I got ACL surgery a year ago and I needed a manipulation 4 months later then 5 months later got a scar tissue removal. When I walk my knee catches. Y?

Possible causes in-- More scar tissue. Or another problem which you've had, in addition to the acl issue. Knee cap issues are very common in young girls and women. Are you having pain at all or is it just catching sensation? With no pain, i would suggest see how things go, and do nothing surgically but do pt. With pain, either get a 2nd opinion. Another possibility may be a referred pain from back or hip area.
More info. I assume the acl graft was intact at second and third surgery? If scar involves area under or in behind patella this best explains catching. If it is in front of the graft, called a "cyclops lesion" that is a different story. Now you most likely need exercises for mobility of the knee and especially patella. Was it a patellar tendon graft or hamstring or something else?