No. In some cases it can be quite helpful, but with most acute injuries it is not needed.
Goal: normal motion. Prior to ACL reconstructive surgery, it is advisable to have a knee that is "ready for surgery". Ideally this means the initial swelling and stiffness have resolved, quadriceps (thigh muscle) strength has returned, and most importantly- full knee motion is regained. Maximization of these three variables preoperatively help limit the morbidity of surgery. Physical therapy can help this process.
Yes. The physical therapy after an ACL reconstruction is nearly as important as the ACL reconstruction itself!
Usually mandatory. Most surgeons that reconstruct torn anterior cruciate ligaments (acl) require physical therapy in some form or fashion for at least 6-12 weeks. Most insurance companies approve such therapy as they realize the evidence-based research that supports the utility of therapy to maximize functional recovery after major reconstructive surgery of the knee. Initial focus of therapy is motion and strength.
ROM/Strength. The first things to do will be to begin range of motion exercises. Then there will be strengthening exercises. This is very important to begin to get you back to as normal or better than your were. Work with your therapist and work hard.
Several. After acl surgery your surgeon will direct your physical therapist to progress you through a structured program designed to regain your knee motion a strength.
Roughly 6 months. This is not my strong suite, as I work with children exclusively. But it is important to rehabilitate under the direct supervision of a skilled physical therapist. Typically the rehab is most intense in the first 6 weeks focused on restoring range of motion. Home exercise program is essential as well. Then several weeks of return to function and eventually sport.
Variable. Physical therapy for acl reconstruction is quite variable and every surgeon has his/her own protocol. Mine is more flexible. As long as you are meeting milestones of range of motion, and increasing quadriceps strength over the first six weeks, I don't required physical therapy. Between 3-4 months after surgery, work is based as much core strengthening as knee. The last step is proprioception.