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Hip and knee clinic: Minimally invasive hip replacement

When is a mini-hip replacement more appropriate than a total hip replacement? Mr Fares Haddad and Mr Nicholas Wardle help GPs advise patients on the decision

When is a mini-hip replacement more appropriate than a total hip replacement? Mr Fares Haddad and Mr Nicholas Wardle help GPs advise patients on the decision

Case history

A 74-year-old woman is seen in her local orthopaedic outpatient clinic. She describes a two-year history of worsening groin pain, which is starting to interfere with her normal activities of daily life. Her pain is centred in her right groin and is always worse on walking, to such an extent that she now has to use a stick to help her mobility. She is woken at night by pain despite regular analgesics. Performing routine foot care and putting on her shoes has become quite an ordeal.

For her age she is remarkably fit and healthy, and she is fortunate to have maintained an average weight. On examination she has an uneven gait to counteract pain, and demonstrates a positive Trendelenburg sign. Her range of motion of her right hip is restricted in flexion, abduction and external rotation with painful end points. Her left hip is normal on clinical examination. Her back and knees have pain-free full ranges of motion.

Diagnosis and management

Arthritis affecting the hip joint is a very common condition. It is important to differentiate this condition from other diagnoses causing pain around the hip joint such as referred pain from lumbo-sacral arthritis and nerve entrapments, and knee arthritis. A proportion of hip arthopathies are secondary to rheumatoid arthritis, however the majority are secondary to wear and tear osteoarthritis. Other conditions leading to destruction of the normal hip joint include post-traumatic arthritis (ie following fractured neck of femur) and avascular necrosis.

The history in this case is highly suggestive of hip arthritis, and the examination confirms this. In every case the assessment should include an examination of both hips as well as an assessment of the back and knee on the affected side. Leg length discrepancy should also be noted.X-rays of the pelvis in the anterio-posterior plane and lateral views of the affected hip are usually sufficient in the absence of other joint symptoms/signs and will demonstrate the cardinal signs of joint space reduction, osteophyte formation, subchondral sclerosis and subchondral cysts.

The extent to which these signs are present dictates the possible surgical options. Because of their better bone stock, younger patients are good candidates for bone preserving hip resurfacing.

Non-operative options

  • Regular analgesia (paracetamol and NSAIDs if not contraindicated)
  • Walking aids and physiotherapy

When these treatments are no longer enough it is reasonable to recommend hip replacement surgery. There is now good evidence that intervention before patients' functional levels deteriorate dramatically leads to better medium-term outcomes.

Conclusion

The reasoning behind smaller incisions is not for improved aesthetics but to produce a comparable post-operative outcome to standard incision hip replacement but with a shorter inpatient stay and recovery time. Any increase in complication rates would be unacceptable.

These new procedures will be greatly enhanced by computer assistance and navigation techniques that will allow correct implant positioning without wide exposure and direct visualisation. Overall the one-incision technique is being widely adopted over the two-incision technique as the operative procedure is not vastly different from standard incision and there is no requirement for intra-operative fluoroscopy. In time mini-hip replacement may become the standard procedure.

Nicholas Wardle is specialist registrar in trauma and orthopaedics at the Royal London Hospital ­ his special interest is joint arthroplasty and reconstruction and he is writing a thesis on bearing surfaces in lower limb arthroplasty.

Minimally invasive hip replacement

The minimally invasive hip replacement or 'mini-hip' has been pioneered in the US, but is available in some form or other at most centres around the UK.

Advantages

  • Smaller and less noticeable scar (8cm or 2/5cm instead of 16-25cm)
  • Minimal interruption and dissection of neurovascular tissues, tendons, ligaments and muscles
  • Incidence of dislocation, infection, nerve palsy and loosening are comparable with standard incision hip replacements
  • Incidence of perioperative medical complications, including cardiac, pulmonary, CNS, GI, and GU complications shown to be reduced
  • Decreased intra-operative blood loss
  • Reduced need for post-operative analgesia
  • Reduced need for post-operative oxygen supplementation
  • Fewer patients with mental status dysfunction
  • Hospitalisation up to 40 per cent shorter
  • Time to recovery reduced by approximately half

The procedure is available on the NHS, although not all surgeons are able or willing to perform the mini-incision variety. The private cost is approximately £10,000.

Who is not suitable for the 'mini-hip'?

This procedure is relatively contraindicated in obese patients and those with severe hip deformity, or who require more complex interventions beyond a standard primary hip replacement.

Contraindications for hip replacement in general are:

  • disabling heart disease
  • uncontrolled high blood pressure
  • an active infection
  • very poor overall health

There are two broad methods of minimally invasive hip replacements ­ a one-incision technique and a two-incision technique.

One-incision technique

The one-incision 'mini hip' uses traditional surgical techniques and prostheses but reduces the size of the surgical incision to approximately 8cm. (The term 'mini' refers to the size of the incision, not the size of the prosthesis.)

The single incision can be made in the anterior or posterior part of the hip. As with traditional surgery, the procedure requires release of some of the muscles around the hip to reach the joint. The posterior approach usually involves releasing some of the external rotator muscles, which are then reattached at the end of the operation. To make the procedure possible through such a small incision special instruments and retractors have been designed.

Two-incision technique

This surgery involves making two incisions, each approximately 5cm long: one incision anteriorly to place the acetabular component of the prosthesis and the other incision posteriorly to place the femoral component.

Two-incision surgery allows the surgeon to navigate between and around the muscles, tendons and other soft tissues of the hip to insert the components of the prosthesis, rather than cutting through these tissues.

However, it is necessary to use fluoroscopy ('live X-ray') during the procedure to ensure the correct placement of the components. There is increased risk of component malpositioning, proximal femoral fracture and trauma to the operative skin wounds.

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