Zimmer Knee Replacements

Zimmer manufactures thousands of orthopaedic products, including its best-selling NexGen Knee implants. While popular, these implants are also known to fail prematurely, causing injury.

Popular Knee Implants Involved in Lawsuits

The Zimmer Manufacturing Company was founded in 1927 by Justin O. Zimmer in Warsaw, Indiana. What began as a small firm selling a novel line of aluminum splints became an expansive, state-of-the-art artificial joint manufacturing and marketing firm by the 1980s.

The company has a catalog of thousands of products, including orthopaedic implant and instrumentation systems, reconstructive spinal and trauma devices, dental implants, and many other surgical products. Zimmer operates in more than 25 countries and sells products in more than 100 countries. Its 2011, global net sales were approximately $4.45 billion, and $2.44 billion is attributed to sales in the Americas. Zimmer's knee implants make up the bulk of its worldwide sales, at $1.82 billion. Zimmer is the largest manufacturer of knee implants in the world, with a 26 percent market share. Zimmer's estimated global market size for knee implants alone is $7.2 billion.

Zimmer entered the knee replacement market in 1968 when it developed its first non-hinged total knee unit, and it sold its first metal-plastic total knee prosthesis in 1973. In 1995, Zimmer introduced the Next Generation (NexGen) Complete Knee Solution System. Since its release, more than 3 million NexGen knee replacements have been performed. To improve upon its popular NexGen design and garner a larger market share, Zimmer released the NexGen Lateral Posterior Stabilizing (LPS) Flex-Fixed Bearing Knee in 2001. This was the first of its High Flex devices intended to provide a greater range of motion than other devices on the market.

The company claimed its NexGen Flex knee implants were designed to emulate the natural function of the knee and provide a greater range of motion. However, devices like the NexGen Lateral Posterior Stabilization (LPS)-Flex, NexGen Cruciate Retaining (CR)-Flex and NexGen Minimally Invasive Solutions (MIS) Tibial Component have been plagued by lawsuits filed by people who needed revision surgery because of complications like pain in the joint, loosening and premature failure of the device.

Zimmer Knee Replacement Products

Zimmer manufactures a wide array of knee replacement products. It offers cemented and non-cemented components, total knee replacement systems, unicompartmental implants, femoral implants, tibial implants and patellar implants. The company also manufactures gender-specific implants intended to give a better fit to female patients.

Knee Implants and Products

Femoral Implants

Innex Knee Femoral CR Cemented Natural Knee-II CR Femoral Cemented Spacer Kit
NexGen CR-Flex Femoral NexGen Gender CR-Flex
Innex Knee Femoral SC Cemented NK II Femoral CR-Flex Cemented
NK II Femoral CR-Flex Cemented NK II Gender Fem CR-Flex Cemented
Nex Gen CR Innex Knee Femoral CR Porous
Natural-Knee II Femoral CR-Flex Porous NK Flex Female Porous
NexGen LPS-Flex NexGen LPS
Natual Knee II Fem PS Cemented NexGen TiV LPS-Flex Femoral
NexGen LCCK NexGen CRA
Natural-Knee II Cemented Revision Femorals NexGen Rotating Hinge Knee
Most Hinged Knee Femorals Most Hinged Proximal Femorals
Most Hinged Distal Femorals Segmental System Femoral
Allegretto Knee Uni Femoral NexGen Patello Femorals

Tibial Implants

M/G Uni Tibial Plate Zimmer Uni Modular Tibial Fixed Plate
Natural-Knee II Uni Metal Tibial Plates M/G Unicompartmental All Poly Tibial
Zimmer Uni All-Poly Tibial Natural-Knee II Uni All Poly Tibials
NexGen CR NexGen LPS
I/B II PS Allegretto Tibial All Poly
Natural-Knee II All-Poly Tibials MG II
NexGen Fluted Option Stemmed NexGen Stemmed Mobile Option
NexGen Option Stemmed NexGen Precoat A/P Wedge Stemmed
NexGen Precoat Pegged NexGen Precoat Stemmed
NexGen MIS Tibial Plates Natural-Knee II Cemented Metal Tibials
NexGen Fluted 7 Degree Option Stem Tibial Plates Innex Mobile Tibial Plate
Innex Tibial Metal Cemented NexGen Porous Stem
NexGen Porous Pegged Continuum
NexGen MIS Porous Tibial Plates Natural-Knee Metal Porous Tibial Baseplates
Trabecular Metal CR Monoblock Tibial Trabecular Metal LPS-Flex Monoblock Tibial
Rotating Hinge Knee Tibial Plate Most Hinged Knee Tibial
GSB Hinged Tibial Plate

