In Transformers Prime, Ratchet at one point says that Soundwave’s anatomy is drastically different from a “normal Cybertronian.” He is the only character we see who has these extendable cable things.
Furthermore, in Robots in Disguise, we finally get to see how incredibly long those things are. Seriously, they’re at least 200 feet long, and that’s just what we visibly see of them.
So, my theory is that Soundwave doesn’t have an internal “skeletal” structure like all other Cybertronians. Instead, his body’s just filled with these cables, all coiled up and twisted together to serve the same basic function as a skeleton.
I’m just saying...