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Questions and Answers
What is the function of the carpometacarpal (CMC) joints?
What is the function of the carpometacarpal (CMC) joints?
Which muscles originate from the dorsal surface of the hand?
Which muscles originate from the dorsal surface of the hand?
What distinguishes the structure of the thumb compared to other fingers in terms of phalanges?
What distinguishes the structure of the thumb compared to other fingers in terms of phalanges?
Which muscles are classified as extrinsic muscles of the hand?
Which muscles are classified as extrinsic muscles of the hand?
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How many interphalangeal (IP) joints does each index, middle, ring, and little finger possess?
How many interphalangeal (IP) joints does each index, middle, ring, and little finger possess?
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Which intrinsic muscle of the hand is responsible for adducting the thumb?
Which intrinsic muscle of the hand is responsible for adducting the thumb?
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What characterizes the role of the interossei muscles in hand movement?
What characterizes the role of the interossei muscles in hand movement?
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What is the primary structural role of the mechanical linkage in a healthy hand?
What is the primary structural role of the mechanical linkage in a healthy hand?
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What describes the movement of the metacarpal during full extension at the CMC joint?
What describes the movement of the metacarpal during full extension at the CMC joint?
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Which ligament is stretched during the thumb's full opposition?
Which ligament is stretched during the thumb's full opposition?
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What is the primary motion allowed at the I.MCP joint?
What is the primary motion allowed at the I.MCP joint?
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What is the significance of full opposition in relation to joint stability?
What is the significance of full opposition in relation to joint stability?
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Which of the following accurately describes the I.MCP joint during active flexion?
Which of the following accurately describes the I.MCP joint during active flexion?
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Which of the following statements about the third degree of freedom in the CMC joint is true?
Which of the following statements about the third degree of freedom in the CMC joint is true?
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What occurs during the reposition phase of the CMC joint?
What occurs during the reposition phase of the CMC joint?
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What happens to the capsular ligaments during full opposition of the thumb?
What happens to the capsular ligaments during full opposition of the thumb?
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What is the primary function of the FPL muscle?
What is the primary function of the FPL muscle?
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Which muscle primarily contributes to opposition by bringing the pulp of the thumb into contact with the last two digits?
Which muscle primarily contributes to opposition by bringing the pulp of the thumb into contact with the last two digits?
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Which of the following actions is NOT associated with the OP muscle?
Which of the following actions is NOT associated with the OP muscle?
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What role does the AbPB play during opposition of the thumb?
What role does the AbPB play during opposition of the thumb?
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Which muscle is heavily involved in the lateral group of thenar muscles during thumb movements?
Which muscle is heavily involved in the lateral group of thenar muscles during thumb movements?
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How does the FPL facilitate the flexion of P2?
How does the FPL facilitate the flexion of P2?
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In opposition movements, which action is NOT performed by the OP muscle?
In opposition movements, which action is NOT performed by the OP muscle?
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Which muscle is primarily responsible for the medial rotation of P1 during thumb opposition?
Which muscle is primarily responsible for the medial rotation of P1 during thumb opposition?
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Which muscle is primarily responsible for flexion when the load is carried distally in a hook grip?
Which muscle is primarily responsible for flexion when the load is carried distally in a hook grip?
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What joint positions are typically maintained in lateral prehension?
What joint positions are typically maintained in lateral prehension?
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Which muscles are primarily active in lateral prehension for maintaining posture?
Which muscles are primarily active in lateral prehension for maintaining posture?
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How is hook grip different from other grips concerning the role of the thumb?
How is hook grip different from other grips concerning the role of the thumb?
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What is a key characteristic of precision handling compared to power grip?
What is a key characteristic of precision handling compared to power grip?
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Which action is performed by the interossei muscles during lateral prehension?
Which action is performed by the interossei muscles during lateral prehension?
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What is the role of wrist flexors during active finger extension?
What is the role of wrist flexors during active finger extension?
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What describes the grip of someone who has lost their thumb but has adapted?
What describes the grip of someone who has lost their thumb but has adapted?
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Which muscles are primarily activated for flexing fingers against resistance?
Which muscles are primarily activated for flexing fingers against resistance?
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What is the primary function of the hook grip in comparison to the lateral prehension?
What is the primary function of the hook grip in comparison to the lateral prehension?
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What effect does paralysis of the intrinsic muscles have on finger flexion?
What effect does paralysis of the intrinsic muscles have on finger flexion?
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In making a strong fist, what role do wrist extensors play?
In making a strong fist, what role do wrist extensors play?
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What happens when the wrist extensors are paralyzed during attempts to make a fist?
What happens when the wrist extensors are paralyzed during attempts to make a fist?
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How do the lumbricals assist in finger flexion?
How do the lumbricals assist in finger flexion?
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What happens to the EDC during active finger extension with the MCP joint blocked from hyperextension?
What happens to the EDC during active finger extension with the MCP joint blocked from hyperextension?
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What is the chronological sequence of joint flexion during hand closing?
What is the chronological sequence of joint flexion during hand closing?
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Study Notes
Hand Anatomy
- The hand comprises 5 metacarpals, collectively known as the "metacarpus."
- Each finger contains phalanges, and a ray describes one metacarpal with its associated phalanges.
- The carpometacarpal (CMC) joints are formed between the metacarpals and the distal row of carpal bones.
- The metacarpophalangeal (MCP) joints are formed between the metacarpals and the proximal phalanges.
- Fingers II-V have two interphalangeal (IP) joints: a proximal (PIP) and a distal (DIP) joint.
