Hip replacement is undoubtedly one of the greatest
achievements of modern medical science. It has mitigated the excruciating pain
and has effectively restored movements to a large extent. Hip joint is a ball
and socket joint. When the hip joint is damaged from arthritis or an injury,
hip replacement surgery may be required. The surgical procedure involves
replacing the diseased cartilage and bone of the hip joint with artificial
ball and stem, called prosthesis, made from chromium and cobalt are commonly
employed for the joint's replacement. They are cemented in the femur central
core with the aid of bony cement known as methylmethacrylate. However
cement-less prosthesis is also used especially in younger patients because it
allows bony ingrowths through its microscopic pores.
Stemmed metal-on-metal (MoM) implants should be
avoided as they have high failure rates. The failure rates are basically due to
metal poisoning and dislocation. The MoM implants can cause the metals to rub
against each other and shed tiny metal particles into the body causing damage
to the soft tissues such as muscles and ligaments. The particles may also enter
the bloodstream causing metal poisoning.
Again, loosening of the prosthesis can result in
dislocation. To avoid this earlier researchers switched to implantation of
large diameter MoM bearing surfaces on stemmed prostheses. However, failure
rates didn't lower. Young adults and women faced greater risks as compared to
So, to find out if MoM bearing surfaces lead to
increased implant survival compared with other bearing surfaces in stemmed hip
replacements, Alison Smith and colleagues from the University of Bristol,
assessed information record of 402,051 hip replacements out of which 31171 were
The recorded information was collected from National
Joint Registry of England and Wales between 2003 and 2011.
The probable failure rates for stemmed MOM
(metal-on-metal) were based upon different sizes of femur head. The researchers
compared the MOM with the prosthesis made from polythene and ceramic.
It was found
that about 6.2 percent of metal-on- metal hip replacements failed within five
years of their implant while only 1.7 percent of metal-on- plastic and 2.3
percent of ceramic-on-ceramic failed.
It was also seen that the failure rate was high with large head size
and less with small head size. Prosthesis made from ceramic-on-ceramic was found to do
better with the large head sizes.
showed higher failure rates in comparison to men with same head size. The failure rate of stemmed MOM in females
was four times greater as compared to other bearing surfaces.
conclusion drawn was -
implant survival rates were obtained with stemmed MOM therefore it should not
be opted for.
Patients with stemmed MOM should be carefully watched and monitored, especially
young females implanted with large sized heads.
Ceramics are found to do well in the large size category.
check-ups are mandatory as a review procedure.
Failure rates of
stemmed metal-on-metal hip replacements: analysis of data from the National
Joint Registry of England and Wales; Alison et al; The Lancet; Online