Podcast
Questions and Answers
What is the primary function of the hand?
What is the primary function of the hand?
The hand serves as a very important sensory organ for perception and is also a primary effector organ for complex motor behaviors.
Which of the following structures support the concavity of the palmar surface of the hand?
Which of the following structures support the concavity of the palmar surface of the hand?
The thumb has three phalanges and two interphalangeal joints.
The thumb has three phalanges and two interphalangeal joints.
False
When gripping a large object, the hand takes on a ______ shape.
When gripping a large object, the hand takes on a ______ shape.
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What is the keystone of the proximal transverse arch of the hand?
What is the keystone of the proximal transverse arch of the hand?
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Which movements occur in the sagittal plane?
Which movements occur in the sagittal plane?
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What is the role of the volar plate in the MCP joint?
What is the role of the volar plate in the MCP joint?
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Match the following joints with their specific characteristics:
Match the following joints with their specific characteristics:
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The axes of the fingers remain parallel when bringing them together.
The axes of the fingers remain parallel when bringing them together.
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Which muscles are part of the hypothenar eminence?
Which muscles are part of the hypothenar eminence?
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What is the primary function of the opponens digiti minimi?
What is the primary function of the opponens digiti minimi?
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What does the carpometacarpal joint of the thumb allow?
What does the carpometacarpal joint of the thumb allow?
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The CMC joint of the thumb has three degrees of freedom.
The CMC joint of the thumb has three degrees of freedom.
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What is the close-packed position of the CMC joint?
What is the close-packed position of the CMC joint?
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The first interphalangeal (IP) joint of the thumb is primarily a _____ joint.
The first interphalangeal (IP) joint of the thumb is primarily a _____ joint.
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What is the primary action of the flexor pollicis longus muscle?
What is the primary action of the flexor pollicis longus muscle?
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Which muscle is primarily responsible for extending P1 over M1?
Which muscle is primarily responsible for extending P1 over M1?
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The adductor pollicis muscle can only act as an adductor.
The adductor pollicis muscle can only act as an adductor.
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What is the main function of the opponens pollicis muscle?
What is the main function of the opponens pollicis muscle?
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What is 'joint play' in the context of MCP joints?
What is 'joint play' in the context of MCP joints?
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During abduction of the index MCP joint, which direction does the proximal phalanx move?
During abduction of the index MCP joint, which direction does the proximal phalanx move?
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The extent of active abduction and adduction at the MCP joints is greater when performed in full flexion compared to full extension.
The extent of active abduction and adduction at the MCP joints is greater when performed in full flexion compared to full extension.
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What type of joint are the PIP and DIP joints classified as?
What type of joint are the PIP and DIP joints classified as?
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How many degrees of flexion do PIP joints allow?
How many degrees of flexion do PIP joints allow?
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What is the primary action of the flexor digitorum superficialis (FDS)?
What is the primary action of the flexor digitorum superficialis (FDS)?
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The extensor digitorum can only extend the PIP and DIP joints when the intrinsic muscles are activated.
The extensor digitorum can only extend the PIP and DIP joints when the intrinsic muscles are activated.
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Which muscle primarily extends the fingers?
Which muscle primarily extends the fingers?
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What do the interossei muscles primarily do at the MCP joints?
What do the interossei muscles primarily do at the MCP joints?
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The interossei muscles provide an important source of dynamic stability to the __________ joints.
The interossei muscles provide an important source of dynamic stability to the __________ joints.
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The lumbricals are associated with which tendons?
The lumbricals are associated with which tendons?
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The flexor digitorum profundus (FDP) is the sole flexor of the PIP joint.
The flexor digitorum profundus (FDP) is the sole flexor of the PIP joint.
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Which muscles are the primary extensors of the fingers?
Which muscles are the primary extensors of the fingers?
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What does EDC stand for?
What does EDC stand for?
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The intrinsic muscles prevent the EDC from hyperextending the MCP joint.
The intrinsic muscles prevent the EDC from hyperextending the MCP joint.
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What role do wrist flexors play during active finger extension?
What role do wrist flexors play during active finger extension?
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Which muscles are primarily involved in flexing the fingers against resistance?
Which muscles are primarily involved in flexing the fingers against resistance?
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When making a strong fist, wrist flexor muscles are activated.
When making a strong fist, wrist flexor muscles are activated.
