I had a thought this morning that a Segway might be better than a wheel chair as the standing would help to prevent contractures. The Segway handles the balance so the rider's muscles focus on standing.
Looks like this is already happening in New Zealand.
https://segwaynz.wordpress.com/2014/04/20/dylan-uses-segway-pt-to-overcome-muscular-dystrophy-mobility-impairment/