Review Question - QID 219113

A 3-week-old male is sent to your office after his pediatrician observed asymmetric inguinal skin folds and expressed concern for possible hip dysplasia. The patient is accompanied by both parents and appears comfortable and in no distress. On examination, the left-sided inguinal skin folds appear more prominent than on the right. Leg lengths are equal, Barlow and Ortolani tests are negative, and an imaginary line connecting the anterior superior iliac spine and the greater trochanter crosses the umbilicus. A Galeazzi test reveals symmetrical femoral lengths, and the patient’s hip can be abducted to the exam table bilaterally. An ultrasound of the left hip is shown in Figure A. What is the structure depicted by the letter “B” in the figure?