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Introduction to Power Grip

 The power grip involves the coordinated action of fingers to clamp an object into the palm.

 Fingers assume sustained flexion, and the palm contours around the object.

 The thumb may either assist in clamping (by adducting) or not be involved at all.

 Power grip contrasts with precision handling, where the thumb is typically in abduction.

2. Four Varieties of Power Grip

 Cylindrical Grip

o Primarily involves flexor muscles, especially the flexor digitorum profundus.

o Flexor digitorum superficialis assists with stronger grips.

o Significant involvement of intrinsic interosseous muscles (responsible for flexion and

abduction/adduction of the metacarpophalangeal joints).

o Thumb plays a variable role, often flexing and adducting to secure the grip.

o Muscles of the hypothenar eminence (e.g., abductor digiti minimi) are active.

o Wrist typically in neutral with slight ulnar deviation to optimize grip strength.

o Ulnar deviation helps stabilize the wrist and contributes to force generation.

 Spherical Grip

o Similar to cylindrical grip but involves more finger spread to encompass the object.

o Increased interosseous muscle activity due to the fingers’ spread.

o Fingers abduct at the metacarpophalangeal joints, and flexors remain active.

o Thumb also plays a critical role in assisting with grip, with similar muscle activity as
cylindrical grip.

 Hook Grip

o Utilized when the fingers form a hook shape to hold an object, typically without
thumb involvement.

o The flexor digitorum profundus is mainly responsible for maintaining the grip.

o Fingers are in flexion, and the thumb is either in extension or not used.

 Lateral Prehension

o Characterized by contact between two adjacent fingers (usually thumb and index).

o Metacarpophalangeal and interphalangeal joints remain extended.

o Involves extensor muscles, including the extensor digitorum communis, lumbricals,

and interossei for movement.

o Typically used for static holding of an object rather than manipulation.

3. Muscle Involvement in Power Grip

 Extrinsic Flexors: Flexor digitorum profundus, superficialis, and flexor pollicis longus for
finger and thumb flexion.

 Intrinsic Muscles: Interosseous muscles, responsible for metacarpophalangeal joint

movement (flexion, abduction, adduction).

 Thenar Muscles: Important in cylindrical and spherical grips for thumb positioning and force.

 Hypothenar Muscles: Active in cylindrical grip, especially in thumb opposition and little
finger assistance.

4. Role of the Thumb in Power Grip

 The thumb can act as an additional surface to clamp the object or assist with the grasp by
adducting.

 In cylindrical and spherical grips, thumb involvement is essential for securing the object.

 Thumb adduction is crucial for strength in power grip, as opposed to abduction in precision
grips.

 The thumb's role varies depending on the grip and object characteristics.

5. Biomechanics of Power Grip

 Wrist Positioning: Slight ulnar deviation and neutral wrist positioning enhance grip strength
by optimizing the function of flexor muscles and stabilizing the hand.

 Metacarpophalangeal Joint: Flexion, abduction, and adduction play key roles in shaping the
grip.

 Joint Stability: Various ligaments and tendons, including the radial collateral ligament,
annular pulleys, and sagittal bands, stabilize the joints during power grip actions.

 Finger Force Distribution: Index and middle fingers are typically stronger in grip strength,
while the ring and little fingers provide additional mobility and assistance.

6. Functional Implications and Applications

 Power grip is essential for tasks requiring forceful or sustained holding of objects, such as
lifting, carrying, or turning objects (e.g., a door knob).

 The strength and stability of power grip are critical for manipulating heavy or awkwardly
shaped objects.

. Overview of Precision Handling

 Definition: Precision handling involves fine motor control and is dependent on intact
sensation.

 Key Feature: The thumb typically serves as one "jaw" of the "two-jaw chuck" and is generally
abducted and rotated from the palm.

 Types of Precision Handling:

o Pad-to-pad prehension
 o Tip-to-tip prehension

o Pad-to-side prehension

2. Pad-to-Pad Prehension

 Function: Involves opposition of the pads (or pulp) of the thumb and finger.

 Muscle Activity:

o The thenar muscles (opponens pollicis, flexor pollicis brevis, abductor pollicis brevis)
are primarily active.

o Adductor pollicis becomes more active with increased pinch pressure.

 Joint Positions:

o The thumb remains in carpometacarpal flexion, abduction, and rotation.

o Finger joints are partially flexed depending on the size of the object.

 Key Role of Sensation: Greatest concentration of tactile corpuscles in the pads of the distal
phalanx of each digit.

3. Tip-to-Tip Prehension

 Key Difference: Requires nearly full flexion of the distal phalanx of both the thumb and
finger.

 Muscular Activity:

o Similar to pad-to-pad prehension but with more demand on the flexor digitorum
profundus, flexor pollicis longus, and interossei muscles.

 Finger and Thumb Positioning:

o The metacarpophalangeal joint of the opposing finger must be ulnarly deviated to

present the fingertip to the thumb.

