There’s no clear proof that anterior cruciate ligament (ACL) reconstruction protects the knee joint from arthritis. In fact, the amount of osteoarthritis reported in knees is the same for patients who have had an ACL repair compared to those who have normal knees.
Scientists at the Henry Ford Health System in Detroit, Michigan, are looking for some answers to this puzzle. They think ACL reconstruction may not restore normal rotation in the knee. The lack of normal rotation may lead to more and more cartilage damage over time. To test this idea they studied six subjects running downhill. They used a special high-speed 3-D system to measure joint motion. The patients’ healthy knees were compared to the knees with ACL repairs.
Everyone was able to run downhill at a jogging pace. No one had pain or limped. Measurements showed forward and backward motions of the tibia (lower leg bone) on the femur (thighbone) were the same on both sides for all patients. This motion is called anterior translation. The real difference was in the outward (external) rotation and in the inward angle (adduction) of the knee. The repaired joints had more of both these motions compared to the normal knee.
The authors think these results show that restoring anterior translation doesn’t mean the joint will function normally again. This finding is surprising, since the goal of ACL reconstruction is to hold the joint stable and to prevent too much of this forward translation.
It looks like the researchers’ first theory was right. Abnormal motions other than joint translation may result in joint damage after ACL repair. This information may help surgeons improve ACL reconstruction techniques. Restoring all joint motions to normal may be the key to reducing osteoarthritis after ACL reconstruction.