Beware: A Surgically Replaced ACL is not like the Original Equipment
The ACL is arguably one of the most important ligaments of the knee. The ligament stabilizes the knee in a front-back direction. The illustration above was traced from a patient’s MRI. Note how the ACL ligament is at about a 45 degree angle and stretches from the far front of the tibia to the back of the femur (figure A). This quasi-horizontal position of the ligament in the knee is important for controlling front-back movement (red arrows). When the ACL is damaged, too much movement will happen between the femur and tibia, causing osteoarthritis to happen much more quickly. When the ACL is completely torn, oftentimes a new ligament is artificially installed via surgery. This surgical implant however is not at this 45 degree angle, but because of technical constraints, is often at a much steeper and almost vertical angle (figure B). This vertical angle of the new ligament is a problem, as it’s not the right angle to prevent much front-back motion. To compensate, the ACL graft is often tightened down, adding compressive loads to the knee that can again increase the amount of arthritis. In addition, in many of these ACL grafts we see shear of the new ligament causing ACL damage over time right where the graft exits the tunnel (figure C). The upshot? No matter how you install a new ACL ligament through surgery, the new ACL will never have all the properties of the original equipment. This can lead to a more rapid onset of arthritis. This also fits with recent research showing that 2/3’rds of athletes don’t return to their pre-injury level of sports even at a year after surgery. Is there another way? If the ACL isn’t completely retracted and if there are viable fibers left, then we advocate using any number of biologic or cellular techniques to strengthen what’s there rather than to yank out a ligament that may be saved, as an ACL surgery alternative. We also see knees where there is clear evidence of a degenerated ACL ligament on MRI and the ligament is loose on exam, but nobody has talked to the patient about the elephant in the room. As you can see above, if we can keep the original orientation of the ACL ligament by augmenting what’s there by an injection, it’s likely to be closer to the original equipment than a surgically installed ligament. For example, we’ve had good success in treating loose ACL ligaments without surgery through the injection of the patient’s own stem cells.