This one is really vague, I know. I'll try to describe it the best I can.
It was a show airing in the early 2000s. A (either Canadian/American/English) male teenager (16+, I believe) gets teleported to another world by a group of semi-deformed (their arms were quite... vainy I think) cultist-like people.
Somewhere along the way, he loses his left arm and it gets replaced by a robotic arm which has the ability to extend IIRC. The world he is on is kind of dark, desolate, 1986 Labyrinth-style planet. The story revolves around the teenager trying to make his way back to Earth.
One specific part of the show I remember is where he's on a train-like transport, on to top of it (typical cliche style) and he uses the robotic arm to go from carriage to carriage.
I think this was a show airing on either CITV or CBBC, though it could have even been channel 5. I remember it was accessible by early 2000's freeview.