What is Uncemented / Cementless Total Hip Replacement

Total hip replacement is a surgical procedure for replacing the hip joint. This joint is composed of two parts – the hip socket (acetabulum, a cup-shaped bone in the pelvis) and the “ball” or head of the thighbone (femur). During the surgical procedure, these two parts of the hip joint are removed and replaced with smooth artificial surfaces. The artificial socket is made of high-density plastic, while the artificial ball with its stem is made of a strong stainless metal. These artificial pieces are implanted into healthy portions of the pelvis and thighbones and affixed with a bone cement (methyl methacrylate).

An alternative hip prosthesis called a “cementless” total hip replacement has the potential to allow bone to grow into it, and therefore may last longer than the cemented hip. This is an important consideration for the younger patient. In some cases, only one of the two components (socket or stem) may be fixed with cement and the other is cementless and would be called a “hybrid” hip prosthesis.

When is total hip replacement considered ?

Total hip replacements are usually performed for severe arthritic conditions. The operation is sometimes performed for other problems such as hip fractures or avascular necrosis (a condition in which the bone of the hip ball dies). Most patients who have artificial hips are over 55 years of age, but the operation is occasionally performed on younger persons.

Circumstances vary, but generally, patients are considered for total hip replacements if : –

Your pain is severe enough to restrict work, recreation, and the ordinary activities of daily living.
Your pain is not relieved by anti-inflammatory medicine, the use of a cane or walker and restricting activities.
You have significant stiffness of the hip.
Your x-rays show advanced arthritis, or other problems.

The orthopaedic surgeon must be very precise in preparing the femur for a cementless impact. The implant channel must match the shape of the implant itself very closely. New bone growth cannot bridge gaps larger than 1 mm to 2 mm. Your surgeon may recommend a period of protected weight-bearing (using crutches or a walker) to give the bone time to attach itself to the implant. This protected weight bearing helps to ensure there is no movement between the implant and bone so a durable connection can be established.

Cementless femoral components tend to be much larger at the top, with more of a wedge shape. This design enables the strong surface (cortex) of the bone and the dense, hard spongy (cancellous) bone just below it to provide support.

The acetabular component of a cementless total hip replacement also has a coated or textured surface to encourage bone growth into the surface. Depending on the design, these components may also use screws through the cup or spikes, pegs, or fins around the rim to help hold the implant in place until the new bone forms. Usually these components have a metal outer shell and a polyethylene liner.

The pelvis is prepared for a cementless acetabular component using a process similar to that used in a cemented total hip replacement procedure. The intimate contact between the component and bone is crucial to permit bone ingrowth.

Initially, it was hoped that cementless total hip replacement would eliminate the problem of bone resorption or stem loosening caused by cement failure. Although certain cementless stem designs have excellent long-term outcomes, cementless stems can loosen if a strong bond between bone and stem is not achieved.

Patients with large cementless stems may also experience a higher incidence of mild thigh pain. Likewise, polyethylene wear, particulate debris, and the resulting osteolysis (dissolution of bone) remain problems in both cemented and uncemented designs. Improvements in the wear characteristics of newer polyethylene and the advent of hard bearings (metal-on-metal or ceramic) may help resolve some of these problems in the future.

Although some orthopaedic surgeons are now using cementless devices for all patients, cementless total hip replacement is most often recommended for younger, more active patients and patients with good bone quality where bone ingrowth into the components can be predictably achieved. Individuals with juvenile inflammatory arthritis may also be candidates, even though the disease may restrict their activities.