New Hip Replacement: MDM - NewsChannel5.com | Nashville News, Weather & Sports

New Hip Replacement: MDM

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NEW YORK, NY (Ivanhoe Newswire) - More than three-quarters of a million people will have a hip replaced this year. But some may be a little gun shy after a large FDA recall of metal-on-metal devices, as they caused inflammation, tissue death, and heart and nervous system problems. Now, a new implant is replacing the metal with something safer.

Doctor Steven Harwin, Chief of Adult Reconstructive Surgery at Beth Israel Medical Center, has been replacing 15 hips a week for 30 years. His patient Gilbert Ramirez talked to us a few minutes before he was going to meet up with Dr. Harwin in the operating room. As a New York City tour guide, he rides transportation all day long.

"You figure there are 20 stops, you're constantly going up and down the stairs. That's when I noticed my hip started to give me a lot of pressure," Ramirez told Ivanhoe. His right hip was wearing bone on bone. "It stops you dead in your tracks."

Gilbert is getting a new type of hip replacement called Modular Dual Mobility hip, or MDM.

"This is what a contemporary hip replacement looks like," Dr. Harwin told Ivanhoe.

It has a metal shell, plastic insert and the implant attaches it to the thigh bone.

"The plastic can wear out," Dr. Harwin said. The new MDM replacement uses a porous titanium socket that allows bone to grow into it. "The range of motion is quite large, and the bearings move in conjunction with each other."

Tony Renteria had the MDM replacement a month ago. Getting around on foot in this city was a must, but he was at a disadvantage. "I could not walk at all," Renteria told Ivanhoe. Now, 30 days after surgery, he's walking without a cane.

"From the next day, I felt absolutely fine. It was like I had no pain whatsoever!" Renteria exclaimed. Tony's path to recovery continues, and he's practically pain free-each step of the way.

While it's relatively new in the United States, the MDM has been used in Europe for decades. Dr. Harwin is one of 30 surgeons worldwide who helped improve the design and update it with more modern, longer lasting materials. He says about 90 percent of traditional hip replacements last 15 years or longer. He hopes the MDM will give patients even better outcomes by helping to reduce dislocation of the implant.

RESEARCH SUMMARY

BACKGROUND: The hip is one of the body's largest joints. It is a ball-and-socket joint. The socket is formed by the acetabulum, which is part of the large pelvis bone. The ball is the femoral head, which is the upper end of the femur (thighbone). The bone surfaces of the ball and socket are covered with articular cartilage, a smooth tissue that cushions the ends of the bones and enables them to move easily. A thin tissue called synovial membrane surrounds the hip joint. In a healthy hip, this membrane makes a small amount of fluid that lubricates the cartilage and eliminates almost all friction during hip movement. Bands of tissue called ligaments (the hip capsule) connect the ball to the socket and provide stability to the joint.

COMMON CAUSES: The five most common causes for hip pain are:

  • Osteoarthritis. This is an age-related "wear and tear" type of arthritis. It usually occurs in people 50 years of age and older and often in individuals with a family history of arthritis. The cartilage cushioning the bones of the hip wears away. The bones then rub against each other, causing hip pain and stiffness. Osteoarthritis may also be caused or accelerated by subtle irregularities in how the hip developed in childhood.
  • Rheumatoid arthritis. This is an autoimmune disease in which the synovial membrane becomes inflamed and thickened. This chronic inflammation can damage the cartilage, leading to pain and stiffness. Rheumatoid arthritis is the most common type of a group of disorders termed "inflammatory arthritis."
  • Post-traumatic arthritis. This can follow a serious hip injury or fracture. The cartilage may become damaged and lead to hip pain and stiffness over time.
  • Avascular necrosis. An injury to the hip, such as a dislocation or fracture, may limit the blood supply to the femoral head. This is called avascular necrosis. The lack of blood may cause the surface of the bone to collapse, and arthritis will result. Some diseases can also cause avascular necrosis.
  • Childhood hip disease. Some infants and children have hip problems. Even though the problems are successfully treated during childhood, they may still cause arthritis later on in life. This happens because the hip may not grow normally, and the joint surfaces are affected. (Source: http://orthoinfo.aaos.org)

