Bone cement failure in knee replacement systems is one of the reasons patients experience loosening knee implants.

Even though most knee replacement surgeries should not require revision surgeries for 15 to 20 years, some patients experience earlier failure due to loosening components.

Over years of wear, the surfaces of the joint materials can wear away, which cause the components to become loose because of bone loss. Sometimes, the surface areas of the metal or plastic components collect bacteria that becomes a full-blown infection in the knee.

Because elderly people are most apt to undergo knee implant surgery, they tend to have weaker bones from the start, which make their bones more susceptible to fractures that can disrupt the stability of the implant.

In other cases, the soft tissue and muscles that surround the knee become too weak to support the person and the knee might feel like it’s buckling when they try to stand or walk. This type of instability also might be the hallmark of a misaligned knee implant.

Determining Cement Failure in Knee Replacement Surgery

In cases where bone cement has failed to keep a good bond, such loosening is called aseptic tibial loosening. The term “aseptic” means that the loosening occurs without an infection being present.

In some instances of aseptic loosening, the body tries to attack the implant and the bone cement because the body interprets the foreign components as invading organisms. The immune system tries to digest the bond and can even begin to attack its own bone, causing weak bones that fracture more easily.

In other cases of aseptic loosening, bone cement failure in knee replacement components is to blame. Patients will have similar complaints of persistent pain and sometimes even a decreased range of motion, but the problems will stem from the lack of the tibial plate’s proper adherence.

Signs of loosening include chronic pain, instability, inflammation or a decreased range of motion. X-rays might show a widening of the interfaces between the bone cement and the prosthetic or even a break within the dried cement.

In the best case scenario, the x-ray will not show a gap of more than 2 millimeters wide. As long as the gap is that small and stays that small without widening over time, the implant’s adherence is considered normal.

When the gap becomes larger than 2 millimeters, the tibial component most likely has loosened, often due to bone cement failure.

Bone cement is available in three viscosities: low, medium and high. Surgeons started to prefer high-viscosity cement because the consistency mixes faster and is easier to control as the doctor sets the implant components in place. Some high-viscosity cement products are under investigation for bonding failure, including:

• Cobalt HV Bone Cement (Biomet/DJO Surgical)
• DePuy CMW 1 Bone Cement
• Simplex HV Bone Cement (Stryker/Howmedica)
• SmartSet HV Bone Cement (DePuy)

DePuy is a subsidiary of Johnson & Johnson and makes two of the types of cement on the list.

The National Center for Biotechnology Information looked at 13 cases of failed knee implants due to cement problems back in 2016. In each of those incidents, high viscosity cement was deemed at fault for failing to hold the bond of the implant component to the tibia. When the NCBI researchers looked at knee implant surgeries that used low or medium viscosity bone cement, the bonds stayed secure.

When an x-ray shows that prosthetic components have moved from their originally intended position, this movement is a sign of loosening.