Challenge of the Week / Basic Science / 10.25.19

A 12-month-old child is referred for short stature. The child has a history of frequent respiratory tract infections. Examination reveals a short neck, coarse facies, and claw hands. Radiographs indicate flaring of the ribs and medial clavicle, anterior vertebral wedging, and odontoid hypoplasia. Which of the following is most likely to limit this child’s mobility?