In the 1980s when ACL reconstruction techniques were less reliable, many patients were advised to stop high level sports. From those patients, we know that about 10-20% of patients are able to compensate with loose ACLs. These patients were able to get back to some degree of sports, even including cutting sports like soccer and skiing.
The problem is that in that same group of patients who tried non-operative treatment with physiotherapy and modification of sports, at least 50-60% of patients returned to their doctors within 2 years, complaining of persistent pain, instability, and an inability to return to a satisfactory level of sports activities.
Furthermore, many patients trying non-operation treatment develop new tears of cartilage and meniscus as a result of the rotational instability in their knees. These unnecessary additional cartilage and meniscus tears might have been prevented if ACL reconstruction had been undertaken earlier. In addition, extra meniscus and cartilage injuries usually worsen the results or surgery, and may add to the risk of early degeneration in the knee.
For this reason, most patients engaging in regular sports activities are advised that ACL reconstruction surgery is the best option to allow a return to sports, and reduces the risk of other new meniscus or cartilage injuries from occurring.