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What is the primary function of wrist extensors during fist making?
What is the primary function of wrist extensors during fist making?
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Paralysis of the wrist extensors can impact the ability to make a fist effectively.
Paralysis of the wrist extensors can impact the ability to make a fist effectively.
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What happens to the sequence of joint flexion if intrinsic muscles are paralyzed?
What happens to the sequence of joint flexion if intrinsic muscles are paralyzed?
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What actions does the first palmar interosseus perform?
What actions does the first palmar interosseus perform?
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What are the types of power grip?
What are the types of power grip?
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What characterizes the spherical grip?
What characterizes the spherical grip?
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What is pad-to-pad prehension?
What is pad-to-pad prehension?
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Lateral prehension includes the use of the thumb.
Lateral prehension includes the use of the thumb.
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Which muscles are primarily active during hook grip?
Which muscles are primarily active during hook grip?
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Prehension describes the ability of the fingers and thumb to ________ or ________ objects.
Prehension describes the ability of the fingers and thumb to ________ or ________ objects.
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What is the primary motion during the first stage of opposition?
What is the primary motion during the first stage of opposition?
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Which of the following is a distinguishing characteristic of tip-to-tip prehension?
Which of the following is a distinguishing characteristic of tip-to-tip prehension?
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Power grip typically involves lower levels of force compared to precision handling.
Power grip typically involves lower levels of force compared to precision handling.
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What phenomenon occurs when active wrist extension helps close the fingers?
What phenomenon occurs when active wrist extension helps close the fingers?
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Study Notes
The Hand's Role and Structure
- The hand is a vital sensory and motor organ, used for complex actions and expressing emotions.
- Its unique structure allows it to close on itself, forming arches for gripping various objects.
- Three arches run in different directions: transverse, longitudinal, and oblique.
- The transverse arches include the carpal arch (wrist) and the metacarpal arch (metacarpal heads).
- The longitudinal arches follow the length of each finger, spanning the metacarpal and phalanges.
- The oblique arches connect the thumb with other fingers, providing opposing movements.
Arches of the Hand
- The hand's concavity is supported by three interconnected arch systems: two transverse and one longitudinal.
- The proximal transverse arch is formed by the static, rigid distal row of carpal bones, creating the carpal tunnel.
- The distal transverse arch passes through the MCP joints, with the central metacarpals serving as its keystone.
- The longitudinal arch follows the shape of the 2nd and 3rd rays, with the CMC joints providing stability at the proximal end.
- The interconnected arches reinforce the hand's structure, ensuring a stable and efficient grip.
Structure of the Hand
- The carpus (wrist) and the carpal bones are essential to the hand's structure.
- Five metacarpals, collectively called the “metacarpus,” form the palm.
- Each digit contains a set of phalanges, with a metacarpal and its associated phalanges forming a ray.
- The carpometacarpal (CMC) joints connect the proximal ends of the metacarpals to the distal row of carpal bones.
- The metacarpophalangeal (MCP) joints connect the metacarpals to the proximal phalanges.
- Each finger (II-V) has two interphalangeal (IP) joints: a proximal (PIP) and a distal (DIP) joint. The thumb has only one IP joint.
Dorsal and Palmar Muscles
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Dorsal:
- Origin: Dorsal interossei (I-IV)
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Insertion:
- Extrinsic: ECRl, ECRB, ECU, Extensor pollicis brevis, Extensor pollicis longus, Extensor digitorum, Extensor indicis, Extensor digiti minimi
- Intrinsic: Adductor pollicis, Dorsal interossei (I-IV)
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Palmar:
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Origin:
- Thenar: Abductor pollicis brevis, Flexor pollicis brevis, Opponens pollicis, Adductor pollicis
- Mesothenar: Palmar interossei (I-IV)
- Hypothenar: Abductor digiti minimi, Flexor digiti minimi, Opponens digiti minimi
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Insertion:
- Extrinsic: FCR, FCU, Flexor digitorum superficialis, Flexor digitorum profundus, Abductor pollicis longus, Flexor pollicis longus, Flexor digiti minimi
- Intrinsic: Palmar/volar interossei, Abductor pollicis brevis, Flexor pollicis brevis, Opponens pollicis, Abductor digiti minimi, Opponens digiti minimi
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Origin:
Hand Movements
- Movements are described from the anatomical position (elbow extended, forearm supinated, wrist neutral).
