Replacing part or half of the hip joint is called a hemiarthroplasty. Most often, the round head of the femur (thighbone) is cut off. A metal implant is used to replace the missing parts. The hip socket or acetabulum is left in place. With a total hip replacement (THR), both parts of the hip are removed and replaced.
Hemiarthroplasties are used most often for hip fractures, early stages of osteonecrosis, and some cases of hip dysplasia. Hemiarthroplasty works well with femoral neck fractures because the hip socket is undamaged.
It has the advantage of preserving the patient's own acetabulum. This is important should the patient ever need a total hip replacement. Good bone stock is a key to success in future surgeries.
With either choice, (THR or hemiarthroplasty), there are risks for complications. The bone around the implant may fracture. The implant may loosen. Joint infection can occur.
But the most common problem is hip dislocation. The highest rates of dislocation seem to occur in patients treated by surgeons who don't do a lot of these operations. The best results occur in high-volume clinics or hospitals with high-volume surgeons.
Hip dislocation is also more common after surgery to convert a hemiarthroplasty to a total hip replacement. If there is a greater risk of hemiarthroplasty failure with revision surgery, then a total hip replacement now may keep that from happening. It may be helpful to have an honest conversation with the surgeon about the pros and cons of each procedure. This may help you and your wife make the best choice for her.