How To Retrieve Clips Which Are Migrated Used For Sterilization?

How many clips are used for a sterilisation? I had 2 removed last year which were discovered after an operation to remove a clot. The clips had migrated and were causing me a lot of pain. I am experiencing the same pain again now a year later and a recent x-ray for my back has revealed that there are more migrated clips. I am due to have them removed soon, but want to know how this happens and how many there are. Thank you. Michelle