Fig. 1

Female, 17 years old, habitual patellar dislocation of the left knee. a Dejour type oftrochlear dysplasia. Type A dysplasia: trochlear morphologic structures are preserved, but the sulcus is shallow. Type B dysplasia: flat, horizontally oriented trochlear joint surface. Type C dysplasia: flat, obliquely oriented trochlear joint surface with facet asymmetry. Type D dysplasia: same as type C but with a prominent bone protrusion. b CT scan image showingtrochlear dysplasia type C; tunnel view showing thepatellar dislocation; osteotomy of tibial tuberosity (+: tibial tubercle; : internal rotation and medial transfer). c Schematic diagram of the elevation of the tibial tubercle and MPFL reconstruction. d Two years after the operation, the X-ray and CT images show a normal patellar position