Hip joint replacements

What is a hip joint replacement?

Hip joint replacement (hip arthroplasty) is the surgical replacement of all, or part, of the hip joint with an artificial device. It can allow considerable improvement in pain and disability for the patient and has become one of the most successful innovations in modern medicine.¹

The procedure can be either a total hip arthroplasty or a hemiarthroplasty.

Total hip arthroplasty

The articular surfaces of the femur and the acetabulum are replaced. This can be:

• Conventional total hip arthroplasty - replacement of the femoral head and neck.

• Resurfacing total hip arthroplasty - replacement of the surface of the femoral head.

Hemiarthroplasty

Hemiarthroscopy may be:

• Unipolar hemiarthroplasty - replacement of the femoral head and neck.

• Bipolar hemiarthroplasty - replacement of the femoral head and neck plus an addition of an acetabular cup that is not attached to the pelvis (ie fits into the existing acetabular cup).

• Resurfacing hemiarthroplasty - replacement of the surface of the femoral head.

A number of surgical approaches to the hip joint are used, each with different advantages and disadvantages. The most commonly used approaches include the direct anterior, direct lateral and posterior approaches.²

How common are hip joint replacements? (Epidemiology)

• Over the 3 years from 1 January 2019 to 31 December 2021, 241,467 primary hip procedures were performed by 2,137 consultant surgeons working across 419 units in England, Wales, Northern Ireland, the Isle of Man and Guernsey.³

• The percentage of total hip arthroplasties being performed on patients younger than 60 is increasing steadily.⁴

Indications

Total hip arthroplasty

• Pain and disability due to degenerative or inflammatory arthritis in the hip joint, where non-operative management has failed and quality of life is being significantly interfered with.¹

• Fracture of the proximal femur.

• A resurfacing total hip arthroplasty may be considered in a young person with osteoarthritis and good bone stock (the advantage is that the femoral neck is preserved which may be advantageous if a later conventional arthroplasty is needed).

Hemiarthroplasty

Usually indicated for patients with a femoral neck fracture who meet the following criteria:⁵

• Poor general health or frailty.

• Pathological hip fracture.

• Severe osteoporosis.

• Inadequate closed reduction.

• Displaced fracture that is several days old.

• Pre-existing hip disease (eg, rheumatoid arthritis, avascular necrosis).

• Neurological disease.

Some considerations

• It is essential to ascertain that the hip is the site of the pathology, as pain in the hip can originate from other sites such as the knee or back. Replacing a hip that is not the cause of the pain will be of no value.

• Total hip replacement should not be undertaken lightly in a younger patient, as they tend to wear out the prosthesis due to a longer and more active life. Revision is much more substantial than the primary operation.

• Adequate quadriceps and other muscles around the joint are essential for rehabilitation. Poor muscles and neurological disease around the joint may be a contra-indication to surgery. The patient must be physically and mentally able to take part in rehabilitation.

When to refer to secondary care

Most people with osteoarthritis of the hip are managed in primary care. The question is when to refer to an orthopaedic surgeon. (The need for immediate admission of a patient with a fractured hip is clear.)

The British Orthopaedic Association suggests that local referral pathways should be drawn up giving criteria for referral.¹

Referral may be based on a locally developed explicit scoring system. This may take into account factors such as 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.¹

Pre-operative care¹

• A pre-admission assessment should take place within six weeks of the operation in secondary care.

• This should include identification of comorbidities and routine pre-operative investigations. However, general health screening should be carried out by the GP before referral to secondary care.

• Information about the operation should be given to the patient, including risks and possible complications. Written supportive information should be given.

• Fully informed consent should be obtained.

• Provisional discharge planning should take place.

In March 2022, the National Institute for Health and Care Excellence (NICE) produced new Quality Standard statements on primary replacement of hip, knee and shoulder. The quality statements relevant for adult hip replacement are:⁶

• Patients planned for hip or knee replacement should be given advice on pre-operative rehabilitation when they are listed for surgery.

• Tranexamic acid should be given to adults having hip or knee replacement during surgery.

• There should be two 'stop moments' during hip replacement surgery to check implant details and the compatibility of all components.

• Before discharge following surgery, the patient should be given advice on postoperative rehabilitation.

Preoperative rehabilitation advice should include advice on:⁷

• Exercises to do before and after surgery that will aid recovery.

• Lifestyle, including weight management, diet and smoking cessation.

• Maximising functional independence and quality of life before and after surgery.

Choice of device and surgical technique

Prostheses for total hip replacement and resurfacing arthroplasty are recommended by NICE as treatment options for people with end-stage arthritis of the hip only if the prostheses have rates (or projected rates) of revision of 5% or less at 10 years.⁸

• There are many different types of device available for joint replacement surgery. Materials used include metal, polyethylene and ceramic. Various methods of fixation include polymethylmethacrylate (PMMA) cement, screw fixation, cementless press fit and porous ingrowth fixation.

