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Massage Today
February, 2001, Vol. 01, Issue 02

You Know It Like the Back of Your Hand

By Neal Cross, PhD, NCTMB

While it is unfortunate that many of you may not have access to human cadavera, the amount of anatomy that may be learned and reviewed on one's own body parts is quite amazing! We often go to the books (two dimensional) first, even when we have a 3-D anatomy right in front of us.

It seems to me that when we do not take advantage of reviewing anatomy on ourselves or on another living person, we are truly missing out on a wonderful opportunity.

There is a level of disconnect in going from cadaveric anatomy in the lab to that warm, pliable tissue we feel on our clients. This disconnect goes away when we study living anatomy. It also makes our hands better educated when exploring bodies. And better-educated hands make for more accurate assessments.

Let's try a simple exercise. I am sitting in a jet somewhere over New York, headed to Chicago, then to Miami. I place my left hand on my left knee, palm down. I observe that the hair pattern changes from dense to sparse as I look distally. The transverse creases on each digit indicate the underlying MCP, PIP and DIP joints. These abbreviations refer to rather cumbersome names: metacarpophalangeal, proximal interphalangeal and distal interphalangeal joints, respectively. A nail covers each digit distally. I see the dorsal carpal venous rete and the origins of the basilic and cephalic veins medially and laterally, respectively. If I extend each digit, I clearly see its extensor tendon move just beneath the skin. I also observe that when I extend any of my fingers, its tendon and an adjacent tendon move.

All this lets me know that I have connecting tendons between the extensor tendons of digits two through five. The pattern of these intertendons varies widely from person to person. I can palpate these tendons. If I palpate carefully, I find that digits two and five each have a pair of tendons. One is from the common digital extensor (extensor communis); the other is from a muscle named for that digit. These are the extensor digit minimi and extensor indicis. I do not have the additional tendons to digits three and four, as some people do. These tendons are from the muscle extensores digiti tertii et quarti. I also note that all of these tendons "disappear" proximally under the extensor retinaculum.

If I abduct a finger against resistance, I can readily palpate a dorsal interosseous. I also know that the four dorsal interossei attach only to digits two, three and four. The third digit has two dorsal interossei, as its midline is the reference for finger movements. If I abduct the thumb and little finger against resistance, I can palpate their abductors one for digit five and two for digit one. When I hyperextend my thumb against resistance, a prominent depression appears proximally to the thumb's base. This is the anatomical snuffbox, bounded by the tendons of the short and long extensors of the thumb and the long abductor. Exploring the distal attachments of these, I can readily palpate more than one tendon associated with two of these muscles.

This is a very common phenomenon, even though it is not mentioned in many standard textbooks. I know of no significant functional consequence, other than perhaps driving a few of my medical students to some level of madness. I can readily palpate the pulse of a branch of the radila artery in the floor of the snuffbox. If I press harder and discover point tenderness, it may be indicative of a scaphoid fracture. This is arelatively common injury caused by falling backward onto a hyperextended wrist.

I can readily palpate all of my phalanges and metacarpals. I can also distinguish the major landmarks on each. If I carefully examine the range of motion of each of the joints in each digit, I note several things. In digits two through five, the range of motion is generous about one axis, but extremely limited about the other two axes. When examining the metacar-pophalgeal joint of the thumb, I notice it has generous motion about two axes and very limited motion about the third. I also discover that the ranges of motion differ if I utilize passive rather than active movements.

So, while sitting here on the plane, I have reviewed most of the salient anatomy of the dorsum of my hand. I have considered what is normal (i.e., usual) and compared my hand anatomy to "textbook" hand anatomy. In this way, I am reminded of the great wealth of variety in the human anatomy. This variation is an easily overlooked feature, yet it is so very important to understanding human form and function. As clinicians, we should strive to learn as much as we about this variation.

Some aspects of our anatomy indicate something especially unique to the individual being examined. Unique to the back of my hand are two scars. One is about two centimeters long, lying transversely at the base of the thumb. This resulted from the errant path of a knife while I was filleting a fish a few years back. The second is a very faint, perfectly rectangular scar overlying the midline of my extensor retinaculum. This was created by a burn from a popcorn popper at a Cub Scout meeting in 1958. I hadn't thought about that in decades.

So as you can see, the human hand is a marvelous instrument far more interesting than peering out the window at the top of the clouds.


Click here for previous articles by Neal Cross, PhD, NCTMB.

 

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