Anterior Cruciate Ligament (ACL) Injury

What is the ACL and why is it relevant?

The ACL is short for anterior cruciate ligament. As with all ligaments; its main function is to connect two bones to offer structural support. The ACL connects the femur (thigh bone) and the tibia (shin bone). Therefore, it is an important structure for stability in the knee joint.

What are the signs and symptoms of an ACL tear?

The following are signs and symptoms where you could suspect an ACL injury(1):

1. Injury occurred during an activity with an increase/decrease in speed (e.g., running) with a

2. Hearing or feeling a ‘pop’ at the time of injury.

3. Inflammation within 2 hours of injury (can include swelling, bruising, red/hot joint, pain,

How is an ACL tear diagnosed?

ACL diagnosis can be made by qualified healthcare professionals (e.g., GP, ortho surgeon, physiotherapist) in the clinic. They will utilize a number of clinical tests, and combine these with your injury history. This is often accurate enough to diagnose an ACL injury however, when the examiner is uncertain an MRI can be used for confirmation(1). There are different grades for ACL tears depending on the severity.There are a few limitations to clinical tests and/or imaging in the immediate stage after injury, as they are usually less accurate due to swelling(1-2).

For a full ACL tear, should you get surgery or not?

For acute ACL tears there has been extensive debate and research about what the best treatment option is(3). The consensus from the most recent research is that both are acceptable options(1,3-4) however, it can depend on several factors(5).

One study (KANON trial) demonstrated that after 5 years follow up there was no difference in function, symptoms, imaging findings and activity participations between people undergoing surgery vs no surgery(6). It is important to note that surgical repair/reconstruction as with all surgeries have a small risk of complications (e.g., cyclops lesion, sepsis)(7-8).

However, it is important to know that for both choices (surgery or no surgery) rehabilitation is crucial for good outcomes(4). Not undergoing surgery does not mean that it will fix itself, while surgery also does not provide a quick fix(9). If the goal is to return to sport, work (if physical), other physical activities, prevent future issues, and have the knee functioning optimally; effort is required(1).

Is it still the same if you have also sustained injuries to other structures (e.g., meniscus, cartilage)

This is not uncommon, injuries that often co-occur include structures such as meniscus, bone, cartilage, other ligaments(1,8,10). When multiple structures have been involved, surgery is considered a superior option(11). 

Why you should start exercise rehabilitation ASAP (even if you are going for surgery)

The consensus is that people with an ACL tear should start rehabilitation as soon as possible for optimal outcomes(1-2,12).If you and your practitioner have decided surgery is your best option, it is not a waste of time for you to start preoperative rehabilitation or ‘prehab’. Prehab can result in superior results following surgery and a quicker return to sport vs no prehab(5). Specifically developing quadriceps strength seems to result in more favourable outcomes(5). 

What are the long-term consequences of non-surgical interventions and surgical interventions?

It is important to set the right expectations for your recovery (to prevent disappointment). Studies have found that some people report that their knee never feels the same again after an ACL injury(1). Early development of osteoarthritis is also common(1,10,12). To avoid this, personalized treatment and rehabilitation is important(1,3,12). 

What would conservative ACL rehabilitation look like?

For conservative treatment there are 3 stages:

1. Acute stage. For optimal results this should start as soon as possible following injury. This

2. Intermediate stage. This stage focuses on neuromuscular training (balance, agility, plyometrics) and strength training(1).

3. Late stage. Should be individualized based on the person's specific goals and physical demands(3,13). This usually includes heavier load strength training, power exercises, agility and sport specific exercises(1).

It could be argued that there should be a fourth stage, where patients continue to participate in exercise and an active lifestyle to prevent early onset of osteoarthritis(12).

There is also growing positive research for the use of blood flow restriction during rehabilitation(5). However, this is not available in all clinics.

Progressions to the next stage are based on being able to meet certain criteria and are less time- based. Time frames will be very different person to person depending on numerous factors (e.g., addition of MCL or meniscus tear, effort/engagement in rehabilitation).

