to sport is delayed from 6 months until 9 months, the rate of re-injury is reduced by 51% (12), so being patient during the rehabilitation process is vital. Ideally, limb symmetry should be as good as possible before returning to sport (13). When returning to field sports, a specific rehabilitation programme should have been completed prior to return, along with fatigue-based testing, to ensure you are able to manage the cardiovascular demands of your sport.
Ultimately return to sport should be a shared decision-making process between the physiotherapist and the patient, considering patient concerns and levels of anxiety on returning to sport. It is important to note that returning to sport does not equal a return to performance.
For patients wanting to achieve a high level of function or return to sport, we would encourage a consultation with a physiotherapist as you will likely require further progression beyond the advanced rehabilitation stage. Before returning to the sport, a rehabilitation programme should incorporate plyometric-based exercises; this might include things like bounding, cutting, and sprinting exercises.
As part of a multi-modal treatment approach, your musculoskeletal physiotherapist may also use a variety of other pain-relieving treatments to support symptom relief and recovery. Whilst recovering you might benefit from a further assessment to ensure you are making progress and establish the appropriate progression of treatment. Ongoing support and advice will allow you to self-manage and prevent future reoccurrence.
11. Other Treatment Options
Most commonly, this injury will require surgery. In some cases, it is possible to improve the condition and get back to a good quality of life without surgery. However, return to full sporting activity is uncommon. The surgery involves taking one of the tendons (normally from the other leg) to make a graft and using that to replace the ligament. Although this is major surgery, successful outcomes are achieved in 85%-90% of the cases. Recovery time from surgery is typically 6-12 months.
References
- Sanders TL, Maradit Kremers H, Bryan AJ, Larson DR, Dahm DL, Levy BA, Stuart MJ, Krych AJ. Incidence of Anterior Cruciate Ligament Tears and Reconstruction: A 21-Year Population-Based Study. Am J Sports Med. 2016 Jun;44(6):1502-7. doi: 10.1177/0363546516629944. Epub 2016 Feb 26. PMID: 26920430.
- Dai B, Herman D, Liu H, Garrett WE, Yu B. Prevention of ACL injury, part I: injury characteristics, risk factors, and loading mechanism. Res Sports Med. 2012 Jul;20(3-4):180-97. doi: 10.1080/15438627.2012.680990. PMID: 22742075.
- Eitzen I, Moksnes H, Snyder-Mackler L, Risberg MA. A progressive 5-week exercise therapy programme leads to significant improvement in knee function early after anterior cruciate ligament injury. J Orthop Sports Phys Ther. 2010;40(11):705-721. doi:10.2519/jospt.2010.3345
- Krause M, Freudenthaler F, Frosch KH, Achtnich A, Petersen W, Akoto R. Operative Versus Conservative Treatment of Anterior Cruciate Ligament Rupture. Dtsch Arztebl Int. 2018;115(51-52):855-862. doi:10.3238/arztebl.2018.0855
- Smith HC, Vacek P, Johnson RJ, et al. (2012). Risk factors for anterior cruciate ligament injury: a review of the literature – part 1: neuromuscular and anatomic risk. Sports Health. 2012;4(1):69-78. doi:10.1177/1941738111428281
- Nathan Wetters, Alexander E. Weber, Thomas H. Wuerz, David L. Schub, Bert R. (2016). Mandelbaum, Mechanism of Injury and Risk Factors for Anterior Cruciate Ligament Injury, Operative Techniques in Sports Medicine, Volume 24, Issue 1, 2016, Pages 2-6, ISSN 1060-1872, https://doi.org/10.1053/j.otsm.2015.09.001.
- Martin Prins. (2006). The Lachman test is the most sensitive and the pivot shift the most specific test for the diagnosis of ACL rupture, Australian Journal of Physiotherapy, Volume 52, Issue 1, 2006, Page 66, ISSN 0004-9514, https://doi.org/10.1016/S0004-9514(06)70069-1.