- Flexion/extension: Sagittal plane
- Abduction/adduction: Frontal plane, with the middle finger as the reference digit.
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Thumb Movements:
- Flexion: Movement of the thumb's palmar surface across the palm (frontal plane).
- Extension: Returning the thumb to its anatomical position and laterally away from it.
- Abduction: Forward movement of the thumb away from the palm (near sagittal plane).
- Adduction: Returning the thumb to the plane of the hand.
- Opposition: Movement of the thumb across the palm, touching the tip of any finger.
- Reposition: Moving from full opposition back to the anatomical position.
Carpometacarpal Joints (II-V)
- The 2nd and 3rd metacarpals are rigidly joined to the carpus, forming the central pillar of the hand.
- The 4th and 5th CMC joints provide mobility and allow “cupping” motion.
- The 5th CMC joint is a saddle shape joint, allowing flexion/extension, abduction/adduction, and limited opposition.
- The motion of the 4th and 5th metacarpals enables the ring and little fingers to oppose the thumb.
Metacarpophalangeal Joints (II-V)
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Structure:
- Large, ovoid articulations formed by the metacarpal heads and proximal phalanges.
- Surrounded by a lax capsule, providing some passive axial rotation.
- Collateral ligaments and the deep transverse metacarpal ligament enhance joint stability.
- The volar plate adds congruency and stability, limiting hyperextension.
- It glides proximally with flexion, preventing pinching of flexor tendons.
- It resists tensile stress, preventing hyperextension, and protects the metacarpal head.
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Osteokinematics:
- Condyloid joint with two axes and two degrees of freedom (flexion, extension, abduction, adduction).
- Flexion: 2nd finger flexes to 90°, 5th finger to 110-115°. Active extension varies, up to 20-40°. Passive extensions can reach 90° in hyperlaxity.
- Abduction/Adduction: 20° on both sides of the midline, with the axis of rotation through the metacarpal head.
- Limited circumduction possible for the index finger.
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Arthrokinematics:
- Biconcave phalanx moving against the biconvex metacarpal head.
- Glide dominates, with slight roll in the same direction as osteokinematic movement.
- Flexion: Increased passive tension in the dorsal capsule and ligaments guide movement.
- Extension: Roll and slide occur dorsally, with the collateral ligaments slackened and the palmar plate unfolded.
- Joint Play: Non-axial accessory motion.
Interphalangeal Joints (II-V) - PIP and DIP
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Each PIP and DIP joint is a hinge joint (one degree of freedom - flexion/extension).
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Structure:
- Composed of the head of a phalanx and the base of the phalanx distal to it.
- Joint capsule, volar plate, and collateral ligaments.
- Distal phalanges sit on the pulley-shaped head of the proximal phalanx.
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Function:
- Collateral ligaments limit abduction and adduction.
- Volar plate limits hyperextension and serves as attachment for the fibrous digital sheath, protecting flexor tendons.
- The fibrocartilaginous volar plate enhances congruency and stability.### IP Joints II-V (PIP, DIP), Osteokinematics
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The fingers flex in a sagittal plane with axes converging at the distal margin of the radial pulse.
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Flexion axes are perpendicular to the joint in full extension and become more oblique during flexion due to articular surface asymmetry and collateral ligament stretching.
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PIP joints flex ~100-120°, with a PROM of 135°.
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DIP joints allow less flexion, ~80-90°.
IP Joints II-V (PIP, DIP), Arthrokinematics
- PIP and DIP joints have similar arthrokinematics due to similar joint structure.
- During active flexion, the concave base of the middle phalanx rolls and slides palmarly.
- Dorsal capsule tension guides and stabilizes roll-and-slide motion.
- PIP is stable in full extension and flexion, but allows some joint play in semiflexion.
- DIP can be passively hyperextended 30° beyond neutral and allows passive abduction and adduction.
- Close-packed position for both PIP and DIP is full extension, likely due to palmar plate stretch.
Muscular Function of the Hand
- Hand muscles are classified as extrinsic (originating in forearm or humerus) or intrinsic (both attachments in the hand).
- Most hand movements require cooperation between extrinsic, intrinsic, and wrist muscles.
Flexion of the Fingers II-V - FDS
- FDS is located in the anterior forearm, deep to wrist flexors and pronator teres.
