What is a hip replacement?
The human hip comprises a ball and socket joint, with the rounded end of the thigh bone (called the femoral head) moving within a rounded socket in the hip (called the acetabulum). Both of these are covered in a slippery cartilage, which makes the joint move smoothly, protects the bone beneath, and absorbs the shock of movement.
When a person develops arthritis this cartilage wears away, making the joint less mobile. Eventually, it will wear away enough to expose the bone beneath causing a great deal of discomfort and pain, and seriously restricting mobility.
A hip replacement operation substitutes the worn out ball and socket joint with artificial components. This usually involves replacing the whole of the end of the thigh bone and creating a new socket. The artificial components are either cemented in place or situated in a way that encourages bone to grow around, and anchor onto, them. Occasionally the implants are held in place with screws.
Around 50,000 hip replacements are carried out in the UK every year, with excellent results in terms of increased mobility and reduced pain.
This article on hip replacement surgery is written by Jackie Griffiths, a freelance journalist who writes health, medical, biological, and pharmaceutical articles for national and international journals, newsletters and web sites.
Types of hip replacement
The most common form of hip replacement comprises a
metal ball and a plastic socket. However, these do have known problems,
so alternatives, such as ceramic joints have also been developed.
Many surgeons also offer hip resurfacing, an operation
in which just the diseased or damaged surfaces of the joint are removed,
and replaced with metal plates. This has the advantage that less of the
original, often healthy, bone needs to be removed.
Why do they wear out?
Plastic socket hip replacements wear out very slowly –
at around 0.1mm per year. This in itself is not enough to cause
problems, however, the plastic fragments this creates are absorbed by
the surrounding tissue causing inflammation and eventually loosening the
As the patient grows older, the thinning of the
surrounding bones, through processes such as osteoporosis, also causes
the joint to slip out of alignment.
In around 10% of all hip replacement operations, further
surgery is needed between ten and fifteen years after the initial