Bone cement is PMMA, invented in the early 1900s and it was then better known as Plexiglas. PMMA is generated from methyl methacrylate (MMA) that is initiated to polymerize using benzoyl peroxide. The bone cement is distributed as a two-part system, consisting of a powder and a liquid. The powder consists of PMMA, MMA, and benzoyl peroxide. The reason for having some of the MMA already polymerized is to limit the shrinkage that occurs when polymerizing monomers as well as to lessen the exothermic energy released by the process. The liquid is MMA. When the polymerization reaction is initiated, the MMA swells as it is turned into PMMA, also the viscosity of the PMMA increases and will be rigid at the end of the reaction. The quality of the bone cement is highly dependent on what homogeneity is achieved when mixing the powder and the liquid. To achieve homogeneity it is important to have a fast mixing system to quickly and evenly mix the powder and the liquid. Mixing the components in a vacuum environment helps eradicate trapped air in the cement. Air bubbles increase porosity and lessen the mechanical strength properties of the material (3).

The cement’s function is to fixate the prosthesis components, and to transfer load from implant to bone as it serves as the bridge between these two modules. The interface between PMMA and the metal implant has been much discussed. When the prosthesis is implanted, a mechanical bond arises between metal and PMMA. However, this bond eventually ceases and thus all implanted stems will exhibit migration. The effectiveness of the interface of the PMMA to the stem is highly dependent on the design of the stem and its effect on the migration. Charnley achieved better results with high-polished stems in comparison with sand-blasted stems (4).

A successful interface between the bone and the cement is largely dependent on revascularization of the bone. Prepressurizing and vacuum mixing the cement allows for a larger percentage of shrinkage, as opposed to hand-mixed cement. The shrinkage permits revascularization to occur faster and prevents necrosis of the bone.

In the first generations of cemented hips the cementing techniques were rather unrefined. The femoral canal was fit out by curetting the cancellous bone and the bone cement was mixed by hand. The cement was placed with a manual antegrade technique into the femur and pressurized by hand.

With the second generation of cementation the bone was prepared with irrigation. The cement was introduced into the femur via a cement gun and a distal cement restrictor was placed to enhance the pressurization (5). It has over time become apparent that pulsatile bone lavage before cementing optimizes the bone bed and cement penetration (6). Pulsatile lavage, placement of the cement via a gun along with a cement restrictor to create a high pressure on the cement, are all mandatory parts of modern cementing techniques (7,8).

The modern cementing technique relies on occluding and sealing of the intramedullary canal to generate the sufficient pressure to enhance cement penetration and strength (9). Outcomes are better with a well-documented cement of medium or higher viscosity (10,11).

The femoral intramedullary canal is opened in the same fashion as for noncemented total hip arthroplasties (THAs). When preparing the femoral canal for the cement, it is important to preserve about 2 to 3 mm of the strong cancellous bone in the canal to allow for the best interdigitation of cement and bone (12). The femoral canal and cancellous bone are then cleaned with pulsatile lavage to remove excess blood, fat, and shattered trabecular bone (Figs. 16.1 and 16.2) in order for the best possible penetration of cement into the intertrabecular spaces. Reaming the femoral canal too aggressively should be avoided because the shear strength of the bone–cement interface will be diminished (11,12,13). The distal femur is blocked with a distal cement restrictor, which comes in various designs and materials. The cement restrictor can show minor migration distally when the cement is added into the femoral canal, but optimally the plug stays in the intended position without leaking when pressure is brought to the cement (Fig. 16.3).

The cement is vacuum mixed and applied retrograde via a cement gun (Fig. 16.4) and the intramedullary pressure of the cement is intentionally increased with a femoral pressurizer to strengthen the cement mass and allow for the best possible penetration into the cancellous bone (Fig. 16.5) (14).

Some stem designs are provided with a distal centralizer, at the tip of the stem, to place it in the center of the femoral canal; this device also comes in various designs (Fig. 16.6).

The stem is then gently immersed at a speed of 1 cm/s (0,25 inch/s) into the cement under pressure and held in the desired position until the cement is dry (Fig. 16.7). These techniques are currently considered to be the “gold standard” of modern cementing technique, which significantly enhance implant survival rate (7) and improve both the long-term abilities and the bone–cement interface (15,16).

The modern acetabular cementing techniques are based on many of the same principles that apply to the femur. These include preparing the bone bed with pulsatile lavage and applying the cement under pressure to have it penetrate the cancellous bone bed.

After reaming—in a similar fashion as used for noncemented cups—anchoring holes are drilled into the acetabular bone bed to provide the cement with an enhanced grip (Fig. 16.8). Pulsatile lavage is performed to clean the cancellous bone from blood and marrow. The cement is then applied to the acetabulum while continuously applying pressure with an acetabular pressurizer or a sponge in a sterile glove (Fig. 16.9) (17). The pressure must exceed 5 kPa, which is the pressure threshold to prevent blood from laminating between the bone and the cement that can compromise anchoring of the cement (18,19).