- Ektas, N., Scholes, C., Kulaga, S. et al. (2019). Recovery of knee extension and incidence of extension deficits following anterior cruciate ligament injury and treatment: a systematic review protocol. J Orthop Surg Res 14, 88 (2019). https://doi.org/10.1186/s13018-019-1127-8
- Van Melick N, van Cingel REH, Brooijmans F, et al. Evidence-based clinical practice update: practice guidelines for anterior cruciate ligament rehabilitation based on a systematic review and multidisciplinary consensus., British Journal of Sports Medicine 2016;50:1506-1515.
- Failla MJ, Logerstedt DS, Grindem H, Axe MJ, Risberg MA, Engebretsen L, Huston LJ, Spindler KP, Snyder-Mackler L. (2016). Does Extended Preoperative Rehabilitation Influence Outcomes 2 Years After ACL Reconstruction? A Comparative Effectiveness Study Between the MOON and Delaware-Oslo ACL Cohorts. Am J Sports Med. 2016 Oct;44(10):2608-2614. doi: 10.1177/0363546516652594. Epub 2016 Jul 14. Erratum in: Am J Sports Med. 2017 Apr;45(5):NP9. PMID: 27416993; PMCID: PMC5537599.
- Rambaud AJM, Ardern CL, Thoreux P, Regnaux JP, Edouard P. (2018). Criteria for return to running after anterior cruciate ligament reconstruction: a scoping review. Br J Sports Med. 2018 Nov;52(22):1437-1444. doi: 10.1136/bjsports-2017-098602. Epub 2018 May 2. PMID: 29720478.
- Grindem H, Snyder-Mackler L, Moksnes H, Engebretsen L, Risberg MA. (2016). Simple decision rules can reduce reinjury risk by 84% after ACL reconstruction: the Delaware-Oslo ACL cohort study. Br J Sports Med. 2016 Jul;50(13):804-8. doi: 10.1136/bjsports-2016-096031. Epub 2016 May 9. PMID: 27162233; PMCID: PMC4912389.
- Kyritsis P, Bahr R, Landreau P, Miladi R, Witvrouw E. (2016). Likelihood of ACL graft rupture: not meeting six clinical discharge criteria before return to sport is associated with a four times greater risk of rupture. Br J Sports Med. 2016 Aug;50(15):946-51. doi: 10.1136/bjsports-2015-095908. Epub 2016 May 23. PMID: 27215935.
- Turpeinen, J‐T, Freitas, TT, Rubio‐Arias, JÁ, Jordan, MJ, Aagaard, P. (2020). Contractile rate of force development after anterior cruciate ligament reconstruction—a comprehensive review and meta‐analysis. Scand J Med Sci Sports. 2020; 30: 1572– 1585. https://doi.org/10.1111/sms.13733.
Other Conditions in
Knees, Orthopaedics
Patellofemoral Pain Syndrome (PFPS)
Knee pain around the kneecap usually worse in static positions, squatting or kneeling.
Patellar Tendinopathy
Knee pain at the lower border of the kneecap which is also known as ‘jumper’s knee’.
Osgood-Schlatter Disease
Pain in an area just below the knee on the shin bone, often with a lump.
Meniscus Injury
Structural knee injury, triggered either by a tear or through wear and tear.
Knee Replacement Surgery
Replacement of the knee hinge joint, typically as a result of severe osteoarthritis or trauma.
Knee Osteoarthritis
Common age related changes to the structure of the knee joint which may be associated with pain, stiffness and loss of function.
Iliotibial Band Syndrome
Presents as pain on the outside of the knee, normally occurring because of overload due to prolonged or repeated bouts of exercise.
Femoral Nerve Radiculopathy
This is where the nerve that supplies the front of the leg is irritated and causes pain/numbess.
Fat Pad Impingement
A rare condition affecting the adipose (fat) tissue that sits under the kneecap (patella) between the joint spaces of the knee.
Degenerative Meniscus
Seen to be normal as we age, but in some situations can result in knee aches, pain or joint swelling.
Bowed Knees
A condition in which the legs are bowed outwards leaving a greater space in between your knees.
Benign Joint Hypermobility Syndrome
Common age related changes to the structure of the knee joint which may be associated with pain, stiffness and loss of function.
Baker’s Cyst
Swelling in the popliteal space (space behind the knee) that causes a visible lump.