Can't we say, "in middle" like "in front"? For example,

"Put the expression in middle."

Or should we say, "Put the expression in the middle." And then, shouldn't we say, "in the front" instead of "in front" in the sentence,

"Put the expression in front."

Or is there a meaning difference between "in the middle" and "in middle" and "in the front" and in front"?

Thank you so much as always and I respect your precious opinions and time as usual.