4. Pad-to-Side Prehension (Key Grip)

 Definition: Thumb is adducted and the side of the index finger is used to hold the object.

 Muscular Activity:

o Increased activity of the flexor pollicis brevis and adductor pollicis muscles.

o Opponens pollicis has reduced activity compared to other forms.

 Precision: Less precise than other forms of precision handling.

 Clinical Significance: Can be performed even with paralysis of hand muscles by using wrist
extensor muscles (known as tenodesis).

5. Tenodesis in Pad-to-Side Prehension

 Definition: Use of active wrist extension to passively close the fingers and passive wrist
flexion to open the fingers.
  Role: Requires functional wrist extensors for closing and opening the hand.

 Clinical Relevance: Important for individuals with spinal cord injuries (C7 level) or paralysis,
relying on wrist extensors for grip and release.

6. Key Muscles and Nerves Involved

 Median Nerve: Controls the thenar muscles (opponens pollicis, abductor pollicis brevis,
flexor pollicis brevis).

 Ulnar Nerve: Controls the adductor pollicis.

 Flexor Muscles: The flexor digitorum profundus and flexor pollicis longus are crucial for
flexion in tip-to-tip prehension.

 Extensor Muscles: Extensor pollicis longus and other extensor muscles help stabilize and
open the hand.

7. Wrist Positioning

 Neutral Flexion/Extension: Common in all forms of precision handling, especially in pad-to-

pad and tip-to-tip prehension.

 Slight Ulnar Deviation: Enhances force and stability, particularly when performing precision
tasks like turning a key in pad-to-side prehension.

Ligaments of the Wrist Complex and Their Functions

The wrist complex is a highly intricate joint, with ligaments playing a crucial role in providing stability,
guiding movement, and controlling the motion of the carpals. The ligaments are broadly classified
into two categories: extrinsic ligaments and intrinsic ligaments.

1. Extrinsic Ligaments

These ligaments connect the carpals to the radius or ulna proximally, and to the metacarpals distally.
They provide significant stability to the wrist by stabilizing the carpals in relation to the forearm and
hand.

Volar Radiocarpal Ligament

 Composition: This ligament is typically described as having three distinct bands:

o Radioscaphocapitate (Radiocapitate) Ligament

o Short and Long Radiolunate (Radiolunotriquetral) Ligaments

o Radioscapholunate Ligament

 Function: The volar radiocarpal ligament plays a crucial role in stabilizing the wrist joint by
maintaining the alignment of the radius and carpals. It prevents excessive dorsal translation
of the carpus and stabilizes the scaphoid.

Radial Collateral Ligament

 Function: This ligament stabilizes the wrist laterally by limiting ulnar deviation (radial
deviation of the wrist). It may be considered an extension of the volar radiocarpal ligament.

Ulnocarpal Ligament Complex

  Composition: This includes the triangular fibrocartilage complex (TFCC), the ulnolunate
ligament, and the ulnar collateral ligament.

 Function: The ulnocarpal complex stabilizes the distal radioulnar joint and the ulnar side of
the wrist, providing stability during motion and preventing excessive motion between the
ulna and carpals.

2. Intrinsic Ligaments

These ligaments interconnect the carpals themselves, playing a key role in maintaining carpal
alignment and preventing excessive movement between the individual bones of the carpus.

Scapholunate Interosseous Ligament

 Function: This ligament is vital for maintaining the stability of the scaphoid and overall wrist
stability. It prevents the scaphoid from shifting relative to the lunate. Injury to this ligament
can lead to scaphoid instability, a major contributor to wrist pathology.

Lunotriquetral Interosseous Ligament

 Function: It helps maintain the stability between the lunate and the triquetrum. Damage to
this ligament may lead to lunate instability, typically accompanied by injury to other wrist
ligaments.

3. Dorsal Carpal Ligaments

The dorsal ligaments help stabilize the carpal bones from the dorsal (posterior) aspect of the wrist.

Dorsal Radiocarpal Ligament

 Composition: This ligament is obliquely oriented and attaches from the distal radius to the
triquetrum, with possible connections to the lunate and lunotriquetral interosseous
ligament.

 Function: It provides stability to the wrist, preventing excessive movement in wrist flexion.
The obliquity of this ligament helps offset the sliding of the proximal carpal condyle on the
inclined radius.

Dorsal Intercarpal Ligament

 Function: This ligament stabilizes the scaphoid and other carpals during wrist movements,
contributing to overall radiocarpal joint stability. It is most active in stabilizing the scaphoid
during wrist range of motion.

Key Observations on Ligament Functionality

 Volar Ligaments: These ligaments are generally thicker and stronger and are placed on
stretch during wrist extension. Their main role is to resist excessive dorsal translation of the
carpals, contributing to wrist stability.

 Dorsal Ligaments: These ligaments are thinner and more elastic, and they are taut during
wrist flexion. They contribute to stabilizing the wrist during flexion and limiting excessive
motion between the carpals and radius.