The first time Richard Norris joined us as a guest blogger his excellent hamstring article went down a treat! In fact it became our very first piece to be featured in the British Journal of Sports Medicine blog. Since then Rich has helped out with an article on calf swelling and DVTs and written for The Sports Physio. Today's piece is on ACL injuries and their management.

Rich is an experienced lower limb specialist, you can follow him on Twitter via @Richnorris00 and find out more about him and his clinic here.

The knee is often referred to as the most complex joint in the human body and is subjected to large forces during sporting activities. These forces are resisted by a number of structures including the five main ‘static’ restraints of the knee: the two cruciate ligaments, the two collateral ligaments and the popliteus tendon. The anterior cruciate ligament (ACL) is arguably the most important and well known of these five structures; if the ACL was in the Jackson 5 it would be Michael… if it were in N-Sync it would be Justin Timberlake.

At any one time there are approximately 85 ACL injuries per 100, 000 citizens in society (Renstrom, 2013) so if you were sat in Barcelona’s football stadium or the Melbourne Cricket Ground at full capacity, there should be 85 people in the crowd with an ACL injury.

Although a direct blow to the knee can injure the ACL you may be surprised to learn that almost 80% of injuries are caused by non-contact events involving a sudden deceleration or change in direction (Renstrom et al, 2008).

This video of Michael Owen rupturing his ACL during the 2006 World Cup demonstrates the mechanism perfectly;


Tiger Woods famously ruptured his ACL when out running in 2007; I’m a massive Tiger fan so I’ll leave you to make up your own jokes about the dangers of running with your pants around your ankles!

Unfortunately if you’re female you are 2.5 times more likely to rupture your ACL than if you were male, with these odds doubling if you participate in team sports (Prodromos et al, 2007). The most cited reasons for these gender differences are

  • Reduced knee and hip bending during landing,
  • Increased “knock-knee’d-ness” (greater genu valgum of the knee).
  • Increased internal rotation of the thigh bone,
  • High quadriceps activity unbalanced by the hamstrings (Hewett et al, 2009)
  • The influence of the menstrual cycle (Zazulak et al, 2006).

As far as I am aware, gender reassignment surgery does not change your risk of injury but a recent literature review does confirm that injury prevention programmes are effective in reducing the incidence of ACL injury (Taylor et al, 2013) when the above factors are addressed with specific exercises.

Picture source

So how do you know if you have torn your ACL?

It never ceases to amaze me how consistent patients are at describing their ACL injury. They will have most likely twisted their knee and felt or heard a pop; sometimes it is another person that hears the pop and tries to help by feeding this information back to the injured party while they are writhing around in agony. The patient is unlikely to be able to continue the activity or even bear weight, and the knee fills up with blood very quickly because the ACL has an abundant blood supply. The patient is pleasantly surprised to find out that X-Rays show no fracture and over the next few weeks the knee feels much better. As the pain settles, walking and even running in a straight line isn’t usually a problem but when attempting to turn or sidestep the knee feels wobbly and the patient may demonstrate their instability by sliding clenched fists against each other (the ‘two fist sign’).

There are numerous special tests to assess the integrity of the ACL. This video demonstrates probably the best all-round test (the Lachman test) in an ACL deficient patient and shows the shinbone sliding forwards excessively on the injured leg. When performing the test the assessor cannot feel the stopping sensation provided by an intact ligament.


At this point I will pose a question… If you had an ACL tear, and you could have the ligament surgically reconstructed whenever you wanted, would you routinely go through with the operation?

As physiotherapists we are expected to deliver evidence-based treatment but until recently there have not been many high-quality studies providing guidance on the best way to manage an ACL injury. In 2010 Frobell et al published a randomised controlled trial (freely available here) to compare the outcome of an immediate operation versus a delayed operation (in those that complained of persistent knee instability). The exercises performed by all subjects were identical and are freely available in the supplementary material section (see tables below). Two years after injury there was no difference in outcome whether surgery was performed immediately, at a later date, or not at all. More importantly about two-thirds of the ‘wait and see’ subjects did not have an unstable knee and therefore were not exposed to the surgery and its associated risks (e.g. infection, DVT, graft failure). These results mirror the data we have collected in practice and I was fortunate enough to present this information via the Chartered Society of Physiotherapy. The longer term results (Frobell et al, 2013) published earlier this year (freely available here) indicate that 49% of the 'wait and see' patients still did not require reconstruction at 5 years.

