Bone cement
Encyclopedia
Bone cements have been used very successfully to anchor artificial joints (hip joints, knee joints, shoulder and elbow joints) for more than half a century. Artificial joints (referred to as prostheses) are anchored with bone cement. The bone cement fills the free space between the prosthesis and the bone
and plays the important role of an elastic zone. This is necessary because the human hip is acted on by approximately 10-12 times the body weight and therefore the bone cement must absorb the forces acting on the hips to ensure that the artificial implant remains in place over the long term.
Bone cement chemically is nothing more than Plexiglas (i.e. polymethyl methacrylate or PMMA). PMMA was used clinically for the first time in the 1940s
in plastic surgery to close gaps in the skull. Comprehensive clinical tests of the compatibility bone cements with the body were conducted before their use in surgery
. The excellent tissue compatibility of PMMA allowed bone cements to be used for anchorage of head prostheses in the 1950s
.
Today several million procedures of this type are conducted every year all over the world and more than half of them routinely use bone cements - and the proportion is increasing. Bone cement is considered a reliable anchorage material with its ease of use in clinical practice and particularly because of its proven long survival rate with cemented-in prostheses. Hip and knee
registers for artificial joint replacements such as those in Sweden and Norway clearly demonstrate the advantages of cemented-in anchorage. A similar endoprosthesis is expected to be introduced in Germany in 2009.
co-polymer beads and or amorphous powder, radio-opacifer, initiator) and a liquid (MMA monomer, stabilizer, inhibitor). The two components are mixed and a free radical polymerization
occurs of the monomer
when the initiator is mixed with the accelerator. The bone cement viscosity
changes over time from a runny liquid into a dough like state that can be safely applied and then finally hardens into solid hardened material. The set time can be tailored to help the physician safely apply the bone cement into the bone bed to either anchor metal or plastic prosthetic device to bone or used alone in the spine to treat osteoporotic compression fractures.
During the exothermic
free-radical polymerization process of the cement heats up. This polymerization heat reaches temperatures of around 82-86°C in the body. This temperature is superior to the critical level for the protein
denaturation in the body. The cause of the low polymerization temperature in the body is the relatively thin cement coating, which should not exceed 5 mm, and the temperature dissipation via the large prosthesis surface and the flow of blood.
The individual components of the bone cement are also known in the area of dental filler materials. Acrylate
-based plastics are also used in these applications. While the individual components are not always perfectly safe as pharmaceutical additives and active substances per se, as bone cement the individual substances are either converted or fully enclosed in the cement matrix during the polymerization phase from the increase in viscosity to curing. From current knowledge, cured bone cement can now be classified as safe, as originally demonstrated during the early studies on compatibility with the body conducted in the 1950s.
More recently bone cement has been use in the spine in either vertebroplasty
or kyphoplasty procedures.
. However, it is now known that this monomer (residual monomer) is metabolized
by the respiratory chain and split into carbon dioxide
and water and excreted. Embolisms can always occur during anchorage of artificial joints when material is inserted into the previously cleared thigh bone cavity. The result is intramedullary pressure increase, which can be regulated by the anesthetist.
If the patient is known to have any allergies to constituents of the bone cement, according to current knowledge bone cement should not be used to anchor the prosthesis. Anchorage without cement - cement-free implant placement - is the alternative.
Unfortunately, it is not always possible to avoid revisions. There can also be different reasons for revisions and there is a distinction between septic or aseptic revision. If it is necessary to replace an implant without confirmation of an infection - i.e. aseptic - now the cement is not necessarily removed completely. However, if the implant has loosened for septic reasons, the cement must be fully removed. In the current state of knowledge it is easier to remove cement than to release a well-anchored cement-free prosthesis from the bone site. Ultimately it is important for the stability of the revised prosthesis to detect possible loosening of the initial implant early to be able to retain as much healthy bone as possible.
A prosthesis fixed with bone cement offers very high primary stability combined with fast remobilization of patients. The cemented-in prosthesis can be fully loaded very soon after the operation. The necessary rehabilitation is comparatively simple for patients who have had a cemented-in prosthesis implanted. The joints can be loaded again very soon after the operation, but the use of crutches is still required for a reasonable period for safety reasons.
