B12 Injections for Injuries?

My girlfriend has been prescribed Vitamin B12 injections for a chronic non-specific and as yet un-diagnosed back condition (Sacroilliac actually). The Docs idea is B12 helps in protein synthesis and nerve regeneration and therefore promote recovery.

Has anybody ever heard of anything like this - or is the Doc just trying to make a buck or two?!

Thanks for any input you may have.