Background

The hand is a perceptual entity that has been described as an information-seeking organ. Its use provides patients with the ability to interpret and analyze tactile properties, such as shape, size, and texture. Hand use also enables patients to manipulate objects in order to identify and handle them effectively. Using coordinated hand function, we manually explore and recognize the relationship of objects to our bodies and to gravity.¹

Hand skills require tactile-proprioceptive and visual information, but if the somatosensory functions are good, then visual feedback is not mandatory. Patterns of hand skills are reach, grasp, carry, voluntary release, in-hand manipulation, and bilateral hand use. The latter two patterns are considered to be more complex skills than the first four. The radial digits are considered to be the skill side (manipulative side) of the hand, while the ulnar digits are considered to be the stability side of the hand.

Definitions²

Reach is defined as moving and extending the arm for placing or grasping an object. Grasp is attaining an object with the hand. Carry is transporting an object in the hand to another place. Voluntary release is intentionally letting go of an object in the hand at a specific place and time. In-hand manipulation means adjusting an object in the hand after grasping it. Bilateral hand use means using two hands together in order to accomplish an activity and follows unilateral hand use developmentally. An example of bilateral hand use is steering a bicycle or throwing a large ball. Bimanual hand use means each hand does different things in the activity. An example of bimanual hand use is tying shoelaces or cutting with scissors.

Hand movements are classified as non-prehensile and prehensile. Non-prehensile movements use the fingers or the entire hand to lift or push an object. Prehensile movements incorporate grasping of an object and can be subdivided into two purposes, precision grasp and power grasp. Precision grasp uses opposition of the thumb to the fingertips. Power grasp uses the whole hand with thumb flexion or abduction according to the control needed for the task.

Another classification system differentiates patterns of grasp by the inclusion or exclusion of thumb opposition. Hook grasp, power grasp, and lateral pinch do not incorporate thumb opposition. Hook grasp is useful for sustaining a grip to carry objects. Power grasp is useful for controlling objects, such as tools. Using a hairbrush is an example of power grasp with oblique positioning of the object in the hand and more flexion of the ulnar digits than the radial digits. Lateral pinch is useful when one needs power to manipulate or hold a small object. Turning a key in the door is an example of lateral pinch.

Tip pinch and palmar grasp differ from hook grasp, power grasp, and lateral pinch because they do incorporate thumb opposition. Tip pinch is demonstrated by opposition of the tips of the thumb and index finger with all joints of the thumb and index finger being partially flexed, forming a circle. Patients with anterior interosseous nerve injury are unable to perform tip pinch because they lack the function of the flexor pollicis longus and the flexor digitorum profundus to the index finger.

Palmar grasp is further categorized into standard, cylindrical, disk, and spherical grasps. With cylindrical grasp, flattening of the transverse arch facilitates holding of the fingers against the object. In disk grasp, there is metacarpophalangeal (MP) hyperextension and finger abduction that is adjusted according to the object’s size. When we open a jar, the hand stabilizing the jar demonstrates a cylindrical grasp, and the hand opening the lid uses a disk grasp. Spherical grasp occurs with wrist extension, digital abduction, and some MP and interphalangeal (IP) flexion, as in holding a tennis ball. This prehension pattern requires control and balance of the intrinsic and extrinsic muscles.

Pinches are classified according to the number of digits involved. Two-point pinch, also called pad-to-pad pinch or pincer grasp, occurs when the thumb opposes the index finger pad only. Three-point pinch or three-jaw chuck grasp occurs when the thumb opposes the index and middle finger pads simultaneously. This pinch provides better prehension stability than does two-point pinch.

Manipulation Skills

There are five pattern types of in-hand manipulation, and in order to perform them, the patient must be able to control the palmar arches. The pattern types are finger-to-palm translation, palm-to-finger translation, shift, simple rotation, and complex rotation. Varying definitions of finger-to-palm translation are offered in the literature. Exner² defines finger-to-palm translation as the grasping of an object with the thumb and finger pads and then moving the object into the palm. This is exemplified by the activity of picking up a button with the thumb and fingers and then moving the button into the palm. Palm-to-finger translation occurs in the opposite direction and is more difficult to do. This is performed when a person has coins in their palm, and they move one coin from the palm to the finger pads in preparation for inserting the coin in a slot. Shift is demonstrated when an object that is being held on the radial aspect of the hand is moved linearly on the finger surface in order to reposition it on the finger pads. Repositioning a pen after grasping it is an example of shift. Simple rotation occurs when an object is turned or rolled less than or equal to 90 degrees in the finger pads. Opening a small bottle cap is an example of simple rotation. Complex rotation is similar to simple rotation, but the object is rotated 180 to 360 degrees. Turning a pencil in order to use the eraser end is an example of complex rotation. In-hand manipulation with stabilization is defined as the performance of any in-hand manipulation skill while the person has other objects stabilized in the hand.