If you or a loved one have undergone knee replacement surgery, you are probably aware that problems can arise down the road, including the possibility of aseptic loosening of implants.

Aseptic loosening of a knee implant system means the implant has become loose, but not because of infection in the joint. The loosening is caused by other means.

How Will I Feel if My Knee Implant is Loose?

Signs of loosening from all causes can include a sudden onset of chronic pain, instability, inflammation or a decreased range of motion, all of which could cause knee problems. 

Why Would My Implant Come Loose?

Over time, the implant components may become loose from the bone, causing the knee to hurt. High-impact sports, obesity, and wear of the components can all contribute to such aseptic loosening of the implant.

In some cases, weak bones can fracture after the knee implant has been secured. In other instances, the soft tissue and muscles surrounding the knee become so weak, the knee might feel as if it is buckling when the patient attempts to stand or walk. Such instability could be indicative of misaligned knee implant components.

Do Materials Used During My Surgery Make a Difference?

The type of bone cement used in securing the implant can make a difference in how well the materials stay tightened to the bone.

When bone cement fails to hold, the patient can experience persistent pain and decreased range of motion because the tibial plate no longer adheres correctly.

Surgeons can choose from three different viscosities of bone cement: low, medium and high. A few years ago, surgeons showed a preference for high-viscosity cement because the consistency makes it easier to control.

Unfortunately, high-viscosity cement products have been linked to an increased risk of failure of components to bond well. High viscosity cements reach a doughy consistency relatively quickly after mixing, which limits the time the surgeon can work with it. However, if the cement is used prior to reaching the doughy consistency, the product may not adhere as well.

In some patients, the body attacks the bone cement and the implant components because the body sees them as foreign invaders. When the body begins to attempt to digest its own bone, the process is called osteolysis, which can weaken the targeted bone and cause it to fracture.

How Can Aseptic Loosening of Implants Be Determined?

An x-ray may show signs of aseptic loosening, such as:

• A widened space between the bone cement and implant component.
• Fragmenting or fracturing of the cement.
• Migration of the implant’s components that should be fixed in place.
• If coated with a porous material, the material might begin bead shedding.

Any space between the bone cement and the implant component that is more than 2 millimeters wide could indicate a loosening of the tibial component.

Are Certain Brands of High Viscosity Bone Cement Under Investigation?

Some of the bone cement products that have been affiliated with aseptic loosening of implants include:

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

Any knee implant system that has failed and required a revision knee replacement surgery three or fewer years after the initial surgery and bone cement was used could be considered a suspicious failure and should be investigated.