Hand Prehension

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Prehension

Grasping or taking hold of an object

4 Phases involved in prehension process?

1. Opening the hand
2. Positioning the fingers and thumb
3. Approaching the object with fingers and thumb/closing on the object
4. Actual grip or grasp

Opening the Hand

Dynamic motion though synergistic action between the finger extensors and wrist flexors
Counteracting synergists

Positioning the fingers and thumb

MCPs and IPs are positioned to conform with type of grasp desired and contour, shape, orientation and size of object

Approaching the object-closing on object

Wrist extension, finger and thumb flexion

Actual Grip/Grasp

Static power grip or dynamic manipulation
Isometric muscle contraction

Power Grip

A forceful act resulting in flexion at all finger joints
Thumb adducting
Isometric contraction
-holding a hammer

Types of Power Grips

Cylindrical Grip
Spherical Grip
Hook Grip

Cylindrical Grip

FDP (closes fingers around object) FDS (helps with force)
Interossei help with MCP flexion
Interossei position MCP in proper ABD (larger object) or ADD (smaller object)
Thumb flexes & ADD
Thenar muscles all active
Hypothenar (ABD digiti minimi, opponens digiti minimi, flexor digiti minimi) active
Ulnar deviation (heavy objects)
-holding a coffee cup

Spherical Grip

I.e. grapefruit, ball
MCP ADD
Dorsal interossei

Hook Grip

I.e. holding a purse
Never includes the thumb
Can be sustained for long periods of time
FDP and FDS (if DIP flexion is needed, FDP must participate)
The thumb is held in extension by thumb extrinsics

Types of Precise Prehension

Pad-to-pad Prehension
Tip-to-tip Prehension
Pad-to-side Prehension

Pad-to-pad Prehension

3 jaw chuck or 2 jaw chuck
Opposition of thumb-distal phalanx
MCPs partially flexed by interossei m.
PIPs partially flexed by FDS
DIPs flexed by FDP

Tip-to-tip Prehension

Most precise for of grasp-Superior pincer
Finger and thumb are more flexed (PIP, DIP)

Pad-to-side Prehension

Lateral pincer
-holding a key
Thumb pad presses against the lateral aspect of the index finger
Least precise form of grasp
Can be done with paralyzed hands through tenodesis actions (via extending of wrist and tension in FDP, FDS, FPL)

Functional Position of wrist and hand

Extension 20*
Slight Ulnar Deviation 10*
MCP 45*
PIPs 30*
DIPs slight
Thumb opposition
-no active lengthening or shortening, resting splint, middle of contrature range

Median Nerve Paralysis

Weak grip
Digits on radial side affected
Flexion and opposition of the thumb lost
Thumb is pulled in a dorsal direction (pulled back)
"Benediction" posture-index and long fingers are extended while other 2 digits are curled
Atrophy-medial epicondyle (flexor muscles all attach)
Weak pronation

Ulnar Nerve Paralysis

4th and 5th digits affected
Atrophy of hypothenar eminence (weakness)
Hollows between the metacarpals
Claw Hand
Small finger tends to be ABD and extended
ABD and ADD mm of digits served by the interosseous muscles are affected

Radial Nerve Paralysis

Atrophy near lateral epicondyle
Long extensors of digits are paralyzed
Wrist Drop develops
Weakness in elbow extension, due to lack of innervation to triceps and anconeus
Wasting in dorsal aspect of forearm due to atrophy of supinator

Median Nerve Innervations

-Flexor carpi radialis
-Palmaris longus
-Flexor digitorum superficialis
-Radial half of flexor digitorum profundus and the 2 radial lumbricals
-Flexor pollicis longus
-Superficial portion of flexor pollicis brevis
-Opponens pollicis
-ADB pollicis brevis (may have ulnar innervation)
-Pronator quadratus/teres

Ulnar Nerve Innervations

-Flexor carpi ulnaris
-Ulnar half of flexor digitorum profundus and the 2 ulnar lumbricals
-All interossei muscles
-All hypothenar muscles
-Palmaris brevis
-Deep portion of flexor pollicis brevis
-ADD pollicis

Radial Nerve Innervations

-Extensor carpi radialis longus/brevis
-Entensor carpi ulnaris
-Extensor digitorum
-Extensor indicis
-Extensor digiti minimi
-Extensor pollicis longus/brevis
-ABD pollicis longus

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