Proxima hip device by Dr.A.K.Venkatachalam of www.hipsurgery.in 

Dr.A.K.Venkatachalam

Consultant orthopaedic surgeon, Chennai talks about hip arthritis and its modern treatment. Earlier hip replacement was the only option for the surgical treatment of hip arthritis. However the emergence of modern day alternatives like hip resurfacing & Proxima hip replacement have made this applicable to the young and middle aged patients.

Have you been advised a hip replacement operation?

If yes, please read the following information on facts about the operation and more advanced bone preserving hip replacement options called Proxima hip replacement and hip resurfacing.

The hip joint may need to be replaced with an artificial joint when it is irreversibly damaged and cannot be salvaged by alternate surgery. The patient complains of pain and restriction of movement. The pain may often be referred to the knee or felt in the knee and no hip symptoms. Occasionally the pain may be felt more in the buttock area rather than in front of the groin.

Who needs a hip replacement?

In India, many young patients with ankylosing spondylitis, avascular
necrosis, post septic arthritis, post traumatic arthritis, are
advised a hip replacement for disabling pain. Thus many hip replacement operations are performed in younger patients. The surgery should cater to the enhanced demands on an artificial joint by younger and more active patients. Naturally an operation designed for Western elderly patients is not suitable for younger patients.
The other category of persons who need hip replacement are elderly with a hip fracture. In this group a partial or total hip replacement may be required. In this group, conventional total hip replacement is the best solution.

What is a total hip replacement?

In this operation the ball shaped upper end of the thigh bone (femur) and the socket (acetabulum) are replaced. The ball is replaced with a long metal stem that is fixed into the upper end if the thigh bone. Its upper spherical end articulates with a cup shaped polyethylene socket that is cemented into the pelvis.

Model of a total hip replacement

Conventional hip replacements sacrifice a great deal of normal bone as the head, neck, and upper part of the thigh bone is removed for implantation of the prosthesis. Moreover wear debris from the polythetheylene liner lead to osteolysis and bone loss. When this first hip is to be changed or revised after its lifespan more bone loss occurs. Conventional hips have a small ball to reduce friction and wear, but the ill effect of this is an increased risk of dislocation. An average dislocation rate of 3- 4 % has been reported. These implants do not last very longer than 20 years and revision rates of 50% at 20 years have been reported. Survival rates are less satisfactory for the relatively younger active patients. Thus a total hip replacement is not an ideal implant for younger patients less than fifty years old who need a new hip. It is however the best option in elderly people.
Problems with conventional total hip replacement:

A total hip replacement is an excellent & time tested operation in the elderly. However in the young problems may arise. These are
(1) Excessive bone sacrifice and loss
(2) Increased risk of dislocation
(3) Patients cannot squat or sit cross legged on the floor with out the risk of dislocation.
(4) Range of movement is less
(5) Patients cannot involve in sports
(6) Poor survival in young and active patients they require earlier revision.
(7) Revision surgery is difficult
(8) The hip feels less like a normal hip
(9) The cup wears with time and plastic from it harms bone
(10) Change in length of the leg after surgery leading to leg length discrepancy.

Why remove normal bone when only the surface of the ball is bad?

This is the logic behind hip resurfacings. This bone preserving hip resurfacing involves replacing only the diseased bony surfaces of the head of femur and acetabulum. This involves sculpting the head of the femur and covering it with a metal cap and fixing an uncemented socket into the acetabulum to receive the head.

Hip Resurfacing-What is it?

A bone preserving hip replacement!

A surface hip replacement is an operation in which the top joint surface of the upper end of the femur bone is scraped and shaped into a cylindrical form from a spherical form. A metal spherical cap is glued or cemented over the cylindrical stump.
This restores the normal shape & size to the upper end of the thigh bone. Next the socket in the hip bone is scraped into a hemisphere. A metal cup is impacted after complete cartilage removal. This cup will integrate with the body’s bone on the back side as it has a layer of the same material as bone. The hip shape is thus restored to normal as shown in the picture below.
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Model of a surface hip replacement

Preservation of bone and less stress shielding makes it easy to revise this hip if needed. The large head size provides a very stable joint and recreates the sensation of a normal hip joint. Patients have gone back to playing Judo and Squash after this operation. Advances metallurgy makes the metal on metal articulation likely to survive longer in the young and active patient. With less metal inside the bone and less invasion of the medullary cavity of the femur, the risk of infection is reduced. Rehabilitation is faster and better.

Advantages of hip resurfacing:
(1) Allows the patient to squat and sit cross legged on the floor safely
(2) Allows a normal range of movement.
(3) Sacrifices only the surface diseased bone and preserves normal bone
(4) Imparts a more normal sensation
(5) The joint is likely to last longer even in younger and active patients.
(6) Earlier and faster rehabilitation
(7) Less risk of dislocation
(8) Easier to revise if needed.
(9) No leg length discrepancy.

Proxima hip replacement - What is it?

Comparison of a total and Proxima hip replacement

This is the latest addition to the armamentarium of the hip surgeon in India. It is a bone preserving hip replacement.

In this operation, the entire diseased head of the femur is removed. The lining of the hip socket is resurfaced with a metal cup. A tiny uncemented hip with a short stem called the Proxima hip is impacted into the upper end of the femur or thigh bone.
The size of the implant matches the natural one and hence the risk of dislocation is almost eliminated. It is recommended when bony destruction is advanced and hence unsuitable for resurfacing and a total hip replacement would be overkill.

The advantages of a Proxima hip over a total hip are

• Bone sparing hip replacement
• Minimally invasive technique for implanting
• Metal on metal joint- longer durability
• Least chance of dislocation.
• Patients can squat and sit cross legged on the floor.
• Absence of thigh pain as the lower portion of the thigh bone is not reamed.
• Can be converted to a total hip later.

So in conclusion although total hip replacements remain an excellent option in a specific elderly age group, Hip replacement alternatives should be strongly considered in the young patient requiring a hip replacement in India.

The author is a consultant Orthopaedic surgeon in Chennai. You can get more information on hip surgery from website http://www.hipsurgery.in