Not sure what Corynebacterium group G is, although I'm not really up on my baterial taxonomy. But in regards to Corynebacterium prosthetic joint infections - well........
effortless - diptheria is indeed caused by Corynebacterium diphtheriae, but this is not the bacterium which causes joint infections.
There is another strain (or species - remember, I'm no taxonomist!!!) called Corynebacterium jeikeium (C. jeikeium). This is often found on the skin of patients in hospital, although normally causes no problems. There was an article published in the Scandinavian Journal of Infectious Diseases in 2005 about C. jeikeium joint infections. They did a literature review and found only two reported cases of prosthetic hip joint infection in the literature. In both cases, the patients required removal of the prosthesis, treatment with intravenous vancomycin for 6 weeks (a really strong antibiotic), and in both patients it took a year to recover.
In this article, they report a case where they just replaced the cup (the pevic side or acetabular component) but left the stem (the femur side) in place. The patient needed life long treatment with oral antibiotics, but they report that the infection has not returned.
So, where does that leave us?
1. These infections are extremely rare
2. They are extremely difficult to treat
3. The only way to guarantee complete eradication of infection is to remove the components and administer antibiotics, and this might take up to a year
4. If the hip is to be retained, life long oral antibiotics will be required.
My suggestion - see an orthopaedic surgeon with experience in hip revision surgery and/or especially infected joint revision surgery. A consult from an infectious diseases specialist should also be sought. However, I suspect that you have probably done this.
I hope your wife is recovering. Keep me posted