The anterior cruciate ligament (ACL) is the most commonly injured ligament of the knee.

Ligaments are tough bands of tissue that connect the ends of bones together. The ACL is located in the center of the knee joint where it runs from the backside of the femur (thighbone) to connect to the front of the tibia (shinbone).


The ACL is the main controller of how far forward the tibia moves under the femur. The mechanism of injury for many ACL ruptures is a sudden deceleration (slowing down or stop), hyperextension, or pivoting in place.  Sports requiring the foot to plant and the body to change direction rapidly (such as basketball) carry a high incidence of injury. Most ACL injuries are noncontact.


Pain and swelling from the initial injury will usually be gone after two to four weeks, but the knee may still feel unstable. The instability and inability to trust the knee for support are what require treatment. Also, long-term instability may lead to early arthritis of the knee.


If the symptoms of instability are not controlled by a brace and rehabilitation program, then surgery may be suggested. The main goal of surgery is to keep the tibia from moving too far forward under the femur bone and to get the knee functioning normally again.


Most surgeons reconstruct the ACL using a graft piece of tendon or ligament to replace the torn ACL. This surgery is most often done with arthroscopy rather than an open surgery.


For a graft, surgeons may use a section of a patient’s own patellar tendon or hamstring tendon.  Sometimes surgeons use allograft material from organ donors, which can be tibialis, patellar, hamstring or Achilles tendons.


The reconstructed ACL is quite strong, with the patella tendon graft often being stronger than the original ACL.  Of course, tendon strength is only one factor in a successful recovery, range of motion being another.  For athletes, proprioception is the most important word in returning from an ACL injury.  Proprioception is our sense of the relative position of neighboring parts of the body and strength of effort being employed in movement.  Elite athletes have incredible proprioception or instinctive muscle memory, call it athleticism.  The best surgery and hard work can help but probably cannot replace natural athleticism.


Patients participate in physical therapy after ACL reconstruction.  Recovery can take 4 to 18 months depending on the patient’s fitness and the physical demands the reconstructed knee needs to meet.  The average patient will do quite well returning to normal activities of daily living, including being a weekend warrior athlete running, tennis, golf.  For the elite athlete dependent on intricate athletic moves, recovery can be a challenge.