The anterior cruciate ligament (ACL) is one of the main ligaments that stabilise the knee. ACL tears are among the most common serious sports injuries, especially in football, basketball, netball, handball and skiing, and they are more common in female athletes. Recovery often takes nine months to a year, and the injury raises the long-term risk of knee osteoarthritis.
This guide explains how ACL injuries happen, the typical symptoms, how they are diagnosed, the choice between surgery and rehabilitation, the recovery timeline, and evidence-based prevention programmes.
Imagine a 22-year-old footballer who plants her foot to change direction. She hears a pop, feels her knee give way and falls. Within hours, her knee is swollen like a balloon. Teammates tell her to rub it and play next week. A week later, her knee still buckles on the stairs. An assessment confirms an ACL tear. Her season is over, but with the right treatment and rehabilitation, her career does not have to be.
How ACL injuries happen
Most ACL tears are non-contact injuries, caused by:
- sudden change of direction or cutting;
- landing awkwardly from a jump with the knee turning inwards;
- sudden stopping;
- twisting with the foot planted.
Direct blows to the knee (for example, a tackle) can also cause ACL tears, often with other injuries to the meniscus or other ligaments.
Symptoms
- A “pop” at the time of injury.
- Rapid swelling within hours.
- Pain and difficulty continuing to play.
- Knee “giving way” or feeling unstable, especially when turning.
- Loss of full movement.
First aid
Stop playing. Use the PEACE and LOVE approach: protect, elevate, avoid anti-inflammatories in the first days if advised, compress, educate; then load gradually, stay optimistic, use vascularisation (pain-free cardio) and exercise. See our sports injury first aid guide. Seek assessment if the knee swells quickly or feels unstable.
Diagnosis
- Clinical examination by a physiotherapist, sports medicine clinician or orthopaedic specialist, including tests such as the Lachman test.
- MRI to confirm the tear and check for meniscus or cartilage damage.
- X-ray to exclude fractures.
Surgery or rehabilitation?
| Option | Often suitable for |
|---|---|
| ACL reconstruction surgery plus rehabilitation | Athletes returning to cutting and pivoting sports, people with repeated instability, combined injuries |
| Structured rehabilitation alone (with option of later surgery) | People with lower activity demands, some athletes after shared decision-making, older adults |
Research shows that some people do well with rehabilitation alone, while others need surgery later. The decision should be shared between the patient and specialists, considering sport, goals, age, instability and other injuries.
Recovery timeline after reconstruction (typical)
| Time | Goals |
|---|---|
| 0 to 2 weeks | Control swelling and pain, achieve full knee straightening, walk with crutches |
| 2 to 6 weeks | Restore bending, normal walking, start strength work |
| 6 weeks to 3 months | Strength and balance; cycling; step-ups |
| 3 to 6 months | Running progression, jumping and landing training |
| 6 to 9 months | Sport-specific drills, agility, cutting |
| 9 months and beyond | Return to sport after passing strength and functional tests |
Returning to sport too early, especially before nine months, is linked to a higher risk of re-injury.
Prevention
Neuromuscular training programmes (such as FIFA 11+ for football) that combine warm-up, strength, balance, plyometrics and landing technique have been shown to reduce ACL injuries, particularly in young and female athletes. Key elements:
- landing softly with knees over toes, not collapsing inwards;
- hamstring and hip strengthening;
- balance and agility drills;
- doing the programme regularly, two to three times a week.
Long-term knee health
People who have had ACL injuries have a higher risk of osteoarthritis. Keeping muscles strong, maintaining a healthy weight and staying active help protect the knee. See our osteoarthritis guide.
Frequently asked questions
Can an ACL tear heal without surgery?
The ligament usually does not heal back to normal, but many people regain good function with rehabilitation. Some need surgery later.
How long is ACL recovery?
After reconstruction, return to sport usually takes at least nine months.
Why are female athletes at higher risk?
Factors include anatomy, hormones, landing mechanics and muscle strength patterns; prevention programmes reduce risk.
What is the best way to prevent ACL injuries?
Regular neuromuscular warm-up programmes focusing on strength, balance and landing technique.
But I feel fine at six months. Can I play?
Feeling fine is not the same as being ready. Return-to-sport decisions should be based on strength, movement and functional tests, as early return increases the chance of another ACL tear.
Your next step: If you coach or play a team sport, introduce a structured neuromuscular warm-up, such as FIFA 11+, at your next training session and keep it going all season.
Related: Sports injury first aid · Sprained ankle · Hamstring injury
Sources: FIFA 11+ injury prevention programme; published systematic reviews on ACL injury prevention and management; clinical practice guidelines on ACL rehabilitation and return to sport.
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