- Its 4 tendons cross the wrist and split at the proximal phalanx to allow FDP tendon passage.
- FDS primarily flexes PIP joints and flexes all joints it crosses.
- It is a weak MCP flexor only when PIP is fully flexed.
- FDS efficiency at PIP is maximized when MCP is kept extended by EDC (synergistic action).
- FDS stabilizes MCP in neutral position synergistically with EDC.
Flexion of the Fingers II-V - FDP
- FDP is located in the deepest forearm muscular plane, deep to FDS.
- FDP tendons pass through the split FDS tendons and attach to the distal phalanx.
- FDP is the sole DIP flexor, followed by PIP flexion due to lack of opposing extensor.
- To measure FDP strength, P2 must be kept extended manually.
- FDP works best when P1 is extended by EDC (antagonistic-synergistic action).
- FDP can assist in flexing all joints it crosses.
- Radial extensors and EDC are stabilizing synergists of flexors.
Flexion of the Fingers II-V – the Pulleys
- Extrinsic flexor tendons travel in protective fibro-osseous tunnels (digital sheaths).
- Digital sheaths contain 5 annular pulleys (A1 to A5) for each finger.
- Major pulleys A2 and A4 attach to phalanx shafts, minor pulleys A1, A3, A5 attach to palmar plate.
- 3 less distinct cruciate pulleys (C1 to C3) exist.
- Pulleys, palmar aponeurosis, and skin hold tendons close to joints to prevent bowstringing.
Extension the of Fingers II-V
- EDC is the primary finger extensor, originating from the lateral epicondyle and inserting into the distal phalanx base.
- EDC is a powerful MCP joint extensor, active in all wrist positions, but facilitated by wrist flexion.
- EDC extends P1 via extensor expansion, P2 via median band, and P3 via lateral bands, with action dependent on wrist position and MP flexion.
- EDC action on P2 and P3 also depends on digital flexor tension.
- Extensor indicis and extensor digiti minimi behave similarly to EDC.
- EDC abducts, EI adducts, but only when interossei are inactive.
Extensor Mechanism of the Fingers
- Extensor mechanism attachment allows EDC to transfer extensor force distally.
- Dorsal hood assists in MCP joint extension.
- Intrinsic muscles attach to extensor mechanism.
- Isolated EDC contraction causes MCP joint hyperextension.
- Full PIP and DIP extension requires activated intrinsic muscles.
Mesothenar - Interosseus Muscles
- Interossei are located between metacarpal bones.
- They generally act at MCP joints for abduction (spreading fingers) or adduction (bringing fingers together).
- 4 palmar interossei adduct 2nd, 4th, and 5th MCP joints.
- 4 dorsal interossei abduct 2nd, middle, and ring MCP joints.
- Abductor digiti minimi (AbdDM) abducts the 5th MCP joint.
- Interossei provide dynamic stability to MCP joints and control axial rotation.
Mesothenar - Interosseus Muscles, cont.
- Interossei contraction flexes MCP and extends IP joints, but action depends on MCP flexion and EDC contraction.
- With MCP extended, interossei extend P2 and P3.
- With MCP flexed, interossei flex MCP and extend P2 and P3.
- EDC and IO act synergistically on P2 and P3 at intermediate MCP positions.
- IO are maximally active with MCP fully extended, EDC is inactive.
Mesothenar - Lumbricals Muscles
- 4 lumbricals have a movable origin on FDP tendons and attach distally to the dorsal hood oblique fibers.
- Lumbricals flex MCP and extend PIP and DIP.
- Lumbricals contain muscle spindles, providing proprioceptive feedback.
- By attaching to FDP tendons, lumbricals coordinate intrinsic and extrinsic muscle interactions.
Mesothenar - Lumbricals Muscles, cont.
- Lumbricals flex MCP and extend PIP/DIP regardless of MCP flexion degree.
- Lumbrical efficiency stems from their anterior position and angle of traction with P1, making them flexor starters of P1.
- Insertion distal to extensor hood allows them to retighten P2 and P3 extensors regardless of MCP flexion.
Function
- Everyday finger movements involve coordinated muscle actions.
- Writing involves interossei flexing MCP, EDC extending MCP, and FDS/FDP flexing P2.
- Hooking involves FDS/FDP contraction and interossei relaxation.
- Tapping involves EDC extending MCP, FDS/FDP flexing P2/P3, then interossei/lumbricals flexing MCP.
