It is hard to do good clinical research, especially when following a young, active and mobile patient population. Evaluation of outcomes of ACL reconstruction is important because techniques change — and the type of graft used (hamstring, patellar tendon, quad tendon and cadaver tendon) is variable.
In some studies, the outcome is whether or not the athlete re-injures their knee, but there are many things we really want to know, such as:
1) when they went back
2) what sport they got back to
3) whether they returned to the same level of competition they were performing at prior to their knee injury
4) whether their knee was stable and asymptomatic with day to day activities, and so on.
High Variability in Outcome Reporting Patterns in High-Impact ACL Literature | The Journal of Bone & Joint Surgery