In 1947, Shiers, a British Orthopaedic Surgeon, developed the first true knee joint replacement,
which was a simple hinge joint, pivoting around a central
pin. From this early design, other types of knee prostheses
evolved, but they all functioned in much the same way as a
basic hinge joint, with no attempt made to replicate the
complex motion of a normal knee. This was primarily because there
was little knowledge of the way in which a physiologically
normal knee moves.
In most types of total knee
replacement devices there are four parts:
a metal "femoral" component which is
placed in the lower end of the femur
a metal "tibial" component which is
placed on the upper end of the tibia
a plastic "insert" which is placed
between the two metal components and effectively replaces
the cartilage
a plastic "patella" component which
is sometimes (though not always) used to resurface the back
of the knee cap
Today, there are three main types of knee
replacement devices:
Fixed Bearing Total Knee Systems:
both
sides of the knee (the inside or medial compartment and
outside or lateral compartment) are replaced in a single
total knee replacement procedure, and with this type of
device the plastic insert is fixed in place.
Mobile Bearing Total Knee Systems:
similar
to that above, but with a plastic insert which is able to
move within the joint, allowing more natural and complex knee movements
and possibly creating less wear.
Unicompartmental knee systems:
this
type of replacement is used where disease is limited to one
compartment in the knee, and is effectively a “half-knee”
replacement
Mobile Bearing Knee Replacement
Mobile bearing knees use a plastic insert
which is allowed to move within the artificial knee joint,
allowing a more natural movement of the knee, and reducing
wear of the plastic insert in higher demand patients. These
devices are thus designed for use in the younger, more
active patient. The design of the Rotaglide Mobile Bearing
Knee allows the plastic insert to both rotate and to move
backwards and forwards. Introduced in 1988, it has the longest clinical history
of this type of knee and may be considered as a fourth
generation knee replacement. It is specifically intended to
provide more normal movement for a replaced knee than the
older, fixed bearing designs and offers the more active
patient the possibility of a long lasting, high demand knee
replacement. Mobile bearing knee replacements are becoming
increasingly widely used as the surgical community accepts
the benefits that these devices are likely to provide.
Virtually every orthopaedic device manufacturer has
introduced a mobile bearing knee within the last five years,
recognising the need to be able to offer younger patients a
long-term solution for their joint disease. Knee
replacements in the 21st century will increasingly be of the
mobile bearing type and the Rotaglide Knee is a clinically
proven and extensively tested design, which has been shown
to have excellent mid-term results, with 99% survivorship at
up to 12 years.
Unicompartmental Knee Replacement
In some patients, disease affecting the
knee joint is limited to one side (or compartment) of the
knee. In the past, a total knee replacement meant that
although the damaged side was being replaced, so was the
other side, which was not affected by the disease. With the
introduction of unicompartmental (or half-knee) replacement
systems, it became possible for surgeons to be more
conservative in their treatment of selected patients, and to
only replace the damaged compartment within the knee. This
type of procedure is considered more conservative than total
knee replacement, since the unaffected side of the knee is
left in place. Moreover, new operative techniques allow this
procedure to be carried out through a much smaller incision
- so-called minimally invasive techniques - which result in
less tissue damage and faster post-operative recovery.
Fixed Bearing Knee Replacement
Fixed bearing knees have been the standard
total knee replacement for many years. In these devices, the
plastic insert is fixed in place on the tibial baseplate.
Fixed bearing knees can and do provide excellent long-term
results, particularly in less active patients. However, as
the average age of knee replacement patients decreases,
younger, fitter patients will place greater demands on their
replaced knees than older, less active patients.
