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Written By Dr Chi-Chong KONG

(Last updated on: Oct 13th  2020)

You are sprinting down the wing, a defender comes for you, you cut inside, but as you push off your knee goes 'pop' and you fall over in agony. You are helped off the field and watch your team win (without you!) with a bag of ice on your knee. After the game your knee feels a bit better, and you join your teammates for a celebratory drink, and when you get home, you feel fine. The next morning your knee is agony! You limp to the doctor, who does an X-ray and tells you the bones are fine. Over the next few weeks your knee gets better, and you are soon back on the pitch – dashing up the wing … you cut inside a defender… and end up face down….

Does this story sound familiar? It is typical of an ACL tear.

What is the ACL?

The ACL is the 'Anterior Cruciate Ligament', a tough band of collagen inside your knee joining your thigh bone to your shin bone. It is a little over an inch long, about as thick as your finger, and consists of two bundles of fibres, (Anteromedial - 'AM' and posteolateral - 'PL'). One controls front to back movement and one controls twisting movements (Fig. 1). It is a vital part of the system that controls the complex gliding and bending movement of the knee which allows people to do everything from walking slowly to ballet and gymnastics.

How does the ACL get torn?

A violent injury like a ski accident or fall can rupture the ACL (Fig. 2), but most ACL injuries are 'noncontact': the ACL can be torn if you twist your knee too far or change direction too quickly. Many women tear their ACLs simply landing badly from a jump in netball or basketball.

Fig. 1 Two bundles in normal anterior cruciate ligament

Fig. 2 Ruptured Anterior Cruciate Ligament 

What will happen to my knee if my ACL is torn?

Left alone, you will experience recurrent knee instability, or 'giving way', leading to meniscal tears, cartilage damage and finally arthritis [1]. The more active you are, the more quickly the arthritis will come on – ten years of football with an ACL tear and you are just about ready for a knee replacement! On the other hand, if you are in your sixties and your sport is cycling, the injury is unlikely to catch up with you.

How do I know if my ACL is torn?

Unfortunately, a substantial proportion of acute ACL ruptures is missed [2]. People improve after the injury, and in many cases return to sport, even though the knee is not 100%.
The knee usually feels loose when examined: if the 'pivot shift' test is positive the ACL is definitely torn [3,4], but if it is a little sore, muscle spasm can easily hide this, giving a false negative result.
Magnetic Resonance Imaging (MRI) shows the ACL (Fig. 3), but it cannot always show whether the ACL fibres are taut and functioning or loose and not functioning. If the MRI shows microfractures (also known as bone bruises) in the outer half of the knee, it is likely that the ACL is completely torn, even if ACL fibres are still visible [5].

Fig. 3 MRI from Shanghai shows intact ACL marked by arrows.
Asia Medical Specialists knee surgeons often diagnose ACL tears in patients who have been having trouble with their knees for a long time, and have not been able to get a firm diagnosis.

What should I do if my ACL is torn?

The modern answer is 'have it reconstructed', to restore normal function and reduce the likelihood of arthritis.

Is ACL surgery absolutely necessary?

Not absolutely. Some people are willing to modify their activities - minimising their pivoting and cutting sports. They may able to function well without an intact ACL. However, there is still a chance that the ACL-deficient knee can 'give way'during regular exercise, resulting meniscal and cartilage injuries and eventually arthritis. Given the good results and relative simplicity of modern ACL reconstruction operations most people choose to ACL reconstruction.

What about bracing?

Unfortunately braces 'lose control' of the knee at the crucial transitions from loaded to unloaded and unloaded to loaded – for example landing from a jump. Thus braces do not allow people to play sport without significant risk to their knee [6].

Are there any age limits for ACL reconstruction?

Not really. Children need their ACLs as much as adults. Sometimes they tear the ACL from the bone, so the ACL can be repaired instead of replaced, but, if the ACL is torn, it needs to be reconstructed. In skeletally immature children a slightly different surgical technique is used to reduce the chance of growth disturbance.

Older people need ACL reconstruction if their knee instability is a problem [7,8]. The oldest person reported in the medical literature to have an ACL reconstruction was a rancher who could not work normally because his knee was unstable. He was 84 [9].

What does ACL reconstruction involve?

ACL reconstruction is performed in a hospital by arthroscopic ('keyhole') surgery. You have an epidural or general anaesthetic. The procedure takes less than 2 hours. You can walk the same day, and though it is sore, it is not painful. Most people go home from hospital the next morning, and return to office jobs after 3 or 4 days. No brace is needed. One can put all one’s weight through the knee, but most people use crutches for a couple of weeks.
Rehabilitation should be supervised by a physiotherapist – ideally one needs about 20 visits over 6 months. Usually one is jogging by 3 months, returning to light sports training at 6 months, and, hopefully, competition the following season, at 9 to 12 months.

