Zimmer NexGen LPS Flex Knee Implant

Section Guide

Zimmer Holdings, Inc., designed the NexGen LPS Flex Knee Implant to be used in total knee replacement surgeries. In those implants, the patient’s activities required a high degree of flexion or an ability to bend the knee deeply.

This product accommodated bending of up to 155 degrees, compared with other knee replacement implants that only accommodated 125 degrees. For the knee to bend, the upper part of the femur – the bone that extends from the pelvis to knee – roles and slides on top of the tibia – the bone that extends from the knee to the ankle. The kneecap then slides over the femur.

The femur replacement component on the LPS Flex Knee implant was designed to have a more extended roundness so that there would be better contact between the femur and the tibia during deep knee bending. It also provided greater clearance for the patellar tendon through the use of a deep cut-out so that the patella component could correctly cover the femur during deep knee bending.

Complications of the NexGen LPS Flex Knee Implant

While the NexGen LPS Flex Knee implant permitted a high degree of flexion, it came at the expense of early loosening of the femur replacement component. In a study published in 2007, researchers evaluated 47 patients who received NexGen LPs Flex total knee replacements – 25 people who had double replacements and 22 who had single replacements. The replacements were performed by the same surgery between March 2003 and September 2004. Researchers found:

Loosening of the femur replacement component in 27 of the participants at an average follow-up of 32 months.
Fifteen knees required revision surgery at an average of 23 months.
Additional flexion resulted from the femur component having loosened.

In the study, researchers wondered about the factors that caused the high rate of loosening of the femur replacement component. Study participants were permitted to take part in activities that required putting weight on the knee and using a high degree of flexion, such as squatting, but only as much as they could tolerate.

They found was that weight-bearing, high flexion activities contributed to the loosening of the device.

In another study published in 2010 that questioned whether high flexion movement contributed to loosening of the femur replacement component, researchers evaluated 218 NexGen LPS Flex knees implanted in 166 patients from October 2001 to February 2005.

They found:

30 knees had early loosening of the femur replacement component an average of 24 months after surgery.
Two knees that were unstable; two fractures developed around the implant; and one failure of the muscle group in the knee known as the extensor mechanism.
And seven knees required revision surgery an average of 49 months after surgery.

Researchers concluded all of these outcomes might be associated with maximum flexion activities, such as squatting and kneeling.

Recalls of NexGen LPS Flex Knee Implants

In December 2010, Zimmer issued a limited voluntary recall for specific lots of the NexGen Complete Knee Solution LPS Flex Gender Femoral Component designed for implantation in women who needed a total knee replacement. Some lots had a nonconforming cam radius – the internal post in the cushion of the tibia replacement component did fit properly into the bar in the femur replacement component known as the cam.

In September 2010, Zimmer sent out notices of “urgent device correction and removal” to distributors, salespersons, risk managers and surgeons. Sales staff and risk managers were instructed to return any of these items they might still have. For surgeons the notice was an FYI, but no action was required.

Lawsuits Related to NexGen LPS Flex Knee Implants

In August 2011, a Judicial Panel on Multidistrict Litigation transferred 18 lawsuits filed against Zimmer NexGen Knee Replacement products including the LPS components and the “Gender Solutions” brand of the LPS components to the U.S. District Court for the Northern District of Illinois for pretrial proceedings.

These were added to the 10 cases that were already pending in that court. Since that time, other cases have also been transferred.

None of these case have come to trial.

Sources:

Cho, S.D., et al. (2010). Three to Six-Year Follow-Up Results After High Flexion Total Knee Arthroplasty – Can We Allow Passive Deep Knee Bending? The Journal of Bone and Joint Surgery – British edition 92-B (SUPP I), 131
Class 2 Recall Zimmer NexGen LPS Flex Gender. (2010, December 2). Food and Drug Administration. Retrieved from http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfres/res.cfm?id=95540
Han, H.S., et al. (2007). High incidence of loosening of the femoral component in legacy posterior stabilised-flex total knee replacement. The Journal of Bone and Joint Surgery – British edition 89-B (11), 1457-1461 doi: 10.1302/0301-620X.89B11.19840
Kang, S., et al. (2010). Are High Flexion Activities After High-Flex Total Knee Replacement Safe? The Journal of Bone Joint Surgery- British edition, 92-B (SUPP II) 322
Legacy Knee LPS-Flex. (2001). Zimmer Holdings, Inc. Retrieved from http://www.zimmer.com/content/pdf/en-US/NexGen_LPS_Flex-Fixed_Brochure_(97-5964-101).pdf
Transfer Order. (2011, August 8). United States Judicial Panel on Multidistrict Litigation. Retrieved from http://garrettlawcenter.com/wp-content/uploads/2011/05/JMPL-nextgen.pdf