“After ACL injury, many people will have a bone bruise, and that typically goes away in a few months,” he said. But 34% of patients develop new bone marrow lesions (BMLs) within two years of an ACL injury, “and it’s unclear why.18 But that number—one in three patients—keeps coming up as having a problematic outcome.” According to his group’s research, BMLs tend to predict progression of OA.19 Bone surfaces in the knee joint also change shape shortly after injury, and may increase the risk of OA progression.
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Explore This IssueFebruary 2019
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“We can detect and measure subtle changes in the first two years after injury,” said Dr. Driban. “But we need to ask ourselves if some of these changes are normal adaptations to new joint loading conditions, and which of these changes represent pathologic changes that either represent early OA or could expose the patient to a greater risk of OA? Once we answer those questions, we can ask: How do we optimize joint health over time in joints with a history of injury?”
Return to activity in this two-year time period may be an unexplored risk factor for OA, and joint tissues may need time to adapt to new loads that are happening. Patients should return to sports and other activities with the fastest, but safest approach, with adequate rest time, he said.
Quadriceps weakness may linger after knee injury, and patients who report good quadriceps strength following post-surgery rehabilitation also tend to report high function.20 “Quadriceps weakness seems to be linked to structural changes, such as worse articular cartilage composition on MRI and tibiofemoral joint space narrowing on X-ray at two years follow-up after injury,” he said.21
Patients experience quadriceps weakness because of a deficit in neural activation in the muscle after injury. During rehabilitation, exercises should be optimized to address these neural changes: Spinal-reflexive excitability can be targeted within two weeks of surgery, and six months after surgery, therapies that improve cortico-motor excitability can be focused on.22 Muscle weakness can alter walking biomechanics, which may predict OA. Quadriceps weakness, pain and fear of re-injury are all reasons why some people never return to their pre-injury levels of activity, he said.
Preventing Post-Traumatic OA After ACL Surgery
Post-traumatic OA is a disease of interplay between biology, such as structural changes, and biomechanics, which are two fundamental controls of articular cartilage health, said Kurt P. Spindler, MD, vice chairman, research, and co-director, Musculoskeletal Research Center at the Cleveland Clinic, Ohio. “In my opinion, the articular cartilage is an innocent bystander: Initially, it is traumatized by injury, and then biological and biomechanical events result in post-traumatic OA.”