When a lady goes to the Mikva she has to ensure that there is no Chatziza. Is a prosthetic arm or leg a Chatziza? Is there a difference if the prosthetic is permanent or removable? (source)
The חכמת אדם in סימן קיט:יח says that fake teeth or fillings are חוצץ. R' Moshe Feinstien in אגרות משה יורה דעה א׳ צז:ו argues, and says that certainly permanent fillings are not חוצץ and suggests that even removable fillings aren'y חוצץ if they are in בית סתרים.
If so, we may extrapolate to other prosthetics. Certainly if they are permanent they should not be חוצץ. If they are removable, being that they are not in a בית סתרים, it would seem that they are חוצץ.