Finger-Joints in Keyboard Technique

1. Each finger has three joints.
   1. hand-knuckle (metacarpo-phalangeal)
   2. Midjoint
   3. Nailjoint.
   The midjoint and nailjoint are both interphalangeal. (See Figure 1 below)
   The hand-knuckles are modified ball-and-socket joints with the lower volar^[1] spherical articular surface wider than the upper (dorsal) art icular surface. Accordingly, movement is essentially directed downward and inward, toward the palm and normally not beyond a straight angle in the opposite direction. Flexion is the active movement and extension is the passive, releasing movement, a physiological distinction that is of great importance in teaching finger-stroke.
   Limited circumduction^[2] , a property of all ball-and-socket joints, is possible at the handknuckles.
   A slight lateral flexion permitting the " hollowing of the hand" is also possible, being greatest for the fourth and fifth fingers. Flexion at the hand-knuckles normally takes place through a maximum arc of 90°, extending from a st raight -angle to a right-angle.
   
   

   

   
   

   Abduction and Adduction

   In addition to these movements, the hand-knuckles permit abduction and adduction (limited sideways motion) to the middle line of the hand. Abduction and adduction are used in playing chords in spread position. On account of the difference between the volar and dorsal articular surfaces, however, abduction and adduction are possible only when the fingers are extended at the hand knuckles. One cannot bend the fingers at the hand-knuckles while the fingers are widely spread, a fact that must be considered when demanding hand-arch in extended chord positions.
   As flexion increases at these joints, ab- and adduction become increasingly difficult, until at right -angle flexion, until are impossible. This inter-relationship illustrates the impossibility of executing widely spread chords on the piano,with an arched hand. The wider the spread the flatter must the hand be, a condition determined not so much by actual distance, as by the anatomical construction. The wider spread the chords, the flatter the hand must be.
   Abduction and adduction are possible when the fingers are at right angles to the hand.
   
   

   Midjoints and Distal Joints

   The midjoints and distal joints (both known as interphalangeal joints^[3] ) are pure hinge joints permitting only flexion and extension. The mid-joint allows flexion and extension through a maximum arc of 120 degrees. The distal joint permits flexion and extension through an arc of 90 degrees. This flexion normally is entirely toward the palm from a straight angle, paralleling the direction of flexion at the hand-knuckles, and acting in conjunction with this in a manner similar to the thumb-movements.