The Hypothenar
- Hypothenar muscles elevate and cup the ulnar hand border, deepening the distal transverse arch.
- ODM opposes the 5th metacarpal toward the middle digit.
- PB tightens the palmar aponeurosis, deepening the palm, helping with grip.
- AbdDM originates from the pisiform, FCU tendon, and pisohamate ligament.
- During resisted or rapid abduction, FCU stabilizes the pisiform, potentially deviating the wrist ulnarly.
Actions of muscles that cross the joints of the small finger
- FCu – flexes wrist, adducts hand
- FDM – flexes MCP
- ODM – opposes the 5th metacarpal
- AbdDM – abducts MCP
- PB – tenses palmar aponeurosis, tightens skin over hypothenar eminence
The thumb – I.Carpometacarpal Joint
- CMC joint is between the trapezium and 1st metacarpal base.
- Its saddle shape enables 2 DoF (flexion/extension and abduction/adduction) and opposition.
- Allows thumb to contact other digits, enhancing dexterity.
- Also permits axial rotation, contributing to opposition.
- Trapezium is concave sagittally, convex frontally. Spherical portion is convex in all directions.
- 1st metacarpal base reciprocates trapezium's shape.
The thumb – I.CMC Joint, cont.
- CMC joint capsule is lax, reinforced by radial, ulnar, volar, and dorsal ligaments.
- Intermetacarpal ligament prevents radial and dorsal displacement of the 1st metacarpal base.
- Dorsoradial and anterior oblique ligaments are key stabilizers.
The thumb – I.CMC Joint Arthrokinematics
- Abduction/adduction generally occur in the sagittal plane.
- Flexion/extension generally occur in the frontal plane.
- Maximum abduction positions the thumb 45° anterior to the palm.
- In adduction, the thumb lies within the hand plane.
Thumb - CMC Joint Arthrokinematics
- During abduction, the metacarpal rolls palmar and slides dorsally on the trapezium
- Abduction elongates the adductor pollicis and most CMC ligaments
- Adduction occurs in reverse order of abduction
- In neutral position, the thumb can extend 10-15 degrees
- Thumb metacarpal flexes 45-50 degrees across the palm
- Thumb metacarpal rolls and slides ulnarly during flexion, with slight medial rotation
- Flexion elongates the radial collateral ligament
- Thumb metacarpal rolls and slides radially during extension on the trapezium with slight lateral rotation
- Extension stretches ligaments on the ulnar side of the joint, like the anterior oblique ligament
- These rotations are not considered a third degree of freedom as they are dependent on other motions
Thumb - CMC Joint Opposition
- Opposition is divided into two phases, abduction and flexion-medial rotation
- Abducted metacarpal flexes and medially rotates towards the small finger
- Posterior oblique ligament is stretched during opposition
- Full opposition stretches capsular ligaments and the radial collateral ligament, resulting in a close-packed position
- Repositioning returns the metacarpal to the anatomical position via adduction and extension-lateral rotation
Thumb - MCP Joint
- Articulation of the convex metacarpal head and concave proximal surface of the proximal phalanx
- Similar structure and arthrokinematics to finger MCP joints
- Osteokinematics differ with less motion in the thumb
- Primary motion is flexion-extension within the frontal plane
- Active flexion is 60 degrees, passive flexion is 80 degrees
- Metacarpal head moves palmar against the proximal phalanx
- Abduction and adduction are limited, considered accessory motions
- Collateral ligaments, bony configuration, and muscles restrict motion and provide stability
- Palmar plate and two sesamoid bones reinforce the joint
- Accessory rotation is present in semi-flexed or extended positions
- Full flexion is the close-packed position
- Accessory motions are crucial for grip actions
- In a closed kinematic chain, CMC and MCP accessory motions combine
Thumb - IP Joint
- Hinge joint of the proximal phalanx head and distal phalanx base
- Similar structure and function to finger IP joints
- Primary motion is flexion-extension
- Active flexion is 70-80 degrees, passive flexion is 90 degrees
- Active extension is 5-10 degrees, passive extension is 20 degrees
- Extension is used for applying force, such as pressing a thumbtack into a board
- Accessory medial rotation is present
- This rotation contributes to overall thumb opposition movement
Thumb Musculature
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Two groups: extrinsic (long) and intrinsic (short) muscles
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Extrinsic Muscles:
