I've been searching for case studies and papers on humerus lengthening. All of them have shown satisfying results, there is some scarring and obviously the process is awkward but there is little pain and seemingly no long-term complications. The worst complication so far seems to be temporary paralysis, but apparently it is always temporary and goes away with PT.
"The humerus is the best place for bone lengthening"
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2323419/We believe that this method is a suitable treatment of humeral shortening as the lengthening procedure is well tolerated, and the risk of complication is small.
With the adequate use of unilateral fixators, total humeral reconstruction can be achieved with a low risk of complication and without the loss of joint movement.
Humeral lengthening by distraction osteogenesis:
A safe procedure?
http://www.actaorthopaedica.be/acta/download/2013-6/06-Ruette%20et%20al.pdfDespite a lot of obstacles, humeral lengthening using
an Ilizarov frame provided a reliable method to treat
the functional or cosmetic problems of upper limb
shortening.
I would have to speak to some doctors and professionals, but if you asked me right now, I'd say it's pretty legit.