Hey man,
You can in theory put a joystick into a keyboard, I have seen stuff done with the IBM nub thing they work pretty fine, and you can put a joystick in an
Arduino Micro But I don't know how you would also hook up a pcb or handier a keyboard with it, but I have seen it done check around geek hack theirs
some stuff with a ATREUS62 and an ibm nub thing,
Might I recommend if you are having pains in your arm getting a set up with any of the following,
A vertical mouse like a Anker really nice been using them for gaming and work, works really well, and also cheap about $12 or so
https://www.amazon.co.uk/Wireless-Vertical-Ergonomic-Optical-1600DPI/dp/B00BIFNTMC/ref=sr_1_1?ie=UTF8&qid=1523009767&sr=8-1&keywords=anker+mouseIf you don't mind small form factor keyboards I would recommend getting an Viterbi Keyboard - 5x7 70% Split Ortholinear, it split so you can angle it
how ever you want, and put the wasd cluster and the anger mouse next to each other making it put far less strain on your arms,
https://keeb.io/collections/frontpage/products/viterbi-keyboard-pcbs-5x7-70-split-ortholinear?variant=1302704554014or maybe if you want low profile switches or something go to novel keys, they got a new split keyboard with is looking pretty nice and is relatively cheap
about 80-100$ including all components such as, keycaps, switches, and the kit which has the electronic components,
So yeah hope that helps