Abstract： Objective To discuss the relationship between the injury patterns of medial patellofemoral ligament(MPFL) and injury degrees of vastus medialis obliquus(VMO) after acute patellar dislocation(PD). Methods Knee joint MRI was performed in 79 patients with acute PD. Images were acquired and evaluated using standardised protocols. Injury patterns of MPFL were grouped by severity (partial tear and complete tear)and location (isolated patellar-side tear (PAT), isolated femoral-side tear (FEM) and combined tear (COM) ) for analysis of the prevalence of VMO injury. The VMO elevation was calculated on sagittal and coronal planes. Results The prevalence rates of MPFL tear and VMO lesion were 96.2%(76/79)and 54.4%(43/79)after acute PD.The prevalence rate of VMO lesion was 40.6%(13/32)and 68.2%(30/44)in the partial and complete MPFL tear subgroups,respectively.Complete MPFL tear subgroup showed higher prevalence rate of VMO lesion when compared with partial tear subgroup(χ2=5.727, P=0.017). The prevalence rates of VMO lesion in the PAT, FEM and COM subgroups were 31.8% (7/22), 67.7% (21/31) and 70% (14/20), respectively. There were statistically significant differences among them(χ2=8.549,P=0.014).About the mean VMO elevation,there were statistically significant differences between the complete and partial MPFL tear subgroups, the FEM and PAT subgroups, and the COM and PAT subgroups (P=0.00). Conclusions Compared with partial MPFL tear, complete tear predisposes to VMO lesion and has a higher elevation of the torn VMO after acute PD.The femoral-sided and combined MPFL tears predispose to VMO lesion and have higher elevations of the torn VMO.