Swelling and pain in the middle finger joint of the hand can be caused by various factors.
For example, gout can lead to gouty arthritis. A blood test will show elevated blood uric acid levels, and there will be local swelling and pain.
Rheumatic and rheumatoid arthritis can also cause joint swelling and pain. A blood test for anti - streptolysin O, C - reactive protein, rheumatoid factor, etc. will yield positive results.

Osteoarthritis of the middle finger is caused by the degeneration and aging of the articular cartilage, resulting in joint swelling and pain.
Additionally, local masses in the bones or soft tissues of the middle finger, such as bone tumors, can also cause swelling and pain in this area.

Therefore, it is recommended that patients go to the hospital for further examinations. They should have a blood test for relevant indicators and take an X - ray of the hand to understand the specific situation before a definite diagnosis can be made.