Prosthetic hip devices
A total hip replacement removes the arthritic, damaged ball of the upper femur (thighbone) as well as the damaged cartilage from the hip socket. The ball is replaced by a metal or ceramic ball that is solidly fixed to a stem inserted into the femur. The socket is replaced with a metal cup, which is fixed to the acetabulum, or socket. Hip replacement has become a common procedure, with Biomet being a leading manafacture of these devises.
The implants are designed to create a new, smoothly functioning joint that prevents painful bone-on-bone contact.
Cemented vs. Cement-Free Components
In total hip replacement, the femoral component can be secured to your body in one of two ways: using bone cement as a grout to fix the components to your bone, or using a "cementless" component that is specially designed to allow your own bone to grow into the surface of the implant. Which component your surgeon chooses for you will depend on a variety of factors, including the condition of your bone tissue. In the United States, the majority of patients receive cement-free implants.
Biomet offers several types of cement-free hip stems with over 10 years of published clinical history. These results generally show that Biomet’s hips have performed extremely well, with fewer failures, less thigh pain, and less implant-related bone loss than many other systems with comparable follow-up.1,2.3
In fact, the vast majority of hip stems that are currently available from other implant manufacturers have no published long-term clinical data, due to the fact that these designs have not been used clinically for very long. Thus, there are no clinical data to indicate the long-term success of these implants.
Porous Coating Allows Bone to Grow into the Stem
For the cementless femoral component to be stabilized, bone must grow into the stem. Biomet applies a coating of titanium alloy to its cementless stems. Using a porous plasma spray known as PPS®, Biomet bombards its implants with small titanium alloy particles, creating a very rough, three-dimensional coating that allows bone to intertwine with the porous surface.
Research has shown that Biomet’s titanium alloy coating is highly biocompatible and typically generates the desired ingrowth.1,2 While many implant manufacturers use a porous coating process of some sort, Biomet uses plasma sprayed titanium alloy exclusively on all its cementless stem implants. Biomet chose the PPS® process because it provides several advantages, including:
- Implant Strength – Other methods of coating implants require that the coating and implant be heated to extreme temperatures, approaching the melting point of the metal. Research has shown that this causes a significant reduction in the implant’s strength.3 The Biomet® PPS® process does not require the implant to be heated to extreme temperatures. As a result, the strength of the implant is significantly higher than that of implants coated in other fashions.
- Surface Roughness Promotes a Tight Fit – In order to achieve solid fixation within the bone, the implant must fit tightly against the bone.4,5 A very rough surface, such as that of Biomet’s PPS®, creates high friction that "bites" into the bone. As a result of the very tight fit achieved, many surgeons are comfortable getting patients on their feet and putting weight on their new hip implants on the day of, or the day after, surgery. This is called "immediate weight-bearing,"6 a technique surgeons use to help you achieve the fastest possible recovery. The sooner you put your muscles to work, the sooner you will resume normal activities.
Femoral and Acetabular Components
The shape and Sizing of the Femoral Implant Promotes Excellent Matching of Your Anatomy
Biomet pioneered the use of tapered stems in total hip replacement in the United States. The goal of the stem’s design and shape is to wedge tightly near the top of the femur, reducing the potential for motion between the stem and the bone, which can cause pain. The inside of the femur in many patients is funnel-shaped, and the stem design reflects that shape, with the goal of creating a tight fit between the bone and the stem.
The tapered design and line-to-line fit allow the stresses of walking and other activities to be transferred to the bone. It is important that the bone be stressed as you walk. Bone that is not stressed may atrophy and weaken. Additionally, Biomet’s hip stems are offered in a wide range of size increments. By providing precise sizing options, Biomet stems provide your surgeon with the best chance of achieving optimal fit.
The femoral stem will be paired with an acetabular component, or socket, completing the "ball-and-socket" function of your hip. The vast majority of acetabular components implanted in the United States are implanted without cement and are designed to help promote bone in-growth fixation. Occasionally, a surgeon will use bone cement to affix a socket, depending on various factors, including the patient’s condition.
Biomet’s RingLoc® acetabular components all employ the PPS® porous coating technology, providing the benefits of strength, fixation, and coating integrity.
Polyethylene, Metal, or Ceramic
Your surgeon has several choices available in articulating surfaces. An articulating surface is where the motion of the joint actually occurs. In the case of the hip, it is where the head of the femoral component meets the acetabular socket. In order to provide smooth motion, the articulating surface must be able to withstand certain activities. Currently, polyethylene, metal-on-metal, and ceramic-on-ceramic are the most common articulating configurations offered. Each has its advantages and its place in the surgeon’s repertoire.
Polyethylene: Molded for Optimal Durability
Polyethylene (plastic) is an excellent material for hip articulation. It has been used in orthopedic implants for decades. Polyethylene, however, can wear over time, generating debris in the joint. This debris can result in an immunological reaction known as osteolysis, which can result in the destruction of bone tissue and implant loosening.1 Not all patients will display osteolysis, even if polyethylene wear occurs.
Newer methods of manufacturing polyethylene components, invented and patented by Biomet, have resulted in significant intermediate-term improvements in durability. These components, which are made from compression molded ArCom® polyethylene, have shown up to 40% wear reduction in actual clinical use.2
Ceramic-on-ceramic is an option for total hip replacement. Manufacturers of ceramic components promote its high wear resistance, as demonstrated in laboratory testing. However, there are no long-term data indicating that ceramic-on-ceramic is more durable clinically than metal- on-metal, another highly durable option.
There are reasons why a surgeon might elect metal-on-metal over ceramic-on-ceramic. First, ceramic is a glass compound, and as such, exhibits different properties than metal.
While there have been some reports of chipping of ceramic compounds reported in orthopedic literature,3-5 no such reports have been published on metal-on-metal components. The high strength of metal-on-metal components also enables the configuration of more implant design options than ceramic, which can mean greater range of motion and increased stability.
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