• The simplest and most commonly used classification is whether prostheses are:
  

  • Cemented.

  • Uncemented.

  • Hybrid (a cemented stem with a cementless cup).

• The surgeon may have a preference for an individual implant depending on factors including their training and consultant colleagues' preference.

• Patient factors including age and underlying health and comorbidities may also influence choice of device, eg, ease of revision is needed in young patients.

• Cemented prostheses: these are thought to make up 90-95% of the UK total hip replacement market. NICE supports and suggests their use. (Although some evidence exists that these guidelines are not being followed.)⁹ They tend to fix well and early mobilisation is usually possible. There is the possibility of a foreign body reaction to the cement, which can affect the surrounding bone.

• Uncemented prostheses: these are generally easier to revise (an advantage in younger people who may outlive the prosthesis) but may take longer to fix and full mobilisation/weight bearing is not possible as early.

• NICE also suggests that more evidence of the performance of hip prostheses over longer periods of follow-up is required. The National Joint Registry will help this.

Metal-on-metal hip resurfacing arthroplasty¹⁰

• In this procedure, the damaged surfaces of the femoral head and the acetabulum are removed and resurfaced: a metal cup in the acetabulum and a metal surface for the femoral head.

• Metal-on-metal hip resurfacing was developed for younger, active patients as an alternative to total hip arthroplasty but it remains controversial.

• Revisions and re-operations are more frequent and occur earlier with metal-on-metal hip resurfacing.

The Medicines and Healthcare products Regulatory Agency (MHRA) has provided advice to assist the early detection of soft tissue reactions in patients implanted with metal-on-metal (MoM) hip replacements:¹¹

• The majority of patients with MoM hip replacements currently have well-functioning hips. However, some patients will develop progressive soft tissue reactions with MoM articulations.

• Orthopaedic experts have observed that soft tissue necrosis may occur in both asymptomatic and symptomatic patients, and believe early detection of these events should give a better revision outcome should this becomes necessary.

• The guidance contains detailed advice regarding monitoring and investigation, including rising blood metal levels indicating a potential soft tissue reaction.

Minimally invasive hip replacement surgery

• NICE supports the use of single mini-incision hip replacement. Fluoroscopic guidance and computer-assisted navigation tools may be used. Benefits may include less tissue trauma, less blood loss and less pain. Appropriate training of the clinician is required and data should be submitted to the National Joint Registry.¹²

• Guidance was also issued by NICE on minimally invasive two-incision surgery for total hip replacement. They confirm the procedure is safe but should be offered by suitably trained surgeons able to offer patients conventional hip replacements and with normal arrangements for clinical governance, consent and audit. Again data should be submitted to the National Joint Registry.¹³

Postoperative care and rehabilitation¹

• Mobilisation postoperatively should include input from a physiotherapy team. Specific advice should be given to the patient about what they can and cannot do.

• Patients should only be discharged when they are considered capable of managing in the environment of their destination.

• Contact telephone numbers in case of problems should be provided.

• Patients should undergo outpatient follow-up within eight weeks of the operation.

• Best practice minimum requirements for subsequent follow-up are at one, five and then each subsequent five years after operation. Clinical examination and X-rays should be carried out to assess for possible implant failure.

NICE recommends that primary care practitioners should refer people who develop new or worsening pain, limp or loss of function related to their joint replacement to an orthopaedic surgical service.⁷

Complications

About 1 in 8 of all total hip replacements requires revision within 10 years; 60% of these are because of wear-related complications.¹⁴

• Postoperative pain and constipation.

• Urinary tract infection or retention of urine: urinary catheterisation for the operation is routine and can lead to these.

• Thromboembolism: prophylaxis is routine but there is still a risk.

• Chest infection.

• Implant fracture.

• Dislocation of the hip: can occur at any stage but usually occurs early.

• Wound infection or dehiscence.

• Infection of the prosthesis: it may be necessary to remove the prosthesis.¹⁵

• Heterotopic ossification: usually asymptomatic but bony ankylosis can occur.

• Mechanical loosening and failure of the prosthesis: can occur in the longer term; can present with pain.

• Particle disease: a foreign-body reaction to implant debris causes focal osteolysis.

After hemiarthroplasty⁵ :

• Fracture of the femur can occur.

• Painful hemiarthroplasty may require conversion to a total hip replacement.

Prognosis

A systematic review and meta-analysis involving 13,212 patients in the period up to September 2017, revealed that prognosis for hip replacement has improved. Doctors can advise patients that in 58% of patients, hip replacements last for at least 25 years.¹⁶

• About 80% of people get a good result, with improved mobility and loss of pain.

• The 30-day mortality rate after elective total hip replacement is about 0.5%.^{17 18}

• After an arthroplasty for a fractured hip, the 30-day mortality rate is 2.4%.¹⁹

• A 3% prevalence of prosthetic loosening is seen at 11 years.

• There is a 1% prevalence of prosthetic infection.