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The thumb contains three phalanges and two interphalangeal joints.
False
The carpometacarpal joints are formed by the proximal ends of the metacarpals and the distal row of carpal bones.
True
Each finger has three interphalangeal joints.
False
Dorsal interossei muscles are intrinsic muscles of the hand.
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The hypothenar muscles include the Opponens pollicis.
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The metacarpus consists of five metacarpal bones.
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Extrinsic muscles of the hand originate from within the hand.
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The proximal interphalangeal (PIP) joints are found in the thumb.
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The carpal bones are located at the wrist.
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The direction of arthrokinematic movement at the MCP joint is opposite to the direction of osteokinematic movement.
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Flexion at the MCP joint increases passive tension in the dorsal capsule.
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Extension at the MCP joint involves a ventral roll and slide of the proximal phalanx.
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Joint play refers to motion that is under voluntary control.
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The extent of active abduction is greater when performed in full flexion than in full extension.
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MCP joints II-V are comprised of a biconcave articular surface of the phalanx and a biconvex metacarpal head.
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During abduction of the index MCP joint, the proximal phalanx rolls and slides in a dorsal direction.
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Joint stability at the MCP joints is higher when the joints are in a flexed position.
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The PIP and DIP joints each consist of two adjacent phalanx heads.
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The palmar plate unfolds to support the head of the metacarpal during full extension.
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The FPL primarily flexes P1 over P2 at the IP joint.
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The FPB is responsible for opposing the thumb to the last two digits.
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The OP does not participate in abduction or flexion movements.
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The AbPB primarily causes extension of P2 on P1 at the IP joint.
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The thumb's I.MCP joint allows for significant active abduction and adduction.
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The close packed position of the I.MP joint is full flexion.
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The combined action of the lateral thenar muscles assists in opposition of the thumb.
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Accessory motions in the thumb are primarily initiated in a flexed position.
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The OP's actions include axial rotation in a lateral direction.
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The interphalangeal joint of the thumb primarily allows movement in two degrees of freedom.
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The active flexion of the thumb's IP joint can reach up to 90°.
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The I.MCP joint is reinforced by a palmar plate and two sesamoid bones.
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The thumb's musculature consists of both intrinsic and extrinsic muscles.
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The accessory motions of the CMC and MCP joints are used in a closed kinematic chain.
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The active extension of the thumb's IP joint can reach 20°.
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The AbPL muscle is inserted into the palmar aspect of the base of the first metacarpal.
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The EDC muscle flexes the MCP joint during finger tapping movements.
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The hypothenar muscles include the opponens digiti mini, which helps in opposition of the small finger.
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The CMC joint of the thumb is a hinge joint.
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The flexor carpi ulnaris contracts to stabilize the pisiform during resisted abduction of the small finger.
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The thumb joint permits no axial rotation.
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The palmaris brevis helps to deepen the concavity of the palm during a power grip.
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The actions of the interossei muscles involve extension of the MCP joint.
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Opposition of the thumb allows it to contact the palmar tips of other digits.
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The description of the thumb joint's movement includes flexion and adduction only.
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The distal transverse arch is deepened by the muscles of the hypothenar eminence.
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Study Notes
Hand Anatomy
-
Hand Structure:
- Consists of 5 metacarpal bones (metacarpus)
- Each digit has phalanges
- Ray: One metacarpal bone and associated phalanges
- Carpometacarpal (CMC) Joints: Articulation between proximal ends of metacarpals and distal row of carpal bones
- Metacarpophalangeal (MCP) Joints: Articulation between metacarpals and proximal phalanges
- Interphalangeal (IP) Joints: Two per finger (II-V): a proximal (PIP) and a distal (DIP) joint. The thumb has only one IP joint.
