Hip Replacements

Hip replacement refers to the process in which a damaged hip joint is surgically replaced with an artificial implant. However, not all implants are safe, and some can cause serious complications.

What is a Hip Replacement?

Hip replacements — the surgical repair of an aged or injured natural hip joint by adding an artificial joint, or implant — date back three centuries. Reasons for these implants are the same now as then: a fracture or similar injury to the hip, arthritis or a wearing down of the joint over time. The goal is to reduce pain and increase mobility.

Although there are varied designs and models of hips built by several manufacturers, there are three basic components of an artificial hip — a stem that is inserted into the femur (thighbone); a ball that attaches to the top of the femur; and a cup that attaches to the pelvis.

Modern implants, increasingly popular since the 1970s, are made from a combination of materials, including plastics, ceramics and metals. Many of the most recent devices were metal-on-metal designs, created with the hope that hip replacements would last longer to give younger, active patients more pain-free mobility for more years.

Hip Replacement Surgery

If conservative treatments like physical therapy and pain medication fail to fix a hip problem, there are several surgical procedures that can provide a solution. Surgeons and patients will discuss the options before scheduling surgery. The decision is based on the age of the patient, as well as the unique problems with the hip joint. Technological developments and medical studies can also influence the decision. Every surgery comes with risks, but the risk can be minimized by choosing the safest, most appropriate procedure for each patient.

The three hip replacement procedures are total hip replacement, partial hip replacement and hip resurfacing.

Total Hip Replacement

A total hip replacement uses an artificial joint to replace the entire hip structure. During the procedure, a stem is inserted into the patient’s femur for stability, and a ball replaces the head of the femur. The socket is also replaced with an artificial cup. Hip implants are usually cemented in place, but some surgeons use a cementless approach instead. A hybrid total hip replacement uses a combination of both, implanting the cup without cement and setting the stem in place with cement.

Total Hip Replacement
Partial Hip Replacement

Partial Hip Replacement

Partial hip replacements (hemiarthroplasty) are recommended when only one part of a hip needs treatment. In most cases, the acetabulum (also known as the socket or cup) is left intact and the head of the femur is replaced with a ball. Some partial hip replacements only address the acetabulum. A partial hip replacement is commonly used to correct a hip fracture occurring at the neck of the femur.

Hip Resurfacing

The primary goal of hip resurfacing is to avoid bone loss. The procedure can delay a total hip replacement in younger recipients, who are likely to outlive the original implant and require a second surgery later. It replaces the socket with an artificial cup and resurfaces the head of the femur instead of removing it. This is accomplished by cementing a covering on top of the femur. This component has a short stem that is inserted into the neck of the femur. Hip resurfacing is often used to help with arthritis.

Hip Resurfacing

Types of Hips

Hip replacement (hip arthroplasty) is the rebuilding or replacement of the hip joint. The hip joint is made up of the femoral head, the ball at the top of the femur, and the acetabulum, the cup-shaped socket of the pelvis. When a person walks or moves their legs, the femoral head moves within the acetabulum in a similar fashion as a ball-and-socket joint. Hip implants are designed to mimic this natural movement as closely as possible.

The primary differences among implants are their size and the material that components are made of. Hip implant components are made of polyethylene (plastic), metal, ceramic or a combination of materials.

Hip Implant Devices

Metal Ball and Polyethylene (Plastic) Cup or Liner (MoP)

These are the most common type of hip implants and have been around since the 1960s. Plastic has a smoother surface finish that allows for less friction while the ball moves within the socket. However, MoP implants produce a lot of plastic debris, which will eventually cause the implant to fail and could lead to a condition called osteolysis.

Metal Ball and Metal Cup (MoM)

MoM implants are very durable and can withstand the active lifestyle of younger patients. They have less wear and can accept larger bearings than implants made of other materials. However, their durability comes at a price. MoM hip implants shed metal particles that have been linked to a number of serious health issues like metallosis. Metal-on-metal implants have recently come under fire due to design flaws and early failure rates. Several manufacturers – including DePuy and Stryker — have recalled one or more all-metal hip implant products.

Ceramic Ball and Plastic Cup or Liner

Unlike the plastic used in the MoP device, the plastic used in these devices is very dense. Although these materials are reliable and provide for a very smooth surface, there is still the issue of wear debris and the potential for osteolysis.

Ceramic Ball and Ceramic Liner

All-ceramic hips are known for their durability and reliability. They have been around since the early 1980s, but they were only recently approved for use in the United States. Although the femoral ball is made from very hard clay that is wear-resistant, these devices have a history of producing a squeaking noise, and shattering.

Ceramic Ball and Metal Socket

The first ceramic-on-metal hip received FDA approval in 2011. The goal is to avoid the problems of metal-on-metal implants. Postmarket studies are underway.