What would rehabilitation post ACL surgery look like?

For the surgical option there are 4 stages:

1. Preoperative stages (pre-hab). For optimal results this should start as soon as possible

2. Acute stage. For optimal results this should start as soon as possible following injury. This

3. Intermediate stage. This stage focuses on neuromuscular training (balance, agility, plyometrics) and strength training(1).

4. Late stage. Should be individualized based on the person's specific goals and physical demands(3,13). This usually includes heavier load strength training, power exercises, agility and sport specific exercises(1).

And possibly as in the above, a fifth stage(12).

Progressions to the next stage are based on being able to meet certain criteria and are less time- based. Time frames will be very different person to person depending on numerous factors (e.g., addition of MCL or meniscus tear, effort/engagement in rehabilitation). However, generally recovery

is longer for people choosing to undergo surgery(1). More considerations also need to be made in rehabilitation if an autograft was used (e.g., hamstring/patellar tendon)(1).

Is there anything else I can do to promote healing and recovery?

There are other modifiable factors that we can target to optimize healing and recovery. Smoking is related with poor healing in general and poor outcomes following ACL injuries and surgeries(14-15). This may be more obvious however, maintaining social relationships and support is important in the recovery from any injury(16).

Sleep also plays a significant role in recovery and general health. Sleep disturbances are also related to worse pain and pain-related outcomes.Nutrition also plays an important role. The following are important to consider for optimal recovery:

• Adequate protein intake. This is crucial for tissue healing and preventing muscle atrophy (loss). The recommended amount of protein intake is based on your physical activity levels. For active individuals 2-3g/kg BW/day is recommended. An emphasis is placed on Leucine (an amino acid) that is important in protein synthesis, mainly found in meat(17-18).

• Opt for complex carbohydrates vs simple carbohydrates (refined, processed foods)(17).

• Avoid foods high in saturated fats (chips, fast foods, processed foods). These can contribute

• Ensure adequate Vitamin A, C, D & E intake. These vitamins play an essential role in tissue

Is it safe to return to sport or other exercise following an ACL injury?

As with any injury, the biggest risk factor for an injury is a previous injury. This is no different for the ACL, the risk of re-injuring your ACL 2-years post-op is 6x as high(5). One third of individuals that have undergone ACL reconstruction experience another ACL tear(1). Experts in the field have therefore been very busy in the development of protocols to minimize this risk and safely return to work and sports(1). Their consensus was that this should be based on physiological factors and psychological factors and less determined by time(1). However, arguments are made that risk of developing osteoarthritis and re-injury is lower if the athlete returns to play 12 months post injury/surgery(1).

Overall, for return to sport, the following should be considered:

• Are you physically ready? There are a battery of tests that when passed, reduce the risk of

• Are you psychologically ready? Are you still fearful of re-injury? Do you feel confident?(20)

• Has healing occurred? Research is not completely clear on this however, return to sport is

What is the role psychology plays?

“You can’t separate mind and body. We’re a unified human.” (Prof Lorimer Mosely). This is also the case for injuries and specifically ACL injuries as these do require a long time to heal and rehabilitation efforts. There will be a long period of time where return to sport is not possible, and you may not be able to participate in other hobbies that are enjoyable. There will be a period where mobilizing will be very challenging. It can also change the family dynamics with someone possibly needing to care for you. You may significantly fear re-injuring your knee throughout the recovery period. All of these factors (and others) can lead to psychological challenges. This is understandable however, you don’t have to suffer in silence. There are many strategies that can be utilized to assist or a psychologist may be able to assist.

What the research says about prevention for ACL re-injuries.

Once you have injured an ACL your risk for re-injury is significantly higher. There are however, a few things you can do to minimize the risk of re-injury(1):

• Don’t participate in activities that require pivoting or cutting.

• Complete your rehabilitation and be able to pass a cluster of tests prior to return to sport.

• Don’t return to sports requiring pivoting prior to 9 months post reconstruction.

