The functional position of the hand represents the most mechanically favorable constellation for certain hand activities. Impaired function can significantly reduce quality of life.
What is the functional position?
The functional position of the hand is commonly used when grasping and holding objects, regardless of whether all or individual fingers are used. The hand is the best-controlled movement organ in humans. The orderly interaction of many movement components allows the execution of numerous functional movement processes and postures. From a biomechanical point of view, the functional position is the most effective position of the joints and joint rows involved for activities that involve grasping and holding objects. The wrist is held in a slight extension (approximately 25° dorsal extension) and a slight outward deviation (ulnarduction), with an inward rotation of the forearm (pronation). The thumb is slightly splayed (opposition), the other fingers are in a slight flexed position (flexion) in all joints. The course of the long tendons of the finger extensors and flexors dictates these positions, which are the most favorable for grasping activities. The extensors, which pull across the back of the hand to the distal phalanges of the fingers, are approximated in the functional position, giving way to finger flexion. The finger flexors are slightly stretched by the wrist position and are passively pulled a bit into flexion, so that complete closure requires little travel or force.
Function and task
The functional position of the hand is commonly used when grasping and holding objects, regardless of whether all or individual fingers are used. In household, handicraft or sports, devices with one grip are often used. Due to better force development, these are held with the fingers while the wrist remains in the functional position. The thumb rests diagonally over the index finger for support. This hand and finger position corresponds to an incomplete fist closure. In the household, cleaning tasks are performed in this way with the broom, the mop or the vacuum cleaner; in sports, activities are performed with the tennis, squash or badminton racket. This hand position is also used for gardening with long or short-handled utensils. For activities that require less force but more fine motor skills, the functional position of the hand is virtually predestined. As a rule, not all fingers are used, but often only the index and middle fingers.
and middle fingers in combination with the thumb. In all joints, the posture during these activities corresponds to the functional position. Even if this position is sometimes abandoned during movements, the body always returns to this position, as it is the most energy-saving. Handicrafts such as knitting, sewing and crocheting are examples of such activities, but so is writing with a pen. The hand posture ensures that the work can be performed with the least possible effort and over a long period of time. The functional posture has a very specific task after injuries or operations in the hand area. It is used in the subsequent immobilization, as the chance of restoring the functions is significantly better. With little effort and only a few degrees of finger flexion, good grip function can be regained very quickly.
Diseases and ailments
Injuries to the hand or fingers can significantly impair hand function. However, subsequent immobilization in a cast or splint is often the more significant factor in the development of limitations if the setting is not chosen correctly. In addition to fractures, ligament and capsule injuries in the finger region, it is primarily the distal radius fracture that makes active assumption of the functional position temporarily impossible. A special form of the disease affecting the functional ability of the hand is Dupuytren’s contracture, in which the tendon plate of the palm (palmar aponeurosis) fibroses and shrinks. Beginning with the little and ring fingers, all fingers are gradually pulled toward the palm and lose their mobility. Peripheral or central nerve lesions may cause failure of individual or all muscles responsible for controlling the functional position of the hand.Damage to the radial nerve leads to the appearance of the so-called drop hand, in which both the dorsal extension of the wrist and the extension of the fingers can no longer be actively performed. Grasping is still possible via the fingers, but is very insufficient due to the unfavorable position in the wrist. A lesion of the median nerve at the elbow affects the flexors of the wrist and fingers. In that case, there is no active grasping function left. If it is in the wrist region, as in carpal tunnel syndrome, only the thumb muscles and the flexors of the index and middle fingers are affected. Grasping is still possible with the other fingers as a residual function. Paraplegia at the level of the 6th cervical segment or higher also leads to a complete loss of hand function, and the functional position is no longer possible. In cases of nerve damage where dorsal extension is still actively possible but finger flexion is no longer possible, therapeutic attempts are made to create a so-called functional hand. This is achieved by positioning the hand in specially made splints, which artificially shorten the finger flexors. Through active dorsal extension, it is thus possible to bring the fingers closer to the palm and grasp light objects. Chronic polyarthritis can result in significant loss of function. This autoimmune disease affects the upper extremity, preferably the wrist and fingers. It is characterized by the fact that the affected joints are destroyed by episodic inflammatory processes. Typical deformities develop, showing both joint stiffness and instability. The functional position of the hand is often impaired at a very early stage.
