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Background:Numerous studies have investigated the influence of osseous factors on patellofemoral joint instability,but research on the influence of dynamic muscle factors in vivo is still in the exploratory stage.This study aimed to use magnetic resonance imaging (MRI)and diffusion tensor imaging (DTI) to evaluate vastus medialis oblique (VMO) fiber bundles in patients with recurrent patellar dislocation to explore the changes in muscle morphology and function.Methods:This prospective study involved 30 patients (7 males and 23 females;average age,21.4 ± 3.8 years) clinically diagnosed with recurrent patellar dislocation in Peking University Third Hospital and 30 healthy volunteers matched for age,sex,and body mass index in our medical school between January 2014 and October 2014.None of the patients had a recent history of traumatic patellar dislocation or transient patellar dislocation.All patients underwent conventional MRI and DTI of the knee.The cross-sectional area of the VMO on MRI and the fractional anisotropy (FA),apparent diffusion coefficient (ADC),and primary (λ1),secondary (λ2),and three-level characteristic (λ3)values on DTI were measured.The independent-samples t-test was used to compare these parameters between the two groups.Results:Compared with the control group,the patient group showed significantly higher FA values (0.39 ± 0.05 vs.0.33 ± 0.03) and significantly lower ADC (1.51 ± 0.13 vs.1.58 ± 0.07),λ2 (4.96 ± 0.13 vs.5.04 ± 0.07),and λ3 values (4.44 ± 0.14 vs.4.58 ± 0.07;t =5.99,t =-2.58,t =-3.02,and t =-4.88,respectively;all P ＜ 0.05).Cross-sectional VMO area and λ1 values did not differ between the two groups (t =-1.82 and t =0.22,respectively;both P ＞ 0.05).Conclusions:The functional status of the VMO is closely associated with recurrent patellar dislocation.MRI,especially DTI (FA,ADC,λ2,and λ3),can detect early changes in VMO function and might facilitate the noninvasive monitoring of the functional status of the VMO in patients with recurrent patellar dislocation.