An ACL injury is a sprain or tear of the anterior cruciate ligament, a key ligament that stabilises the knee during twisting and changes of direction. It usually happens in sport when landing, pivoting or stopping suddenly. Treatment is either structured rehabilitation alone or reconstruction surgery with rehabilitation, and both rely on a long, progressive exercise programme.
Also known as anterior cruciate ligament tear, ACL rupture, torn ACL
Symptoms
- A pop or giving-way sensation at the time of injury, often in sport
- Rapid swelling of the knee within a few hours
- Pain and difficulty continuing to play
- A feeling that the knee is unstable or 'gives way' when turning
- Loss of full movement in the weeks after injury
Causes and risk factors
- Sudden change of direction, pivoting or stopping while running
- Landing awkwardly from a jump, especially with the knee falling inwards
- Direct contact or tackles to the knee
- Playing pivoting sports such as football, netball, basketball, rugby and skiing
- Being female in contact sports, and previous ACL injury
What the evidence says helps
- Exercise-based injury prevention programmes that include jumping and landing (plyometric) exercises reduced ACL injury risk by around 60% in pooled sports trials.2
- In young active adults with an acute ACL tear, a randomised trial found structured rehabilitation with the option of later surgery gave similar results at two years to early reconstruction, and many people in the rehab group avoided surgery.3
- A Cochrane review found no clear difference in knee function between surgery and rehabilitation at two and five years, but the evidence came from a single small trial and is low quality.4
- Surgery tends to give a more mechanically stable knee, so people who have ongoing giving way, or who want to return to pivoting sport, may be advised to consider reconstruction.34
- After reconstruction, returning to pivoting sport at nine months or later, and only once thigh strength is close to the other side, was linked to a much lower risk of re-injury.5
Things you can try at home
- Early on, protect the knee, use ice and elevation to control swelling, and work on getting the knee fully straight
- Start gentle thigh muscle activation and walking as comfort allows
- Commit to rehabilitation for many months, whether or not you have surgery
- Do not rush back to pivoting sport; base return on strength and function tests, not just time
- Once back in sport, keep doing an injury prevention warm-up
When to get urgent help
Contact your GP urgently, call NHS 111, or call 999 in an emergency if you have:
- After a fall, collision or twisting injury you cannot put weight on the leg, the knee looks deformed, or it swells up within a few hours: go to A&E or an urgent treatment centre.
- Your foot or lower leg becomes numb, cold, pale or weak: seek urgent medical help (A&E).
- Your calf becomes painful, swollen, warm or red, especially after surgery, a long journey or a period of immobility: call NHS 111 or see a GP urgently. Call 999 if you also have chest pain or breathlessness.
- After surgery, your wound becomes increasingly red, hot, painful or discharges, or you develop a fever: contact your surgical team or NHS 111 urgently.
- Your knee locks and you cannot straighten it, or it suddenly gives way repeatedly: see a GP or urgent care promptly.
How Apollo can help
We assess your knee after injury, explain your options and help you understand the decision between rehabilitation alone and surgery, referring you on for an orthopaedic opinion where appropriate. Our team provides prehab before surgery and structured post-operative rehabilitation, progressing from early movement to strength, running and sport-specific training. We use VALD strength and jump testing to help guide return-to-sport decisions rather than relying on time alone.
No GP referral needed. Clinics in Sheringham, Coltishall and Norwich.
Related reading
Frequently asked questions
Do I need surgery for a torn ACL?
Not always. Research shows some people do well with structured rehabilitation alone, while others, especially those with repeated giving way or who want to return to pivoting sport, may benefit from reconstruction. The decision is best made with an orthopaedic surgeon and your rehab team.
How long is recovery after ACL surgery?
Rehabilitation usually takes nine to twelve months before returning to pivoting sport. Research suggests returning before nine months, or before strength has recovered, increases the risk of re-injury.
What is ACL prehab?
Prehab is exercise before surgery to reduce swelling, restore full movement and build strength. Going into surgery with a calm, strong knee is generally thought to make early rehabilitation easier.
References
- Montalvo AM, et al. (2019). Anterior cruciate ligament injury risk in sport: a systematic review and meta-analysis of injury incidence by sex and sport classification. Journal of Athletic Training. View source
- Al Attar WSA, et al. (2022). Injury prevention programs that include plyometric exercises reduce the incidence of anterior cruciate ligament injury: a systematic review of cluster randomised trials. Journal of Physiotherapy. View source
- Frobell RB, Roos EM, Roos HP, Ranstam J, Lohmander LS (2010). A randomized trial of treatment for acute anterior cruciate ligament tears. New England Journal of Medicine, 363(4), 331–342. View source
- Monk AP, Davies LJ, Hopewell S, et al. (2016). Surgical versus conservative interventions for treating anterior cruciate ligament injuries. Cochrane Database of Systematic Reviews. View source
- Grindem H, et al. (2016). Simple decision rules reduce reinjury risk after anterior cruciate ligament reconstruction: the Delaware-Oslo ACL cohort study. British Journal of Sports Medicine. View source
This page is general information, not a diagnosis or a substitute for medical advice. If you are worried about your symptoms, speak to your GP or a registered healthcare professional. Content prepared from the sources above, November 2026.