Bone cement has proven particularly useful because specific active substances, e.g. antibiotics, can be added to the powder component. The active substances are released locally after implant placement of the new joint, i.e. in the immediate vicinity of the new prosthesis and have been confirmed to reduce the danger of infection. The antibiotics act against bacteria precisely at the site where they are required in the open wound without subjecting the body in general to unnecessarily high antibiotic levels. This makes bone cement a modern drug delivery system that delivers the required drugs directly to the surgical site. The important factor is not how much active substance is in the cement matrix but how much of the active substance is actually released locally. Too much active substance in the bone cement would actually be detrimental, because the mechanical stability of the fixed prosthesis is weakened by a high proportion of active substance in the cement. The local active substance levels of industrially manufactured bone cements that are formed by the use of bone cements that contain active substances are approximate (assuming that there is no incompatibility) and are significantly below the clinical routine dosages for systemic single injections.
Bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
and plays the important role of an elastic zone. This is necessary because the human hip is acted on by approximately 10-12 times the body weight and therefore the bone cement must absorb the forces acting on the hips to ensure that the artificial implant remains in place over the long term.
Bone cement chemically is nothing more than Plexiglas (i.e. polymethyl methacrylate or PMMA). PMMA was used clinically for the first time in the 1940s
1940s
File:1940s decade montage.png|Above title bar: events which happened during World War II : From left to right: Troops in an LCVP landing craft approaching "Omaha" Beach on "D-Day"; Adolf Hitler visits Paris, soon after the Battle of France; The Holocaust occurred during the war as Nazi Germany...
in plastic surgery to close gaps in the skull. Comprehensive clinical tests of the compatibility bone cements with the body were conducted before their use in surgery
Surgery
Surgery is an ancient medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, or to help improve bodily function or appearance.An act of performing surgery may be called a surgical...
. The excellent tissue compatibility of PMMA allowed bone cements to be used for anchorage of head prostheses in the 1950s
1950s
The 1950s or The Fifties was the decade that began on January 1, 1950 and ended on December 31, 1959. The decade was the sixth decade of the 20th century...
.
Today several million procedures of this type are conducted every year all over the world and more than half of them routinely use bone cements - and the proportion is increasing. Bone cement is considered a reliable anchorage material with its ease of use in clinical practice and particularly because of its proven long survival rate with cemented-in prostheses. Hip and knee
Knee
The knee joint joins the thigh with the leg and consists of two articulations: one between the fibula and tibia, and one between the femur and patella. It is the largest joint in the human body and is very complicated. The knee is a mobile trocho-ginglymus , which permits flexion and extension as...
registers for artificial joint replacements such as those in Sweden and Norway clearly demonstrate the advantages of cemented-in anchorage. A similar endoprosthesis is expected to be introduced in Germany in 2009.
Composition
Bone cements are provided as two-component materials. Bone cements consist of a powder (i.e., pre-polymerized PMMA and or PMMA or MMAMethyl methacrylate
Methyl methacrylate is an organic compound with the formula CH2=CCOOCH3. This colourless liquid, the methyl ester of methacrylic acid is a monomer produced on a large scale for the production of poly .-Production:...
co-polymer beads and or amorphous powder, radio-opacifer, initiator) and a liquid (MMA monomer, stabilizer, inhibitor). The two components are mixed and a free radical polymerization
Radical polymerization
Free radical polymerization is a method of polymerization by which a polymer forms by the successive addition of free radical building blocks. Free radicals can be formed via a number of different mechanisms usually involving separate initiator molecules...
occurs of the monomer
Monomer
A monomer is an atom or a small molecule that may bind chemically to other monomers to form a polymer; the term "monomeric protein" may also be used to describe one of the proteins making up a multiprotein complex...
when the initiator is mixed with the accelerator. The bone cement viscosity
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
changes over time from a runny liquid into a dough like state that can be safely applied and then finally hardens into solid hardened material. The set time can be tailored to help the physician safely apply the bone cement into the bone bed to either anchor metal or plastic prosthetic device to bone or used alone in the spine to treat osteoporotic compression fractures.
