Carbon Nanotubes in Acrylic Bone Cement - Biologically Responsive Biomaterials for Tissue Engineering - page 172

relieve pain and to maintain function of the joint [ 73 ]. When replacing a total joint,
the diseased or damaged parts are removed and artificial parts, i.e. prostheses or
implants, are fitted. TJR may be performed on a variety of joints, including hip, knee,
ankle, shoulder, elbow, fingers and wrist. However, hip replacements are by far the
most common, as reported, for example, in Norway between 1987 and 2004 [ 28 ] .
During TJRs, the most commonly used method of implant fixation is with a load
transferring grout-like material, typically an acrylic based bone cement. The major
advantage of these cemented joint replacements is the reduced operation recovery
time: once polymerised the cement is capable of bearing load and offers immediate
stability. However, if the cement mantle becomes loose, the surrounding bone may
resorb and ultimate failure of the implant may occur. Uncemented implants were
introduced to overcome these shortcomings and others, such as cement wear parti-
cles, residual monomer and highly exothermic polymerisation reaction causing cel-
lular necrosis of the surrounding bone. Uncemented implants typically use a
roughened porous surface to promote bone growth around the prosthesis [ 39 ] .
However, the bone cavity produced during the operation needs to be precisely
shaped to ensure that the implant is held initially in place through an interlocking
mechanical fixation between the implant and the bone. It is also essential that the
surrounding bone is healthy to enable this technique to be successful. In addition,
the recovery time is long as the bone is required to regenerate.
A combination of cemented and uncemented implants is also employed and often
termed a “hybrid”. More recently, resurfacing arthroplasty has been introduced,
where less of the bone is removed compared with conventional TJR. Resurfacing
procedures not only require the removal of less bone, but also cause fewer compli-
cations during revision surgeries because the femoral canal remains intact [ 2 ] . On
average, the number of primary arthroplasties in developed nations is increasing
each year [ 28, 43, 65 ] .
Figure 8.1 demonstrates the proportion of cemented, uncemented and hybrid
replacements. The total number of TJRs performed in England and Wales is
significantly greater than Sweden and Norway. In 2004, for example, 48,987 THRs
were recorded in England and Wales, compared to just 13,366 in Sweden and 7,061
in Norway. However, it should also be noted that the population of England and
Wales (approximately 55 m) is significantly greater than Sweden and Norway
(approximately 13 m). This equates to approximately 1 in every 1,100 people in
England and Wales, and 1 in every 650 people in Sweden and Norway.

8.2 Acrylic Bone Cement

8.2.1 Composition

Acrylic bone cement is primarily composed of poly methylmethacrylate (PMMA).
Most commercial acrylic bone cements comprise a two part self-curing acrylic
polymer, usually formulated at a 2:1 powder-to-liquid ratio. These components are