When should lag screws or plates be removed?

The most unequivocal reason to remove implants is infection. It is difficult to clear up any infection without removal of the metal. Before any consideration is given to implant removal following routine fracture healing, however, it should be recognised that there are significant disadvantages:
Expense: implant removal is a major expense since it demands aseptic technique, a moderate amount of equipment, post-operative bandaging and stall confinement. Both general anaesthesia and antibiotic prophylaxis may also be needed.
Cosmetics: it is important to point out to an owner that removal of plates/screws/wires etc. almost uniformly will result in a larger blemish at the surgical site. It seems almost inevitable that greater fibrosis develops when a plate is removed.
Risk: refracture following plate removal is probably the most significant complication to be considered ...