If you don’t believe me, take the earlier example of Tiger Woods; he won five out of six tournaments with no ACL before having surgery!

Tables adapted from Frobell et al. (2010) – Supplementary material (freely available here).

One argument against the ‘wait and see’ approach is that an unstable knee causes more meniscus (footballer’s cartilage) tears, which is thought to encourage the early development of osteoarthritis, especially in children (Roos, 2005). However, the five-year findings showed no significant difference between subjects for meniscus surgery or osteoarthritis regardless of whether surgery was performed or not. In addition Moksnes et al (2013) found similar results regarding meniscus surgery and the percentage of children requiring ACL reconstructions. An earlier study (Moksnes et al, 2012) (freely available here) concluded that:

“… based on the existing evidence and considering the risks involved with surgical treatment, we propose that all children undergo a well-designed, non-operative rehabilitation program after injury (and are) monitored for recurrent giving-way episodes and activity levels”.

Whether the longer-term results in these subjects paint a different picture remains to be seen. Two important points to mention are that the subjects in the study were not professional athletes and substantial rehabilitation is required, but this is also the case after surgery.

Furthermore it is a false assumption that everyone who undergoes ACL surgery will return to pre-injury levels of activity. Ardern et al (2011) found that only 63% of surgical patients return to their pre-injury level and 44% return to competitive sport, despite the fact that 90% of people tested normal or nearly normal objectively. Fear of re-injury was the most common reason cited for a reduction or cessation of activity, and this is supported by Flanigan et al (2013) who noted fear of reinjury in half of their subjects.


So with this new knowledge, would you routinely go through with the operation?

Personally I would follow this advise provided in the BOA Blue Book for ACL injuries (freely available here), which states:

“Reconstruction is indicated in ACL deficient patients with symptomatic instability or a desire to compete in high risk activities”

High-risk activities would include those that put yourself or others at risk of injury, should the knee give way. For example if you work at height or need to carry people out of burning buildings on a regular basis then the risks involved if your knee unexpectedly gives way are too great.

I would also have the operation if I magically turn into a professional footballer (I am a free agent at present).

So if an ACL injury is confirmed, consider whether this is actually symptomatic (giving way) before rushing in to surgery. ACL reconstructions aim to stabilise an unstable knee… but if it's not unstable in the first place, what purpose does it serve?




ARDERN, C. L., WEBSTER, K. E., TAYLOR, N. F. & FELLER, J. A. 2011. Return to sport following anterior cruciate ligament reconstruction surgery: a systematic review and meta-analysis of the state of play. Br J Sports Med, 45, 596-606.

BOA Blue Book

FLANIGAN, D. C., EVERHART, J. S., PEDROZA, A., SMITH, T. & KAEDING, C. C. 2013. Fear of reinjury (kinesiophobia) and persistent knee symptoms are common factors for lack of return to sport after anterior cruciate ligament reconstruction. Arthroscopy, 29, 1322-9.

FROBELL, R. B., ROOS, E. M., ROOS, H. P., RANSTAM, J. & LOHMANDER, L. S. 2010. A randomized trial of treatment for acute anterior cruciate ligament tears. N Engl J Med, 363, 331-42.

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, 346, f232.

HEWETT, T. E., TORG, J. S. & BODEN, B. P. 2009. Video analysis of trunk and knee motion during non-contact anterior cruciate ligament injury in female athletes: lateral trunk and knee abduction motion are combined components of the injury mechanism. Br J Sports Med, 43, 417-22.

MOKSNES, H., ENGEBRETSEN, L. & RISBERG, M. A. 2012. The current evidence for treatment of ACL injuries in children is low: a systematic review. J Bone Joint Surg Am, 94, 1112-9.

MOKSNES, H., ENGEBRETSEN, L. & RISBERG, M. A. 2013. Prevalence and Incidence of New Meniscus and Cartilage Injuries After a Nonoperative Treatment Algorithm for ACL Tears in Skeletally Immature Children: A Prospective MRI Study. Am J Sports Med, 41, 1771-9.

PRODROMOS, C. C., HAN, Y., ROGOWSKI, J., JOYCE, B. & SHI, K. 2007. A meta-analysis of the incidence of anterior cruciate ligament tears as a function of gender, sport, and a knee injury-reduction regimen. Arthroscopy, 23, 1320-1325.e6.

