Hi, thanks for writing to HCM.
Development of pain and swelling around the implant (plate) is not a good sign. It may indicate an infection inside. The lump is unlikely to be callus
as such an amount of callus formation (size of a lump) is rare in tibial bone.
An xray of the involved area will show the status of the bone and the implant. CT scan
may be needed to detect any soft tissue
I suggest you to consult your treating doctor for further management.
Hope this information is helpful. Good day