Hi, thanks for writing to HCM.
From the description, I suspect that you might have developed tendinitis
of extensor tendon.
An xray is necessary to ruleout any bony problem at that level.
Momentarily, use ice packing, analgesic
anti inflammatory medicines like motrin
, local application of painkiller gel for few days.
If the symptoms are not resolving, consult an orthosurgeon for further workup and management.
Hope this information is helpful. Good day