Total hip replacement

The surgery involved in total hip replacement and the associated risks.

Total hip replacement (THR) is one of the most effective surgical procedures in the modern world. Over 70,000 hip joints are replaced each year in England and Wales. However, the procedure is not without risk and it is important to discuss these with patients.

In my own unit, the average length of stay after hip replacement surgery is now around three to four days. Many patients are admitted on the morning of surgery. The procedure lasts for one to two hours and is most commonly performed under spinal anaesthetic. A scar is left on the side of the hip typically about six inches long.

Surgical approach and methods

When referring a patient for THR, it is important to refer to a surgeon who performs them regularly. Many patients will have researched their operation and may ask for specific technologies and surgical approaches. However, most surgeons develop a surgical approach and device that suits them and then master it in the course of their careers.

Most THRs are performed through an antero-lateral approach or a posterior approach. At one point there was a trend to use the posterior approach.

In more recent years the anterior approach has become preferred by some surgeons as it represents an inter-nervous plane and is thought to be associated with shorter hospital stays and less pain as the patient mobilises.

Some surgeons use a minimally invasive technique, usually involving two small separate incisions. It is more difficult to operate through a small incision, however many patients are drawn to this concept, particularly in the private sector.

Risks associated with THR

The most realistic risk to consider is infection. Deep infection occurs in about 1% of joint replacement cases. Patients with diabetes, those taking steroids or immunocompromised for any other reason carry around a 2% risk of infection. To reduce these risks, patients are now injected with IV antibiotics at the beginning of the procedure and the operating theatre has a clean air filter. Many surgeons now wear protective overalls for THR.

Deep infection is a serious complication. If infection is caught early it may be possible to wash out the infection with copious salt water. Pus samples help to identify the infecting organism and the patient can be treated with high-dose antibiotics. However, a significant proportion of such patients will simply re-infect.

If the infection has been present for more than a couple of months bacteria form a slime layer on the surface of the metal and plastic that is impervious to antibiotics. Once infection is firmly established it is necessary to remove the hip replacement completely and replace it.

A deeply infected THR is commonly replaced as a two-stage process. The first stage removes the infected THR. Once the infection has cleared the second operation places the new THR. Two-stage procedures are far more inconvenient for the patient but have a higher percentage success rate (up to 80%, compared with around 60% for single stage replacement).

In a small proportion of patients the hip joint has to be excised resulting in the patient either mobile with crutches or mobile only in a wheelchair. This is known as a Girdlestone’s procedure.

About 2% of THRs dislocate. Dislocation is painful and inconvenient for the patient but can usually be resolved with a short manipulation under anaesthetic (MUA). Very occasionally it may be necessary to operate to achieve reduction. Some surgeons advise the patient to wear a brace around their waist that helps to keep the hip in position for the first few weeks after dislocation. Its main function is to keep the hip in slight abduction.

Leg length discrepancy
The single most common complication is leg length discrepancy. Patients are frustrated but can usually cope with a small heel raise.

The mortality rate in THR is probably about one in several hundred. For patients in their thirties the risk is perhaps one in a thousand. Older patients with multiple comorbidities are at significantly greater risk.

Sciatic nerve palsy
Sciatic nerve palsy is a possible complication of THR. In many cases it never recovers and the patients need a foot drop splint for life.

Some years ago it became apparent that the hard metal on the head of a hip replacement tended to erode the softer plastic in the socket. This led to the generation of microscopic debris particles and many surgeons reached the conclusion that it was this generation of debris that triggered the phenomenon known as aseptic loosening. Since then, a huge amount of work has gone into trying to reduce the generation of debris and people have experimented with both ceramic and metal joint surfaces arguing that ‘hard bearings’ will neither erode nor generate debris.

Ongoing pain
In some patients pain continues despite the THR. This may be because the pain did not actually come from the hip. Low back pain can radiate to the buttock and be mistaken for hip pain; clearly, this would not benefit from THR. Similarly, many patients have tenderness over the greater trochanter that may respond to cortisone injections.

Patients with a previous history of DVT are at increased risk after a THR and some surgeons would change the medication for these patients. Most units use drugs and TED stockings to reduce the risk of DVT formation.

Fatal PE after THR is of the order of 1 in 500, although estimates for this vary between units.

THR technologies

Hip resurfacing
In the 1990s there was a surge in interest in hip resurfacing. This technology relied on two metal surfaces and involved very large head sizes. Whereas the Exeter hip often uses a 28mm head and the Charnley hip uses the small 22mm head, the hip resurfacing technique might use a 40 or even 50mm wide head, ie similar size to that of the patient’s original joint. A larger head size ought to have led to a reduced dislocation rate. There are also several conceptual advantages of hip resurfacing including its non-violation of the femoral shaft, which makes revision procedures much easier.

Once hip resurfacing became established, several manufacturers began to produce similar implants. However, follow up studies cast doubt on the viability of both hip resurfacing and metal-on-metal articulation and recent recommendations suggest that resurfacing should not be performed in women or men with smaller joint sizes. The trend now seems to be drifting back towards metal-on-plastic joints.

Ceramic heads
Ceramic femoral heads are very hard and difficult to scratch, however in the 1980s it was common for ceramic heads to shatter and require revision surgery. Modern third-generation ceramics hardly ever do this.

Oxinium heads
Oxinium is a material sometimes used in hip replacements. It consists of a zirconium alloy metal substrate that transitions into a ceramic zirconium oxide outer surface and it is claimed to have a low risk of shattering and a very smooth surface. It is more expensive than ordinary metal.

Much talk exists of the relative advantages of cemented and un-cemented hips. In fact both work quite well, especially in the hands of experienced surgeons who use a specific prosthesis regularly.

Revision hip

If a hip fails for any reason, then it may be necessary to operate a second time to revise the hip to a new prosthesis. Some surgeons now specialise in revisions, which are more challenging than the primary procedure. The chance of a hip requiring revision surgery increases by around 1% each year after 10 years, and about one in 10 hips need a second procedure.

Revision surgery is usually performed in older patients. Dislocation and infection risks probably double every time an operation is performed, as does the risk of DVT/PE. The procedure takes longer and is associated with longer in-patient stays, a high risk of blood transfusion and ITU/HDU stays. Similarly, mortality will be higher in revision surgery and in some cases surgeons may recommend the patient living with a loose or painful hip replacement over the risks of revision surgery.

After surgery patients are advised to avoid extreme movements as this might lead to dislocation. Sitting in a low chair, or indeed a low car, is to be avoided. Squatting is particularly associated with risk.

Patients vary in their speed of recovery. Some are still using two crutches when they return to clinic at six weeks and some are walking with a normal gait and no walking aids. Young, fit adults recover faster than the elderly.

  • Mr Cutts is a consultant orthopaedic surgeon at James Paget Hospital in Norfolk

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