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The distal tip of a finger serves as the primary opposing jaw in a two-jaw chuck.
True
In pad-to-pad prehension, the pulp of the thumb opposes the tip of the finger tip.
False
Eighty percent of precision handling falls under pad-to-pad prehension.
True
The interosseous muscles only assist in the flexion of the MCP joint during manipulation.
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The FDS muscle is responsible for the passive extension of the DIP joint during a pinch.
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The thumb must be in CMC extension for effective pad-to-pad prehension.
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The AdP muscle is ineffective when M1 starts from a position of full abduction.
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The first palmar interosseus muscle does not perform adduction.
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The global contraction of the medial thenar muscles can bring the thumb pulp into contact with the ulnar aspect of P1 of the index.
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Opposition begins when M1 is raised directly above the median plane of the palm.
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The actions of the AdPL in the first stage of opposition include adduction and extension of M1 posteriorly.
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During full palmar prehension, the AdP does not contribute to the flexion of P1.
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The thenar muscles and AbPL function together in a two-stage action for thumb opposition.
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The interosseus muscle acts as an extensor due to its insertion blending with that of the first interosseous.
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The plane of the nail during opposition is turned at an angle of 45-60°.
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The ulnar nerve supplies the muscles crucial for holding objects firmly between the thumb and index finger.
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Hook grip primarily involves the fingers and does not include the thumb.
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The major muscles involved in hook grip are the extensor digitorum and the interossei.
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Lateral prehension is characterized by contact between two adjacent fingers while maintaining MCP joints in flexion.
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In the hook grip, the thumb is held in full flexion.
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Lateral prehension allows for the manipulation of objects using the hand.
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Precision handling requires less motor control and less dependency on sensation compared to power grip.
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The flexor digitorum profundus is involved when the load is carried more distally in hook grip.
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Lateral prehension is specifically used for holding and manipulating large, heavy objects.
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Thumb amputees can develop a notable degree of lateral prehension.
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The extensor digitorum is the primary muscle engaged during lateral prehension.
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The arthrokinematics at the MCP joint involve a biconvex articular surface of the phalanx moving against a biconcave metacarpal head.
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Flexion at the MCP joints reduces passive tension in the dorsal capsule and collateral ligaments.
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Extension at the MCP joint results in a roll and slide occurring in a ventral direction.
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Joint play is a type of voluntary motion that can be controlled actively.
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During abduction of the index MCP joint, the proximal phalanx rolls and slides in a ulnar direction.
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Active abduction and adduction at the MCP joints are greater when performed in full flexion compared to full extension.
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The PIP and DIP joints of the fingers consist of two phalanx heads.
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The palmar plate unfolds to support the head of the metacarpal during full extension.
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In the neutral position of the MCP joint, the collateral ligaments are taut, providing minimal movement.
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The EPB and EPL both insert into the base of proximal phalanges (P1).
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The FPL is an extensor muscle of the thumb.
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The triangular space known as the anatomical snuffbox is defined by the tendons of three muscles.
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The OP muscle arises from the flexor retinaculum and inserts into the anterior aspect of M1.
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The FPB has a single tendon that is inserted into the medial aspect of the base of P1.
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Intrinsic muscles of the thumb are primarily supplied by the ulnar nerve.
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The AddP muscle has two heads that converge to a common tendon upon their insertion.
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The 1st palmar interosseus muscle inserts into the lateral tubercle of the base of P1.
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The AbPB is a muscle that originates from the flexor retinaculum and the crest of the scaphoid.
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The sesamoid bones are associated with the interaction of the FPB and FPL muscles.
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Study Notes
MCP Joint Arthrokinematics
- Arthrokinematics at MCP joints are based on the biconcave articular surface of the phalanx moving against the biconvex metacarpal head.
- Flexion stretches the dorsal capsule and collateral ligaments, increasing passive tension.
- The increased passive tension helps guide the joint's natural arthrokinematics and maintain firm contact between the articular surfaces.
- The increased natural joint stability of the flexed MCP joints helps activated muscles to stabilize the joints during grasp.
- Extension involves rolling and sliding in the dorsal direction.
- At 0° extension, collateral ligaments slacken, increasing passive mobility.
- The palmar plate unfurls to support the metacarpal head at 0° extension.
Interphalangeal Joints (PIP, DIP)
- Composed of the head of a phalanx and the base of the phalanx distal to it.
- Extensor pollicis brevis (EPB) and extensor pollicis longus (EPL) are inserted into the proximal and distal phalanges, respectively.
- The three tendons of EPB, EPL, and abductor pollicis longus (APL) bound a triangular space on the dorsal and lateral aspects of the thumb.
- The flexor pollicis longus (FPL) lies on the palmar side and traverses the carpal tunnel.
Thumb Musculature - Lateral Group
- Consists of three muscles in the thenar eminence: flexor pollicis brevis (FPB), opponens pollicis (OP), and abductor pollicis brevis (AbPB).
