3147 YLH How to prepare Cement for Joint Replacements

Hello. Bone cement, or Polymethyl Methacrylate, is used for prosthetic fixation in orthopaedics. This video will describe the properties of cement, and the procedure for safe preparation in theatre. There are some important properties of cement that you need to understand to be able to use it safely. Cement is flammable and must be stored under controlled conditions. The cement properties and its constituents differ according to the product. The surgeon must assess for allergies before the operation. The chemicals in the cement produce a strong smell that may affect some people. Caution should be taken to maintain ventilation and to monitor theatre staff exposed to the fumes. Different cements have different setting times depending upon their viscosity, as well as the ambient temperature and humidity of theatre. The two primary components of bone cement are the polymer, a powder, and the monomer, a liquid. Typically, bone cement will also contain a contrast medium and an antibiotic. Cement insertion can cause a temporary drop in the patient’s blood pressure, as well as serious adverse reactions including anaphylactic shock, cardiac arrest, and pulmonary embolism. It is important that the anaesthetist is informed and is present during insertion of bone cement into the patient. In addition to the polymer and monomer, you will also need a mixing bowl, suction tubing and spatula. Because cement is flammable, it must be prepared in a sealed mixing bowl. The use of suction prevents air bubbles forming which act as an impurity, weakening the cement and leading to prosthesis failure. There are three stages to cement preparation; mixing, working and setting. The mixing stage is the period when the polymer and monomer are combined. Empty the powder into the bowl. Unravel the suction tubing and attach to the lid of the mixing bowl. Fix it to the theatre’s vacuum suction system. Carefully snap off the top of the ampoule of liquid monomer, making sure no glass shards fall into the powder. Pour the liquid into the mixing bowl at the same time as starting the timer. Someone in theatre should announce the time at 30 second intervals. Immediately attach the lid firmly to the mixing bowl, and turn on the suction. Mix the cement in one direction at a steady pace for at least 30 seconds. Different cements need to be mixed for different lengths of times but in general, the more you mix the cement, the sooner it thickens and is ready for use. Once the cement has thickened, turn off the suction and remove the lid from the mixing bowl. Use the spatula to assess the quality of the cement. You can see that at this stage the cement is too liquid to be used. The cement is ready once it has a play dough-like consistency and a matte appearance. This takes about 5 minutes. You can touch the cement to judge its consistency; before it is ready it will stick to your gloves. The working stage is when the cement can be manipulated and the prosthesis inserted. During this time the cement will become increasingly more viscous and will generate heat. In the setting stage the cement will harden and set completely. Pressure should be applied to the prosthesis during this time to ensure it sets in the required position.