Patellar Implants

NexGen All Poly Patella NexGen Augmentation Patella
NexGen Porous Trabecular Metal Patella IB/II Patella
Natural-Knee II CRK All-Poly Patellar Components Natural-Knee II-Patella Metal Backed
GSB Patella Innex Patellas All Poly
Natural-Knee Patella Durasul Natural-Knee II Flex Patella Metal Backed
Natural-Knee II Flex Patella All Poly Natural-Knee II Flex Patella Durasul
Prolong NexGen Patella Natural-Knee II Durasul All-Poly Patella
After the NexGen LPS-Flex, Zimmer released additions to the NexGen Flex line, including:
Since 2003, roughly 150,000 NexGen Flex knees have been sold.
NexGen Complete Knee Solution Cruciate Retaining-Flex Femoral Components (CR-Flex)
NexGen Complete Knee Solution Gender Solutions Female LPS-Flex (GSF LPS-Flex)
NexGen Complete Knee Solution CR-Flex Gender Solutions Female CR-Flex (GSF-Flex)
NexGen Minimally Invasive Solutions (MIS) Total Knee Procedure Stemmed Tibial Components

NexGen LPS-Flex

The NexGen LPS-Flex was the first device in the NexGen Flex line of products. The company claims that the design of the LPS-Flex knee provides greater patellar clearance that reduces tension during deep flexion, and that special pegs on the femoral component provide enhanced stability.

This device is a posterior stabilized component. Zimmer's surgical technique for this implant involves removing the cruciate ligament — a large ligament at the back of the knee. The LPS-Flex is designed to support the knee even without this ligament. This model shares common components and elements of its design with the NexGen CR-Flex.

While Zimmer designed the NexGen LPS-Flex knee implant to provide exceptional range of motion, follow-up studies on patients fitted with the device have returned mixed results regarding their ability to achieve deep flexion. Numerous investigators have found that the LPS-Flex’s design offers relatively minor gains in range of motion. In addition, these features may weaken the stability of the implant and increase stresses on the device, which can result in loosening and other complications that cause premature failure.

In a study published in 2007, researchers evaluated the results of 47 NexGen LPS-Flex total knee replacement patients, including 25 who were fitted with double replacements and 22 who had one knee replaced. A single surgeon performed the knee replacements between March 2003 and September 2004.

After an average of 23 months, 15 knees required a revision surgery to correct pain, loosening and other complications. These devices showed loosening of the femoral component where surgeons cemented the device to bone. By an average of 32 months, researchers found that the device’s femoral component loosened in 27 patients.

NexGen CR-Flex

Zimmer released the NexGen CR-Flex in 2003. This is a cruciate ligament retaining device, which means that the surgeon preserves this ligament to provide more stability. According to Zimmer, this device is "intended for patients who have good bone stock and whose ligaments provide adequate joint stability."

While the CR-Flex is marketed to active individuals, Zimmer claims that these knee implants are designed even for people who might not have the need for higher flexion.

According to Zimmer marketing brochures, the company constructs CR-Flex components with advanced materials, such as Prolong Highly Crosslinked Polyethylene plastic. Zimmer states that this material offers improved resistance to wear, pitting, cracking and oxidative degradation. For certain patients, the company offers minus sizing for the CR-Flex knee’s femoral components — a favorable option that allows surgeons to correct common complications without the need for additional bone or ligament removal.

In March 2010, Dr. Richard Berger and Dr. Craig Della Valle, a colleague from the Rush University Medical Center, presented the results of “The High Failure Rate of a High-Flex Total Knee Arthroplasty Design,” a study they conducted on the NexGen CR-Flex Porous Femoral Component. Berger and Della Valle described their findings at a national conference for the American Academy of Orthopedic Surgeons.

Typically, manufacturers design knee implants to last an average of 12 to 15 years, without needing revision. The Rush University Medical Center doctors concluded that the CR-Flex porous femoral component, while still commercially available, ought to be withdrawn from the market and “should not be used by any patient” because it could require revision surgery long before its expected lifespan. Despite these findings, the NexGen CR-Flex Knee was never recalled.

NexGen MIS Tibial Component

The NexGen MIS Tibial component is designed for use with the LPS-Flex and CR-Flex in minimally invasive knee replacement procedures. The implant's size allows surgeons to implant it through a smaller incision in the knee and minimize the cutting of soft tissue, muscle and ligaments. Ideally, minimally invasive procedures have shorter recovery times, less blood loss and greater range of motion because of muscle-sparing techniques.

The MIS Tibial component is assembled in the patient's knee, and doctors have a choice of stem length to anchor the device to the top of the tibia. Zimmer claims the design provides better load-bearing capabilities and stability.

