Hip replacement (hip arthroplasty) has been in evolution for over 60 years. Interestingly, the current implants used today are very similar to the ones originally developed by John Charnley in his original work in the development of the hip implant. Many ideas have been tried. During this period of refinement, there have been concepts that didn't work as intended. While the evolution is not over, there has been significant progress toward implants that satisfy the requirements for an ideal hip prosthesis.
Hip replacement (hip arthroplasty) has been in evolution for over 60 years. Interestingly, the current implants used today are very similar to the ones originally developed by John Charnley in his original work in the development of the hip implant. Many ideas have been tried. During this period of refinement, there have been concepts that didn't work as intended. While the evolution is not over, there has been significant progress toward implants that satisfy the requirements for an ideal hip prosthesis.
All hip systems involve the use of four common components. (see illustration) There is a shell, a liner to the shell, a head or ball, and a stem that goes in the femur. Keeping this system as simple as possible seems to have proven wise, as there are very few deviations from this with supported clinical benefit, and several with unintended faults.
All hip systems involve the use of four common components. (see illustration) There is a shell, a liner to the shell, a head or ball, and a stem that goes in the femur. Keeping this system as simple as possible seems to have proven wise, as there are very few deviations from this with supported clinical benefit, and several with unintended faults.
The majority of surgeons in the US use a titanium stem and titanium shell with surface coatings and textures that improve the ability of the bone to bond with the implant. This is a critical step for the success of the hip. The implants adhere to the bone with a friction fit initially, but will loosen if the bone does not eventually chemically bond to the metal surface. This usually happens within the first two months.
The majority of surgeons in the US use a titanium stem and titanium shell with surface coatings and textures that improve the ability of the bone to bond with the implant. This is a critical step for the success of the hip. The implants adhere to the bone with a friction fit initially, but will loosen if the bone does not eventually chemically bond to the metal surface. This usually happens within the first two months.
There is some debate about what is an ideal bearing surface for the interface between the head and the liner. (see illustration below) Putting two hard surfaces (hard-on-hard) rubbing against each other with a fluid lubricant can potentially create a situation with almost no wear, like in a car motor. While this is conceptually ideal, there are significant issues with "hard-on-hard" bearing surfaces: metal on metal, ceramic on ceramic, or hybrid. They can function well, but any possible theoretic benefit likely does not outweigh the risk. The risk of these surfaces comes from the potential for fracture of the material, intolerance to impact or debris, and most commonly, generation of metal particles in the hip space. These particles can induce rapid corrosion, wear, and formation of inflammatory masses that can be challenging to manage and may require revision of the hip, loss of muscle attachments, hip instability, and infection.
There is some debate about what is an ideal bearing surface for the interface between the head and the liner. (see illustration below) Putting two hard surfaces (hard-on-hard) rubbing against each other with a fluid lubricant can potentially create a situation with almost no wear, like in a car motor. While this is conceptually ideal, there are significant issues with "hard-on-hard" bearing surfaces: metal on metal, ceramic on ceramic, or hybrid. They can function well, but any possible theoretic benefit likely does not outweigh the risk. The risk of these surfaces comes from the potential for fracture of the material, intolerance to impact or debris, and most commonly, generation of metal particles in the hip space. These particles can induce rapid corrosion, wear, and formation of inflammatory masses that can be challenging to manage and may require revision of the hip, loss of muscle attachments, hip instability, and infection.
Because of the above, most surgeons use a ceramic head on polyethylene plastic (soft) liner interface. Current plastics appear to have minimal detectable wear over the lifetime of the implant, regardless of activity. They are tolerant to impact, easily exchanged if needed, do not produce toxic particles, metal ions, or corrode. I follow hips that are 30+ years old with this combination. When the implant is placed correctly with a modern plastic liner, I have not seen significant wear. This is in agreement with current laboratory and clinical data.
Because of the above, most surgeons use a ceramic head on polyethylene plastic (soft) liner interface. Current plastics appear to have minimal detectable wear over the lifetime of the implant, regardless of activity. They are tolerant to impact, easily exchanged if needed, do not produce toxic particles, metal ions, or corrode. I follow hips that are 30+ years old with this combination. When the implant is placed correctly with a modern plastic liner, I have not seen significant wear. This is in agreement with current laboratory and clinical data.
Current reports support a lifetime of the implant of 25-35 years. This includes hips that fail for malposition. Without malposition and just looking at wear as an endpoint, the answer would be longer. I think it is very likely your hip replacement will outlast you. The primary reason I chose the Anterior Approach to the hip, is it allows me to use x-ray imaging and computer navigation intra-operatively to help assure that the position of the implants and restoration of the hip geometry is correct. These techniques are not required and the vast majority of hip implants are placed using traditional methods. It is what I am comfortable with and what I believe will help avoid complications and wear in the long run.
Current reports support a lifetime of the implant of 25-35 years. This includes hips that fail for malposition. Without malposition and just looking at wear as an endpoint, the answer would be longer. I think it is very likely your hip replacement will outlast you. The primary reason I chose the Anterior Approach to the hip, is it allows me to use x-ray imaging and computer navigation intra-operatively to help assure that the position of the implants and restoration of the hip geometry is correct. These techniques are not required and the vast majority of hip implants are placed using traditional methods. It is what I am comfortable with and what I believe will help avoid complications and wear in the long run.
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