During the exothermic
Exothermic reaction
An exothermic reaction is a chemical reaction that releases energy in the form of light or heat. It is the opposite of an endothermic reaction. Expressed in a chemical equation:-Overview:...
free-radical polymerization process of the cement heats up. This polymerization heat reaches temperatures of around 82-86°C in the body. This temperature is superior to the critical level for the protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
denaturation in the body. The cause of the low polymerization temperature in the body is the relatively thin cement coating, which should not exceed 5 mm, and the temperature dissipation via the large prosthesis surface and the flow of blood.
The individual components of the bone cement are also known in the area of dental filler materials. Acrylate
Acrylate
The acrylate ion is the ion of acrylic acid.Acrylates are the salts and esters of acrylic acid. They are also known as propenoates ....
-based plastics are also used in these applications. While the individual components are not always perfectly safe as pharmaceutical additives and active substances per se, as bone cement the individual substances are either converted or fully enclosed in the cement matrix during the polymerization phase from the increase in viscosity to curing. From current knowledge, cured bone cement can now be classified as safe, as originally demonstrated during the early studies on compatibility with the body conducted in the 1950s.
More recently bone cement has been use in the spine in either vertebroplasty
Vertebroplasty
Vertebroplasty and kyphoplasty are similar medical spinal procedure where bone cement is injected through a small hole in the skin into a fractured vertebra with the goal of relieving the pain of vertebral compression fractures...
or kyphoplasty procedures.
Important information for the use of bone cement
What is referred to as bone cement syndrome is described in the literature. For a long time it was believed that the incompletely converted monomer released from bone cement was the cause of circulation reactions and embolismEmbolism
In medicine, an embolism is the event of lodging of an embolus into a narrow capillary vessel of an arterial bed which causes a blockage in a distant part of the body.Embolization is...
. However, it is now known that this monomer (residual monomer) is metabolized
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
by the respiratory chain and split into carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
and water and excreted. Embolisms can always occur during anchorage of artificial joints when material is inserted into the previously cleared thigh bone cavity. The result is intramedullary pressure increase, which can be regulated by the anesthetist.
If the patient is known to have any allergies to constituents of the bone cement, according to current knowledge bone cement should not be used to anchor the prosthesis. Anchorage without cement - cement-free implant placement - is the alternative.
Revisions
Revision is the replacement of a prosthesis. This means that a prosthesis previously implanted in the body is removed and replaced by a new prosthesis. Compared to the initial operation revisions are often more complex and more difficult, because every revision involves the loss of healthy bone substance. Revision operations are also more expensive for a satisfactory result. The most important goal is therefore to avoid revisions by using a good surgical procedure and using products with good (long-term) results.Unfortunately, it is not always possible to avoid revisions. There can also be different reasons for revisions and there is a distinction between septic or aseptic revision. If it is necessary to replace an implant without confirmation of an infection - i.e. aseptic - now the cement is not necessarily removed completely. However, if the implant has loosened for septic reasons, the cement must be fully removed. In the current state of knowledge it is easier to remove cement than to release a well-anchored cement-free prosthesis from the bone site. Ultimately it is important for the stability of the revised prosthesis to detect possible loosening of the initial implant early to be able to retain as much healthy bone as possible.
A prosthesis fixed with bone cement offers very high primary stability combined with fast remobilization of patients. The cemented-in prosthesis can be fully loaded very soon after the operation. The necessary rehabilitation is comparatively simple for patients who have had a cemented-in prosthesis implanted. The joints can be loaded again very soon after the operation, but the use of crutches is still required for a reasonable period for safety reasons.
Bone cement has proven particularly useful because specific active substances, e.g. antibiotics, can be added to the powder component. The active substances are released locally after implant placement of the new joint, i.e. in the immediate vicinity of the new prosthesis and have been confirmed to reduce the danger of infection. The antibiotics act against bacteria precisely at the site where they are required in the open wound without subjecting the body in general to unnecessarily high antibiotic levels. This makes bone cement a modern drug delivery system that delivers the required drugs directly to the surgical site. The important factor is not how much active substance is in the cement matrix but how much of the active substance is actually released locally. Too much active substance in the bone cement would actually be detrimental, because the mechanical stability of the fixed prosthesis is weakened by a high proportion of active substance in the cement. The local active substance levels of industrially manufactured bone cements that are formed by the use of bone cements that contain active substances are approximate (assuming that there is no incompatibility) and are significantly below the clinical routine dosages for systemic single injections.