Is it possible that micro movements could occur in a non displaced distal fibula fx but not show on x-ray or ct and could that cause delayed union?

Yes: Motion at a fracture site may reflect to inadequate immobilization due to cast failure or excessive patient activity.

Not likely: An isolated nondisplaced distal fibula fracture is a stable injury. The treatment is pain control and activities as tolerated with or without ankle support. Although delayed or nonunions can occur, they are not common at the distal fibula.