There are a lot of airlines I can't possibly see this happening on. One of those airlines is United, but in odd-numbered rows.

I once had a piece of a seat (on another airline) puncture my hand (it was a bit more complicated than this, but imagine a thin two-inch nail sticking out of the tray table folding mechanism). The crew helped me bandage it up, and was very apologetic. The airline took the seat out of service for the next flight, until it could be returned to a hub to be fixed.

I had to go to urgent care the next morning (missing work), get an x-ray, a TDAP shot, some antibiotic cream, etc. So it was not just "a scratch".

Overall, I was pretty happy with the airline's response, so I don't even think I wrote in a complaint. Stuff happens. If you react well, and it's minor, I'm likely to let it go.

But if their initial response had been "no this didn't happen" or "we're not going to help you", maybe I would have gone to a personal injury lawyer.

I'm not a doctor (or lawyer for that matter), but I have no idea how different people would react to a gash in their leg caused by blunt trauma, in a low pressure environment. Maybe it would swell up. Maybe not. But if it's causing you pain or hassle (like needing a cane for a week or two), and United is being dismissive, then I support the decision to consult with a lawyer.

For every story that gets posted to FT, I suspect there are hundreds of identical stories that don't get posted. If the seat design or crew behavior is causing physical harm, hopefully escalating this could effect change so that it happens to fewer people in the future.