Regarding the Pathodynamics of the Hand

February
2013
Issue no. 6

Austin D. Potenza, MD, FACS

​I am no longer in active practice but have been teaching young medical students for the last five or so years. It has been personally rewarding and challenging. I have tried to teach them principles and to give them an appreciation of functional anatomy.

I offer some excerpts from teaching material I have provided my students. The material is, I am sure, old hat to our membership, but it may have some usefulness in their teaching.

My philosophical approach to the hand and the function of hand surgery is as follows:

The hand is the essential part of our anatomy through which we engage our environment. Teleologically, it is our effector organ and one may think of it in man as the ultimate purpose of the upper extremity; the latter enables us to position our hands most effectively to engage the world about us.

I have enclosed a portion of the material concerned with certain dynamics of the hand. Again, I apologize to all. It may be helpful in teaching. I can recall going back to my college mathematics books many years ago in order to better understand and appreciate Landsmeer's calculations. As we recall, he was the professor of anatomy at Leiden University in the Netherlands.

Regarding the Pathodynamics of the Hand:
 
I have referred to the contributions of Landsmeer earlier in understanding Addendum #3.

Some comments that the joints of wrist, metacarpo-phalangeal joints and the inter-phalangeal joints taken together are an intercalated system. They are dynamically interdependent because in the anatomic position their primary axes of motion are parallel and they are collectively moved by muscles (and, of course, their tendons) that each often influence multiple joints. At rest, they are in dynamic balance. To appreciate this, place your forearm and hand on a table while sitting  comfortably and relaxed. With the axis of primary motion of the wrist held perpendicular to the flat surface of the table, you will note that the attitude of the anatomy of the joints of the distal portion of your upper extremity automatically take the following attitude:

  1. Wrist – slightly dorsiflexed (extended)
  2. Metacarpo-phalangeal joints- slightly flexed
  3. Interphalangeal joints- slightly flexed
    (the thumb adopts a comparative attitude but we will not pursue that at this time).

This attitude of the wrist and hand at rest is brought about by the anatomic arrangement, and the dynamic balance of the muscles and their tendons that course through and about them. (Remember that in life all our muscles manifest electrical activity and are in dynamic tension to some degree even at “rest”).

When we understand this and view it in light of Prof. Landsmeer’s calculations I arrived at following conclusion, expressed in seemingly simplistic but very understandable and useful terms:

In the live human being, with regard to a system of intercalated joints, when  one joint zigs, the  next  joint will zag and so on for as many as there are joints contained in the system. A zig-zag collapse of the system eventually occurs.

This does not seem profound, but it is. You will encounter the results of this phenomenon
in your clinics. To wit:

The rheumatoid patient with an extensor deformity (or attitude) of the wrist will also manifest a flexion deformity at the metacsrpo-phalangeal joints. In time there will be a hyperextension deformity of the proximal interphalangeal joints with flexion deformity of the distal interphalangeal joints (the swan-neck deformity).

The rheumatoid patient with a flexion deformity of the wrist will have a hyperextension deformity of the metacarpo-phalageal joints and flexion deformities of the proximal interphalangeal joints.

You will also see these dynamically imposed deformities follow injury with ADP.