What is the surgical technique?

Asia Medical Specialists knee surgeons perform a modern 'anatomical double-bundle ACL reconstruction' (Figs. 4 & 5). This technique accurately reproduces the normal anatomy of the uninjured ACL. Two of your own hamstring tendons are used to recreate the two bundles of the ACL. The hamstring tendons re-grow, like a lizard’s tail [10]. If there are any other problems in the knee, such as meniscal tears, these are treated at the same time.

Fig. 4 Arthroscopic view during ACL reconstruction showing how the two bundles of the ACL cross

Fig. 5 Reconstructed two bundles of anterior cruciate ligament 

Why double-bundle, instead of single-bundle?

Conventional 'single-bundle' methods of ACL reconstruction reproduce only the anteromedial bundle of the ACL, which does not restore normal stability, particularly tibial rotation [11,12]. Although single-bundle ACL reconstruction is far better than having an ACL-deficient knee, the results are not perfect.

On long term follow-up after single bundle ACL reconstruction, 10-30% patients complain of knee pain and residual instability, while arthritis has been observed on X-rays in up to 90% of patients [13,14].

Biomechanical studies of double-bundle ACL reconstruction have shown superior rotational stability to single-bundle ACL reconstruction [15].
Recently, prospective randomised controlled trials have compared single-bundle to double bundle techniques, and shown the double-bundle results to be superior [16,17,18].

It is very likely that the improved short-term results will be maintained in the long-term.

What can I expect after ACL reconstruction?

Asia Medical Specialists knee surgeons have had excellent results with double bundle ACL reconstruction. Many patients say their knee feels 'normal' – which is high praise, and most patients return to sport at the same level as prior to their ACL injury – including professional sportspeople, dancers, acrobats and other high-demand individuals.
For more information, a patient information video is available, it will walk you through the diagnosis of Anterior Cruciate Ligament (ACL) rupture, ACL reconstruction surgery pre-op preparation, the surgery itself, and post-op rehabilitation.


1. Anstey DE, Heyworth BE, Price MD, Gill TJ. (2012). "Effect of timing of ACL reconstruction in surgery and development of meniscal and chondral lesions." Phys Sportsmed Feb;40(1):36-40.

2. Guillodo Y, Rannou N, Dubrana F, Lefevre C, Saraux A. (2008). "Diagnosis of anterior cruciate ligament rupture in an emergency department." J Trauma Nov;65(5):1078-82.

3. Fetto JF, Marshall JL. (1979). "Injury to the anterior cruciate ligament producing the pivot shift sign." JBJS Am Jul;61(5):710-4.

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8. Osti L, Papalia R, Del Buono A, Leonardi F, Denaro V, Maffulli N. (2011). “Surgery for ACL deficiency in patients over 50.” Knee Surg Sports Traumatol Arthrosc. Mar; 19(3):412-7.

9. Miller MD, Sullivan RT. (2001). “Anterior cruciate ligament reconstruction in an 84-year-old man.” Arthroscopy Jan;17(1):70-2.

10. D. Leis HT, Sanders TG, Larsen KM, Lancaster-Weiss KJ, Miller MD. (2003). “Hamstring regrowth following harvesting for ACL reconstruction: The lizard tail phenomenon.” J Knee Surg. Jul; 16(3):159-64.

11. Tashman S, C. D., Anderson K (2004). “Abnormal rotational knee motion during running after anterior cruciate ligament reconstruction.” Am J Sports Med 32: 975-983

12. Yagi M, W. E., Kanamori A. (2002). “Biomechanical Analysis of an Anatomical Anterior Cruciate Ligament Reconstruction.” Am J Sports Med 30: 660-666

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14. Fithian DC, P. E., Stone ML (2005). “Prospective trial of a treatment algorithm for the management of the anterior cruciate ligament-injured knee.” Am J Sports Med 33(3): 333-334.

15. Hemmerich A, van der Merwe W, Batterham M, Vaughan CL. (2011). “Double-bundle ACL surgery demostrates superior rotational kinematics to single-bundle technique during dynamic task.” Clin Biomech (Bristol, Avon). Dec; 26(10):998-1004.

16. Kondo E, Yasuda K, Azuma H, Tanabe Y, Yagi T. (2008). “Prospective clinical comparisons of anatomic double- bundle versus single-bundle ACL reconstruction procedures in 328 consecutive patients.” Am J Sports Med. Sept;36(9):1675-87.

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18. Song EK, Oh LS, Gill TJ, Li G, Gadikota HR, Seon JK. (2009). “Prospective comparative study of ACL reconstruction using the double-bundle and single-bundle techniques.” Am J Sports Med. Sep;37(9):1705-11.

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