The answer to this question would be: synarthrosis
There are 3 kinds of join classification based on the range of motion of the joint. Diarthrosis would be joint with the highest mobility, amphiarthrosis offers lesser mobility and synarthrosis offer very little movement.
The immobilization is trying to minimalize the movement so the answer should be synarthrosis. The example of synarthrosis join would be the suture in skull
