Name: Dr. Nihar Modi
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An ACL (anterior cruciate ligament) tear is one of the most well-known and feared sports injuries. If you recently injured your knee and wonder whether you may have torn your ACL, or if you have just been diagnosed and want to understand what lies ahead, this guide is for you.

We will cover what the ACL is, how it gets injured, what it feels like, how it is diagnosed, and your treatment options.

What Is the ACL?

The anterior cruciate ligament is a strong band of fibrous tissue inside your knee that connects the thigh bone (femur) to the shin bone (tibia). Along with three other ligaments, it keeps the knee stable during movement, particularly the rotational and forwards-backwards forces involved in cutting, pivoting, and landing. 1

The ACL is one of the knee's most critical stabilisers. When it tears, the knee often loses its ability to function reliably under the demands of sport or vigorous physical activity.

How Does an ACL Tear Happen?

ACL injuries most commonly occur without any direct contact to the knee. The typical mechanisms include:

Sudden change of direction or cutting movements: planting the foot and pivoting sharply, common in football, kabaddi, tennis, and squash
Landing awkwardly from a jump: with the knee in a vulnerable, internally rotated position
Sudden deceleration: stopping abruptly at speed
Direct contact: such as a tackle that forces the knee into an abnormal position

It is important to note that the majority of ACL tears occur in non-contact situations, meaning the injury happens because of how your own body moves, not because someone hit you. 2

Who Is at Risk?

ACL injuries can affect anyone, but certain factors increase the risk:

Female athletes are 2–8 times more likely to sustain an ACL injury than male athletes in comparable sports, likely related to differences in anatomy, hormonal influences, and movement patterns. 3
Sports requiring cutting, jumping, or pivoting: football, basketball, netball, kabaddi
Previous ACL injury: having torn one ACL significantly increases the risk of injuring the opposite knee or re-injuring the same knee
Poor neuromuscular control and landing mechanics
Weak hamstrings relative to quadriceps

Symptoms of an ACL Tear

At the Time of Injury

The classic presentation of an ACL tear is quite distinctive:

A sudden, audible or felt "pop" at the moment of injury, heard by yourself or even those nearby
Immediate pain that can be severe
Rapid swelling of the knee, typically within the first 2–4 hours (caused by bleeding into the joint, called haemarthrosis)
Inability to continue playing: most athletes with a significant ACL tear find they cannot carry on
Difficulty bearing weight on the affected leg

In the Days and Weeks That Follow

Once the initial swelling and pain begin to settle:

A feeling of instability as if the knee might "give way," particularly with twisting movements
Loss of range of motion: difficulty fully straightening or bending the knee
Persistent swelling that fluctuates with activity
Quadriceps weakness and muscle wasting around the knee 4

Some people, particularly those who are less physically active, may manage day-to-day activities reasonably well despite a complete ACL tear. However, sporting activity and dynamic movements typically remain significantly compromised.

How Is an ACL Tear Diagnosed?

Clinical Examination

A skilled orthopaedic surgeon can often make a provisional diagnosis of an ACL tear based on the injury history and a careful physical examination. Specific tests used include:

Lachman's test: the most sensitive and reliable clinical test for ACL integrity, assessing forward movement of the shin bone relative to the thigh bone 5
Anterior drawer test: assessing forward tibial translation with the knee bent at 90 degrees
Pivot shift test: a dynamic test that reproduces the giving-way sensation

MRI Scan

An MRI (Magnetic Resonance Imaging) scan is the definitive investigation. It provides detailed images of the soft tissue structures inside the knee, confirming the ACL injury, assessing whether it is a partial or complete tear, and identifying any associated injuries to the menisci or other ligaments, which are present in a significant proportion of ACL injuries. 6

Treatment Options

The appropriate treatment for an ACL tear depends on several factors: your age, activity level, sport, the presence of associated injuries, and how the knee functions day to day. Treatment is broadly divided into non-operative management and surgical reconstruction.

Non-Operative Management

Not every ACL tear requires surgery. Some individuals, particularly older patients with lower activity demands, or those with partial tears, can achieve a satisfactory outcome with structured physiotherapy and rehabilitation focused on:

Reducing swelling and restoring range of motion
Strengthening the muscles around the knee, particularly the hamstrings and quadriceps
Neuromuscular and proprioceptive training to restore dynamic stability
Activity modification

However, individuals who wish to return to sports involving cutting and pivoting, or those who experience persistent instability despite rehabilitation, are generally advised to consider surgical reconstruction. 7

ACL Reconstruction Surgery

ACL reconstruction is a well-established, keyhole (arthroscopic) surgical procedure in which the torn ligament is replaced with a graft, a piece of tendon taken from elsewhere in the body.

