There are many causes of foot and thumb pain, but the most common ones are the following: 1. The presence of nail infections can cause pain in the patient’s foot and thumb. If a patient has a bunion, it can also cause pain in the thumb. 3. osteoarthritis, rheumatism, rheumatoid arthritis and gouty arthritis can also cause pain in the thumb. 4. trauma to the thumb, causing tendon Rupture, fracture, dislocation, soft tissue injury, will also cause painful symptoms in the foot bunion.