Recovery of knee range of motion after ACL repair varies from patient to patient and doctor to doctor. Some of it depends on the type of repair you had. The rehab program can make a difference, too. Each doctor has his or her own expectations about knee motion after the operation.
Did the doctor tell you to expect the knee to be tight for months? You may want to bring your question up at the time of your next follow-up appointment. Full recovery of knee extension can occur within the first month. It usually takes longer (up to two months) to get full flexion back.
There is a special device that can be used to measure joint laxity or looseness. It measures how much the bones forming the knee joint slide against each other forward and back or side to side. This measure can be used to define "success" or "failure" after ACL. Recent studies suggest using five or more millimeters of joint glide as a failed ACL