Swelling and pain in the index finger that cannot be bent may be caused by trauma, tenosynovitis, rheumatoid arthritis and other factors. 1. Trauma: Injury to the index finger during activity, damage to the ligaments of the finger joints or fracture can cause swelling and pain in the index finger joints and inability to bend. 2. Tenosynovitis: Tenosynovitis is an acute or chronic inflammatory reaction of the tendon sheaths, which is mostly seen in manual laborers or instrumentalists, etc. It mostly occurs in the finger joints, and it can cause pressure and pain in the fingers, swelling and limitation of activities. 3. Rheumatoid arthritis: Rheumatoid arthritis is an autoimmune disease with erosive arthritis as the main symptom. When it involves the finger joints, it can lead to pain, swelling and limitation of finger joints, which mostly manifests itself as stiffness of the fingers when waking up in the morning. Swelling and pain in the index finger can not be bent may be caused by other reasons, it is recommended that the patient timely consultation, identify the specific causes, and follow the doctor’s instructions for targeted treatment.