Your surgeon may discuss some of these additional options with you.
Fixed-bearing versus rotating knee platform. In a fixed-bearing knee prosthesis — the most common type — the tibial component of the prosthesis is topped with a flat metal piece that securely holds a polyethylene insert. When the knee is in motion, the femoral component glides across the polyethylene. In a rotating platform knee prosthesis, the polyethylene insert can rotate slightly, theoretically lessening stress and wear on the implant and improving movement.
Studies comparing the two types of knee replacements have offered mixed results, but over all, rotating knee prostheses appear to be associated with a greater risk of complications. Rotating platform knee replacements are often used for revision of a previous total knee replacement in patients with substantial bone loss.
Gender-specific knees. Knee implants used to come in a limited variety of shapes and sizes. Now there are implants that are specifically designed for a woman's anatomy, known as gender-specific knees. However, in a study that followed 85 women with knee replacements for two years after surgery, the gender-specific knees scored about the same as standard knee replacements in terms of range of knee motion and patient satisfaction.
Partial knee replacement ("mini-knee"). If your knee damage is limited to one of the bumps (condyles) on the end of your femur, you may benefit from a partial (unicompartmental) replacement that leaves the rest of the joint intact. This technology has been around for decades, but became more popular once surgeons were able to install the partial implant through a small incision (about three inches rather than eight) with minimal impact on muscles and ligaments — a surgery nicknamed the "mini-knee."
The potential advantages are clear: less blood loss, shorter hospitalization, and quicker recovery. However, a unicompartmental replacement lasts only about 10 years, compared with 15 to 20 years for a total knee replacement. They aren't well suited for people who are very bowlegged or knock-kneed. You may be offered this option only if damage is limited to one portion of the knee, if the damage results from a traumatic injury rather than arthritis, if your ligaments are intact, and if your knee still contains a fair amount of healthy cartilage. The ideal patient for this surgery remains an older, thinner person rather than a younger, more active one. It may be suggested to buy time before total knee replacement in someone young and active, however.
Minimally invasive knee surgery. Minimally invasive knee surgery accomplishes the same goal as traditional knee replacement, using the same types of artificial knee implants as those used in traditional procedures, but through much smaller incisions. Despite the name, it is still major surgery. The size of the incision depends on the person's size (bigger knees mean bigger incisions). On average, the incision for minimally invasive surgery is four to six inches, compared with an eight- or 10-inch incision with traditional knee replacement. Some minimally invasive techniques require small incisions to be made in the quadriceps muscle, while "quadriceps-sparing" techniques protect the quadriceps tendon and muscle. The results from several studies comparing minimally invasive surgery to traditional knee replacement have shown some benefits, including less blood loss, shorter hospital stay, and better range of motion. However, other studies show a higher complication rate with minimally invasive surgery, including less precise placement of knee implants.
Patellar resurfacing. In some knee replacements, the kneecap is unaltered, and the artificial implant is shaped to glide easily beneath it. But in another approach, called patellar resurfacing, the surgeon attaches a separate piece to the back of the kneecap to fit smoothly with the implant, resurfacing the patella. Studies of patellar resurfacing have offered varying results: some find it reduces long-term pain, and others find it leads to more complications and a higher failure rate. A meta-analysis of 1,223 knee replacements suggested that patellar resurfacing may modestly reduce the risk of revision surgery and pain at the front of the knee. Some surgeons resurface the patella in most knee replacements; others try to avoid this step unless special circumstances warrant it. Patellar resurfacing may be a better option for younger patients, in whom the results tend to be more predictable.
Loosening, bone loss, being very active or overweight, and the wearing away of the artificial joint that typically occurs after 15 to 20 years can all necessitate revision surgery. Knee and hip replacements typically last longer in older people, who tend to be less active than their younger counterparts, who put more wear and tear on a replacement joint. For knee or hip replacement surgery, there is a 1% failure rate per year (that means that revision surgery is needed within one year).
If your implant fails, surgery to replace it takes longer and may be more complicated than your original operation. There is also more risk involved. The in-hospital death rate for revision hip replacements is more than double that of first-time total hip replacements. Patients who have less pain and fewer additional medical conditions before revision surgery are more likely to experience better pain relief as a result of the surgery.
Look for a surgeon with experience doing both implants and revisions. Before you have revision surgery, your doctor will perform a thorough physical exam. If you're much older than the first time around, you may need to take more precautions such as banking extra blood for the lengthy procedure.
During surgery, the surgeon removes the old implant and damaged bone or joint tissue surrounding it. Depending on the amount and condition of the remaining bone tissue, you may need bone repairs or a bone graft to create a stable site for the new implant. Rehabilitation is similar to the initial replacement but takes longer after revision, and the outcome is often inferior. For example, your range of motion in the joint may be more restricted or your leg alignment less even, and even after healing you may need to use a cane to keep full weight off the joint.
Hopefully, with improved implant designs and newer materials such as cross-linked polyethylene, total joint replacements will last longer, making revision surgery less likely in the future.
More Mobility = Weight Gain?
Many overweight people who have painful knees or hips anticipate that having a joint replacement will ultimately help them shed weight by helping them be more active.
While this expectation seems plausible, in many cases patients actually put on more weight after having surgery. A 2005 study in Orthopedics documented this phenomenon — at least one year following hip or knee replacement surgery, patients gained an average of three pounds, with younger patients adding the most weight.
Researchers aren't sure why this occurs. One theory is that increased mobility after surgery leads people to make more frequent trips to the refrigerator and go out to eat more often. Whatever the reason, don't assume that joint replacement surgery will automatically help you slim down. To lose weight, you'll need to adhere to a regular exercise program and reduce your total caloric intake.