Types of Hip Replacement Joints
Hip replacements are one of the most frequent and effective medical interventions, exhibiting the highest quality of life improvements of all treatments in medicine. Because of the very large number of elderly people who require hip and knee replacement, the technology of hip replacement has progressed greatly since the 1960s when the first real ones were inserted. This has meant a variety of major hip replacement methods and a large number of different hip prosthesis types.
A hip arthroplasty definition is that the damaged or arthritic parts are reconstructed or replaced by artificial components.
Total Hip Replacements
Total hip replacement designs involve a metal femoral stem component which may have a collar or be collar-less like the Exeter, and are of a tapering design to fit in the femoral canal with PMMA cement. They articulate with a socket made of high density polyethylene which is also cemented in many cases into the pelvis, but is also applied without cement. The metal on plastic system gives very low friction and wear but there have been some problems reported with small particles of wear debris contributing to bone loss around the implants.
Cemented types of hip replacement include the Exeter, the Stanmore and the Charnley, the latter being the first of the true types of total hip replacements, developed in the UK in the 1960s. All these types hip replacement prosthesis have excellent, long-term and published results in reputable medical journals, showing that their implants remain working well for over fifteen years in the vast majority of patients.
Cementless types of hip replacement have been designed to avoid the perceived problems of cementing in components, i.e. loosening of the interface between the cement and the bone. Once loosened, the joint often needs to be re-operated on, a much more complex operation than the original one.
Cementless implants are covered in a porous coating which aims to encourage the bone to grow up to and into the surface structure of the implant, forming a strong lock which will last. These implants are often used in younger patients so that the inevitable revision will be easier to perform, but whether their overall survival is as good as cemented implants is not clear. Thigh pain may be an issue and for more active patients who are younger this could be unhelpful.
Resurfacing takes a different approach to hip replacement surgery and again claims to be better for younger people who are more active, allowing early activity and a reduced likelihood of dislocation. The Birmingham Hip removed much less bone from the hip area, just a shallow amount from both the socket and the femoral head, leaving the majority of the hip bone present.
The cut surfaces are replaced by hemispherical metal implants which articulate together will very low wear, avoiding the issues with wear particles from plastic implants. Normal mechanical stresses are taken by the bone in the hip area and this is claimed to maintain the bone in the region, allowing hip replacement to be performed later if it should be required.
Hip replacement causes vary and the Austin Moore hemiarthroplasty is a large diameter ball with a stem down the femur and mostly used to replace the femoral head in cases where a fractured neck of femur is high and likely to compromise the blood supply to the head. The socket is not replaced and a risk is that significant pain will still be experienced post operatively due to the socket and that another procedure will be required.
Further reading about types of hip replacement is available from About.com:Orthopedics and at Arthritis.org.