Hip arthroplasty technology has evolved a great deal since its original development by Dr. John Charnely 60 years ago, but in many ways the wisdom of the fundamentals he set forth are still being rediscovered today. Many new prostheses have tried to improve upon his original design. In the end we have generally returned to his original concept. All hip systems have four fundamental components which include a shell, a liner, a femoral head, and a femoral stem. See the diagram to the left. The femoral head and liner comprise the "bearing surface" of the hip.
Hip arthroplasty technology has evolved a great deal since its original development by Dr. John Charnely 60 years ago, but in many ways the wisdom of the fundamentals he set forth are still being rediscovered today. Many new prostheses have tried to improve upon his original design. In the end we have generally returned to his original concept. All hip systems have four fundamental components which include a shell, a liner, a femoral head, and a femoral stem. See the diagram to the left. The femoral head and liner comprise the "bearing surface" of the hip.
Much of the controversy and evolution of the modern hip prosthesis has revolved around improving durability and stability of the prosthesis. Wear and dislocation are primary areas of failure. To this end many bearing surfaces have been developed: ceramic on ceramic, metal-on-metal and hybrid systems. These have evolved to try to mitigate wear and improve longevity and are considered to be "hard-on-hard" bearing surfaces. Theoretically they function similar to a car engine where hard surfaces are separated by a thin lubricant layer that can have nearly no wear in an ideal scenario.
Much of the controversy and evolution of the modern hip prosthesis has revolved around improving durability and stability of the prosthesis. Wear and dislocation are primary areas of failure. To this end many bearing surfaces have been developed: ceramic on ceramic, metal-on-metal and hybrid systems. These have evolved to try to mitigate wear and improve longevity and are considered to be "hard-on-hard" bearing surfaces. Theoretically they function similar to a car engine where hard surfaces are separated by a thin lubricant layer that can have nearly no wear in an ideal scenario.
Unfortunately, in the human body is not exactly like a car. There have been issues with production of toxic metal particles, immune mediated soft tissue masses, catastrophic failure due to impact and brittleness of the implants, and intolerance to scratches and other imperfections. Most surgeons in the United States have returned to a "hard-on-soft" bearing surface similar to that which John Charnely originally developed. This is a hard metal head of cobalt chrome or ceramic on a polyethylene plastic liner. See the figure below.
Unfortunately, in the human body is not exactly like a car. There have been issues with production of toxic metal particles, immune mediated soft tissue masses, catastrophic failure due to impact and brittleness of the implants, and intolerance to scratches and other imperfections. Most surgeons in the United States have returned to a "hard-on-soft" bearing surface similar to that which John Charnely originally developed. This is a hard metal head of cobalt chrome or ceramic on a polyethylene plastic liner. See the figure below.
Here again there is no free lunch and there are issues with polyethylene plastic. Plastic does wear and in the past there have been issues with plastics that had suboptimal material properties or issues with their sterilization that caused them to be brittle. These have been resolved.
Here again there is no free lunch and there are issues with polyethylene plastic. Plastic does wear and in the past there have been issues with plastics that had suboptimal material properties or issues with their sterilization that caused them to be brittle. These have been resolved.
Modern plastics show minimal detectable wear when components are placed in the appropriate position. They are resistant to scratching and deformation and accept impact without failure. They appear to be more accommodating to the forces seen in a human body.
Modern plastics show minimal detectable wear when components are placed in the appropriate position. They are resistant to scratching and deformation and accept impact without failure. They appear to be more accommodating to the forces seen in a human body.
Many of the components utilized today for primary hip arthroplasty are beginning to appear similar in appearance, materials, and technology. I think this supports the idea that we are approaching a common ideal hip prosthesis. Most have a titanium shell and femoral stem with surface textures designed to promote ingrowth and bonding of bone to the implant surface. This is a critical step in the success of the hip. Most systems have moved away from having small modular parts and pieces that are prone to corrosion or failure. There are areas of development whose clinical benefit remains to be determined. In general, use of these time-tested yet highly evolved designs appears to be the correct choice.
Many of the components utilized today for primary hip arthroplasty are beginning to appear similar in appearance, materials, and technology. I think this supports the idea that we are approaching a common ideal hip prosthesis. Most have a titanium shell and femoral stem with surface textures designed to promote ingrowth and bonding of bone to the implant surface. This is a critical step in the success of the hip. Most systems have moved away from having small modular parts and pieces that are prone to corrosion or failure. There are areas of development whose clinical benefit remains to be determined. In general, use of these time-tested yet highly evolved designs appears to be the correct choice.
In the end, what determines the success of the procedure will be the application of the the implant, and not the implant design itself.
In the end, what determines the success of the procedure will be the application of the the implant, and not the implant design itself.
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