Anterior cruciate ligament injury should no longer be considered solely as an acute traumatic event affecting short-term sports participation, but increasingly as the beginning of a long-term knee joint health condition that may lead to post-traumatic knee osteoarthritis. Despite major advances in anterior cruciate ligament surgical reconstruction and rehabilitation, structural and symptomatic features of post-traumatic knee osteoarthritis may emerge within the first 5 years after injury and nearly 40% of individuals may develop radiographic signs of knee osteoarthritis within 10 to 15 years after injury. This international perspective highlights the growing concern surrounding premature knee osteoarthritis in athletes following anterior cruciate ligament injury and emphasizes the expanding role of sports physiotherapists beyond return to sport. Residual instability, neuromuscular deficits, altered knee joint loading, and persistent inflammatory processes may contribute to long-term cartilage degeneration and functional decline. Sports physiotherapists are therefore uniquely positioned to contribute not only to rehabilitation and secondary prevention, but also to long-term knee joint health and activity education, early detection of knee osteoarthritis-related symptoms, individualized load management, and multidisciplinary management strategies. A shift toward lifelong knee health management after anterior cruciate ligament injury appears necessary to better support athletes throughout their sporting careers and beyond.