Knee replacements are surgical substitutions of a knee joint, where the femur and tibia bone meet, with an artificial joint, or implant. Although the procedure might seem like a modern one, it actually dates back to the mid-1800s. Medical device companies refined all manner of artificial joints over the past three decades as doctors discovered more demand for them. An increased number of younger (and more active) potential recipients are wearing down or injuring their joints and asking for permanent or semi-permanent medical solutions.
Conditions that lead up to a knee replacement are varied. Some are hereditary – arthritis, osteoarthritis, rheumatoid arthritis and developmental abnormalities, for instance – while others are acute, such as avascular necrosis (bone death), obesity or emergency traumas. Repeat injuries can also account for the need for a replacement. Doctors recommend knee replacement surgery when patients endure constant pain or when daily life is affected by poor mobility.
In 2010, nearly 700,000 knee replacements were performed in the United States. Seven years earlier, the number of knee replacements totaled a little more than 450,000. The number is rising – and it’s expected to continue rising – in large part because a generation of baby boomers sits steadfastly at middle age: between 48 and 66 years old. This is the new prime age for knee replacement patients.
The American Academy of Orthopaedic Surgeons estimates that by 2030, the number of total knee replacement surgeries will increase to nearly 3.5 million a year. Expected rises in obesity rates in the United States and an increased need for revision surgery – a second or even third knee replacement surgery that aims to correct serious complications from the initial surgery – are among the reasons for the projected increase.
Although many device companies design and manufacture knee implants, which in turn can be made from a variety of metals, plastics and ceramics, artificial knee joints consist of three components: a femoral component (metal), tibial component (metal and plastic) and patellar component (plastic). Recipients can have a partial knee replacement or a total knee replacement. The difference depends on the recipient’s condition and pain level.
While knee implants give many recipients a second chance at walking and living a more normal life, complications do occur. Most problematic is a loosening of the implant, which can be caused by a defective implant or poor positioning at the time of surgery. Implant loosening is a primary cause for revision surgery. Recipients who need revision surgery within a few years after their original implant surgery may be able to pursue legal action against the implant manufacturer. Manufacturers that are facing knee replacement lawsuits include Zimmer Holdings, DePuy Orthopaedics, Stryker, Smith & Nephew and Biomet.
Knee Implant Devices and Components
The knee joint forms where the femur (thighbone) meets the tibia (shinbone) and fibula (runs alongside the tibia). The patella (kneecap), located on the front of the knee, moves up and down against the femur. These bones are connected by ligaments, muscles and cartilage that help form the joint hinge and give the joint its flexibility. Although there are four bones around the knee joint, only the femur, tibia and patella are affected by an implant.
Components of a Knee Implant
Femoral Component: This metal piece attaches to the end of the femur. It has a groove that allows the patellar component to slide up and down smoothly as the knee bends and straightens.
Tibial Component: This flat, two-piece metal and polyethylene (plastic) part is attached to the tibia. The metal part sits on top of the tibia and has a stem that is inserted into the tibia for stability. The plastic part, or tibial spacer, acts as a cushion between the metal tibial component and the metal femoral component.
Patellar Component: This plastic piece is dome-shaped to match the resurfaced shape of the patella. Because the patella rests against the femur, the alignment of the patellar component and femoral component is crucial for proper function. The patella is held in place by the quadriceps tendon and patellar tendon.
The three components of a knee implant are usually cemented in place, but some doctors use a cementless technique that helps the bone grow into the implant to help increase stability.
A cementless technique may be used on patients who are young, healthy and have strong bone structure around the knee. Because bone cement can break away and cause an implant to loosen, cementless knee replacements are less likely to loosen over time. Cemented knee replacements are considered better suited for older, less active patients.
Types of Knee Implants
There are multiple types of knee implants that doctors and patients can discuss before choosing the best option. The decision is based on a patient’s condition and activity level.
Types of Knee Implants
|Fixed bearing||Less mobile and not as strong as other implants. Best suited for patients who are not overweight and who do not have an active lifestyle.|
|Mobile bearing (rotating platform)||Allows the plastic cushion of the tibial component to rotate, giving patients greater flexibility on the medial (inner) and lateral (outer) sides of the knee. Works well for young and active patients.|
|Medial pivot (mobile bearing)||Replicates the natural function of the knee. It rotates, twists, bends, and flexes like a natural knee joint.|
|Posterior cruciate ligament retaining (non- constrained)||Keeps ligaments intact.|
|Posterior cruciate ligament substituting (constrained)||Replaces ligament with plastic component. Recommended for patients with severely damaged knees or weak ligaments. Also used in revision surgery.|
|Gender specific||Tailored for women.|
Knee Implants and the FDA’s 510(k) Program
Before a device can be implanted – and before it can even reach a doctor – it must be approved by the U.S. Food and Drug Administration (FDA). One of the ways the FDA signs off on these implants – and also on other devices – is through its 510(k) program. Gaining FDA approval for a new medical device can take years because of testing that’s required. But, the FDA’s 510(k) program enables manufacturers to speed up the approval process, if a device is similar to another one that has already received approval.
Device manufacturers are incentivized to send new products through the program because the approval process is much less rigorous – less testing and fewer clinical trials – than the FDA’s normal approval channels. A majority of knee replacement components are approved under the 510(k) program.
Knee Replacement Surgery
Knee replacement surgery is recommended when conservative treatments like physical therapy, braces, steroid injections and anti-inflammatory medication fail to alleviate pain. The decision to have surgery is based on a patient’s age, activity level and joint condition. If a patient requires surgery on both knees, it’s called a bilateral knee replacement. The two procedures can be done simultaneously or doctors may choose to use a staged bilateral approach that schedules the second surgery several days, weeks or months later.
