when to consider a fussion?

hello thank you for all hte help in the past:)  my daughter is 3 yrs.  we did a spinal x-ray to get a base line on her scoliosis after her detethering in november.  as of aug 2000 she was at 28 degrees and has progressed to 40 degrees as of march7 2001.  
she has 3 hemivertabre but also weakness although mild in her trunkm can this be contributing to the curve and not just be due to the deformed vertabre?  also at what point do they usually do a fussion on a small child is it when they progress to what degree or if there is progression?  will bracing maybe help?

again thank you for all your help,
joanna
katelynn 3( tcs, spinal lipoma, syrnix, cong scoliosis, part sacral agenesis, dev delays mildm hypotonia, si, seizure, bilateral renal reflux, right kidney damage,mild mitral valve regurgittation and stenosis)

[CCF Neuro[P]-M.D.-RPS]

Dear Joanna:

There isn't a particular degree that everyone gets a fusion.  Usually when respiratory function is beginning to be compromised that they consider fusion.  Bracing may help and that is usually the first mode of correction.  Unfortunately, most of the time this is not effective in neurological disorders.

Sincerely,

CCF Neuro MD