FIGURE 1.

Schematic diagram summarizing the graft healing process after anterior cruciate ligament (ACL) reconstruction. After ACL reconstruction (ACLR), inflammatory occurs, attracting immune cells and mesenchymal stromal cells (MSCs) to the injured site. The original cells in the tendon graft undergo necrosis and are replaced by MSCs infiltrating into the graft. Both MSCs and the inflammatory cells produce angiogenic factors and the MSCs proliferate and differentiate. The differentiated MSCs produce extracellular matrix and remodeling enzymes to incorporate the tendon graft-to-bone tunnel by Sharpey’s fibers and is associated with improved biomechanical properties of the healing complex. However, there is regional variation in healing along the bone tunnel. The original ACL insertion site is not re-established. The tendon graft mid-substance theoretically should remodel to a ligament. However, it degenerates due to excessive inflammation and poor angiogenesis after ACLR. Created with BioRender.com.