Metal-on-Metal Hip Implants

Metal-on-metal hip implants produced one significant complication: metal ions can rub off of the devices and enter a recipient's bloodstream, creating a metal poisoning know as metallosis. Other complications with these implants include a loosening of the hip implant, joint dislocation and, in one case a squeaky hip.

These complications may lead recipients to pursue corrective actions that are both physical and financial. Many people with problematic artificial hips opt for revision surgery, a corrective procedure that gives them a new hip implant. Many of those same patients — and others — opt for legal action by suing device manufacturers, claiming the companies knew their hip systems were defective.

All hip replacement systems must be approved by the U.S. Food and Drug Administration (FDA) before being used in the United States. Device companies use the FDA’s 510(k) program to gain approval. The program allows the companies to streamline the approval process instead of making them undergo much more rigorous testing. Some of the largest device manufacturers are DePuy Orthopaedics, Zimmer Holdings and Stryker Orthopaedics. All three companies are facing issues with faulty hip devices.

The FDA's 510(k) Program

Metal-on-metal hip systems are classified as Class III (higher risk) devices but are regulated under the Food and Drug Administration (FDA) 510(k) premarket notification program. That means they are not required to undergo premarket testing or clinical trials before they are used in patients. Under the 510(k) program, manufacturers simply have to state that their products are similar to products already on the market.

In May 2011, the FDA ordered 21 manufacturers of metal-on-metal products to conduct postmarket studies. A year later, an FDA panel found that there is little reason for surgeons to continue to use metal-on-metal implant systems. The FDA states that “a decision on the proper classification of metal-on-metal hip systems is forthcoming.”


Complications and Implant Failure

As with any surgery, complications can arise following hip replacement procedures. Some problems can be detected immediately, while others may not surface for years. Serious situations may require patients to undergo a second surgery, called revision surgery.

Some of the complications associated with hip replacements are tied to the materials used in the implants. Metal-on-metal implants can lead to metallosis, which is a serious condition that occurs when metallic debris builds up in the soft tissue of the body. Osteolysis, another serious complication that can occur following hip replacement surgery, is the loss of bone around the implant as the body works to “clean up” foreign particles that are produced by the device during normal movement. This can lead to loosening and failure of the implant.

Other complications can include:
Implant dislocation Avascular necrosis (bone death)
Infection Loosening of the implant
Heterotopic ossification (soft tissue becomes calcified) Fracture

Revision Surgery

Following up to 10 percent of hip replacement surgeries, patients require one or more revision surgeries for further repair. Younger patients will most often require revision surgery, because hip implants are not designed to last more than 15-20 years. Recently, a rash of defective implants has meant more repeat surgeries for more patients. Often, these surgeries are necessary just a few years after the original operation.

Revision surgery is performed to replace one or more artificial hip components that have loosened, worn out, become dislocated or caused other serious complications. These procedures are tougher for surgeons and patients alike, since typically more bone must be removed and new implant parts inserted. The mortality rate also rises: For original hip replacement procedures, the death rate is 1 percent; for revision surgeries, the rate is 2.5 percent.

Hip Replacement Lawsuits

Even though the FDA does not require premarket testing of hip implants, device manufacturers are obligated to design and sell safe products, and warn consumers about any risks associated with their devices. When they fail to do so, patients have a right to seek justice in court. Through no fault of their own, they may have received a defective hip implant or one that has since been recalled.

Legal claims against hip implant manufacturers – including DePuy, Stryker and Zimmer — can help patients cover the high costs of ongoing medical care and any future surgeries that may be required. A legal settlement can also make up for some of the pain and suffering that patients must endure as they seek resolution to a painful hip problem. Punitive damages can discourage manufacturers from acting recklessly in the future.

Hip Implant Manufacturers

Dozens of medical device manufacturers sell hundreds of hip components, and they often advertise their products directly to the consumer. Orthopaedic surgeons, however, are the most qualified to make the decision about which implant components to use in surgery. Most hip implant systems come with several options for surgeons — including different materials, modular necks and stems and/or a variety of femoral ball sizes.

Several of the world’s largest hip implant manufacturers – including DePuy, Stryker and Zimmer — have been forced to recall some of their most popular products after early failure rates and other metal-on-metal complications. Smaller brands – including Smith & Nephew, Biomet and Wright – also are under fire for selling defective implants.

Medical device manufacturers involved in hip component recalls

DePuy, a division of Johnson & Johnson, developed three hip replacement designs since 2000 with high failure rates: the Pinnacle Hip Replacement System, the ASR XL Acetabular System and the ASR Hip Resurfacing System. The problems with all three systems arise from their metal-on-metal components, and the two ASR systems were recalled in mid-2010. According to evidence presented at the first ASR trial in January 2013, DePuy knew at the time of the recall that the all-metal ASR device was expected to fail within five years in 40 percent of patients.

DePuy is facing an estimated 12,000 lawsuits from patients who received one of its ASR hip implants. According to Bloomberg, DePuy has agreed to pay $2.5 billion to settle 7,500 of those lawsuits.

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