Lucas should have given Obi-wan a robot leg in the ANH Special Edition in 1997 so that people would have speculated endlessly over the next 8 years about when during the prequels he lost it, then never have him sustain this injury, making it clear that it just happened sometime later and had no bearing on the plot.
Ben Kenobi did have a robotic right hand in the 1975 third draft, so this is more plausible than it sounds on the face of it.