Plate removal operations, usually can affect your thumb function due to two main reasons, the first is that to remove the plate the muscle supplying your thumb is raised from the bone, thus it causes temporary weakness, this will surely recover in a time period of 3 to 4 weeks, the other reason less probable is the injury to the tendon to thumb, since function of all other fingers are normal, there is less possibility of any nerve injury, and thus a NCV is not recommended, The best you can get done now is a USG of the forearm, to see the contunity of structures.

Physiotherapy will help you to recover.but if there is no improvement in 6 to 8 wks,then NCV of the  nerves of the arm should  be  done.