(a) Preoperative axial MRI of both knees in a six-year-old boy shows a deep femoral trochlea with a septum (red arrow), dividing the knee joint in a medial and lateral half and positioning the patella on the lateral side of the septum; patella ossification center (*). (b) Sagittal MRI through the lateral femoral condyle articulating with the patella ossification center (*); septum (red arrow).