If I Need a Total Hip Replacement, What Are My Options?
Cemented Total Hip Replacement
Over the past 40 years, there have been many improvements in both the materials and the methods used to hold the femoral and acetabular components in place. Today, the most commonly used bone cement is an acrylic polymer called polymethylmethacrylate (PMMA).
A patient with a cemented total hip replacement can put full weight on the limb and walk without support almost immediately after surgery, resulting in a faster rehabilitation. Although cemented implants have a long and distinguished track record of success, they are not ideal for everyone.
Cemented fixation relies on a stable interface between the prosthesis and the cement and a solid mechanical bond between the cement and the bone. Today's metal alloy stems rarely break, but they can occasionally loosen. Two processes, one mechanical and one biological, can contribute to loosening.
In the femoral component, cracks (fatigue fractures) in the cement that occur over time can cause the prosthetic stem to loosen and become unstable. This occurs more often with patients who are very active or very heavy. The action of the metal ball against the polyethylene cup of the acetabular component creates polyethylene wear debris. The cement or polyethylene debris particles generated can then trigger a biologic response that further contributes to loosening of the implant and sometime to loss of bone around the implant....
Cemented Total Hip Replacement in India
Cement fixation has a 30-year history in total hip arthroplasty. Cement fixation is a durable and reproducible means of fixation in a variety of hips. A key determinant to a cement mantle's longevity is the technique of cementing. This article reviews what has been learned in the past and outlines the state of the art in cement technique today.
One of the relatively recent changes in cement and arthroplasty is that a multitude of cements are available on the market. Although the durability of well-made cement mantles around implants is fairly consistent among cements, the products differ in terms of viscosity, working time, and setting. A surgeon must know the details of the particular cement he or she intends to use, as it will influence the cement technique. Working time and setting time vary among the different cements.
Data have shown that different types of femoral stems should be inserted with different types of cements. For example, a rougher stem should be inserted in an earlier phase of cement polymerization, whereas a smoother stem should be inserted in a more doughy state. Therefore, a surgeon who uses a smooth stem should use cement with a longer doughy phase, whereas a surgeon who uses a rougher stem should use cement with a longer liquid phase. Failure to appreciate the working characteristics of the different cements can potentially lead to complications during the surgery...
Cementing Technique
Bone preparation is critical for long-term survivorship of both the cemented stem and the cup.4 The aim is to provide a clean, stable bony bed for cement interdigitation into the remaining cancellous bone and to maintain stable interfaces between the implant and cement, and the cement and the bone.
Most investigators would agree that a surgeon should remove all loose cancellous bone but leave the remaining dense bone nearest to the cortex to enhance interdigitation of the cement into the remaining bone. This increases the shear strength of the cement and gives the best contact of the cement mantle to the remaining bone stock. Reaming with cylindrical or tapered reamers in the femur is often performed to remove the loosest bone but should be done by hand to leave a remnant of cancellous bone. It is important not to ream away all cancellous bone, as this will leave a smooth inner cortex and diminish the ability for the cement to bond to the bone.
Some implant systems are designed to be reamer-less and all bone preparation is meant to be done by a broach. Broaching, which compacts the bone rather than removes it as a reamer does, is an important step in the femoral preparation. The broaches, which in many systems are also used for sizing and trialing of the femoral implant, create a reproducibly larger envelope of 2 mm to 3 mm circumferentially around the stem. This allows for a uniform thickness of the cement mantle around the stem. Aggressive broaching should be avoided to prevent denuding of the inner cortical bone...
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