- Abductor Pollicis Longus (AbPL): Abduction and extension of M1, especially with flexed wrist, also weak radial deviation with stabilized M1, forms a force couple with intrinsic muscles
- Extensor Pollicis Brevis (EPB): Extension of P1 over M1, lateral movement of M1, extension-adduction of CMC, also radial deviation with unstabilized wrist
- Extensor Pollicis Longus (EPL): Extension of P2 over P1, extension of P1 over M1, medial movement of M1, adduction of M1, flattens the palm, antagonist of opposition muscles, forms a functional set with the lateral thenar group, can extend the wrist if unopposed
- Flexor Pollicis Longus (FPL): Flexion of P2 over P1, flexes P1 over M1, terminal prehension
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Intrinsic Muscles:
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Lateral Group:
- Flexor Pollicis Brevis (FPB): Opposition, flexion of P1 on M1, medial rotation
- Opponens Pollicis (OP): Abduction of M1, flexion of M1, medial rotation, essential for all thumb grips
- Abductor Pollicis Brevis (AbPB): Abduction of M1, flexion of P1 on M1, medial rotation, essential for opposition, forms a couple with AbPL
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Medial Group:
- First Palmar Interosseus (I.PIO): Adduction of M1, flexion of P1, extension of P2, essential for holding objects between thumb and index finger
- Adductor Pollicis (AdP): Adduction or flexion of M1 depending on starting position, abduction or extension with different starting position, active in various prehension, also flexion and lateral rotation of P1, extension of P2
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Thumb - Opposition
- Complex motion initiating with raising M1 above the palm plane
- AbPL and thenar muscles work in two stages:
- AbPL abducts and extends M1
- Thenar muscles (FPB, AbPB, OP) flex and slightly adduct M1 with medial rotation
- These stages occur simultaneously
- Adductor pollicis acts at the end of the movement
Actions of Thumb Muscles
- AbPL: Abduction and extension of M1
- EPB: Extension of P1 over M1, lateral movement of M1
- EPL: Extension of P2 over P1, extension of P1 over M1, medial movement of M1
- FPL: Flexion of P2 over P1, also flexes P1 over M1
- FPB: Opposition, flexion of P1 on M1, medial rotation
- OP: Abduction, flexion and medial rotation of M1
- AbPB: Abduction and flexion of M1, flexion of P1 on M1, medial rotation, essential for opposition
- AdP: Adduction or flexion of M1 depending on position, abduction or extension with different position, active in various prehension
- I.PIO: Adduction of M1, flexion of P1, extension of P2
Modes of Prehension
- Ability of fingers and thumb to grasp or seize objects
- Classified based on force:
- Power Grip: High force for heavy tasks, fingers flexed, thumb for stabilization
- Precision Grip: High accuracy, low force, fingers and thumb hold object, palm not involved
- Both can be differentiated by dynamic and static phases
- Power grip has a static phase where the grip and object are moved through space
- Precision grip does not have a static phase, fingers grasp for manipulation
Power Grip
- Fingers clamp onto object in the palm
- Fingers flex in degrees depending on object size, shape, and weight
- Palm conforms to object
- Thumb adducts for additional surface
- Four types:
- Cylindrical
- Spherical
- Hook
- Lateral prehension
Cylindrical Grip
- Primarily uses flexors
- FDP muscle is primary, especially for dynamic closing
- FDS muscle assists for greater force
- Interossei are primarily flexors and abductors/adductors at the MCP joint
- Ulnarly deviate MCP (adduction of index, abduction of other fingers) to align with the thumb
- This creates ulnar subluxation forces, counteracted by radial collateral ligaments, annular pulleys, and sagittal bands
- EDC muscle tension can stabilize these elements, increase joint stability
Power Grip
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Thumb:
- Flexor pollicis longus (FPL) and thenar muscles are active in thumb opposition and adduction.
- Thenar muscle activity varies based on web space width, CMC rotation, and pressure.
- Adductor pollicis (AdP) is more active during power grip than precision handling.
- Extensor pollicis longus (EPL) stabilizes the MP joint or acts as an adductor.
- Hypothenar muscles are typically active - abductor digiti minimi (ADM) flexes and abducts (ulnarly deviates) the 5th MP joint.
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Cylindrical Grip:
- Wrist is in neutral flexion/extension with slight ulnar deviation.
