Conventional Total Hip Replacement (THR) is a very
successful procedure for the treatment of arthritis of
the hip, a condition causing considerable pain and loss
of movement. The hip is a ball and socket joint, which
allows the upper leg to move from side to side, back to
front, and to rotate. The joint is made up of the head
of the femur (the ball), which fits into the acetabulum
(the socket). In the healthy hip, both the head of the
femur and the acetabulum are covered with cartilage, a
smooth surface which allows the joint to move freely.
The
very earliest THR, in 1938, involved an implant with
both surfaces made from metal – known as a
metal-on-metal bearing. During the 1950’s and early
1960’s, a number of surgeons developed hip implants
using this type of bearing, although these were not
resurfacing devices. Many of these designs were not very successful,
but the implants that did not loosen early have
generally lasted very well.
In
the early 1960's, a British Surgeon, Sir John Charnley,
developed a new type of THR which is still in use today.
This procedure involves cutting the worn head off the
femur and replacing it with a metal ball and stem in the
shaft of the femur, and a plastic cup in the pelvis, as
shown in the diagram below. Both are typically anchored
to the bone by “bone cement”. This has become a very
common surgical procedure, with some 50,000 hip
replacements* being carried out in the UK every year –
about 200 every working day.
The
main problem with Total Hip Replacement using
polyethylene cups is that the polyethylene gradually
wears, eventually reaching a point where the replacement
joint no longer functions properly. In
older people, with a lower activity level, this may not
happen for 20 or more years, but in younger, more active
patients, this may happen much sooner.The
other problem is that although the plastic itself is inert (well tolerated by the body)
as the metal rubs against the plastic, tiny particles of
the plastic are worn away. This plastic debris can cause an
irritation. As the particles get between the bone and
the artificial joint, this irritation causes surrounding
bone to be absorbed by the body, leading to loosening of
the artificial joint.
To
overcome these problems in younger, more active patients
requiring hip replacement, a different type of implant
was needed and this was the reason Corin developed Hip
Resurfacing.
