A hip replacement may be cemented, cementless, or hybrid (an amalgamation of cemented as well as cementless elements), depending up on the kind of fixation that is employed to secure the implant in place. Your surgeon will assess your specific situation and make an appropriate decision. Ask your doctor which type of implant will be used for you and why that option is suitable.
Cemented Total Hip Replacement
With time, there have been several advances and improvements in the materials as well as the techniques used for hip replacement surgery. Today, the most frequently used bone cement is an acrylic polymer called polymethylmethacrylate.
If you opt for a cemented hip replacement, it enables you to put complete weight on the leg and walk without support, thus, bringing about quicker rehabilitation. However, cemented implants are not recommended for everyone.
Cemented hip replacement depends up on a stable interface between the cement and the prosthesis and a good bond between the bone and the cement. The bond between cement and bone is usually very reliable and hard-wearing. Cemented total hip replacement is advised for older patients, for those having rheumatoid arthritis, and for younger patients having poor bone quality and density or compromised health; given that, these patients are less likely to put too much stress on the cement which could trigger fatigue fractures.
Cementless Total Hip Replacement
Certain implant designs attach directly to the bone without the use of cement. These implants are larger and longer than those used with cement. The surface topography of these implants is favorable for new bone growth. Cementless implants call for greater healing time than cemented replacements, since they depend on new bone growth for steadiness. The new bone growth cannot link gaps that are larger than 1 - 2 mm. You will have to use crutches or a walker to give the bone time to attach itself to the hip implant.
Protected weight bearing guarantees that there is no movement between the bone and the implant and consequently a sturdy connection gets established.
Cementless femoral designs are larger at the top, and have wedge shape. This enables the strong surface of the bone and the dense, hard spongy bone to provide better support. The acetabular component has a coated surface that promotes bone growth. The close contact between the bone and the component is vital for bone in-growth.
Cementless implants have brilliant long-term outcomes; however, they become loose if a strong bond between the stem and bone is not achieved. Patients may also complain of thigh pain. Cementless hip replacements are recommended for younger, active patients, and patients who have good bone quality where bone in-growth can be attained.
Hybrid Total Hip Replacement
Hybrid total hip replacement comprises of one piece, more often than not, the acetabulum, inserted without cement, and the other piece, generally the stem of the femur, inserted with cement.
Partial Hip Replacements
A partial hip replacement is advocated in case only one part of the joint is diseased or damaged. By and large, the acetabulum is left as it is and the head of the femur is substituted using components like those used in a total hip replacement.
Hip resurfacing is a relatively newer technique wherein the socket is replaced similar to a total hip replacement; the femur, however, is resurfaced with a hemispherical component. This fixes over the head of the femur with cement around and has a short stem that gets inserted into the neck of the femur. Hip resurfacing is usually conducted in younger patients.
Types of Implants Used
Metal and Plastic Implant
These are the commonest materials used in hip implants. A metal prosthesis is used to substitute the ‘ball and the socket’ and a plastic spacer is positioned in between.
Metals that are used are stainless steel, titanium and cobalt chrome. The plastic is called polyethylene. The hip implant is held to the bone either by press-fit or cement. In the press-fit technique, the implant fits in the bone, and new bone forms around the implant to secure it in position. When the hip implant is cemented, special bone cement is used to hold the prosthesis in place.
These implants use similar materials, with no plastic piece in between. They do not get worn out as rapidly as the metal and plastic implants. Nonetheless, there is concern regarding the debris that is generated from the metal-on-metal implants. Ions get released into the blood, and there concentration increases with time. There isn’t any data that shows that the metal ions cause any kind of disorder or cancer, but one doesn’t know for certain.
These are the most resistant of all the hip implants. Ceramics are also smoother and more scratch resistant than any other material. On the other hand there is a concern that the ceramic implants may break within the body.
Metal and Highly Cross-linked Polyethylene
A new type of plastic has also been designed, that is more resistant to wear and tear. These highly cross-linked plastics are made so that they wear slower as compared to the traditional plastics. They have been accessible only since a few years, so whether they work better than the traditional plastic implants will not be known for some time.