The Biology of ACL Reconstruction and Regeneration

One of the best examples of the wonders of modern medicine is Anterior Cruciate Ligament reconstruction.  Because the body is unable to heal the ACL on its own, it requires reconstruction in order to restore normal function to the knee.  The process of ACL regeneration relies heavily on the biology of your knee.

When I reconstruct your ACL, I take a tendon, either from an organ donor or from a different part of your body, then place it where I want a ligament to grow.  Your body uses this tendon as a scaffolding to regenerate a new anterior cruciate ligament.  This process occurs and 3 phases.  The initial phase is characterized by necrosis or cell death.  During the first 4 weeks after surgery, your body tears down all of the living cells in the graft, leaving only nonliving tissue as a blueprint for the final ligament.  The second portion of the regeneration process is called the proliferation phase.  This usually occurs in the second and third month after surgery.  This is characterized by influx in your own body’s cells into the remaining scaffolding.  The scaffolding also undergoes changes that cause significant weakness in the graft.  6-8 weeks after surgery is typically thought of as the weakest point and the time where of the structure of the graft needs the most protection.  The final phase, the ligamentization phase begins about 3 months after surgery.  During this time, the graft is slowly and steadily getting stronger and becoming more like the original ACL.  There is no clear end point however there is plenty of evidence suggesting that the graft will continue to mature over the following year.