I have a pin in my big toe after bunion surgery a few years ago, how has the bunion reappeared (not as bad as before surgery) if the toe has a pin to keep straight?

Shoes too small or foot problem.

The surgery could have failed a thus the deformity is reoccurring when doing Buions surgery the appropriate diagnosis and surgery type are very important. Not al bunions are alike and neither is the surgery one fits all. You should go back to the surgeon and have the surgeon provide you with an explanation. Sometimes a bunion might require another procedure. Also recommend second opinion