Any prosthetic related equipment packed in your luggage is considered a medical device, and you will not have to pay a baggage check fee at the airport. Just let the agent know you have prosthetic equipment in your luggage when checking in.
Also, if your are packing any equipment in your carry-on luggage, it’s wise to put it in a separate bag labeled “prosthetic supplies” and take it out before running it through the x-ray machine. That way, if the TSA personnel determine any of the equipment looks “suspicious” and requires further investigation, they won’t need to search your entire carry-on bag.
Happy travels! 😉