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Background: The origin of patellofemoral pain (PFP) may be associated with the inability of the patellofemoral joint cartilage to absorb and distribute patellofemoral joint forces.Hypothesis: When compared with a pain-free control group, young active women with PFP will demonstrate differences in their baseline patellar cartilage thickness and transverse (T2) relaxation time, as well as a less adaptive response to an acute bout of joint loading.Study Design: Controlled laboratory study; Level of evidence, 3.Methods: Ten women between the ages of 23 to 37 years with PFP and 10 sex-, age-, and activity-matched pain-free controls participated. Quantitative magnetic resonance imaging of the patellofemoral joint was performed at baseline and after participants performed 50 deep knee bends. Differences in baseline cartilage thickness and T2 relaxation time, as well as the postexercise change in patellar cartilage thickness and T2 relaxation time, were compared between groups.Results: Individuals with PFP demonstrated reductions in baseline cartilage thickness of 14.0% and 14.1% for the lateral patellar facet and total patellar cartilage, respectively. Similarly, individuals with PFP exhibited significantly lower postexercise cartilage thickness change for the lateral patellar facet (2.1% vs 8.9%) and the total patellar cartilage (4.4% vs 10.0%) when compared with the control group. No group differences in baseline or postexercise change in T2 relaxation time were found.Conclusion: The findings suggest that a baseline reduction in patellar cartilage thickness and a reduced deformational behavior of patellar cartilage following an acute bout of loading are associated with presence of PFP symptoms. [ABSTRACT FROM AUTHOR]