Finger prehension

Has no impairment of a hand or finger which interferes with prehension or power grasping ... 

FIGURE 32.12 Otto Bock System Electrohand (Otto Bock Orthopedic Industry. Inc., Dud-erstadt, Gmnany). The hand consists of a mechanism over which a liner is placed. A cosmetic glove is then pulled over the liner. (Note Otto Bock does not provide silicone gloves.) Liner creases have been placed in the finger thumb web space in an effort to reduce its elastic resistance. Also shown is a pair of tweezers that are provided with each hand to make tip prehension possible. Prosthetic hands have very poor tip prehension without the aid of some sort of extra tool such as these tweezers. 

FIGURE 32.18 Schematic of the prehension patterns of the hand as defined by Keller, Taylor, and Zahn (1947) (al) palmar prehension (three-jaw chuck), (o2) palmar prehension (two finger), (b) tip prehension, (c) lateral prehension, (<0 hook prehension, (e) spherical prehension, (/) cylindrical prehension. In a handlike prosthesis, it takes two to four independently controlled degrees of freedom to implement these prehension patterns. In a non-hand-like device, a single-degiee-of-free-dom device such as a split hook can be used. 

FIGURE 32.22 Sketches of the three types of gloves used by SCUBA divers (a) a mitten is warmest but has the poorest function (b) compromise glove provides warmth and allows diver to achieve the prehension patterns of Keller et al. (1947) (c) standard glove with individual fingers provides the least warmth but the most function. 

In the area of surgery, Beasley (1983) described a surgical procedure to provide a functional four-DOF hand for persons with C5-C6 quadriplegia. This procedure makes possible precision prehension with careM positioning of the stabili d thumb to oppose the actively flexed index and middle fingers. The result is a functional hand that retains some of its sense of touch. 

In prehension by subterminolateral oppo-sition the pad of the thumb holds an object, such as a coin, pressed against the radial surface of the first phalanx of the index finger. 

Palmar prehension is used to grasp heavy, relatively large objects. The entire hand is wrapped around the object. The thumb opposes the force of the other four fingers. 

Prehension by digitopalmar opposition entails grasp of a small-diameter object by the fingers pressing against the palm. The thumb is not involved. 

Prehension between lateral aspects of the fingers is exemplified by holding a cigarette. 

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