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.
What are the different types of 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 joint.
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 treatment.
How long do they last?
How long an artificial hip will last is more related to the individual than to the age of the implant and depends on a number of factors, including:
- The activity level of the patient
- The age of the patient
- The quality of the underlying bone
- The design of the implant
- The original cause of the hip degeneration
- The skill of the surgeon
Studies show that the average hip replacement (metal and plastic) lasts around ten to fifteen years, although in some cases they can last up to a quarter of a century.
- In patients aged over seventy, 95% of hip replacements last ten to fifteen years
- In patients aged forty to sixty, only 70-80% of hip replacements last beyond eight years
- In one Swedish study of patients under fifty-five years of age, the failure rate for hip replacement was 19% at ten years, rising dramatically to 67% at sixteen years
Ceramic hip replacements are expected to have a much longer lifespan; however the technology is relatively new so there is little data to support this.
Metal resurfacing has a much higher endurance, especially with younger patients, with 96% surviving at seven years in patients aged forty to sixty. However, metal resurfacing does have a higher initial failure rate than for a total hip replacement.
Conclusion - How long will it last?
Since younger patients tend to have more active lifestyles their hip replacements tend to wear out much quicker than older patients. For this reason, many surgeons will try to delay a hip replacement for as long as possible in the hope that it will last for the rest of the patient’s natural life.
Unfortunately, this means that the group that needs hip replacement surgery most to maintain their active lifestyle, are the least likely to receive it.
For this reason, many younger patients are putting their faith in the expected longevity of ceramic hip replacements, even though these are as yet unproven. It is up to each individual, working with their consultant and surgeon, to decide on the best option for their age, lifestyle, and condition.
For older patients, traditional hip replacements represent a highly successful and reliable treatment with few complications.