“There is no excuse for poor cement technique!” This quote was heard quite often from Dr. Krackow, and in every case he paid close attention to detail during this step of the total knee arthroscopy (TKA) procedure. Much has changed since the first edition of this textbook, but the polymethylmethacrylate (PMMA) that is used today is the essentially the same as that used in the early 1990s. Many more surgeons are now using a higher viscosity cement, but the one addition that has changed is the more frequent use of antibiotics in the cement. The advantages of adding antibiotics are not a topic for this chapter, and most agree that its use in higher-risk individuals is most likely beneficial. There has also been a surge in the use of cementless fixation in primary TKA, but to date registry information continues to show good long-term survivorship for cemented primary TKA.
Cement can be classified according to viscosity. Low-, medium-, and high-viscosity cements are available from a number of manufacturers. The type of cement surgeons use is greatly influenced by their training and what they have been used to over their residency and fellowship. Dr. Krackow’s preference was always a low-viscosity cement. For operating room (OR) efficiency, many surgeons have switched to higher viscosity options because of a shorter time to a “working phase.” No matter the choice, surgeons must be familiar with the manufacturer’s recommendations for mixing, the working window recommendations, and the need to have a team approach in which everyone in the OR understands the importance of each step of the cementation procedure. An adequate number of assistants to ensure retractors are held in place and an OR technician who has been adequately trained in the manufacturer’s procedures to optimally mix and prepare the cement are essential.
Step 1: Exposure
Proper exposure and retractor placement are essential so that all surfaces to be cemented can be properly prepared. We prefer to have the knee hyperflexed with medial and lateral soft-tissue sleeve retractors and the patella everted. The addition of a posterior cruciate ligament (PCL) type retractor to sublux the tibia forward also is recommended. Adequate exposure of the tibia to allow seating of the baseplate without interference from the femoral surfaces should be ensured ( Fig. 11.1 ).
Step 2: Bone Surface Preparation
Any areas on the tibia or distal femur (especially the lateral condyle of a valgus deformed knee) that are sclerotic should be drilled to ensure mechanical penetration into the area for fixation. We find a 2-mm drill bit to be sufficient for this step. Pulse lavage of the tibia/femur and patellar surfaces is then carried out to the point that no “blush” of blood or remnant of fatty fluid from the intramedullary contents is evident. A thorough drying of the surfaces and the keel preparation of the tibia are then carried out, and dry sponges are placed to keep these surfaces dry until ready for cementation (see Fig. 11.1 ). Adding a small-tip suction to a tibial bone block pin site can aid in keeping any marrow contents from rising to the surface during this drying time. If an intramedullary rod was used for femoral instrumentation, a bone block of the canal also can help keep surfaces dry. Dr. Krackow routinely used thrombin- or epinephrine-soaked sponges on the cancellous bone to enhance drying of the marrow contents.
Step 3: Cement Mixing
Although many surgeons likely take this step for granted, it is extremely important to understand the steps that the manufacturer recommends for the brand of PMMA being used. Some recommend that the liquid monomer go first into the vacuum mixer, whereas others recommend that the powder polymer go in first. Some brands of cement do not recommend mixing lot numbers into the same mixer (most surgeons use two large batches of cement for a primary TKA). Attention to detail matters in this step. Regardless of cement type, we always recommend vacuum mixing and the use of a gun to pressurize the cement into the cancellous bone bed.
Step 4: Cement Application Onto Implant Surfaces
It is optimal to make sure application to the metallic implant surfaces is carried out first and that this is done in the first or middle-third time window for the manufacturer’s recommended length of working time after mixing is complete. Biomechanical studies have shown that if cement is applied onto the implant surfaces in the latter third of the recommended working window, bond strength to the implant is significantly decreased. In this earlier working window the cement may have a sheen to it, and it will better bond to the implant surface. It also will stick to gloves at this point. This is one reason we recommend the use of the gun to apply the cement to the implant surface without touching it at this phase ( Fig. 11.2 A–B).
Step 5: Bone Surface Pressurization
There should be a final inspection of the bony surfaces to ensure that there are no marrow contents or irrigation fluid present. While the cement is being prepared, a small metal tip suction placed into the proximal tibial cancellous bone can aid in keeping the cut surface dry and free of marrow contents that can weaken the cement-implant interface (see Fig. 11.1 ). When dry surfaces are confirmed, the keel and then the tibial cut surface are pressurized ( Fig. 11.3 ). We use the spatula included in most mixing sets to push the cement into the cancellous trabeculae as well. The tibial baseplate is then impacted with care to seat the implant in a symmetrical fashion ( Fig. 11.4 ). This is important to keep the bony envelope of the keel preparation intact and also to ensure equal pressurization of the bony surfaces as the implant is completely impacted. The extruded cement is “cut” (not pulled away) circumferentially from the edges of the baseplate with an elevator.