3147 YLH How to prepare Cement for Joint Replacements
0 (0 Likes / 0 Dislikes)
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.