Objective To investigate the relationship of step length to the sex-specific prevalence and worsening of magnetic resonance imaging (MRI)-detected structural damage in the patellofemoral (PF) joint among a cohort of older women and men with or at risk of knee osteoarthritis (OA). Methods The Multicenter Osteoarthritis Study is a cohort study of persons ages 50-79 years with or at risk of knee OA. Step length was assessed using the GAITRite walkway (CIR Systems) at the 60-month visit, and cartilage damage and bone marrow lesions (BMLs) were graded on MRI at the 60- and 84-month visits. Step length was divided into sex-specific quintiles, and the relationship of step length to the prevalence and worsening of cartilage damage and BMLs in the PF joint was examined using logistic regression, adjusting for age, body mass index (BMI), leg length, and tibiofemoral joint structural damage. Results In 1,053 knees, 4,094 and 4,083 PF joint subregions were studied for the cartilage and BML analyses, respectively. Mean ± SD age was 65.6 ± 8.1 years and mean ± SD BMI was 29.1 ± 4.7 kg/m2; 62% of participants were female. In women, compared to those with the shortest step length, those with the longest step length had 0.62 (95% confidence interval [95% CI] 0.43-0.88) and 0.59 (95% CI 0.40-0.87) times the odds of cartilage damage and BMLs, respectively. There was no cross-sectional association in men, and no longitudinal association in either sex. Conclusion Women with PF joint structural damage may adapt their gait by shortening their step length, but this may not be sufficient to reduce the risk of worsening damage over time.