Page 96 - ASOP ROT Study Guide

3. ARTHROPLASTY

The name "arthroplasty" literally means "to reshape a joint". Before effective replacement joints were developed
surgeons attempted to remodel a distorted joint by cutting it and often covering the surface with a material from the
body, such as muscle. These techniques were entirely inadequate. Now arthroplasty is taken to mean the
replacement of one or both surfaces of a joint.

Patients should understand the limitations of joint replacement surgery - it can relieve pain and the restriction of
movement which pain brings, but is not likely to alleviate disability due to stiffness caused directly by the
disease within the joint.

3 . 1 The Limitations of Joint Replacement

The reason why arthroplasty of the hip is held in such high regard is due to the success of the operation. The
current level of 50,000 cases per annum in the UK was achieved largely through the work of Sir John Charnley.
For the majority, artificial joints work very well indeed and well in excess of ninety percent will still be m situ
after ten years. However, the majority of cases are older patients who are not naturally as active as the young
and because of retirement from work can regulate their activities to protect their new artificial joint.

It is not always appreciated that the consequences of the operation failing early can be devastating. This will be
discussed below, but in broad terms it is important to appreciate that a hip replacement is an artificial joint, not a
transplant. From the moment it is put in, it begins to wear out, whereas a natural joint has the capacity to
regenerate. The strategy of replacement should be to provide a joint which outlasts the likely life-span of the
patient. At our current level of knowledge this cannot be guaranteed for the younger patient, and so alternatives
are still required.

3 . 2 The Principles of Joint Replacement

The same basic rules discussed above apply to all joints and provided that they can be obeyed, arthroplasty
may be performed. The replacement of the knee joint now is a very successful operation, although like
the hip it is more successful in older patients. In the United Kingdom osteoarthritis of the knee is the most
common disabling form of the disease and the emergence of a successful prosthetic joint is very
encouraging.

In the upper limb, the relationship between pain relief and function is quite different from that observed in the
lower limb. In the case of the arm, the loads involved are quite low but the range of motion required for normal
function of the elbow and shoulder joints is large. Remember that arthroplasty tends to improve pain related
loss of function but does relatively less for intrinsic stiffness. This is because soft tissue distortion of the
capsule and ligaments tends to remain after replacing the articular surfaces. In the upper limb this poses a
problem if arthroplasty is contemplated. For example, the elbow must flex to ninety degrees to permit eating
(try reaching your mouth with an arm fixed at a greater angle) and must extend more or less fully to reach the
anus for cleansing. Therefore any surgery must cater for these two fundamental activities of daily living.

Slowly we are seeing elbow and shoulder joint replacements approaching these high functional requirements
but not so for the fingers or the wrist.

3 . 3 Arthroplasty

The key to understanding joint arthroplasty is to appreciate the requirements of an artificial joint. The new
joint must be capable of a functional and pain free range of motion, but be able to withstand the significant
forces placed upon it without undue wear and without working loose. It must achieve all this whilst having
the same stability as the natural joint.

On first reflection it is perhaps surprising that the hip joint proved to be the first really successful replacement
as this joint has tremendous demands placed upon it. However, although the loads are large this is offset by the
generally stable configuration of a ball and socket and the fact that the functional range of hip motion is in