Welcome to the forum, Tom.
I'm pretty sure that Karen Ocker had a cast fusion without instrumentation. She shows up frequently on the forum. You can PM her and ask her about it. I believe she eventually had revision surgery. I think she'd definitely be worth talking to about your case. You can type in her name and look up any relevant threads, also.
1985 - Dx w/ painful AIS at 16 with 39* upper LEFT thoracic single curve.
2000 - 41*
2010 - 46* (T1 - T6) 38* (T6-L2) Now a double thoracic
2012 - Dx w/ Cervical Muscle Dystonia.
DDD L5/S1 with left nerve impingement
Left SI joint dysfunction