The arthritis pain in your knee is worse, and the exercise that once helped you feel better has become unbearable. Your doctor suggests a total knee replacement (TKR).

When you research the procedure, you discover there are gender-specific knees, which are knee replacement models designed for women, and dozens of other options, too – different materials, sizes and models from a variety of manufacturers.

How do you choose? Generally, you don’t. Surgeons typically determine which implant they’ll use when they are in the operating room and actually looking at the structure and size of your bones.

Prior to surgery, however, you should have an informed conversation with the doctor about your options so you can ask good questions about why a particular model might be chosen, and determine if you’re comfortable with the doctor’s approach and experience – or whether you’d like a second opinion.

Here are some key details.

Gender specific knees. “Knee implants were originally based on an average of shapes and sizes of both men and women,” explains Matthew J. Kraay, MD, professor of orthopaedic surgery at Case Western Reserve University School of Medicine in Cleveland. “Researchers then looked at the anatomy of women’s knees [and found] the biggest difference is that a woman’s knee is narrower.”

Makers of artificial knees then developed implants with this in mind – but that doesn’t necessarily mean they’re better for most women. After all, manufacturers produced a variety of knee-replacement sizes before gender-specific knees (GSK) came into the picture about five years ago.

In fact, there is no scientific evidence that a gender-specific knee improves surgery outcome – though it still might be the best choice for you because of fit. “The GSK gives surgeons more choices for a patient with a narrow knee. It is similar to shoes coming in both B and D widths,” says Dr. Kraay.

New materials. Each replacement knee is made up of three major parts. Typically, the femoral component is implanted in the large bone above the knee and is usually made of a highly polished, strong metal such as stainless steel, titanium or chrome and cobalt alloys.

The tibial component is placed in the bone below the knee and is made of a durable plastic held in a metal tray. The patellar component, also plastic, is attached to the underside of the kneecap.

Within the past decade, the Oxinium knee replacement entered the marketplace.

It uses a kind of metal alloy that transforms to have a ceramic outer surface as oxygen from the body penetrates it. This makes the surface particularly smooth and hard, theoretically reducing joint friction and extending the life of the replacement.

“This is an advance in metallurgy, but we don’t yet know if it will actually translate into any clinical benefit,” says Thomas Ambrose, MD, associate professor of orthopaedic surgery at the Indiana University School of Medicine in Indianapolis.

Most companies making TKR systems have been working on making both the metal smoother and the plastic stronger, and stronger plastic may have an advantage. “When plastic wears, it generates microscopically small particles,” Dr. Ambrose says. “The body sees these as foreign, mounting an inflammatory response to remove the particles.”

Surgeon skills and experience. Don’t focus so much on the implant that you overlook other critical factors.

“The most important thing is not the implant but who is going to put it in,” says Dr. Kraay. “One of the best predictors of success in TKR is the experience of the surgeon, with the number of procedures done in the hospital you select following right behind.”

Dr. Ambrose agrees, noting that research has shown better patient outcomes if the surgeon does at least 50 knee replacement surgeries a year.

“Most TKR surgeries done even 15 years ago are still working today,” he says. “This is long before advances in metallurgy, plastic sciences or even the current understanding of the importance of proper installation. We have gained a lot of knowledge over the years that will probably translate into an even bigger longevity benefit than the bells and whistles.”