You may well have trigger points in your forearm. Trigger points in the forearm refer pain to other places and can refer pain into the hand. For example, many instances of carpal tunnel pain actually turn out to be TPs in the forarm in both the flexor and extensor muscles. Of course, you could also have tendonitis and/or arthritis in those knuckle joints too, as you state.
I suspect you may have TPs in the flexor digitorum muscles. TPs in this muscles can send fairly sharp pains (almost a burning pain) to the inside of the fingers. This TP can be caused by overuse of grasping things, just as you mention.
Look for TPs in the upper forearm and they’ll usually be fairly deep. Using the thumb of your other hand, push inward/massage any really sore spots you find. Don’t over do this. Massage for a couple of minutes about six times a day. It may take a day or three to remove the TPs.
Let me know how you do.
You have received a lot of good advice, ak267.
As for which medical profession to consult, I suggest a good sports medicine practice, which will have a lot of different modalities to use.
Some stretches that may help:
For flexors: Put warm water in the sink so you are warming muscles and fascia as you press you palms on the bottom of sink so the wrists are in extension. Position shoulders with arms straight (elbows locked directly above hands as you press down and hold a slow 10 count. Repeat and relax several times.
2: Stand with arms at sides, elbows straight. Cup hands with palms up and rotate forearms as far as they turn in both directions keeping palms up. Now switch and put hands in extension, back of hand upward, and rotate forearms as far as they turn in both directions. Do it slowly and repeat both flexion and extension positions several times
3. Door frame stretch: Stand in a doorway with your hands on the frame at eye level. Put one foot forward and lean through the doorway. Feel the stretch in the pectoralis muscles. Alternate feet to stretch both sides. Next put one hand (this is done one hand at a time) on the top frame of the doorway and lean forward. (this stretches the pectoralis minor muscle which functions to rotate the shoulder forward and down).
4. Scalenes are three muscle that attach to the sides of your neck vertebrae and to the 1st and 2nd ribs. They rotate the head and elevate the ribcage when you take a deep breath. They are capable of causing a soft tissue impingement of the median, radial and ulnar nerves where they emerge from the side of the neck.
A. Anterior Scalene: Place your hand over you head, finger just above your ear and slowly pull your head to your shoulder and hold it there for the slow ten count, switch hands and take your head to the opposite shoulder. Repeat three times and take it slow. For a little more, do an isometric resistance when you have you head as far as it goes toward the shoulder: gently try to raise your head back up while holding it down with your hand. Note: take it easy; the point is to just add some resistance to fatigue the muscles and allow the stretch receptors to release a bit. Don’t take any stretch past a bit of discomfort and never into pain.
B. Medial scalene: Position you hand over your head and posterior to the 1st stretch and bring your head toward the front of your shoulder (as if you are going to sniff your armpit :) ). You will feel the stretch on the posterior side of the neck. Try the isometric resistance again. Repeat several times.
C. Posterior scalene: Position you hand over your head and above the orbit of your eye and pull your head toward the back of your shoulder but keep the head upright so you feel the stretch on the anterior side of your neck. Try the isometric resistance again. Repeat several times.
Analyze your activities and see if you can discover what actions have contributed to the dysfunction. If you need to consult an athletic trainer concerning your body mechanics in regard to those activities, do so. Correcting faulty mechanics can help a lot. Try all the non-invasive methods first, before thinking about surgery. Surgery changes your structure and mechanics for good. Make sure, if you do opt for surgery, to find an orthodpod who specializes in this sort of procedure and make sure you understand the various outcomes and percentage chances of relief.