Final answer:
Developmental dysplasia of the hip is the condition called when a person has hip dysplasia at 16-18 months.
Step-by-step explanation:
The condition called when a person has hip dysplasia at 16-18 months is Developmental dysplasia of the hip. Hip dysplasia is a condition where the hip joint does not develop properly, causing the hip socket to be shallow and the hip joint to be unstable. It is important to diagnose and treat hip dysplasia early to prevent long-term complications.