Well he tends to hunch his back up when he's *working*. He's also generally roundish and short of limb.
But mostly his back is quite hairy. I heard him tell a story the other night on radio, that he was filming a scene which required him to perform in a hot tub. When he got out of the hot tub naked and wet with his back hair sticking up, the director yelled "geez Ron you look like a hedgehog".