Hand Muscles
-
Dorsal Surface:
- Muscles that originate: Dorsal interossei (I-IV)
- Muscles that insert:
- Extrinsic: ECRL, ECRB, ECU, Extensor pollicis brevis, Extensor pollicis longus, Extensor digitorum, Extensor indicis, Extensor digiti minimi
- Intrinsic: Adductor pollicis, Dorsal interossei (I-IV)
-
Palmar Surface:
- Muscles that originate (intrinsic):
- 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
- Muscles that originate (intrinsic):
MCP Joint Arthrokinematics (II-V)
-
Flexion:
- Glide dominates with a slight roll
- Direction of arthrokinematic movement and osteokinematic movement are the same
- Increased passive tension in the dorsal capsule and collateral ligaments
- Increased joint stability in flexion helps muscles during grip
-
Extension:
- Roll and slide occur in a dorsal direction
- At 0° extension, collateral ligaments slacken, increasing passive mobility
- Palmar plate unfolds to support metacarpal head
-
Abduction:
- Proximal phalanx rolls and slides radially
- Motion is limited in flexion due to taut ligaments and increased compression force
-
Adduction:
- Similar to abduction, but in the opposite direction
- Limited motion in flexion due to ligament tension
Interphalangeal Joint Arthrokinematics (II-V - PIP, DIP)
- Composed of the head of one phalanx and the base of the phalanx distal to it
- During tapping movements:
- Extensor digitorum communis (EDC) extends MCP
- Flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDP) flex PIP and DIP
Hypothenar Muscles
- Muscles: Flexor digiti minimi, abductor digiti minimi, opponens digiti minimi, and palmaris brevis
- Action: Raise and "cup" the ulnar border of the hand, deepening the distal transverse arch
- Opponens Digiti Minimi (ODM): Opposes the 5th metacarpal towards the middle digit
- Palmaris Brevis (PB): Tightens the palmar aponeurosis, deepening the palm, helping to stabilize it during a spherical power grip
-
Abductor Digiti Minimi (AbdDM):
- Proximal attachments to pisohamate ligament, pisiform bone, and flexor carpi ulnaris tendon
- Resisted or rapid abduction of the small finger causes the flexor carpi ulnaris (FCU) to contract, stabilizing the pisiform
- This can deviate the wrist ulnarly, opposed by the abductor pollicis longus (AbPL)
Thumb Carpometacarpal Joint
- Articulation between trapezium and base of 1st metacarpal
- Saddle shape joint with 2 degrees of freedom:
- Flexion/extension
- Abduction/adduction
- Allows thumb to fully oppose, enhancing dexterity
- Permits axial rotation (~17°)
- Opposition: Circumduction motion resulting from combined movements
- Limited hyperextension
Thumb Metacarpophalangeal Joint
- Active abduction and adduction are limited, considered accessory motions
- Collateral ligaments, bony configuration, and muscles (AbPL, AbPB, FPB) restrict these motions and provide longitudinal stability
- Palmar plate and 2 sesamoid bones reinforce the volar surface
- Some accessory rotation
- Closed kinematic chain: Combined accessory motions of CMC and MCP during grip
Thumb Interphalangeal Joint
- Hinge joint between the head of the proximal phalanx and base of the distal phalanx
-
Primary motion: Flexion/extension (1 degree of freedom)
- Active flexion: 70-80°
- Passive flexion: 90°
- Active extension: 5-10°
- Passive extension: Beyond neutral to about 20°
- Accessory medial rotation during opposition
Thumb Muscles
-
Extrinsic (Long) Muscles:
- Abductor Pollicis Longus (AbPL): Inserted into the A-L aspect of the base of the 1st metacarpal (M1)
-
Intrinsic (Short) Muscles:
-
Flexor Pollicis Longus (FPL):
- Primary function: Flexes P2 over P1 (IP Joint)
- Secondarily flexes P1 over M1 (MCP Joint)
- Essential for terminal prehension
-
Flexor Pollicis Brevis (FPB):
- Part of lateral thenar muscle group
- Primary action: Brings thumb pulp into opposition with last 2 digits
- Flexes P1 on M1 (MCP) with help of AbPB and 1st palmar interosseus
- Produces medial rotation
- Affects flexion and abduction at the CMC joint
-
Opponens Pollicis (OP):
- 3 Primary Actions:
- Abduction of M1 at CMC joint, especially during opposition
- Flexion of M1 and M2 during opposition
- Medial axial rotation
- Active in all grips involving the thumb
- 3 Primary Actions:
-
Abductor Pollicis Brevis (AbPB):
- Separates M1 and M2 during opposition
- Moves M1 anteriorly (abduction) and medially (flexion)
- Flexes P1 on M1 (MCP)
- Causes medial rotation of P1
- Extends P2 on P1 (IP) via an expansion joining the extensor pollicis longus (EPL)
-
Flexor Pollicis Longus (FPL):
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Description
Test your knowledge on the anatomy of the human hand, focusing on its structure and the various muscles present. This quiz covers the metacarpal bones, phalanges, and the intricate joint system, along with muscle origin and insertion points. Perfect for students of anatomy and medical professionals alike!