RENSTROM, P., LJUNGQVIST, A., ARENDT, E., BEYNNON, B., FUKUBAYASHI, T., GARRETT, W., GEORGOULIS, T., HEWETT, T. E., JOHNSON, R., KROSSHAUG, T., MANDELBAUM, B., MICHELI, L., MYKLEBUST, G., ROOS, E., ROOS, H., SCHAMASCH, P., SHULTZ, S., WERNER, S., WOJTYS, E. & ENGEBRETSEN, L. 2008. Non-contact ACL injuries in female athletes: an International Olympic Committee current concepts statement. Br J Sports Med, 42, 394-412.

RENSTROM, P. A. 2013. Eight clinical conundrums relating to anterior cruciate ligament (ACL) injury in sport: recent evidence and a personal reflection. Br J Sports Med, 47, 367-72.

ROOS, E. M. 2005. Joint injury causes knee osteoarthritis in young adults. Curr Opin Rheumatol, 17, 195-200.

TAYLOR, J. B., WAXMAN, J. P., RICHTER, S. J. & SHULTZ, S. J. 2013. Evaluation of the effectiveness of anterior cruciate ligament injury prevention programme training components: a systematic review and meta-analysis. Br J Sports Med.

ZAZULAK, B. T., PATERNO, M., MYER, G. D., ROMANI, W. A. & HEWETT, T. E. 2006. The effects of the menstrual cycle on anterior knee laxity: a systematic review. Sports Med, 36, 847-62.


  1. Good read dudes! After rehabbing lots of surg and non surg I always ask patient about future. BOA advice is logical. But i will give em low down on research. If you want to play at high level then do it. If you wont go back then dont bother. Simple. That’s how I roll. But always make clear in anycase the rehab will be uber hard work.

  2. Great read, very interesting. After having ACL reconstructive surgery myself, I agree with the fact that having an unstable knee is good reason to have surgery. I obviously have no experience of having a secure and stable knee post ACL tear but like you said, depending on what your baseline is after the injury, this should influence your decision to have or not have surgery.

  3. Thought this was a great article – except for the title! I thought the evidence you cited was excellent however you failed to mention that the long term outcomes from ACL injuries is too often osteoarthritis. In fact, 50% of those who tear their ACL, have clinical and radiographic signs of OA (Lohmander, 2007). ACL injuries ARE bad, and the fact that surgery is unequivocal in improving outcomes should be the point! OA is a leading cause of chronic pain and disability worldwide, and the mobility disability that results can then contribute to many other life threatening conditions (ie. cardiovascular disease.) Just some more food for thought!

    • Alison, the evidence for OA in reconstructed knees versus deficient knees is not any different. If you were wishing to preserve your knees from OA by having a reconstruction you would be mislead. The outcomes are unfortunately the same regardless of surgery…

  4. As a fairly newly qualified Physio starting out on my professional journey this has been a fantastic read. The sign posting to literature is highly useful and i hope to use the knowledge I have built up to educate my patients on the outcomes of surgery and the exercise protocols from the Frobell et al. Rehab protocol will be really useful to guide my treatments. Thanks!

  5. My ACL was removed when i was a college senior, didn’t know it. Still played racquetball, was a runner, triathlete, marathoner, skier, ice/roller hockey etc. Is it really that necessary of a ligament?? I think my meniscus is far more important and wish I had it over the ACL. just saying…

  6. i tore my acl in my right leg playing soccer 14yrs ago and had replacement surgery … i did so because i wanted to continue playing the aforementioned sport … sadly … the knee did not return to its former full range of motion … it feels very tight when i bend it …

    6yrs ago i tore the acl in my left knee … but after rehabilitation it felt stable and strong … and the surgeon i spoke to said that if the knee isn’t giving way … and isn’t negatively impacting on my quality of life … why have an acl replacement?

    at first i was a little surprised … because i thought an operation was essential to stave off arthritis … but i was told that there was NO evidence to suggest a person without an acl will develop arthritis more quickly than a person who has an acl reconstruction …

    so i took a ‘wait and see’ approach … and since this injury i run 2-3 times a week … work out at the gym … and ride 10kms to work … and the knee still feels great and still feels stable … so i have decided not not to have an operation …

    the one activity i don’t feel confident participating in is … soccer … because of all the twisting and turning involve … but this is no great loss …

    i am 53

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