Bone cement has retained a prime position in the field of orthopedic and trauma surgeries due to its extensive use in successful implant fixation during joint replacement surgery. They are the biomaterials that can be employed to fix previously implanted artificial prostheses especially if the area around them gets infected.
Bone cements are applied in liquid form due to convenience followed by hardening which may take some time. The addition of antibiotics such as gentamycin into the bone cements can be used to treat infections caused by Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans.
PMMA-based implanted bone cement visible within the joints
Applications of bone cement technology
Bone cements have vast applications in the field of orthopedic surgery. Its affordable cost and longer retention with minimal need of fixation and refilling makes it a priority for the physicians as well as for the patients themselves. Some of its uses are as given below:
• Bone cement can be used for fixing the implants during joint replacement surgery.
• It also finds application in anchoring the artificially employed joints i.e. hip joints, elbow joints, shoulder and knee joints.
• With recent advancements, bone cements can be used to deliver drugs to the joints. Antibiotics, for instance, are one of the medications frequently needed for the treatment of infections where artificial prosthetics are implanted. Bone cements, when mixed with such drugs, can transfer it to the target site where the antibiotics heal the infections upon release.
• Bone cement can act as a support material in people with inherently poor bone quality or in those with certain bone diseases such as osteoporosis, osteoarthritis, and osteomalacia.
• Calcium phosphate based bone cement can be employed in filling the fractured bones as its retention period, like other bone cements, is between 10 to 20 years.
Another key advantage for using bone cements is the affordability of the procedure. Without incorporated antibiotics, a standard dose of bone cements cost between $ 40 to 185 USD while with antibiotic addition, the total expense per dose jumps between $ 117 to 663 USD.
Chemistry of bone cements
Polymethyl methacrylate, abbreviated as PMMA, is one of the chemical compounds present in bone cement. It is referred to as a ‘cement’ because of its ability to connect and bond two bones together. PMMA is a biocompatible material prepared by combining liquid MMA monomers, the liquid phase, with powdered MMA styrene co-polymers, the polymeric phase, followed by polymerization. Hydroquinone, an inhibitor, is also added to stop the mixture from premature polymerization although it is optional to add a coloring agent such as chlorophyll. PMMA is applied on one bone and the implant is placed onto it making it a space-filler material sandwiched between two surfaces. It does not itself have adhesive properties, rather it interlocks the ends of two surfaces together resulting in a strong connection.
Other chemical materials such as calcium phosphate cement (CPC) and glass polyalkenoate cement (GPC) are also employed in the dental, bone as well as cranial surgeries.
Step-by-step process of bone cement preparation: (a) transfer of ingredients, (b) mixing, (c) implantation, and (d) shows the bone after the bone cement application
Advanced cement mixing system by Stryker
Advanced cement mixing and delivery system manufactured by Stryker is one of the finest bone cement blending machines. It provides easy loading quick mixing and undemanding transfer of chemical compounds. The blending is done using an ergonomic handle with or without the application of a vacuum in nearly no time i.e. within 3 to 4 minutes. The device has a built-in charcoal filter along with a lockdown lid both of which help contain the release of harmful fumes of bone chemicals such as polymethacrylate (PMMA) into the surrounding air thus resulting in reduced exposure of the working staff.
The blade biasing system with its dual blade design deeply scrapes the bowl thus eliminating any chances of material wastage. The machine also has 2:1 gear ratio for blades which enables quicker mixing. The instrument also holds a three-batch capacity. Paddling is efficient and smooth making almost no noise at all as the mixing blades provide unmatched mixing quality. After the completion of homogeneous mixing, the obtained cement product is less porous, a property which makes it stronger as well as increases its retention time in the body.
Advanced cement mixing system by Stryker: Image showing the mixer, syringes, and the bone cement materials
Drug-incorporated bone cements
Artificial prosthetics are particularly prone to bacterial infections as the defense system of the body treats the implanted object as a foreign body. This weakens its protection resulting in the start of an infection by an invading microorganism like Staphylococcus aureus, Pseudomonas aeruginosa and Candida albicans. To treat such a condition, bone cements can be charged with antibiotics along with other excipients such as essential oils, graphene and gold or silver nanoparticles. This way, they perform dual function i.e. act as drug delivery systems as well as anchoring materials. Upon application, the drug seeps out of the cement and clears out the affected area from pathogens.
Preparation of antibiotic incorporated bone cement
How bone cement is applied?
Bone cement can be applied using various methods which vary with the change of bone cement material, the purpose as well as the place of application.
• All the ingredients are blended together until a homogeneous dough is obtained with minimal air entrapment.
• Once the dough is dry enough that no sticking is visible with the surfaces, it should be kneaded by hand. Application of a dough with runny consistency rather than a viscous one can increase its chances of getting leached into the surrounding areas.
The required consistency of the bone cement mixture
• Application is done by hand. All the open surfaces should be filled properly.
• In case of antibiotic-incorporated bone cement, extrusion by syringe is preferred. In this case, the dough must have the ideal viscosity to flow out of the nozzle. However, the dough is ready to be applied only when its surface becomes dull and the initial shine which appeared after mixing subsides.
• Once filling completes, an adequate amount of pressure is applied until the dough hardens giving a firm texture indicating higher stability. The amount of this pressure must be greater than the normal blood pressure. Otherwise, the filling will be pushed out of the bone.
Bone cement application with the help of a syringe
What can go wrong?
Although bone cements are a good and safe way of fixing bone issues, it may come with some side effects too. However, their severity may vary from patient to patient.
• Pain in the treated area
• Hypotension (low blood pressure)
• Hypoxia (decreased oxygen level in the body)
• Thrombophlebitis (formation of blood clots in the body which may block circulation along with inflammation)
• Irregularities in the heart beat (short-term)
• Disturbed heart rhythm
• Displacement of the applied prosthetic
• Sepsis (infection at the operation site)
• Trochanteric bursitis (inflammation of bursa, a fluid-filled sac near the hip joint)
• Heterotropic new bone formation (formation of bone material in the soft tissues of the body where bones are not supposed to be present)
• Cardiac arrest
• Foreign body reaction
In case of any of the above side effects after a bone cement application surgery which have not subsided after a few hours, it is advised to contact your health care provider for further assistance.
The application of bone cement is one of the important techniques in the field of orthopedic and dental surgery. It enables the bone implants to stay in place for a time span exceeding a decade. Bone cements are both easy to formulate and undemanding to apply. Moreover, their cost and durability make them superior to other available procedures. Among the easily available machines, cement mixing system by Stryker is a smart choice as this universal mixer quickly prepares the dough of bone cement safely and conveniently with or without drugs and other additives. Additionally, the cost and efficiency of the method is also attractive feature for those looking for a rapid solution for their bone issues.