I'm applying this year, so take what I say with a grain of salt (though this is not just my opinion, but more based on what attendings have told me).
You don't just want to re-write your CV in paragraph format; they have your CV and know how to read.
The 2 big areas to address are why you're interested in orthopaedics and why you would make a good resident. This is not applying to medical school where they wanna see your potential and idealistic belief that you'll change the world or something. This is much more of a job interview, and they want residents who will make their lives easier, not harder. Try to convey that.
It is probably a good idea to include some mention of where you see yourself in the future too (as ddmo said). Again, this is not medical school, so don't go crazy saying you're going to change the world. If you've done work in a developing country, then it probably is not bad to say you'd like to continue to do that. If you haven't though, it just comes across as a disingenuous, empty statement. Worse yet, they could ask about it at the interview, and you will look like an ass if they call you out for it (i.e. how do you know you wanna do it in the future if you have no experience doing it now?).
On the length, I was told to keep it to a 1 page word document. You'll find when you load it to ERAS you just copy and paste and it counts characters. They provide enough characters to have a personal statement that is longer than a page, but I would still stick to a page max. Quality over quantity. Remember, this is ortho, not internal medicine. They don't want you to just baffle them with bull**** and come up with as much crap as you can. At best a long personal statement is annoying; at worst the BSing takes away from strong points.
I don't know how much I agree with people who say the personal statement doesn't really matter either. For ortho, we all have good step 1 scores, a few research experiences (maybe a publication or two or more), strong letters, etc., so the personal statement gives you a chance to stand out a little bit (although you could argue most of us like ortho for the same reasons).