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22 terms

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