December 18, 2017

The Evolving Use and Benefits of Cementless Total Knee Replacements

By Jon H. Swenson, M.D., F.A.A.O.S., Hampton Roads Orthopaedics & Sports Medicine

 

Cementless total knee replacements have gained popularity in the past five years, thanks to improved technology that allows for even more precise fit and enduring adhesion.

Using advanced 3D printing systems and lasers, we are able to shape titanium powder into rough, porous metal surfaces. The metal surface has a rough texture which helps it to “stick” to the bone when impacted. A patient’s natural bone then can grow into those microscopic, sponge-like holes on the prosthetic’s coating over time, creating a strong, long-term bond.

As is the case with cemented joints, surgeons also carefully shape natural bone so the prosthetic fits snugly. In addition, four pegs and a central stem anchor the implant in place during bone growth into its complexly patterned surface, which generally occurs over about six weeks.

The basic difference is this: cemented bonds, which affix with a fast-drying acrylic polymer, are strongest immediately after surgery, but they often break down and weaken after a decade or two. Non-cemented joints – also referred to as press-fit implants – are designed to gain strength over time and ultimately form a more permanent bond.

While data is still emerging, research to date has shown success rates at least equal to – and possibly greater than – cemented prostheses. A 2012 study, for example, found 96 percent survivorship after 18 years, longer than the 10- to 15-year rate generally quoted to our knee replacement patients. That can be particularly beneficial for younger or more active patients.

Cementless prostheses often reduce time in the operating room by 15 or 20 minutes, as surgeons don’t need to wait for bone cement to set. That can potentially trim costs and reduce uncommon complications such as blood loss and infection.

The non-cemented approach also tends to involve less bone loss should a patient ever require revision surgery, as any cement debris in surrounding tissues must be removed to prevent irritation and inflammation.

All that said, cemented joint replacements have been used successfully for many years, and they do remain the best choice for about 10 percent of my patients. Most of those have bones weakened by osteopenia, osteoporosis, vitamin D deficiency, rheumatoid arthritis or some other form of connective tissue disease.

In these cases, which frequently involve more elderly patients, natural bone likely would not effectively affix to, or grow into, the artificial joint. Bone cement, on the other hand, can immediately anchor deficient bones to the prosthesis.

In my experience, post-operative pain levels and recovery time are similar for patients who receive both types of replacement joints. Surgeons also are developing hybrid solutions that use both cementless and cemented components in different parts of the knee joint.

I expect the use of cementless knee replacements to continue to expand as improved fixation methods. The same is true of hip, shoulder and possibly other types of total joint surgeries.  Over time, we also will gain better insights into long-term results, along with more specific indications and contraindications, for these promising technologies.

Dr. Swenson has practiced orthopaedic surgery on the Peninsula since 1991. He completed orthopaedic surgery training at the world-renowned Campbell Clinic in Memphis, Tenn., and specializes in sports medicine and minimally invasive joint replacement of the knee, hip and shoulder. www.hrosm.com.