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Sun 1 Oct 2006 12:00 AM

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Joint replacement of the hip and knee

Arthroplasty can offer patients a new lease of life, but who should be referred and when?

It is estimated that musculoskeletal complaints make up approximately 20% of a general practitioner’s workload.

Certainly, for patients aged over 55, osteoarthritis is one of the most common and disabling conditions seen, typically affecting the hip and knee joints.

Although many patients with degenerative joint disease can be treated without surgery, for those who have exhausted conservative methods such as analgesics, anti-inflammatory medications or activity modification, joint replacement has proved to be an effective solution.

Arthoplasty is not new.

For nearly a century, surgeons have been implanting materials into diseased and painful joints to relieve pain.

But recent developments in the field have seen hip and knee implants created from stronger, more durable materials, using more customised designs, and implanted using minimally-invasive techniques.

Consequently, recovery time is shorter and outcomes are vastly improved, making the procedure an option for many more patients who suffer limited function and painful joints.

In the US the number of hip and knee replacements is increasing.

In 2003, there were 220,000 hip and 418,000 knee replacements, representing an increase of 50,000 and 150,000 respectively from 1999, according to the National Center for Health Statistics.

The rise in procedures “parallels the aging of our population,” says Dr Andrew Freiberg, chief of the arthroplasty service at Massachusetts General Hospital, explaining that osteoarthritis remains the most common indication.

But while elderly people are the primary recipients of joint replacements, arthroplasty is not restricted to this age group.

In the US, the average age of hip and knee replacement patients decreased from 82 to 65 and 67 years respectively, between 1999 and 2003.

“Arthroplasty is very successful in allowing people to be functional in their social lives and their work, and people don’t need to wait until they are old to have the procedure,” Freiberg says.

Certainly, congenital or developmental disorders requiring surgery can occur at any age.

Conditions such as Legg-Calve Perthes disease, one of the more common causes of hip pain in the first decade of life, or trauma to the hip, including fractures of the femoral neck, femoral head or dislocation of the hip joint, all have the potential to cause degeneration later in life.

Childhood disorders leading to severe degeneration of the knee are not as common as hip disorders, but conditions such as multiple epiphyseal dysplasia or spondyloepiphyseal dysplasia can lead to premature degeneration of the articular cartilage or to malalignment.

More commonly, young patients suffer degeneration of the knee as a result of an earlier traumatic injury.

Reconstructive surgery is also particularly effective in treating inflammatory conditions such as rheumatoid arthritis or ankylosing spondylitis, which can affect a person at any age.

“Physicians are more comfortable with the concept of giving a younger person a joint replacement rather than putting them in a wheelchair or giving them a narcotic,” says Freiberg.


Candidates for joint replacement

The main indication for total joint arthroplasty is intractable pain that can no longer be successfully controlled by conservative therapy alone.

The aims of the procedure should be pain relief and improvement in function.

Physicians should advise patients who may be considering elective surgery to weigh the potential improvements they might gain from joint replacement against the risks of the procedure.

Like any surgery, arthroplasty carries the risk of infection, blood clots, and complications from anaesthesia.

Specific complications include nerve damage, dislocation after surgery, and wearing out or loosening of the joint over time.

In addition, because the longevity of total joint arthroplasty is limited to 10-20 years, young active patients are not ideal candidates.

Total knee replacement is most commonly performed in people whose knee joint failure is caused by osteoarthritis, but patients suffering from inflammatory arthritis are also good candidates.

Candidates should show radiographic evidence of joint damage, moderate to severe persistent pain that is not adequately relieved by non-surgical methods, and clinically significant functional limitation resulting in diminished quality of life.

Patients with rheumatoid arthritis and other inflammatory joint diseases may need additional therapies to achieve control of disease activity before proceeding with the surgical procedure.

Primary contraindications for total knee replacements are active local or systemic infection and other medical conditions that substantially increase the risk of serious perioperative complications.

Obesity itself is not a contraindication, but obese patients are at increased risk of delayed wound healing and infection.

Relative contraindications include severe peripheral vascular disease and some neurologic impairments.

Total hip replacement can benefit people suffering from a variety of hip problems.

As with total knee arthroplasty, common conditions include osteoarthritis, rheumatoid arthritis, traumatic arthritis and avascular necrosis.

Other abnormalities of the hip joint that could result in a need for a hip replacement include bone tumours that change the shape and congruency of the joint and disrupt blood supply, and Paget’s disease.

Hip arthroplasty candidates are those patients who have disabling pain and functional limitation of the hip(s) in spite of adequate medical therapy.

Symptomatic arthritis and major disruption of the anatomy of the hip are the usual indications.

The use of arthroplasty in patients with malignancy must be evaluated against considerations of life expectancy and possible alternative procedures.

The relative contraindications of youth, obesity, and neurological disease should be weighed against the disability caused by the clinical problem.

Aside from medical emergencies such as myocardial infarction and respiratory failure, or the presence of active hip infection, there are no absolute contraindications.

Advances in arthroplasty

A total hip replacement removes the ball of the upper femur as well as the damaged cartilage from the hip socket and replaces with a metal or ceramic ball that is solidly fixed to a stem inserted into the femur.

The socket is replaced with a metal cup, which is fixed to the acetabulum.

A knee replacement, or resurfacing arthroplasty, is the resurfacing of the femur, tibia and often patella by replacing lost cartilage with metal and plastic.

The supporting extra-articular ligaments and tendons are retained to maintain joint stability and allow mobility.

Arthroplasty technology and techniques have come a long way in recent years, making the procedure simpler and the joints last longer.

Today, metal-on-metal, ceramic-on-ceramic, and cross-linked polyethylene implants result in less friction and lower wear-rates than their metal-on-polyethylene predecessors.

Further, they are expected to last more than ten years.

In addition, the total joint replacement procedure is easier today because of the modularity of implants, allowing surgeons to replace parts of the joint instead of the whole thing.

The success of primary total knee replacement in most patients is supported by more than 20 years of follow-up data showing rapid and substantial improvement in the patient’s pain, functional status, and overall health-related quality of life in about 90% of patients.

Moreover, around 85% of patients are satisfied with the results of surgery.

Data suggest that these improvements in patient-reported outcomes persist in both the short- and long-term studies.

Such evidence led the US National Institutes of Health to conclude in its 2003 consensus development conference, “total knee replacement is a safe and cost-effective treatment for alleviating pain and restoring physical function in patients who do not respond to non-surgical therapies,” adding, “there are few contraindications to this surgery as it is currently used.”

A decade ago, the conference concluded that, based on evidence of that time, “total hip replacement is an option for nearly all patients with diseases of the hip that cause chronic discomfort and significant functional impairment.”

Future developments

“We continue to refine our implantation techniques and post-operative pain management,” says Freiberg.

“Right now we are studying the long-term performance of excellent bearing surfaces such as highly cross-linked polyethylene.

And we’re developing things in the laboratory that might one day allow for more biological solutions.”

“The aim of total joint arthroplasty should be pain

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