- The thumb has two phalanges and one interphalangeal (IP) joint.
Hand Muscles
-
Dorsal surface:
- Dorsal interossei (I-IV) originate on the dorsal surface.
- Extrinsic muscles inserting on the dorsal surface include ECRL, ECRB, ECU, Extensor pollicis brevis, Extensor pollicis longus, Extensor digitorum, Extensor indicis, and Extensor digiti minimi.
- Intrinsic muscles inserting on the dorsal surface include Adductor pollicis and Dorsal interossei (I-IV).
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Palmar surface:
- Intrinsic muscles originating on the palmar surface include:
- Thenar: Abductor pollicis brevis, Flexor pollicis brevis, Opponens pollicis, Adductor pollicis with 2 heads.
- Mesothenar: Palmar interossei (I-IV).
- Hypothenar: Abductor digiti minimi, Flexor digiti minimi, Opponens digiti minimi.
- Intrinsic muscles originating on the palmar surface include:
Thumb Joints
-
I.CMC Joint:
- Extension involves a lateral (radial) roll and slide of the metacarpal on the trapezium, with slight lateral rotation.
- Opposition is divided into two phases: abduction of the thumb metacarpal in phase 1, followed by flexion and medial rotation in phase 2.
- Full opposition stretches ligaments and maximizes joint congruity and stability, considered the close-packed position.
- Repositioning the CMC joint to the anatomic position involves adduction and extension-lateral rotation of the thumb metacarpal.
-
I.MCP Joint:
- Articulation between the convex head of the 1st metacarpal and the concave proximal surface of the proximal phalanx of the thumb.
- Similar basic structure and arthrokinematics to finger joints.
- Primarily allows one degree of freedom (DoF): flexion and extension in the frontal plane.
- Active flexion is about 60°, passive flexion is 80°, and extension returns to neutral.
Thumb Muscles
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FPL:
- Primarily flexes P2 over P1 (IP joint).
- Requires EPB contraction to prevent flexion of P1, creating synergistic action.
- Secondarily flexes P1 over M1 (MCP joint).
- Important role in terminal prehension.
-
FPB:
- Participates in movements produced by the lateral thenar group.
- Primarily brings the thumb pulp into opposition with the last two digits.
- Flexes P1 on M1 (MCP) with the help of AbPB, the medial sesamoid muscle, and the 1st palmar interosseus.
- Produces medial rotation.
- Flexes and abducts the CMC joint.
- Combined action with lateral thenar muscles leads to thumb opposition with the assistance of AbPL.
-
OP:
- Three primary actions:
- Abduction of M1 with respect to the carpus (CMC), especially in the long path of opposition.
- Flexion, bringing M1 and M2 closer during maximal opposition.
- Axial rotation in a medial direction.
- These movements are essential for opposition.
- OP is active in all thumb-involving grips.
- Three primary actions:
-
AbPB:
- Maximally separates M1 and M2 during opposition.
- Moves M1 (CMC) anteriorly (abduction) and medially (flexion).
- Primarily flexes P1 on M1 (MCP).
- Mediates medial rotation of P1.
- Extends P2 on P1 (IP) through an expansion that joins the EPL.
Hand Grip Types
-
Hook Grip:
- A specialized form of power grip relying on the fingers, potentially including the palm but excluding the thumb.
- Primarily uses FDP and FDS muscles.
- Load sustained depends on the load's position relative to the phalanges, with more distal loads requiring FDP involvement.
- Thumb is in moderate to full extension by thumb extrinsic muscles.
-
Lateral Prehension:
- Unique grasp involving contact between adjacent fingers.
- MCP and IP joints are typically extended, with simultaneous abduction and adduction of contiguous MCP joints.
- EDC and lumbricals actively extend the MCP and IP joints.
- Interossei muscles perform abduction and adduction.
- It's a power grip due to static object holding with more proximal joint movements.
- Used for holding objects without manipulation.
-
Precision Handling:
- More variable positions and muscle requirements than power grip.
- Requires finer motor control and intact sensation.
- EDC effectively tenses the extensor mechanism to extend the IP joints only with the MCP joint blocked from hyperextension.
- Wrist flexors activate during rapid finger extension to offset the EDC's extension potential at the wrist.
- Slight wrist flexion helps maintain the EDC's optimal length during active finger extension.
Hand Closure: Finger Flexion
-
Finger flexion:
- Muscles used depend on the flexed joints and force requirements.
- Strong flexion against resistance or at high speed involves FDP, FDS, and IO muscles.
- Lumbricals passively assist.
- Active flexion stretches the lumbricals proximally due to FDP contraction and distally due to the extensor mechanism's migration.
- This stretch generates a passive flexion torque at the MCP joint.
- PIP and DIP joints flex first, followed by MCP joints.
- Intrinsic muscle paralysis alters the sequence, delaying MCP joint flexion.
-
Fist making:
- Requires synergistic activation from the wrist extensor muscles.
- Primary function of the wrist extensors (including EDC) is to neutralize the strong wrist flexion tendency of the extrinsic finger flexors.
- Wrist extension maintains optimal length of the extrinsic finger flexors.
- Wrist extensor paralysis results in wrist and finger flexion when attempting to make a fist.
- Overshortened, activated finger flexors and overstretched EDC result in ineffective grip.
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Description
Test your knowledge of hand anatomy and the associated muscles. This quiz covers the structure of the metacarpals, phalanges, and the various joints in the hand, along with their associated muscles on both the dorsal and palmar surfaces. Challenge yourself to understand the intricate details of hand anatomy.
