An 11-month-old girl, well-known to your clinic since birth, arrives for a well-child visit. The parents report that their baby drags her legs rather than crawling on both hands and legs. They are concerned that this is abnormal. The father says that the child only recently began crawling and she does not pull to a stand. You noted at her 6-month visit that she was not rolling over or sitting; previous visits were unremarkable as was the mothers pregnancy and vaginal delivery. While examining the baby, you note that when she is held by the axillae her legs are extended and crossed (i.e. the scissoring posture).
What is the most likely diagnosis? Why?
What would be three differentials in this case? Why?
What developmental milestones are expected at this age?
What do you believe is your best course of action/treatment plan for this appointment? Why