I have a non union of my right tibia which was fractured later last year. the gap is about 3mm. is it necessary to do surgery to correct this ?

Correct the cause: The key to treating a nonunion is identifying why it failed to heal in the first place. Infection? Smoking? Poor nutrition? Inadequate immobilization/ stability? (hypertrophic nonunion) An inadequate healing response? (atrophic nonunion). Certainly, a year is enough time for a tibia fracture to heal under normal circumstances. Correct the cause. Alternatives to surgery may be a bone stimulator.