The round swelling that has developed weeks after the surface wound healed strongly suggests that a tiny fragment of the plant thorn (mull) or organic debris broke off and remains trapped under the skin. What is Likely Happening:-- 1. Foreign Body Granuloma. 2. Delayed Inflammatory Reaction. Please consult a general surgeon. The doctor will examine the finger joint. In some cases, a high-resolution ultrasound or minor exploratory procedure is needed to locate and completely extract the tiny remnant of the thorn.The swelling and mild pain typically will not fully resolve until the retained foreign fragment is completely removed. Depending on what they find, the doctor may prescribe a short course of anti-inflammatory medication or localized treatment once the debris is cleared.

Hello, please upload a picture so that we can actually see the problem.