Background:​ Knee and hip injuries have been linked with osteoarthritis in cross-sectional and case-control studies, but few prospective studies have examined the relation between injuries in young adults and risk for later osteoarthritis.

Objective:​ To prospectively examine the relation between joint injury and incident knee and hip osteoarthritis.

Design:​ Prospective cohort study.

Setting:​ Johns Hopkins Precursors Study.

Participants:​ 1321 former medical students.

Measurements:​ Injury status at cohort entry was recorded when the mean age of participants was 22 years. Injury during follow-up and incident osteoarthritis were determined by using self-administered questionnaires. Osteoarthritis was confirmed by symptoms and radiographic findings.

Results:​ Over a median follow-up of 36 years, 141 participants reported joint injuries (knee alone [n = 111], hip alone [n = 16], or knee and hip [n = 14]) and 96 developed osteoarthritis (knee alone [n = 64], hip alone [n = 27], or knee and hip [n = 5]). The cumulative incidence of knee osteoarthritis by 65 years of age was 13.9% in participants who had a knee injury during adolescence and young adulthood and 6.0% in those who did not (P = 0.0045) (relative risk, 2.95 [95% CI, 1.35 to 6.45]). Joint injury at cohort entry or during follow-up substantially increased the risk for subsequent osteoarthritis at that site (relative risk, 5.17 [CI, 3.07 to 8.71] and 3.50 [CI, 0.84 to 14.69] for knee and hip, respectively). Results were similar for persons with osteoarthritis confirmed by radiographs and symptoms.

Conclusions:​ Young adults with knee injuries are at considerably increased risk for osteoarthritis later in life and should be targeted in the primary prevention of osteoarthritis.