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Understanding the Cause of Osteoarthritis After ACL Injury

Studies show that people with a ruptured ACL are four times more likely to develop osteoarthritis (OA) of the knee compared with those who have a normal, intact ACL. In this article, researchers review the possible reasons why this may happen.

Abnormal motion in the knee joint is seen right away after ACL injury. The term used to describe joint motion in this context is kinematics. It's possible that abnormal kinematics from ACL deficiency could lead to changes in the way the joint is loaded (or unloaded).

The ACL keeps the tibia (lower leg bone) from sliding too far forward under the femur (thigh bone). Without this restraint, the joint can't keep proper alignment during motion. The contact points between the two bones can change. And when these two bones don't mesh just right, some structures can get pinched or rubbed unevenly.

This occurs primarily during weight bearing activities such as walking, jogging, or running. It is especially present for athletes during sports activities. And even when the ACL is repaired, abnormal kinematics puts the person at increased risk of OA.

Over time, abnormal loads or shifts in loads may lead to degenerative changes in the joint. The chondrocytes (cartilage cells) are sensitive to mechanical and biologic changes of this type. But chondrocytes are not able to adapt to these changes when they occur as a result of new loading patterns.

The authors conclude that altered joint motion is the beginning of joint degenerative changes leading to OA. Knowing this helps us understand the need to restore normal kinematics during walking after ACL injury. This study shows that it may be possible to avoid premature OA.

References: Ajit M. W. Chaudhari, PhD, et al. Knee Kinematics, Cartilage Morphology, and Osteoarthritis After ACL Injury. In Medicine & Science in Sports & Exercise. February 2008. Vol. 40. No. 2. Pp. 215-222.

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