Common graft choices include:

Hamstring tendon (gracilis and semitendinosus): the most commonly used graft in many centres; taken from tendons at the back of the thigh with minimal donor-site morbidity
Bone-patellar tendon-bone (BPTB): often considered the "gold standard" for high-demand athletes; taken from the front of the knee
Quadriceps tendon: an increasingly popular option, particularly for revision procedures or larger graft requirements

The choice of graft is discussed with each patient individually, taking into account their anatomy, activity level, and sport. 8

What to expect from the surgery:

ACL reconstruction is typically performed under general or spinal anaesthesia as a day-case or overnight procedure. The surgeon makes small incisions around the knee and uses a camera (arthroscope) to visualise the inside of the joint. The surgeon removes the torn ACL remnant, drills tunnels in the bone, and passes the graft through and secures it with fixation devices.

Rehabilitation After ACL Reconstruction

Rehabilitation is as important as the surgery itself. A structured, phased physiotherapy programme typically spans 9-12 months and progresses from:

Early phase: reducing swelling, restoring movement, and beginning gentle strengthening
Mid phase: progressive strengthening, balance, and proprioception training
Late phase: sport-specific training, agility, and plyometric exercises
Return-to-sport assessment: using objective criteria (strength testing, movement analysis) to guide safe return to training and competition 9

Returning too early, before the graft has fully incorporated and the knee has regained adequate strength and neuromuscular control, significantly increases reinjury risk.

Associated Injuries to Be Aware Of

ACL tears frequently occur alongside other injuries within the knee, which must also be addressed for the best outcome:

Meniscus tears: present in up to 50% of ACL injuries at the time of diagnosis 10
Cartilage damage: chondral lesions may be identified at the time of arthroscopy
MCL or other ligament injuries in more complex trauma

This is why a thorough MRI assessment before surgery is essential to plan the procedure fully and avoid missing associated pathology.

Long-Term Considerations

With appropriate treatment and rehabilitation, the majority of patients who sustain an ACL tear can return to their pre-injury level of sport and activity. However, it is important to have realistic expectations:

Complete recovery and return to sport typically take 9-12 months following reconstruction
There is a small but meaningful risk of reinjury if return-to-sport criteria are not fully met
Long-term studies have shown that ACL injuries are associated with an increased risk of knee osteoarthritis, particularly if associated meniscus damage is also present 11

Key Takeaways

ACL tears most commonly occur without direct contact, through cutting, pivoting, or landing
The classic presentation includes a "pop," rapid swelling, and knee instability.
Diagnosis is confirmed with clinical examination and MRI
Treatment ranges from physiotherapy alone to arthroscopic ACL reconstruction, depending on the individual's needs
Rehabilitation lasting 9–12 months is essential following surgery for safe return to sport

If you have experienced a knee injury and are concerned about your ACL, we encourage you to seek assessment from an orthopaedic sports medicine specialist. An accurate diagnosis and a well-tailored treatment plan make a significant difference to your outcome.

References

Duthon VB, et al. "Anatomy of the anterior cruciate ligament." Knee Surgery, Sports Traumatology, Arthroscopy. 2006;14(3):204–213. https://doi.org/10.1007/s00167-005-0679-9
Boden BP, et al. "Mechanisms of anterior cruciate ligament injury." Orthopedics. 2000;23(6):573–578. https://doi.org/10.3928/0147-7447-20000601-15
Myklebust G, Bahr R. "Return to play guidelines after anterior cruciate ligament surgery." British Journal of Sports Medicine. 2005;39(3):127–131. https://doi.org/10.1136/bjsm.2004.010900
Hartigan EH, et al. "Influence of the side of single-leg squat limb: ACL and quadriceps strength asymmetry." Clinical Orthopaedics and Related Research. 2009;467(1):207–213. https://doi.org/10.1007/s11999-008-0455-1
Torg JS, et al. "Clinical diagnosis of anterior cruciate ligament instability in the athlete." American Journal of Sports Medicine. 1976;4(2):84–93. https://doi.org/10.1177/036354657600400206
Ng WH, et al. "MRI assessment of ACL injuries: current concepts." Skeletal Radiology. 2011;40(7):841–855. https://doi.org/10.1007/s00256-011-1126-6
Frobell RB, et al. "A randomised trial of treatment for acute anterior cruciate ligament tears." New England Journal of Medicine. 2010;363(4):331–342. https://doi.org/10.1056/NEJMoa0907797
Prodromos CC, et al. "A meta-analysis of the incidence of anterior cruciate ligament tears as a function of gender, sport, and a knee injury-reduction regimen." Arthroscopy. 2007;23(12):1320–1325. https://doi.org/10.1016/j.arthro.2007.07.003
Grindem H et al. "Simple decision rules can reduce reinjury by 84% after ACL reconstruction: the Delaware-Oslo ACL cohort study." British Journal of Sports Medicine. 2016;50(13):804–808. https://doi.org/10.1136/bjsports-2016-096031
Bellabarba C, et al. "Isolated meniscal injuries without ligamentous disruption." Clinics in Sports Medicine. 1997;16(1):1–14. https://doi.org/10.1016/S0278-5919(05)70003-5
Lohmander LS, et al. "The long-term consequences of anterior cruciate ligament and meniscus injuries." American Journal of Sports Medicine. 2007;35(10):1756–1769. https://doi.org/10.1177/0363546507307396

ACL Tears: Symptoms, Diagnosis & Treatment Options