• Continue to participate in strength training. The ACL ligament has been shown to increase in

References

1.      Filbay, S. R., & Grindem, H. (2019). Evidence-based recommendations for the management of anterior cruciate ligament (ACL) rupture. Best practice & research. Clinical rheumatology, 33(1), 33–47. https://doi.org/10.1016/j.berh.2019.01.018 

2.      Park, Y. G., Ha, C. W., Park, Y. B., Na, S. E., Kim, M., Kim, T. S., & Chu, Y. Y. (2021). Is it worth to perform initial non-operative treatment for patients with acute ACL injury?: a prospective cohort prognostic study. Knee surgery & related research, 33(1), 11. https://doi.org/10.1186/s43019-021-00094-3 

3.      Saueressig, T., Braun, T., Steglich, N., Diemer, F., Zebisch, J., Herbst, M., Zinser, W., Owen, P. J., & Belavy, D. L. (2022). Primary surgery versus primary rehabilitation for treating anterior cruciate ligament injuries: a living systematic review and meta-analysis. British journal of sports medicine, 56(21), 1241–1251. https://doi.org/10.1136/bjsports-2021-105359 

4.      Culvenor, A. G., & Barton, C. J. (2018). ACL injuries: the secret probably lies in optimising rehabilitation. British journal of sports medicine, 52(22), 1416–1418. https://doi.org/10.1136/bjsports-2017-098872 

5.      Jenkins, S. M., Guzman, A., Gardner, B. B., Bryant, S. A., Del Sol, S. R., McGahan, P., & Chen, J. (2022). Rehabilitation After Anterior Cruciate Ligament Injury: Review of Current Literature and Recommendations. Current reviews in musculoskeletal medicine, 15(3), 170–179. https://doi.org/10.1007/s12178-022-09752-9 

6.      Frobell, R. B., Roos, H. P., Roos, E. M., Roemer, F. W., Ranstam, J., & Lohmander, L. S. (2013). Treatment for acute anterior cruciate ligament tear: five year outcome of randomised trial. BMJ (Clinical research ed.), 346, f232. https://doi.org/10.1136/bmj.f232 

7.       Kambhampati, S. B. S., Gollamudi, S., Shanmugasundaram, S., & Josyula, V. V. S. (2020). Cyclops Lesions of the Knee: A Narrative Review of the Literature. Orthopaedic journal of sports medicine, 8(8), 2325967120945671. https://doi.org/10.1177/2325967120945671

8.      Anderson, M. J., Browning, W. M., 3rd, Urband, C. E., Kluczynski, M. A., & Bisson, L. J. (2016). A Systematic Summary of Systematic Reviews on the Topic of the Anterior Cruciate Ligament. Orthopaedic journal of sports medicine, 4(3), 2325967116634074. https://doi.org/10.1177/2325967116634074 

9.       Zadro, J. R., Harris, I. A., Abdelshaheed, C., Broderick, C., Barton, C. J., Linklater, J., & Maher, C. G. (2019). Choosing Wisely after a sport and exercise-related injury. Best practice & research. Clinical rheumatology, 33(1), 16–32. https://doi.org/10.1016/j.berh.2019.02.002 

10.  Domnick, C., Raschke, M. J., & Herbort, M. (2016). Biomechanics of the anterior cruciate ligament: Physiology, rupture and reconstruction techniques. World journal of orthopedics, 7(2), 82–93. https://doi.org/10.5312/wjo.v7.i2.82 

11.  Lynch, A. D., Chmielewski, T., Bailey, L., Stuart, M., Cooper, J., Coady, C., Sgroi, T., Owens, J., Schenck, R., Whelan, D., Musahl, V., Irrgang, J., & STaR Trial Investigators (2017). Current Concepts and Controversies in Rehabilitation After Surgery for Multiple Ligament Knee Injury. Current reviews in musculoskeletal medicine, 10(3), 328–345. https://doi.org/10.1007/s12178-017-9425-4 