WIPING OUT PAIN: The Modular Dual Mobility (MDM) hip replacement uses a small metal or ceramic head that fits into a larger high- tech plastic head. The large plastic head then fits inside a smooth metal cup. Because of the large plastic head, the MDM renders the joint extremely stable so that active patients can engage in recreational and sports activities. The large head also allows a greater, more normal range of motion than standard implants. The small head moves within the plastic large head, and it in turn moves in the socket. This design is called a "dual mobility" cup.

  • Materials: Using a combination of high-tech, new-generation plastics, ultra- smooth metals, ceramics and porous metals, the wear rate has been reduced over 97% and a long-lasting natural adherence to the bone occurs
  • Surgical Technique: Minimally invasive surgical techniques use smaller incisions, cause less muscle damage and allow patients to recover faster.
  • Recovery: After less-invasive MDM hip replacement, patients recover faster with no precautions after surgery. Patients can sit, stand, walk and move their hip without fear of it coming out of place. Most patients are recovered in three to four weeks and can drive, travel and return to normal activities. Patients have an excellent chance that their replaced hip will provide them a high quality of life for decades to come. (Source: http://www.chpnyc.org/pressroom/MDMHip.pdf)

INTERVIEW

Steven F. Harwin, MD, FACS, Chief of Adult Reconstructive Surgery and Total Hip and Knee Replacement at Beth Israel Medical Center in New York City, talks about a new improved hip replacement that is helping people to get their lives back.

How many replacements do you do a day, a week?

Dr. Harwin: I do about 15 joint replacements a week. I operate 3 days a week.

How many years have you been doing hip replacements?

Dr. Harwin: Over 30 years.

How does the hip joint work?

Dr. Harwin: The hip joint is a ball and a socket. The socket is called the acetabulum. The head of the femur is the ball, articulating with the socket giving a very large range of motion with excellent stability. it is quite a large ball in a large socket and that is the natural anatomy. All joints of the body are covered with cartilage which is the white, shiny stuff that you see when you break open a chicken joint. That is a shock absorber and it keeps the bones from having friction. When that cartilage starts to wear out or is damaged, it leads to arthritis. What happens is that friction builds up and it is painful for the patient. The hip can catch and give way and give a feeling of instability and of course pain. This is something that limits patient's lifestyles. It ruins the quality of life. Patients, especially the baby boomers, are entering the time when their hips may start to wear out and they want to be as active as possible. Not only for their general health but also for their cardiovascular system, so that they need to be able to do exercise of some sort, even fast walking, to get the heart rate up. With arthritis they cannot do that. People get heavier since they cannot exercise because of the pain. People will turn to alternative, nonoperative treatments including anti-inflammatory and pain medications, physical therapy, injections, and alter their lifestyle. People just do not want to change their lifestyle and activities if they do not have to. They will turn to hip replacement to relieve their pain and restore their mobility.

Are you seeing younger patients than ever before?

Dr. Harwin: Young and younger. If you spoke to me 15 years ago, my average patient would be about 65 years of age. Now, my average patient is about 62 and coming down. The patient that we are going to operate today is 50 years old and significantly disabled. He is a tour bus operator here in New York. He makes about 20 or more stops every day where he lets passengers off, so he must go from the top deck to the bottom deck to the street 20 times and he just could not do it anymore. His hip was painful. He could not mount the stairs. He tried all kinds of remedies and it just would not take away his pain or restore his mobility and so he came to see me and we talked about the options. We decided together on total hip replacement.

How much has hip replacement changed throughout the years?

