Hip Joint Replacements - What a GP Needs to Know

Other terms include: Hip arthroplasty, total hip replacement (THR), hip hemiarthroplasty.

It is the surgical replacement of all or part of the hip joint with an artificial device. A total hip replacement is often called a Charnley replacement whilst a hemiarthroplasty in which only the head of femur is replaced and not the socket is called an Austin-Moore. Bipolar hemiarthroplasty uses a femoral prosthesis with an articulating acetabulum. The acetabular cartilage is not replaced. The aim is to decrease the friction and wear between the femoral head prosthesis and the cartilage of the acetabulum.
Metal, polyethylene and ceramic may be used.

Approximately 43,000 hip replacements are performed annually in the UK¹ and the number is rising. Between 1991 and 2001 the number rose by 18% with the number of revisions doubled.² The increase in primary operations was in the over 60s. Revisions were mostly in the elderly. Assuming no change in the age and sex specific arthroplasty rates, the estimated number of hip replacements will increase by 40% over the next 30 years because of demographic change alone. The proportionate change will be substantially higher in men (51%) than women (33%), with a doubling of the number of male hip replacements in those aged over 85. Changes in the threshold for surgery may increase this further-up to double the current number.³

It is essential to ascertain that the hip is the site of the pathology as pain in the hip can originate from other sites like the knee or back and replacing a hip that is not the cause of the pain will be of no value.
THR should not be undertaken lightly in a younger patient as they tend to wear out the prosthesis with longer and more active life. Revision is much more substantial than the primary operation.
This surgery is often conducted on the old and infirm. They need a thorough assessment of fitness for operation including the ability to complete the necessary post-operative rehabilitation. The operation can be conducted under regional rather than general anaesthetic but it is still a long and demanding procedure.
Adequate quadriceps and other muscles around the joint are essential for rehabilitation. Poor muscles and neurological disease around the joint are a contraindication to surgery. So is gross obesity . The patient must be physically and mentally able to take part in rehabilitation.

Total hip replacement is performed where there is disease of both articular surfaces as in osteoarthritis and rheumatoid arthritis . Fractured neck of femur may produce necrosis of the femoral head after disruption of the vascular supply and a hemiarthroplasty is used. It may also be used for a displaced fracture.
In primary care, the question is who to refer to an orthopaedic surgeon for such an operation. The need for immediate admission of a patient with a fractured hip is clear, but there is guidance from Clinical Knowledge Summaries about referral for elective total hip replacement.⁴ Most people with OA of the hip are managed in primary care.

• Encourage mobility
• Give analgesia as required
• If obese, encourage weight loss
• A stick may be helpful. It is held in the hand on the opposite side to the painful hip.

A consensus on indications for surgery include:

• Severe daily pain, and X-ray evidence of joint space narrowing
• Night-time pain in people may well be a clinical marker of severe OA.

Local protocols should be drawn up for criteria for referral when the symptoms impair quality of life. Referral should be based on an explicit scoring system that should be developed locally, and should take into account the extent to which the condition is causing pain, disability, sleeplessness, loss of independence, inability to undertake normal activities, reduced functional capacity or psychiatric illness.

There are a great many different types of device available for joint replacement surgery although they are similar in principle.
The acetabulum can be made of polyethylene with or without a metal backing. The prosthesis can be fixed to bone by cement, spikes, screws, or by bone ingrowth or press fit.
The femoral replacement is made of metal or ceramic and it can be fixed by cement or may be cementless with bone ingrowth or press fit.
Most devices have not been adequately subjected to rigorous assessment in controlled trials to ascertain how they compare. There was a call for a national arthroplasty register in the BMJ in 1996.⁵ A National Joint Registry⁶ now exists.

Minimally invasive surgery for total hip replacement is not so much "keyhole" surgery as with arthroscopy or laparoscopy but it does involve rather less generous access. It requires 2 incisions and fluorscopy to ascertain correct positioning. NICE found little evidence of adequate comparison with standard techniques in terms of outcome. The overall impression was quite positive although it was insistent upon the need for adequate training for such techniques.

The modern trend for discharge between 3 and 5 days means that a considerable amount of care that was formerly in hospital is now in the community.
Rehabilitation before operation and in hospital are important but not given here.
From discharge to 4 weeks the protocol includes:

• Strengthening exercises include seated leg extension, lying hip abduction, standing hip extension and abduction, knee bends and bridging
• Stretching exercises to increase flexibility of hip muscles
• Progression of walking distance
• Progression of independence.