Despite the common problem among many knee implants of device loosening, 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 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.

Problems with Zimmer Knee Replacements

Zimmer's original NexGen knee products, which are still popular, had an acceptable revision rate and were relatively reliable. The original design only offered 120 degrees of flexion, and Zimmer wanted to be the first company with a product to offer 155 degrees of flexion. However, when the company altered the original NexGen design and created the NexGen Flex, it was not required to test these knew devices before releasing them for consumer use. Without clinical trials, patients who received a NexGen Flex implant were given an untested and unproven device.

The FDA has received hundreds of reports of serious problems related to the NexGen Flex devices. These complications have forced a number of people to undergo complex revision surgery procedures to replace the implant.

Surgeons have found problems with Zimmer’s product and advised the company of the high number of revision surgeries. In March 2010, Dr. Richard Berger and Dr. Craig Della Valle from the Rush University Medical Center concluded in their study on the CR-Flex component that it should be withdrawn from the market and that it should “not be used by any patient” because of its high failure rate and poor design.

Some of the problems reported include:
Severe knee pain Swelling
Poor range of motion Loosening of knee component
Device failure

While the average lifespan of a knee implant is usually 15 to 20 years, a 2007 report in the Journal of Bone and Joint Surgery showed that 38 percent of LPS-Flex knees loosened after only just two years. In addition, 56 percent of patients in the study were forced to have revision surgery because of pain in the knee. Several studies, in fact, have questioned the efficacy of Zimmer's NexGen Flex implants. Researchers found that these devices are prone to early loosening and that there was no significant increase in range of motion among the CR-Flex, LPS-Flex and their non-flex counterparts. Also, 1 in 5 people implanted with Zimmer's NexGen Flex knees is extremely limited in high-flexion activities like squatting, kneeling and sitting on the heels — activities that Zimmer claimed would be possible with this implant.

In addition, the NexGen MIS Tibial Component is also prone to early failure. It was designed to be assembled in the patient's knee through a small incision of about 4 to 5 inches. Zimmer claimed this surgical procedure using the MIS Tibial Component would promote shorter hospital stays and quicker recovery times. Instead, the difficult procedure resulted in increased device failure, loosening and revision surgeries.

Zimmer Knee Recalls

Despite the complications arising from the NexGen LPS-Flex and CR-Flex, Zimmer has not issued recalls for these devices. In April 2010, Zimmer issued an "Urgent Field Safety Notice"/"Urgent Device Correction" letter in response to the high failure rate of the NexGen MIS Tibial Component. The letter urged physicians to discard all previous instructions regarding the implantation of the device and relabeled the product.

Sept. 13, 2010

The FDA classified this action on the part of Zimmer as a Class II Recall. At the time of the recall, more than 68,000 MIS Tibial Components had already been implanted.

Jan. 25, 2012

The FDA issued another Class II Recall for another one of Zimmer's knee implant components: the Natural-Knee II Durasul All-Poly Patella. The company recalled this product because it was subject to fracture. Nearly 110,000 of these components had been implanted at the time of the recall.

March 2015

The FDA issued a notice of Zimmer's voluntary Class II recall for its Persona Trabecular Metal Tibial Plate because of increased loosening and radiolucent lines. About 11, 658 units are involved in the recall which covers all sizes and lots of the product.

Zimmer NexGen Knee Lawsuits

In recent years, Zimmer has been confronted with hundreds of lawsuits over its NexGen Flex Knee products. These lawsuits have since been consolidated in the U.S. District Court of Northern Illinois.

Lawsuits claim that Zimmer's NexGen Flex Knee design is faulty because the devices have an unacceptable failure rate. According to the Master Long Form Complaint filed in MDL No. 2212, plaintiffs allege that the NexGen Flex knees also "fail to provide additional or meaningful flexion beyond 120 degrees." In addition to the lawsuits plaguing its NexGen Knee line of products, Zimmer was forced to pay $169.5 million to settle civil charges filed against the company by the Securities and Exchange Commission (SEC). The SEC said that Zimmer had essentially "bribed" doctors to use its products by offering them paid consulting agreements and other financial compensation.

The following Zimmer NexGen Flex Knee devices are included in the multidistrict litigation (MDL):
NexGen Complete Knee Solution Legacy Posterior Stabilized-Flex Femoral Components (LPS-Flex)
NexGen Complete Knee Solution Cruciate Retaining-Flex Femoral Components (CR-Flex)
NexGen Complete Knee Solution Gender Solutions Female LPS-Flex (GSF LPS-Flex)
NexGen Complete Knee Solution CR-Flex Gender Solutions Female CR-Flex (GSF-Flex)
All NexGen MIS Total Knee Procedure Stemmed Tibial Components

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