- Increased object weight leads to increased ulnar deviation.
- Strong Flexor carpi ulnaris (FCU) contraction increases tension on the transverse carpal ligament (TCL).
- Ring and little fingers contribute 70% of index and middle finger flexor force.
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Spherical Grip:
- Similar to cylindrical grip with a wider finger spread.
- More interosseous muscle activity.
- MCP joints abduct instead of ulnar deviating.
- Phalanges are not parallel.
- Extensors balance flexors and control hand opening.
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Hook Grip:
- Specialized power grip primarily of fingers.
- Thumb is excluded.
- Sustained over time.
- Flexor digitorum profundus (FDP) and flexor digitorum superficialis (FDS) are primarily active.
- Thumb is held in extension by extrinsic thumb muscles.
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Lateral Prehension:
- Contact between two adjacent fingers.
- MCP and IP joints are in extension.
- Extensor muscles dominate.
- Extensor digitorum communis (EDC) and lumbricals are active.
- Interossei muscles perform abduction and adduction.
Precision Handling
- Requires more precise motor control and intact sensation.
- Thumb serves as one "jaw" of a two-jaw chuck.
- Second "jaw" is formed by the distal tip, pad, or side of a finger.
- Three-jaw chuck uses two fingers opposing the thumb.
- Three types:
- Pad-to-pad prehension
- Tip-to-tip prehension
- Pad-to-side prehension
Pad-to-Pad Prehension
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Finger:
- Opposing the pulps of the thumb and finger.
- Index finger typically used in two-jaw chuck, middle finger added in three-jaw chuck.
- MCP and PIP joints partially flexed, DIP may be fully extended or slightly flexed.
- FDS flexes the DIP when extended.
- FDP is active when partial DIP flexion is needed.
- Interossei muscles contribute to MCP flexion and abduction/adduction.
- VI and DI muscles work reciprocally during dynamic manipulation.
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Thumb:
- CMC flexion, abduction, and rotation (opposition).
- MCP and IP joints may be partially flexed or fully extended.
- Thenar muscles (OP, FPB, APB) are controlled by the median nerve.
- AdP activity increases with pinch pressure.
- FDP flexes the distal phalanx when required.
- Extensors open the hand, release, and stabilize.
- EPL maintains IP extension during light contact on the proximal pad.
Tip-to-Tip Prehension
- Similar to pad-to-pad prehension.
- Thumb and finger IP joints must be fully flexed.
- MCP joint of opposing finger is ulnarly deviated (adducted).
- Requires FDP, FPL, and interossei muscles to function effectively.
Pad-to-Side Prehension
- Least precise precision handling.
- Thumb is adducted and less rotated.
- FPB activity increases, OP decreases compared to tip-to-tip.
- AdP activity increases compared to tip-to-tip and pad-to-pad.
- Slight IP joint flexion of the thumb is required.
Tenodesis Action
- Wrist extension activates intact ECU, ECRL, and ECRB muscles, generating passive tension in finger flexor tendons, flexing MCP and IP joints.
- Wrist relaxation releases the grip.
- Active wrist extension closes the fingers, passive wrist flexion opens the fingers.
- Can achieve a cylindrical grip.
Opening the Hand: Finger Extension
- Primary extensors are EDC and intrinsic muscles (lumbricals and interossei).
- EDC extends the MCP joint.
- Intrinsic muscles:
- Direct effect: Proximal pull on the extensor mechanism
- Indirect effect: Preventing MCP joint hyperextension.
- Wrist flexors are activated to offset the EDC's extension potential.
Closing the Hand: Finger Flexion
- Muscle activation depends on the joints being flexed and force requirements.
- FDP, FDS, and IO muscles active during resistance or high speed.
- Lumbricals passively assist.
- PIP and DIP joints flex before MCP joints.
- Intrinsic muscle paralysis delays MCP joint flexion.
Closing the Hand: Finger Flexion and Fist Making
- Strong fist requires strong synergistic activation from wrist extensor muscles.
- Wrist extensors prevent excessive finger flexor wrist flexion.
- Paralyzed wrist extensors result in wrist and finger flexion, ineffective grip.
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Description
Test your knowledge about the anatomy and functions of the hand with this comprehensive quiz. Learn about various structures, joints, and muscles involved in hand movements. Ideal for students of anatomy or physical therapy.
