2. INTRODUCTION
Bone cement chemically is nothing more than
Plexiglas (i.e. poly methyl methacrylate or PMMA).
PMMA was used clinically for the first time in the
1940s in plastic surgery to close gaps in the skull.
The bone cement fills the free space between the
prosthesis and the bone and plays the important
role of an elastic zone.
3. COMPONENTS
Bone cements consist of two primary components:
A powder consisting of copolymers based on the
substance poly methyl methacrylate (PMMA), and a
liquid monomer, MMA. These two components are
mixed at an approximate ratio of 2:1 to form a poly
methyl methacrylate cement.
Exposure to light or high temperatures can cause
premature polymerization of the liquid component.
Hydroquinone therefore is added as a stabiliser or
inhibitor to prevent premature polymerization
4. In order to make the cement radiopaque, a contrast
agent is added. Commercially available cements use
either zirconium dioxide (ZrO2) or barium sulphate
(BaSO4). Zirconium dioxide is one hundred times less
soluble than barium sulphate and has less effect on
the mechanical properties of the cement.
During the exothermic free-radical polymerization
process, the cement heats up. This polymerization
heat reaches temperatures of around 82–86 °C 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.
5. POLYMERIZATION
When the polymer powder and monomer liquid meet, the
polymerization process starts. During polymerization of
the monomer, the original polymer beads of the powder
are bonded into a dough-like mass. The mass hardens
approximately 7-15 minutes after the start of mixing,
depending on temperature.
The polymerisation process can be divided into four
different phases: mixing, waiting, working and hardening
phase.
• MIXING PHASE
In the mixing phase, the cement should be mixed
homogeneously, minimising the number of pores. Vacuum
6. • WAITING PHASE
During this phase, the cements achieve a suitable viscosity
for delivery of bone cement. The cement is still a sticky
dough.
• WORKING PHASE
The working phase is the period during which the cement
and the implant can be introduced with ease. The cement
must not be sticky, and its viscosity should be suitable for
application. If viscosity is too low, the cement may not be
able to withstand the bleeding pressure and prevent blood
from entering the cement.
• HARDENING PHASE
During this phase, the cement hardens and sets
completely. Hardening is influenced by the cement
7. PROPERTIES
• VISCOSITY
During the reaction, the cement viscosity increases, slowly
at first, then
later more rapidly.
Viscosity affects the
following:
• Mixing behaviour
• Penetration into
cancellous bone
• Resistance against
bleeding
8. Bone cements may be divided into two kinds: low
viscosity and high viscosity.
Low viscosity: These cements have a long-lasting
liquid, or mixing phase, which makes for a short
working phase. As a consequence, application of
low viscosity cements requires strict adherence to
application times.
High viscosity: These cements have a short mixing
phase and loose their stickiness quickly. This
makes for a longer working phase, giving the
surgeon more time for application.
9. Mechanical properties
The bone cement is subjected to high mechanical
stress in the body. In vivo, the biomechanical
situation is rather complex, involving different types
of loading (bending, compression, shear), which
must be tested. The international standard ISO 5833
describes the methods for determining compressive
strength, bending strength and bending modulus.
As the cemented implant is subjected to not only
static load but also dynamically alternating loads,
the fatigue properties of the cement affect survival
of the implant.
11. DIGITAL
All antibiotic bone cements can be applied digitally. The cement
is mixed thoroughly but carefully to minimize the entrapment of
air. Once dough is formed the surgeon should wait until the
cement no longer adheres to the glove and the surface has
become dull as opposed to shiny. The cement can then be taken
into gloved hands and kneaded thoroughly. It is vital that
premature insertion of cement is avoided as this may lead to a
drop in the patient's blood pressure. Importantly, this stage will
occur at different times for different cement types.
The time of cement application and prosthesis insertion is at the
discretion of the surgeon and will depend upon the surgical
procedure used. In general, implant insertion should be delayed
until the cement has developed a sufficient degree of viscosity to
resist excessive displacement by the implant. However, implant
12. Syringe application
Antibiotic bone cements may be applied using a suitable
cement gun and syringe. The surgeon should use their
experience to judge when the cement has reached an
appropriate viscosity to be extruded. This will not occur until
after the cement has formed dough. A small amount of
cement should be extruded from the syringe and visually
assessed to ensure that the surface of the cement appears
dull and excessive flow under gravity has ceased.
