The locking finger has no connection what so ever with Suddeck (a strange word to use nowadays) It is a problem (most likely) of the tendon of the midfinger. AS example a nodule on the tendon might give to much friction with the surrounding sheet (like a brake cable on a pushbike when the cable is worn, and you brake it will not spring back) or the original direction of the tendon has changed due to the fracture. If possible ask for an new X-ray and compare with a previous. Use an atonomy book to look at how the tendons would aligne with the bony structures. (better would be a scan but this will be to time consuming and to costly) Palpate the tendons carefully, do not inflict pain since this could well restart a sudeck (if there was a proper one in the first place).
Best of luck.