Walking for short people

Question
I'm 5 ft tall even.  I should've been taller but I have severe scoliosis and spinal fusion with some curvature still left in my spine.  Everywhere I read says that 4.5 mph is a walk, but there is no physical way I can walk at that speed, for me that's a run.  Is that because of my height or possibly my back problems?  Is there a different standard for below average height people?  Does having to run at that speed change my calories burned estimate since I'm actually running and not walking like most guides think?

Answer
Size has nothing to do with it. The truth is, 4.5 mph is a very awkward speed, representing extremely fast walking or slow running. It really makes little difference. Humans burn about 100 calories per mile whether they are running or walking. Heavier people burn somewhat more, lighter people burn somewhat less. There is no exact figure because people vary so much in how efficient they are.

If you can run comfortably at any speed, you get slightly more health benefit from the exercise. But for most people, walking is quite sufficient, although it takes longer to burn the same number of calories.