Prior to extrusion, it is recommended that a cement restrictor
be inserted, at the required depth into, the prepared bone
cavity. Introduction of bone cement into the prepared cavity
should be carried out in a retrograde fashion. Once the cavity
13. APPLICATION AREAS
Application Areas include information on hip, knee and spine
replacement.
APPLICATION OF BONE CEMENT IN TOTAL HIP REPLACEMENT:-
FEMUR BONE FIXATION
Bone cement
80 grams of cement is normally sufficient for stem fixation.
14. Cement mixing
The cement is mixed and collected in the cartridge under
vacuum. The cartridge is then positioned in the cement gun
Pulse lavage
Make a final pulse lavage before injecting the cement.
15. Cement delivery
Use a long nozzle in order to reach the
distal femoral plug.
Inject the cement in retrograde
fashion, letting the cement gun work
its own way out of the femur.
Delivery of cement should never be
done when the cement is in low
viscosity stage. Normally wait
approximately 3 minutes (depending
on type of cement used) after start of
mixing.
Apply the proximal seal and
pressurize the cement.
16. Distal centralizer
Apply the distal centralizer to the
stem. The centralizer should be
used to avoid malposition of the
stem in both planes.
Introduction of the stem
Gently introduce the stem and hold in place
until the cement has polymerized.
Even cement mantle
With the stem in final position, you
should have a 2 - 3 mm cement mantle
around the stem and approximately 10
mm between the tip of the stem and the
plug.
This will yield optimal stress
distribution.
18. • Hypotensive episodes and cardiac arrest have been reported
during cement insertion.
• Pressurization and thorough cleaning of the bone with
expulsion of bone marrow has been associated with the
occurrence of pulmonary embolisms, and this risk has been
found to be increased in patients with highly osteoporotic
bone and patients diagnosed with femoral neck fracture.
• Reaming of the marrow cavity can have similar effects on
mean arterial pressure as the introduction of the bone
cement. Marrow cavities should be vented when the cement is
introduced digitally.
• The premature insertion of bone cement may lead to a drop
in blood pressure, which has been linked to the availability of
19. • This drop in blood pressure, on top of hypotension induced
either accidentally or intentionally, can lead to cardiac
arrhythmias or to an ischaemic myocardium.
• However, according to a report, the possible risk of death
associated with the use of cemented implant is confined to
early postoperative and perioperative period.
• The hypotensive effects of methyl methacrylate are
potentiated if the patient is suffering from hypovolaemia.
20. The most frequent adverse reactions reported with acrylic bone
cements are:
• Transitory fall in blood pressure.
• Elevated serum gamma-glutamyl-transpeptidase (GGTP) upto
10 days post-operation.
• Thrombophlebitis.
• Loosening or displacement of the prosthesis.
• Superficial or deep wound infection.
• Trochanteric bursitis.
• Short-term cardiac conduction irregularities.
• Heterotopic new bone formation.
• Trochanteric separation.
22. • One of the major drawbacks of bone cement in joint
replacement is cement fragmentation and foreign body
reaction to wear debris, resulting in prosthetic loosening and
periprosthetic osteolysis.
• The production of wear particles from roughened metallic
surfaces and from the PMMA cement promotes local
inflammatory activity, resulting in chronic complications to
hip replacements.
• Histologically, a layer of synovial like cells which line the
bone cement interface supported by a stroma containing
macrophages and wear particles, has been described in loose
prostheses.
• A third of dense fibrous tissue contains polymethyl
23. • Activated macrophages express cytokines
including interleukin-1, interleukin-6 and
tumour necrosis factor alpha, which mediate
periprosthetic osteolysis.
• Bone cement generates heat as it cures and
contracts and later expands due to water
absorption.
• It is neither osteoinductive nor osteoconductive
and does not remodel.
• The monomer is toxic and there is a potential
for allergic reactions to cement constituents.