Dr. Harwin: The way we relieve pain is by removing those joint surfaces that are rubbing together. Once you do that, the body does not perceive pain. Conventional total hip replacements are very successful. If you look at long-term results in our medical literature, the survivorship of a contemporary hip replacement is about 90% or more at 15 years. Now, many people will think, oh…so it needs to be redone in 15 years, but that is not the case. With a 90% survivorship, only 10 out of 100 may need to be re-operated for one reason or another. One of the common reasons is that the hip may wear out. The plastic that cushions the new hip can wear out and cause problems. The hip can also dislocate, coming out of place, requiring further surgery. Contemporary hip replacements are successful, but they do have limitations.

What does a contemporary replacement look like?

Dr. Harwin:. The natural hip consists of a ball and socket. The socket in the pelvis is replaced with a metal shell that has a plastic insert fixed within it. That is coupled with an implant which is what we call the femoral component. We remove the head of the femur, the ball, and then we slip an implant inside the thigh bone. Then, once that is placed inside the thigh bone, that is the articulation and it restores pain and motion. The problem with contemporary hip replacements is that the plastic can wear out and the hip itself either early on after the operation or late can dislocate. It can come out of the joint because sometimes one can exceed the range of motion or put the hip throughout a very large range of motion which can cause impingement and the hip comes out of place. That has been a problem that we have worked for years to try to solve. One alternative was an operation which used larger heads and the only way to do that was to use a metal articulation for the socket and a very large metal head. But what happens in some cases is that the metal-on-metal articulation causes particles to break off and float in the joint and in the blood stream. They can cause allergic reactions and other problems in patients who have had metal-on-metal implants. We set out to avoid the problem by gaining the benefits of a large head with good stability and range of motion coupled with a longer lasting thicker plastic ball that is mobile in the socket, and articulates with the smaller femoral head component. The mobile bearing hip uses a "dual mobility" concept, where the large plastic ball is free to move in the socket and the smaller femoral head ball is free to move inside the plastic.

Did you help develop it?

Dr. Harwin: Mobile bearing hips were first developed in the 1970s and has undergone evolutionary refinement. These days, there is not one person who will design an implant. I work with a group of over 25 surgeons from around the world. We do this in conjunction with specialized bioengineers who are specialists in not only what we call kinematics, that is how the joint moves and works, but also in the biology and materials of the bearing surfaces. They have helped us to develop these new bearing surfaces and these new designs. A mobile bearing hip uses a socket made of a very high tech titanium with a surface that allows one's own bone to grow into it. This is called Tritanium.

Is the surface porous?

Dr. Harwin: It is porous and it is rough; kind of like Swiss cheese with a sandpaper finish. It reproduces the normal marrow bone or cancellous bone, as we call it. Once this is placed inside the new socket we create, the body grows right into it. The fixation is quite firm with a very low rate of loosening of the implant. Once this is placed, a highly polished metal liner is fixed to the inside. This surface articulates with a large plastic ball that itself articulates with a smaller ball within it. In turn, that head is part of the femoral component that is placed in the thigh bone. . The plastic is made of X3-polyethylene, which is a highly cross-linked plastic, with very good wear characteristics. We are kind of going back to the future with what we would call a low friction arthroplasty, with less wear. Arthroplasty is the technical term for joint replacement. The nice thing about the mobile bearing hip is that not only do we have a large plastic head that articulates, but inside that large plastic head, we have a smaller head that also articulates, so that the range of motion is greater and the bearings move in conjunction with each other with more stability. This has benefits for patients. It allows patients to do fairly normal and recreational activities with a stable, very mobile joint. Another potential benefit is better durability because this has a very large, thick, plastic head which will resist wear. It is not as thin as the fixed bearing implants and therefore has the potential for being very long lasting.

Are there any risks that there are more moving parts now?

Dr. Harwin: Any joint replacement carries with it certain risks, but for hip replacements the benefits greatly outweigh the risks. Patients should discuss their own specific risks and benefits with their surgeon.

FOR MORE INFORMATION, PLEASE CONTACT:

Vera Ricciardi, Practice Administrator
Denise M. Mazza, Office Manager
(212) (861) 9800 
www.drharwin.com

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