Leg length is measured before operation to prevent postoperative leg-length discrepancy. Measurement is radiological and clinical. Leg lengths can change according to how the prosthesis was fixed or stabilised or depending on how much bone was removed. After operation any leg-length discrepancy must be corrected by appropriate orthoses or heel lifts to prevent abnormal gait or back pain.

Most orthopaedic surgeons like an x-ray of the hip before referral. This is not because the degree of radiological joint destruction correlates with the need for surgery but to ascertain that there is disease of the hip and that the pain has not arisen from elsewhere.
For the elderly and infirm FBC, U&E, LFTs, CXR, ECG and spirometry will all be required but usually arranged by Secondary Care in the pre-operative assessment.

The prosthesis is not like the original hip and has a limited range of movement. There are restrictions that the patients must know:

• Avoid crossing your legs when sitting, standing, or lying
• When sitting, keep your feet about 6 inches (15cm) apart
• When sitting, keep your knees below the level of your hips. Avoid low chairs. A pillow can be used to keep the hips higher than the knees.
• On rising from a chair, slide toward the edge of the chair and then use crutches or walking frame for support
• Avoid bending from the waist. A long-handled shoehorn or a sock aid may be valuable. An extension or "grabber" is helpful for objects that are too low to reach.
• In bed, place a pillow between the legs to keep the joint properly aligned
• A special abductor pillow or splint may be used to keep the hip in correct alignment
• An elevated toilet seat keeps the knees lower than the hips when sitting on the toilet
• Some departments issue a guide to "safe sex" giving positions in which there is not undue stress on the prosthesis. Do not assume that such advice is irrelevant to the over sixties.

Cemented prostheses allow for weight bearing as tolerated from the outset but with cementless or bone-ingrowth devices weight restriction is limited for 6 weeks.

• This is a substantial operation and adequate analgesia is required. This, with reduced mobility and reduced food intake makes constipation a common problem.
• Urinary catheterisation for the operation is routine so there is risk of UTI or retention of urine
• Prophylaxis against thromboembolism is routine but the operation still carries a significant risk. A swollen leg should arouse suspicion of DVT and sudden shortness of breath with or without pleuritic pain or haemoptysis suggests PE. Clinical diagnosis of DVT is about 50% accurate but Doppler examination will improve this.
• Chest infection is a risk
• Dislocation of the hip can occur at any stage but if it occurs it usually does so early. This is best detected by x-ray.
• Wound infection or dehiscence are a possibility
• Infection of the prosthesis is disastrous as it is not possible to cure an infection with a foreign body in situ and it may well be necessary to remove the prosthesis. X-rays can be misleading for diagnosis⁷ but ultrasound⁸ and even MRI scanning⁹ are useful. The metal used is not magnetic.
• The mortality after elective total hip replacement is incredibly low at 0.29% as shown in figures from the Mayo Clinic¹⁰ but after an arthroplasty for a fractured hip the 30 days mortality is nearly 10 times as high at 2.4%.¹¹

About 80% of people get a good result with improved mobility and loss of pain. The prosthesis tends to loosen after 20 years and may need revision but younger patients often wear out the articular surfaces before then.

In 1923, Dr. Marius Smith-Peterson, of Massachusetts General Hospital, used a glass cup to cover and reshape an arthritic femoral head. The original glass cup failed but it led to the development of similarly-shaped implants of strong and durable plastic and then metal materials. Subsequently, metallic femoral devices with anatomically-sized heads and variable femoral stems were developed.

Many surgeons and bioengineers contributed to the concepts, techniques and designs of implants for total hip replacement, but the name most associated with early hip joint replacement is Sir John Charnley. He reported his experience with a steel femoral component and a plastic socket cup in 1961. He also revolutionized the field with the use of the self-curing acrylic cement used to fix the implants into the bone. These advances greatly improved the success rate of total hip replacement. The Charnley concepts of the hip implants are still in use today in large measure. He came from Manchester. He was born in 1911 and died in 1982.

Dr Austin T Moore was an orthopaedic surgeon in South Carolina. He performed one of the first total hip replacements in 1940 but it was the hemi-arthroplasty to which he lent his name. His first did this in 1942. He was born in 1899 and died in 1963.