Not to muddy the waters with crap gleaned off of the internet.
January 9, 00:13:05Z AA 54 is cleared for takeoff
00:14:48Z Hey Tower American uh 54 we need to uh abort the takeoff, turn off and head back to the gate.
No, I guess somebody has a cut in the back. So we need maybe some medical assistance at the gate.
...
American 54, do you need us to call the paramedics for you?
Uh negative, American 54
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Contacting ground, they request paramedics. The details that followed were "We have a flight attendant who has um had a previous injury and uh she managed to break open the injury it was bleeding of enough significance that she felt like we needed to uh go back to the gate and uh have it taken care of. We're not sure if she's just gonna to get off the airplane or if uh she's gonna um have the paramedics treat her and then we * on with her. We're still -- that remains to be seen, but that's basically what happened."