12.  Whittaker, J. L., Culvenor, A. G., Juhl, C. B., Berg, B., Bricca, A., Filbay, S. R., Holm, P., Macri, E., Urhausen, A. P., Ardern, C. L., Bruder, A. M., Bullock, G. S., Ezzat, A. M., Girdwood, M., Haberfield, M., Hughes, M., Ingelsrud, L. H., Khan, K. M., Le, C. Y., Losciale, J. M., … Crossley, K. M. (2022). OPTIKNEE 2022: consensus recommendations to optimise knee health after traumatic knee injury to prevent osteoarthritis. British journal of sports medicine, 56(24), 1393–1405. https://doi.org/10.1136/bjsports-2022-106299 

13.  Wilk, K. E., Macrina, L. C., Cain, E. L., Dugas, J. R., & Andrews, J. R. (2012). Recent advances in the rehabilitation of anterior cruciate ligament injuries. The Journal of orthopaedic and sports physical therapy, 42(3), 153–171. https://doi.org/10.2519/jospt.2012.3741 

14.  Dunn, W. R., Wolf, B. R., Harrell, F. E., Jr, Reinke, E. K., Huston, L. J., MOON Knee Group, & Spindler, K. P. (2015). Baseline predictors of health-related quality of life after anterior cruciate ligament reconstruction: a longitudinal analysis of a multicenter cohort at two and six years. The Journal of bone and joint surgery. American volume, 97(7), 551–557. https://doi.org/10.2106/JBJS.N.00248 

15.  Filbay, S. R., Roos, E. M., Frobell, R. B., Roemer, F., Ranstam, J., & Lohmander, L. S. (2017). Delaying ACL reconstruction and treating with exercise therapy alone may alter prognostic factors for 5-year outcome: an exploratory analysis of the KANON trial. British journal of sports medicine, 51(22), 1622–1629. https://doi.org/10.1136/bjsports-2016-097124 

16.  Podlog, L., Heil, J., & Schulte, S. (2014). Psychosocial factors in sports injury rehabilitation and return to play. Physical medicine and rehabilitation clinics of North America, 25(4), 915–930. https://doi.org/10.1016/j.pmr.2014.06.011 

17.  Smith-Ryan, A. E., Hirsch, K. R., Saylor, H. E., Gould, L. M., & Blue, M. N. M. (2020). Nutritional Considerations and Strategies to Facilitate Injury Recovery and Rehabilitation. Journal of athletic training, 55(9), 918–930. https://doi.org/10.4085/1062-6050-550-19 

18.  Papadopoulou S. K. (2020). Rehabilitation Nutrition for Injury Recovery of Athletes: The Role of Macronutrient Intake. Nutrients, 12(8), 2449. https://doi.org/10.3390/nu12082449 

19.  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. British journal of sports medicine, 50(15), 946–951. https://doi.org/10.1136/bjsports-2015-095908 

20.  Christino, M. A., Fleming, B. C., Machan, J. T., & Shalvoy, R. M. (2016). Psychological Factors Associated With Anterior Cruciate Ligament Reconstruction Recovery. Orthopaedic journal of sports medicine, 4(3), 2325967116638341. https://doi.org/10.1177/2325967116638341 

21.  Filbay, S. R., Roemer, F. W., Lohmander, L. S., Turkiewicz, A., Roos, E. M., Frobell, R., & Englund, M. (2023). Evidence of ACL healing on MRI following ACL rupture treated with rehabilitation alone may be associated with better patient-reported outcomes: a secondary analysis from the KANON trial. British journal of sports medicine, 57(2), 91–98. https://doi.org/10.1136/bjsports-2022-105473 

22.  Grzelak, P., Podgorski, M., Stefanczyk, L., Krochmalski, M., & Domzalski, M. (2012). Hypertrophied cruciate ligament in high performance weightlifters observed in magnetic resonance imaging. International orthopaedics, 36(8), 1715–1719. https://doi.org/10.1007/s00264-012-1528-3 

This blog was written by Samuel Bulten