Joint replacement the second time around

Newswise — Americans are getting more new hip and knee implants than ever before—nearly a half-million a year. This boom in joint replacement has made the procedure somewhat routine and widely available.

But when it comes time to have that initial implant replaced, due to wear or failure, the procedure is anything but routine, according to an article in the March issue of Cleveland Clinic Arthritis Advisor.

“Revision surgery is a far longer and more complex procedure than initial surgery,” says Kenneth Marks, M.D., an orthopaedic surgeon at Cleveland Clinic. “It requires more time and expertise to remove the old implant and do a customized repair and realignment of the existing bone to ensure that the new implant will be held firmly in place.”

Growing demand

Though the challenge of revision surgery is higher, the demand is climbing. More and more patients who got their first new hip or knee at age 55 or 60 are outliving the useful life of their implants.

Advanced age is becoming less of an impediment. Even among people 80 and older, the benefits of joint revision surgery—pain elimination, increased mobility, greater range of motion—can outweigh the risks, as long as you’re healthy enough to undergo such surgery in the first place.

Why revision?

Though implants may need to be replaced for a variety of reasons, the most common one is loosening. Loosening starts with the tiny particles that eventually wear off the plastic liner or insert within the hip or knee.

As some of these particles slowly find their way to where implant meets bone, they get absorbed by cells (macrophages) capable of triggering bone reabsorption (osteolysis). Over time, this dissolving away of bone leads to implant loosening and pain.

Implant designers have slowed the creation of such particles by using harder, cross-linked plastics, and have nearly eliminated them altogether with newer ceramic-on-ceramic and metal-on-metal designs. The result has been increased implant longevity, meaning implants can now be done earlier to meet the longer lifespan of people who get them.

Other less-common reasons revision surgery may be needed include inadequate bone ingrowth, infection, dislocation, and fracture. When hip implants are inserted without cement, they depend on the growth of bone into the porous surface of the implant over time to ensure stability. Should this process not be fully achieved due to poor bone metabolism, the implant can more easily loosen later.

Infections can also be a cause of hip or knee implant removal, either early on, due to bacteria getting into the incision site, or years later, should blood-borne germs reach the implant and prove resistant to antibiotic therapy. Falls leading to fracture, or dislocation can also necessitate removal and replacement of the implant.

Follow the pain

Increasing pain near the implant, or greater difficulty in placing weight on it are early indications that revision surgery may be needed.

“The location of your pain tells us which part of your implant may be loose,” says Dr. Marks. “If it’s more of a groin pain, then the acetabular side is likely the problem. If it’s more of a thigh pain, then the loosening is typically on the femoral side.”

With knee implants, pain just below the knee suggests that the metal implant in the tibia may be loose, but pain that is felt throughout the knee may indicate infection.

Scans show the way

Whatever clues your pain provides need to be confirmed with an X-ray scan. “We can see if there is poor ingrowth on a hip implant, or if the plastic insert in your knee is worn,” says Dr. Marks.

If an X-ray suggests serious bone erosion, such that what remains may not be enough to provide sufficient contact between the bone and new implant, a computed tomography (CT) scan will be done to get a more precise view of the erosion. This will help the surgeon determine what needs to be done to repair the damage before proper alignment of a new implant is possible.

Out with the implant

A variety of factors make hip or knee revision surgery a much more lengthy, complex procedure than the initial surgery. “It’s not unusual for these surgeries to last five to eight hours or more,” says Dr. Marks.

Removing the old implant is a problem not faced the first time around. Not only must the previous device be taken out, but any cement that remains inside the bones must be cleaned out, as well. In hip revisions, the upper shaft of the femur that surrounds the old implant will often be cut away in two or three long sections (osteotomy) to enable implant removal and cleaning of the femoral canal. These pieces later will be reassembled and wired together around the stem of the new implant.

In with bone grafts

The most customized part of a hip or knee revision is the strategy used for restoring the damaged joint surfaces. “There is no one typical way to do this,” says Dr. Marks. “It varies with the degree and location of erosion, and the surgeon’s experience.”

At a minimum, there needs to be at least 50 percent surface contact between bone and the implant for a lasting, secure grip to be possible. Any less and the pits, holes, and other cavities need to be repaired using bone grafts, usually a thick paste of bone chips (morselized bone) made by grinding up cadaver bones.

In a hip revision, bone paste may be used to strengthen the pelvic socket or repair erosion along the inner canal of the femoral shaft. And if the erosion is severe, the socket may need to be rebuilt and reinforced using wire mesh or a titanium ring, in order to regain more normal biomechanics.

In a knee revision, if the end of the femur is weak, even after trimming away damaged bone, the central canal will need to be partially filled with morselized bone. In some cases, metal wedges may be required to better secure the attachment of the new femoral component.

Risks reduced

The many factors that complicate revision surgery—less healthy bone, an older patient, greater infection risk, and a customized array of bone, implant, grafts, and support structures—mean that it’s easier for at least one of these things to go wrong over time.

“Hip and knee revisions typically last about eight to 10 years, compared to the 20 or more years you can expect with a first-time implant,” says Dr. Marks.

Though still a serious operation, joint revision is not as fraught with risk as it used to be. “We used to discourage revisions due to obesity, advanced age, and other complications,” says Dr. Marks. “But as we’ve gained experience in limiting the risks, we’ve become more permissive. As long as you’re healthy enough to undergo major surgery, you’re healthy enough to have a revision.”

WHAT YOU CAN DO

Don’t overdo it. Excessive and repetitive overloading of your hip or knee implant can lead to premature loosening.

Let the pain guide you. Increasing pain in the area of your implant is the first indication you may need revision surgery.

Seek a specialist. The complications of revision surgery mean that it’s best to seek out a surgeon who does a large number of revisions.

Don’t give up on rehab. Though rehab is similar the second time around, it takes longer to regain muscle strength and range of motion due to additional scarring.