A material made by mixing PMMA powder with liquid methyl methacrylate and polymerizing it in the body to fix artificial joints to bone. It fixes them not by adhesion but by filling the gap and interlocking mechanically.
Japanese name: 骨セメント
Bone cement appears in 2 practice questions across 1 topic, including Biomaterials.
Field: Biomaterials
Bone cement became widespread after Charnley introduced it around 1960 for fixing artificial hip joints. It is packed into the bone while still soft just after mixing, and when a stem or other component is inserted, the cement flows into the gaps between the spongy irregularities of the bone and the implant and hardens. Its role is not to bond chemically but to penetrate the irregularities, interlock mechanically and transfer load to the bone over a large area, which is why it is likened to a grout that fills gaps. Being able to bear weight right after surgery is a major advantage over cementless fixation.
The powder consists mainly of PMMA particles and contains the initiator benzoyl peroxide and a radiopacifier, barium sulfate or zirconia, which makes the cement visible on X-ray images. The liquid is methyl methacrylate monomer with an aromatic amine accelerator that lets the reaction proceed at room temperature and a stabilizer that prevents polymerization during storage. When the two are mixed, the accelerator decomposes the initiator to form radicals, the monomer polymerizes and binds the powder particles together, and the whole mass hardens. The time to pass from liquid through a dough-like state to hardening changes greatly with temperature, so the temperature of the operating room and of stored materials is controlled.
The properties of bone cement are set by ISO 5833 and ASTM F451, which require, among other things, a maximum exotherm temperature in the test mold of no more than 90 °C, a setting time of 5–15 minutes (ASTM F451) or 3–15 minutes (ISO 5833), and a compressive strength of at least 70 MPa; ISO 5833 also specifies a bending strength of at least 50 MPa and a bending modulus of at least 1800 MPa. PMMA is strong in compression but weak in tension and fatigue, and air bubbles trapped during mixing become origins of fatigue cracks. Mixing under vacuum to reduce bubbles is therefore widely used.
Some bone cements contain antibiotics to prevent infection and are used, for example, in revision surgery for infected artificial joints. For spinal compression fractures caused by osteoporosis, there is also a treatment that injects bone cement into the collapsed vertebral body to relieve pain. On the other hand, in long-term use, loosening at the interfaces between cement and bone or implant, cracking of the cement by fatigue and bone resorption caused by wear debris become problems. A complication is also known in which the pressure of packing drives monomer and marrow fat into blood vessels and lowers blood pressure. For these reasons, whether to use cement is decided according to the patient's age and bone condition.
Answer: C. When PMMA powder is mixed with the liquid monomer, it polymerizes at room temperature and hardens while releasing heat
Bone cement is used by kneading PMMA powder with liquid methyl methacrylate (the monomer) during surgery. Addition polymerization by radicals generated from the initiator proceeds at room temperature, and the cement hardens in around 10 minutes. This polymerization is exothermic, and the points to watch are thermal damage to surrounding tissue from the temperature rise during hardening, residual monomer, and polymerization shrinkage. Bone cement does not bond chemically; as a filler that fills the space between the irregular bone surface and the implant and interlocks mechanically, it distributes and transfers the load to the bone. PMMA is a thermoplastic, but its melting temperature is far too high for use inside the body, so it is introduced as monomer and polymerized in the body.
No. Bone cement does not bond chemically to bone or implant but fixes them by filling the gaps and interlocking with the irregularities. Washing blood and fat off the bone surface and pressurizing the cement so that it penetrates deep into the irregularities therefore determine the strength of fixation.
Polymerization is exothermic, and in the test mold the temperature rises considerably, but in the body the cement layer is thin and cooled by blood flow, so the peak is lower. Even so, the surrounding bone cells may be damaged, so it is recommended not to make the cement layer thicker than necessary.
Calcium phosphate cement hardens when its powder is mixed with an aqueous solution and turns into apatite or other phases by a hydration reaction; it bonds to bone and may be replaced by bone over time. Its strength is lower than that of PMMA bone cement, however, so it is used not for fixing artificial joints but for filling bone defects that carry little load.
Bone cement is used by kneading PMMA powder with liquid methyl methacrylate (the monomer) during surgery.
Which statement about PMMA (polymethyl methacrylate) bone c…Being resorbed in the body and replaced by bone is a property of bioresorbable materials such as β-TCP, and fixation with bone cement is a different method called cemented fixation.
Which statement correctly describes osseointegration, as th…Osseointegration Passivity Hydroxyapatite Biocompatibility Biodegradable polymer Stress shielding Superelasticity β titanium alloy