Quick answer: A torn ACL (anterior cruciate ligament) can be treated with structured rehab alone, or with reconstruction surgery followed by rehab. In trials of young, active adults, starting with rehab and having surgery later only if needed gave similar results at 2 and 5 years, and about half had not needed an operation by the end of the trials. Surgery is more likely if your knee keeps giving way, other parts of the knee are also injured, or you want to return to sports with jumping, cutting and pivoting.
What is an ACL injury?
The ACL is one of the main ligaments inside the knee. It stops the shinbone sliding forward and helps control twisting. Most ACL injuries happen without contact, when you land, stop suddenly or change direction. A pop, swelling within a day and the knee feeling unstable or giving way are common signs.
Female athletes have 2 to 8 times the rate of ACL injury seen in males, probably because of a mix of knee shape, movement patterns and hormones. Read more in our article on ACL injuries in women.
Option 1: rehab first, with surgery later if needed
Rehab builds the strength and control of the muscles around the knee so it can work well without a reconstructed ligament. It does not rebuild the ligament, although in one trial, signs of the ACL healing showed on MRI at 2 years in about 1 in 3 people who started with rehab, and in about half of those who had not had surgery by then.
- What the trials show: a Cochrane review, based on one trial in young, active adults, found no difference in knee function at 2 or 5 years between early reconstruction and rehab with surgery later only if needed. In a second trial, early surgery gave slightly better self rated knee function at 2 years, but it is unclear whether the difference matters, and half of the rehab group did not need surgery.
- Who it can suit: people whose knee does not keep giving way, people who do sports with less pivoting, and people who would rather try rehab first.
- If it doesn’t work: if the knee keeps giving way despite good rehab, surgery is still an option later.
Option 2: reconstruction surgery
A reconstruction replaces the torn ligament with a tendon graft, usually through keyhole (arthroscopic) surgery. Reconstruction is recommended over trying to repair the torn ligament. If you and your surgeon decide on surgery, earlier reconstruction (within about 3 months) is generally preferred, because the risk of further cartilage and meniscus damage starts to rise.
- Your own tendon (autograft): recommended over donor tissue. A patellar tendon graft may lower the risk of the graft failing, while a hamstring graft causes less pain at the front of the knee and when kneeling.
- Donor tendon (allograft): tissue from a donor. Allografts fail more often, especially in young, active people.
Which option is right for me?
Your surgeon and physiotherapist will look at:
- Instability: a knee that keeps giving way despite good rehab usually needs surgery.
- Other injuries: combined injuries, such as a repairable meniscus tear, often lead to surgery. A torn MCL (the ligament on the inside of the knee) often does well without its own operation.
- Your sport and goals: activity level matters more than age. Sports with jumping, cutting and pivoting put more demand on the knee.
- Your preferences: the risks of surgery, the time you can give to rehab and how soon you want to return to sport.
Children and teenagers
Rehab and surgery are both options for children with open growth plates. Surgeons use techniques that protect the growth plates. After surgery, experts suggest that children wait at least 12 months before going back to pivoting sport. The plan should be agreed between the child, their family and the specialist team.
Recovery after ACL surgery
Rehab after a reconstruction usually moves through stages, and your surgeon and physiotherapist will set the timing:
- Early stage: controlling swelling, getting the knee fully straight, switching the thigh muscles back on and walking normally.
- Strength stage: building strength in the thigh, hip and calf muscles.
- Running and agility: a gradual return to running, then jumping, landing and changing direction. See our guide to returning to running after an ACL injury.
- Return to sport: only after passing strength and hop tests.
Functional knee braces are not recommended for routine use after reconstruction.
When can I return to sport?
Most people return to sport 6 to 12 months after surgery. Waiting matters: in one study, the risk of injuring the knee again fell by 51% for each month that the return to sport was delayed, up to 9 months. Passing return to sport tests matters too. In a study of male professional athletes, those who had not met all six discharge criteria had about 4 times the risk of the graft rupturing.
After a reconstruction, 81% of people return to some sport, 65% return to their previous level and 55% return to competitive sport.
Will I get arthritis?
The risk of knee arthritis is higher after an ACL injury, whether or not you have surgery. Keeping the knee strong and staying active are still worthwhile.
Can ACL injuries be prevented?
Yes, to a degree. Injury prevention programmes that train strength, balance, landing and cutting technique reduce the risk of a first ACL injury. Our ACL injury prevention article explains more.
When to get help
See a doctor or physiotherapist straight away if a knee injury causes a pop, swelling within a day or the knee giving way. See a doctor the same day or go to A&E if you can’t move the knee or put weight on the leg, or if the knee is badly swollen. Call 999 or go to A&E if the knee has changed shape, or if your foot or lower leg is numb, tingling, cold, or a blue or grey colour.
Frequently asked questions
Can a torn ACL heal without surgery?
Sometimes. In one trial, about 1 in 3 people who started with rehab showed signs of healing on MRI at 2 years, rising to about half of those who had not had surgery by then. In two trials, about half of the people who started with rehab had not needed a reconstruction by the end of the trial.
Do I need surgery for a complete ACL tear?
Not always. Many people do well with rehab first. Surgery is more likely if the knee keeps giving way, other structures are injured or you play pivoting sports.
How long is recovery after ACL surgery?
Most people return to sport 6 to 12 months after surgery. Waiting at least 9 months and passing strength and hop tests lowers the risk of injuring the knee again.
Which graft is best for ACL reconstruction?
Your own tendon is recommended over donor tissue. A patellar tendon graft may lower the risk of graft failure, and a hamstring graft causes less kneeling pain. Your surgeon will advise.
Will I get back to my sport?
Most people return to some sport. About two thirds return to their previous level and just over half return to competitive sport.
Sources
- Cochrane: surgery versus rehab for ACL injuries
- Reijman et al. 2021, BMJ: early surgery versus rehab with optional delayed surgery (COMPARE trial)
- Filbay et al. 2023, BJSM: ACL healing on MRI after rehab alone
- AAOS clinical practice guideline: ACL injuries
- OrthoInfo (AAOS): ACL injury, does it require surgery?
- OrthoInfo (AAOS): ACL injuries
- Grindem et al. 2016, BJSM: return to sport timing and reinjury
- Kyritsis et al. 2016, BJSM: discharge criteria and graft rupture
- Ardern et al. 2014, BJSM: return to sport after ACL reconstruction
- IOC consensus 2018: ACL injuries in children
- Mayo Clinic: ACL injury
Need help with this? Our ACL rehab programme team at Total Health by Hong Kong Sports Clinic can assess you and start treatment in your first session, in Central or Kai Tak. Message us on WhatsApp to book.
