When the thumb or finger locks up it is called a Trigger Thumb or Trigger Finger. They are slightly different in the mechanism that may be causing each. The cramping can be painful.
For a trigger thumb, the tendon of the long flexor of the thumb seems to actually get caught between tight muscles, preventing movement. There also may be involvement of a little “sesamoid bone” imbedded within the tendon of the thumb. With a trigger finger, the muscles cramp up to stiffen the finger. There are some suggestions that there is swelling in the tendon sheath, but that is not well supported. Sometimes the digit snaps open, even making a sound as it does so.
Trigger thumb usually can be released, at least temporarily, by forcing the digit to open. Putting pressure on the tendon of the thumb while trying to open it seems to help. Trigger finger also needs external force. Injections have been given to assist the release and sometimes surgery is used. Spontaneous resolution usually happens within six months according to Travell and Simons.
I don’t see any information from my search about releasing spasms manually, but in my own experience that has helped. Both short and long flexors must be treated and more treatments may be needed to prevent recurrence.
Cramping may be due to nutritional or systemic causes such as an imbalance or insufficiency in the calcium complex or a B vitamin deficiency. Acidic pH or lactic acid buildup, use of medications, poor circulation and problems with hydration can also cause cramping. Vitamin C can help.
Here are two web sites with good information.
This is a series on arm and hand pain from my Neuromuscular Therapy center near Boston. If you missed the beginning, go back to the “Checklist of Causes.”