February 11, 2016
We all know someone who has torn their ACL. The vast majority of these athletes have surgery to reconstruct the ACL and return to their previous level of activity. However, we know that there is a high incidence of arthritis in patients who tear their ACL, whether or not they have surgery. Research studies show that anywhere from 10% to 90% of people show some level of post-traumatic arthritis following ACL injuries. This large variation is due the degree of arthritic changes that were used as the cutoff in studies. Barenius et al American Journal of Sports Medicine 2014 showed that ACL reconstructed knees had a 3 times greater incidence of post-traumatic arthritis regardless of graft type using a grade of 2 or greater on the Kellgren-Lawrence (Scale is 0-4 with grade 2 showing significant osteophytes and/or cartilage reduction up to 50%). They also showed an even greater incidence of arthritis in patients with combined ACL and meniscus injuries. Why is this? Isn’t an ACL reconstruction supposed to fix the knee and prevent arthritis?
An ACL reconstruction will not prevent arthritis. The surgery is done to regain stability of the knee to prevent further injury to the meniscus and articular cartilage due to episodes of the knee giving way. Research is still trying to figure out the definitive cause of post-traumatic arthritis in order to effectively minimize or potentially eliminate it. Currently, we break down the potential causes into two groups: time of the injury and post-surgical. Time of the injury factors include the “bone bruise”, inflammation, and meniscal injury. Nearly all ACL injuries show a bone bruise on MRI. Research has indicated that this bruise results in damage to the articular cartilage and underlying subchondral bone. The theory is that over time, this damage progresses and eventually results in post-traumatic arthritis. Inflammation from the initial injury results in a catabolic inflammatory process causing abnormal tissue remodeling and damage. Meniscal injury has shown to be the greatest predictor of future arthritic changes. Bindle et al Journal of Athletic Training 2001 showed that as little as a 10% loss of meniscus volume may increase tibiofemoral contact pressure by 65 %. Potential post-surgical factors include altered knee kinematics, inflammation, and inadequate rehabilitation. Altered gait kinematics are seen in the reconstructed knee as compared to the uninvolved knee. These altered kinematics result in an abnormal shift of contact pressures and is likely to contribute to the development of post-traumatic arthritis. Post-surgical inflammation not only negatively effects the knee cartilage as mentioned above, it can potentially cause surgical tunnel widening resulting in ACL graft laxity which may further alter knee kinematics. Lastly, inadequate rehabilitation may have an effect on arthritis as well. Not fully regaining range of motion and strength as well as not fully normalizing gait and movement patterns may negatively alter knee kinematics.
You may be wondering, why the concern about post-traumatic arthritis? I’ll just get a knee replacement when I’m older, right? The concern is for the patients that develop significant and symptomatic arthritis at a younger age. Nebelung et Arthroscopy 2005 found that in a group of elite athletes who underwent ACL reconstruction, all had degenerative changes by 35 years and 42 % had undergone a total knee replacement. These patients had significant symptoms and functional limitations requiring knee replacement. Obviously, they were no longer able to participate in sports and had difficulty at work and with daily activities. As we continue to narrow down on the cause/causes of post-traumatic arthritis in order to better manage, and hopefully eliminate it, we must continue to council athletes on the long term complications of ACL injury and the best evidence in managing these injuries.