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Story of the thumb

How important is the thumb to the hand? Dr. S. RAJA SABAPATHY and Dr. SANDEEP J. SEBASTIAN tell us the ...

"In the absence of any other proof, the thumb alone would convince me of God's existence"

Sir Issac Newton

ONE tends to suddenly look at one's thumb, twiddle it bit and say in ready agreement, "My God! We really can't do without it." Truly, we would not be able to even hold this newspaper or turn its pages without the thumb.

The story of the thumb started over two million years ago, when our ancestors achieved an erect posture. This freed their hands for purposes other than locomotion. The evolution of the hand with a thumb set apart from the fingers meant that men and women could develop special abilities in manipulation, communication, hunting, gathering, feeding, crafting, caring, sexual contact and many other categories of behaviour mostly denied to other primates.

Much has been made of the ways in which man is a unique animal. The absence of the thumb, whether congenital or following an accident, significantly alters the functional capacity and aesthetic symmetry of the hand. Is there anything science can offer people who have lost the thumb? Methods for repair and reconstruction of the thumb have been developed and refined over the last century, borrowing and adapting techniques from many branches of surgery. Plastic surgery and orthopaedic surgery have been the main contributors to the emerging specialty of hand surgery.

Hand surgeons are dedicated to the repair and restoration of function and appearance of the whole hand and upper limb complex. The average normal x-ray length of the thumb is 11cm and it consists of bony framework of four bones and three joints. Six muscles dedicated to the movements of the thumb alone power the thumb. The average area of skin covering the thumb is nearly 26-27 sq. cm. and the quality of sensations provided by the thumb tip is the highest in the entire body with the ability to distinguish two points just a millimetre apart. In fact, a greater portion of the brain's specialised nerve cells is needed for the thumb than the toes, foot and leg put together.

One aims to create a thumb that is functional as well as aesthetic. The aesthetics of the hand are valued second only to the face. The patient will use an aesthetically pleasing reconstruction. A thumb that is functional from the surgeon's point of view, but is seen as ugly by the patient will most of the time be buried in a pocket. The advent of microsurgery in the early 1960s revolutionised Hand Surgery. With rapid advances in instrumentation, magnification, and technique, the re-attachment of a patient's own amputated thumb (replantation) became a distinct possibility. Microsurgical replantation involves in addition to fixation of bone for stability and tendon repair for mobility, the repair of nerves and blood vessels with diameters as small as a millimetre. Microsurgeons take between 6-8 fine sutures using special instruments to join these vessels. A replanted thumb would give the best functional as well as aesthetic result. However for this, the amputation must not be severely crushing in nature and the amputated parts must be brought properly preserved, as early as possible, preferably within 6-8 hours of injury. Replantation also needs a surgeon trained in microvascular techniques with adequate infrastructure to repair blood vessels with diameters less than a millimetre.

Sometimes the amputated part cannot be retrieved or is too damaged for replantation. Again microsurgery has answers. With further refinements in microsurgical techniques, using a toe to replace the thumb became possible. The great toe is used more commonly for thumb reconstruction in the West, while the second toe is used more in Asia due to use of open footwear.

The question then arises "How were thumbs being reconstructed before the advent of microsurgery?" The most commonly used method of thumb reconstruction was the osteocutaneous technique. Here, the thumb is reconstructed using a tube of skin incorporating a piece of bone. The skin tube is raised from areas of the body where the tissues are supple and there is minimal subcutaneous fat. The usual sites are the groin, the chest wall or the forearm. The bone can also be taken from several places, commonest being the iliac crest (pelvic bone).

This technique requires multiple stages separated by a period of three to four weeks. In order to achieve sensation at the tip of the new thumb, an island of skin from the middle finger can be transferred along with its nerve and artery. While it does not involve the use of a remaining finger or a toe, ensuring better patient acceptability, such a reconstructed thumb has no joint of its own and depends on the remaining joints for its mobility. Also the cosmetic result is imperfect, owing to the absence of the nail and the difficulty to achieve semblance to a normal thumb.

Occasionally babies are born without a thumb or with a rudimentary thumb. In such cases, the thumb is reconstructed using the adjacent normal fingers, commonly the index finger. It requires movement of the index finger carrying with it the blood vessels, nerves and the tendons moving it. This mobilised finger is then fixed in a strategic position relative to the other fingers so that it functions as the thumb. It is a single stage procedure that also reconstructs the joints.

The main disadvantage is the sacrifice of a normal functioning finger to replace the thumb. This surgery can be done as early as one year. The timing is important because the impression of the thumb is formed in the brain around one year of age and the child will adapt to the new thumb with ease.

In conclusion, the patient whose hand performance is severely impaired by loss of the thumb, and in whom a reconstructive effort is indicated, can choose from a variety of surgical possibilities. These procedures require not only a cooperative patient, but a highly skilled hand surgeon familiar with intricate reconstructive procedures of this nature supported by a physiotherapy and rehabilitation unit to aid in the restoration of thumb function after surgery.

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