All ACL injuries need at least 9 to 12 months of high-quality, comprehensive, and consistent rehab to get the best chance of a good recovery, regardless of whether these are managed with rehab first or surgery. There are no shortcuts.
Both treatment options lead to similar levels of knee function (what your knee can do, e.g. using stairs and running), knee strength, activity levels, return to sport, quality of life, and knee symptoms (like pain, stiffness, swelling) at 2 and 5 years after injury, but surgery also has some risks (such as infections, fractures, stiffness, numbness, and blood clots).
About 1 in 10 people who have surgery require a second operation in the 2.5 years after reconstruction due to a problem arising from the initial surgery. The risk of reoperation is higher in people who have surgery earlier (within 6 months of injury).
When people try rehab before considering surgery, over half of them decide that they do not need surgery. If you are not satisfied with how your knee feels and functions after completing a rehab programme, you can still choose to have surgery. Research also shows that people who complete a full rehab programme before ACL surgery recover better and have better knee function than those who have surgery straight away.