Index and middle fingers lock together. middle finger feels tight and slightly swollen.

Trigger finger: Your symptom sounds like trigger finger. It could painful at times. Some times steroid injection helps, some times you need to have released. Usually done by Orthopedic doctors.

See hand surgeon.: You need to see a hand surgeon for further evaluation and management. A hand surgeon is a specialized orthopedic surgeon.

This is complex: It is best that you see a Rheumatologist for these concerns to rule out Rheumatoid arthritis.Your underlying radicular symptoms are also interesting given your young age and I presume you are being seen by a neurologist or spine specialist.More tests need to be done to evaluate for 1 possible cause including degenerative disc disease, RA, trigger finger vs. Dequervains vs. Scleroderma for starters

Trigger finger: Generally, locking of the fingers or thumbs are caused by trigger fingers. This is a benign condition in which the tendon becomes entrapped around a structure called the A1 pulley. If this is painful, an injection or surgery can improve the symptoms. If this is not painful, you can live with this as long as you have full range of motion and full function.