I'm in physical therapy after surgery monteggia fracture, but still can't twist my armfor pronation/supination. possibly my tendon/ligament torn?

Follow-up required: There are multiple reasons why you lack pronation/supination after a monteggia injury. Among these are- incomplete reduction of the radial head dislocation, synostosis (abnormal bony union) between the radius and ulna, injury to the posterior interosseus nerve or other nerve. A concomitant tendon injury is less likely. You need to follow-up with your surgeon to assess the possible causes.