The decision to have a total versus a partial knee replacement is based on a doctor’s recommendation after a full patient evaluation is performed.
Total Knee Replacement
A total knee replacement is actually the resurfacing of the bones in all three compartments of the knee joint: the medial compartment, the lateral compartment and the patellofemoral (front) compartment. The procedure resurfaces the end of the femur, the top of the tibia, and the patella. The ligaments that support the knee can be left in place or removed, depending on their condition and the type of implant chosen. Any existing cartilage between the femur and tibia is replaced with a plastic cushion.
Partial Knee Replacement
A partial knee replacement, which is a unicompartmental or bicompartmental knee replacement, is a procedure that resurfaces one or two bones of the knee. Partial implant components are named for the area of the knee they resurface: medial unicondylar component, lateral unicondylar component and femoro-patellar component. A partial knee replacement can also include a knee osteotomy, in which a surgeon removes or adds a wedge of bone to the tibia or femur to take some of the weight off of the damaged part of the knee.
Knee replacement surgery, like every surgery, carries a certain level of risk. If a patient receives a defective implant, however, serious complications can follow and may require one or more revision surgeries.
Serious complications from a knee replacement can arise within a few weeks, months or years after surgery and may include:
- Loosening of the implant
- Osteolysis (bone loss)
- Bone fracture
Although rare, metallosis is possible after knee replacement surgery. Metallosis, also known as metal poisoning, can occur when metal implant pieces rub against each other and release tiny metal particles into the knee joint and bloodstream. This can happen when the plastic cushion separating the femoral and tibial components wears down from high usage. This usually takes a few years to occur, and revision surgery is required.
Knee replacements generally last more than 20 years, but not all patients experience the same results. For patients whose artificial joint wears out earlier than expected – or who received a defective implant – revision surgery is required. Any serious complication can also lead to revision surgery. In addition, younger recipients require revision surgery when the first implant wears out.
Revision surgery rates for knee replacements are quickly rising in the United States. In 2005, about 38,000 revision knee surgeries were performed. By 2030, estimates are there will be nearly 268,000 performed each year – a 600 percent increase.
Implants that are used in revision surgeries typically have thicker, longer stems for added stability and to replace bone loss. In addition, surgeons typically implant a constrained (hinged) knee during revision surgery because it provides strength for severely damaged knees and weak ligaments.
Knee Replacement Lawsuits
Knee implant manufacturers are obligated to design and market safe devices, but when complications are overlooked or undetected, patients suffer the consequences and often have to undergo revision surgery. A repeat surgery may be required after implant loosening, dislocation, infection or bone fractures. Patients who are faced with mounting medical bills and ongoing pain often turn to the legal system to pursue compensation.
Manufacturers of a recalled or defective knee implant can be held accountable for issuing patients a device that was prone to fail or cause complications. Without penalty, there is nothing to discourage manufacturers from producing faulty implants in the future.
Knee Implant Manufacturers
Artificial knee joint manufacturers face increased scrutiny — and thousands of lawsuits — over recalled products and high failure rates. In 2007, four of the nation’s largest knee implant manufacturers agreed to pay $310 million in penalties to settle federal charges stating that they paid surgeons to use their devices. The companies that had to pay were Zimmer Holdings, DePuy Orthopaedics, Smith & Nephew, and Biomet. Stryker Orthopaedics agreed to federal supervision for 18 months in lieu of a monetary penalty.
Zimmer Holdings manufactures three knee components that have higher than normal failure rates: the NexGen CR High-Flex femoral component, the NexGen LPS High-Flex femoral component and the NexGen MIS Tibial Component. Zimmer recalled the MIS Tibial Component in 2010 after reports indicated the component’s locking screws and stem extensions failed to interlock correctly.
In early 2002, Sulzer Medica — which has since changed its name to Centerpulse and was acquired by Zimmer in 2003 — paid $1 billion to settle thousands of lawsuits filed by patients who received faulty hip or knee implants. The settlement came a little more than a year after the defective implants — including the Natural Knee II Tibial Baseplate — were recalled over an oily substance that had been left on some of them during the manufacturing process.
DePuy is one of the largest joint replacement manufacturers in the world and is known for its High-Flex knee implants: the Sigma CR150 High-Flex Knee System and the Sigma RP-F Knee System.
However, DePuy has recalled several knee components over the years. In 2008, the company recalled its LCS Knee Implant-Meniscal bearing insert over mislabeling. In 2009, an international recall was issued on the LCS Duofix Femoral Component, a part that failed to reach the United States because the FDA didn’t approve it. The recall was issued because the device had higher than normal revision rates.
Smith & Nephew
In 2003, Smith & Nephew recalled its Oxinium Genesis II and Oxinium Profix II knee devices after reports of pain, loosening and revision surgeries. In 2008, the company recalled its TC-PLUS, VKS and RT-PLUS knee models because the implants contained higher-than-specified levels of iron.
A third recall was issued in 2010 for the Journey Uni Tibial Baseplate knee component because the base plates and inserts were prone to breaking.
In January 2012, Stryker Orthopaedics recalled 26,000 of its EIUS Unicompartmental Knee Systems over higher revision rates. The recall came several years after the FDA warned Stryker about procedural problems at two of its joint manufacturing facilities in Ireland and New Jersey. The 2007 warning letters targeted two knee replacement components — the Duracon and the Scorpio — and other joint components.
In 2007, Biomet recalled its Vanguard PS Open Box Femoral Component because it was mislabeled. In 2008, the company issued another recall for the Vanguard DCM PS Plus Tibial Bearing implant because the sizing information was incorrect.
In addition, in 2005, Biomet recalled surgical instruments used to perform knee replacements. The instruments may have been assembled improperly.