Zimmer, Inc. designed the NexGen MIS Tibial Component to better meet the demands and challenges of a minimally invasive approach to total knee replacement surgery.
The device is not an entire knee prosthesis, but one of more than 40 components surgeons can use with Zimmer’s flagship NexGen line of knee products.
Every artificial knee implant used in total knee replacement surgery is comprised of four primary parts:
- A tibial component that attaches to the tibia (shinbone)
- A femoral component that attaches to the femur (thigh bone)
- A weight-bearing plastic insert called an articulating surface that fits between the tibial and femoral components
- An artificial patella (kneecap)
The full name of the MIS Tibial Component is Zimmer NexGen Complete Knee Solutions Minimally Invasive Solution Total Knee Procedure Stemmed Tibial Component Fixed Bearing Preacoat. The device is compatible with several Zimmer knee replacement systems, including the NexGen CR/CR-Flex knee and the NexGen LPS/LPS-Flex knee.
The popularity of minimally invasive knee replacement surgery has grown significantly in recent years, with numerous clinical studies demonstrating faster short-term recovery, shorter hospital stays and less postoperative pain for patients whose surgeons used the technique.
Zimmer modified the design of its standard tibial components to address challenges created by the smaller incisions used in minimally invasive knee surgery, including limited visibility for surgeons and less clearance room for certain components.
The NexGen MIS Tibial Component boasts several design features that help surgeons bypass these problems while reducing the risk of damage to the tibia and kneecap. The device has a low-profile keel, which is the portion of the component surgeons insert into the top of the tibia before cementing it in place. With a keel length less than 20 mm, surgeons can easily insert the tibial component through a small opening while sparing damage to soft tissue, tendons and muscle.
The MIS Tibial Component’s keel also features broad proximal fins that lock into the densest part of the tibia to improve the stability of the joint. The fins work in conjunction with a drop-down stem extension, which surgeons insert into the top of the tibial component and slide down the center of the tibia to further strengthen the joint. Surgeons can choose between a 45 mm or 75 mm stem extension, allowing them to personalize the artificial knee according to specific patient needs.
Complications with the Zimmer NexGen MIS Tibial Component
As with any artificial knee replacement system, patients implanted with the NexGen MIS Tibial Component face the risk of certain complications that cause the joint to fail prematurely. One of the most common causes of early failure in total knee replacements is called aseptic loosening.
This problem occurs when normal wear on the joint releases microscopic debris that triggers a response from the body’s immune system. As immune cells attempt to clear away the debris, they also weaken the bond between the knee implant and the patient’s bones. The loosening that results is often painful and requires a second procedure, called a revision surgery, to replace the failed knee.
Despite the common problem of loosening among many brands of knee implants, several studies have described significantly higher and earlier rates of aseptic loosening with the NexGen MIS Tibial Component. One case series followed the postoperative results of 460 patients fitted with 529 MIS Tibial Components. Eight of these patients experienced early loosening of the tibial component that required a revision surgery. The average time to revision for these patients was 17 months.
In a separate follow-up study involving 403 MIS Tibial Components, 21 devices showed signs of aseptic loosening after less than four years of implantation. Another study showed an even higher rate of loosening with 130 MIS Tibial Components and a similarly designed tibial component manufactured by Smith & Nephew. Nine of these devices experienced loosening after little more than one year.
In the clinical studies described above, researchers could not determine the cause of the tibial component failures with complete certainty. However, they offered several possible explanations. One possibility is that the loosening is related to minimally invasive surgical techniques.
Because surgeons implant the MIS Tibial Component through a small incision while the knee is extended, they have much less visibility than surgeons using more standard approaches. With poor visibility, surgeons may fail to properly cement the component to bone or implant the knee misaligned, which could contribute to loosening.
Researchers also speculated that defects in the MIS Tibial Component’s design might contribute to its early failure. Although the U.S. Food and Drug Administration (FDA) approved the component after Zimmer proved it was substantially similar to its traditional tibial plate designs, subtle differences in the MIS Tibial Component’s geometry may contribute to a loss in bone density that increases susceptibility to loosening. Larger, long-term follow-up studies are now underway that will hopefully shed more light on the true incidence of the MIS Tibial Component’s early failure, as well as the underlying cause.
FDA Recall and Manufacturer Action
In April 2010, Zimmer sent an Urgent Device Correction letter to surgeons after clinical data revealed an increased potential for early loosening with the MIS Tibial Component. The manufacturer stated that surgeon feedback and data review indicated that loosening may occur if the component is not fully cemented or if a drop-down stem extension is not used. Zimmer added a warning to the component’s label that explained these problems. The company also sent surgeons updated materials regarding proper surgical technique for the device.
Within the next six months, the FDA received 114 complaints of early loosening of the MIS Tibial Component that required revision surgery. This prompted the agency to issue an official Class 2 Recall of the device. Another important reason behind the recall was that Zimmer provided improper instructions and warnings to surgeons stating that the drop-down stem extensions were not required. The recall affected 68,383 products worldwide.
Lawsuits Related to the NexGen MIS Tibial Component
Starting in 2010, patients began filing legal claims against Zimmer over complications they had with numerous NexGen-branded knee components. Plaintiffs allege that design defects in Zimmer’s products caused loosening that contributed to premature device failure.
Litigation over this matter includes the NexGen MIS Tibial Component and the following NexGen products:
- NexGen CR-Flex Porous Femoral Component
- NexGen CR-Flex Precoat Femoral Component
- NexGen Gender Solutions CR-Flex Precoat Femoral Component
- NexGen LPS Flex Precoat Femoral Component
- NexGen LPS-Flex Option Femoral Component
- NexGen Gender Solutions LPS-Flex Femoral Component
As the number of lawsuits over NexGen products continued to grow in courts across the United States, the U.S. Judicial Panel on Multidistrict Litigation transferred many cases to an Illinois U.S. District Court for more efficient handling. This created multidistrict litigation (MDL) 2272: Zimmer NexGen Knee Implants Products Liability Litigation. The MDL, under the oversight of Judge Rebecca R. Pallmeyer, includes more than 1,000 lawsuits as of September 2013. Legal experts predict a significant number of additional claims will be filed in the near future.