- These muscles are supplied by the median nerve.
- The two heads of the FPB originate from the carpal tunnel and the flexor retinaculum.
- The OP arises from the flexor retinaculum and runs to the anterior aspect of the metacarpal.
- The AbPB originates from the flexor retinaculum and the scaphoid.
Thumb Musculature - Medial Group
- Consists of two muscles supplied by the ulnar nerve: the first palmar interosseus (I.PIO) and the adductor pollicis (AdP).
- The I.PIO is inserted into the medial tubercle of the base of the proximal phalanx and into the dorsal hood.
- The AdP has two heads that converge into a single tendon inserted into the medial sesamoid bone and the medial aspect of the proximal phalanx.
- The AdP is crucial for opposition, bringing the pulp of the thumb into contact with the index and middle fingers.
- The AdP and abductor pollicis longus (APL) form a force couple essential for opposition.
Adductor Pollicis (AdP)
- The AdP moves the carpometacarpal (CMC) joint.
- The direction of movement depends on the starting position of the metacarpal.
- It can act as an adductor or flexor if the metacarpal starts from full abduction or extension.
- It can also act as an abductor or extensor.
- It is active during palmar and pulp-to-pulp prehension, especially during pulp-to-side prehension.
- It exerts a slight flexion and lateral rotation action on the proximal phalanx.
- It acts as an extensor on the distal phalanx because its insertion blends with that of the I.PIO.
First Palmar Interosseus (I.PIO)
- Has similar actions to the AdP:
- Adduction of the metacarpal.
- Flexion of the proximal phalanx.
- Extension of the distal phalanx.
- The contraction of the medial thenar muscles brings the pulp of the thumb into contact with the radial aspect of the index finger.
- These muscles, supplied by the ulnar nerve, are essential for holding objects firmly between the thumb and index finger.
Opposition
- A complex motion that requires raising the metacarpal directly above the plane of the palm.
- The plane of the nail is turned at an angle of 90-120°.
- Achieved by the functional couple of the AbPL and thenar muscles in two stages:
- The AbPL abducts and extends the metacarpal anteriorly and laterally.
- The lateral group of thenar muscles (FPB, OP, and AbPB) further flex and adduct the metacarpal.
Hook Grip
- A specialized form of power grip primarily relying on the fingers.
- May involve the palm but never includes the thumb.
- Sustained for prolonged periods.
- Primarily relies on the flexor digitorum profundus (FDP) and flexor digitorum superficialis (FDS) muscles.
- The load sustained depends on the position of the load relative to the phalanges.
- The thumb is held in moderate to full extension by the extrinsic thumb muscles.
Lateral Prehension
- A unique grip where contact occurs between two adjacent fingers.
- MCP and IP joints are maintained in extension.
- MCP joints simultaneously abduct and adduct.
- The extensor musculature predominates to maintain posture, with extensor digitorum communis (EDC) and lumbrical muscles extending the MCP and IP joints.
- Interossei muscles perform abduction and adduction at the MCP joint.
- Classified as power grip because it involves static holding performed by the more proximal joints.
- Although not a “powerful” grip, it is not used to manipulate objects in the hand.
Precision Handling
- More variable than power grip, requires finer motor control, and depends on sensation.
- The thumb acts one "jaw" of a "two-jaw chuck" which is abducted and rotated from the palm.
- The second "jaw" is formed by the distal tip, pad, or side of a finger.
- When two fingers oppose the thumb, it is called a three-jaw chuck.
- Three varieties:
- Pad-to-pad prehension
- Tip-to-tip prehension
- Pad-to-side prehension.
Pad-To-Pad Prehension
- Involves opposing the pulp of the thumb to the pulp of the finger.
- The pad of the distal phalanx has the highest concentration of tactile corpuscles in the body.
- Represents 80% of precision handling forms.
- The index finger is typically used in a two-jaw chuck, and the middle finger is added in a three-jaw chuck.
- MCP and PIP joints are partially flexed, DIP may be fully extended or slightly flexed.
- When the DIP is extended, the FDP muscle is active.
- Extension of the DIP is caused passively by flexion of the middle phalanx against the thumb.
- Interossei muscles are active to supplement MCP joint flexor force and provide abduction or adduction.
- During dynamic manipulation, the VI and DI muscles work reciprocally.
- In a static, firm pinch, the interossei muscles may co-contract again.
Pad-To-Pad Prehension: Thumb Position
- The thumb is held in CMC flexion, abduction, and rotation (opposition).
- The first MCP and IP joints may be partially flexed or fully extended.
- Thenar muscle control is provided by the OP, FPB, and APB muscles, innervated by the median nerve.
- The AdP activity (ulnar nerve) increases with increased pinch pressure.
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Description
Explore the intricacies of arthrokinematics at the MCP and interphalangeal joints. This quiz covers flexion and extension movements, impact on passive tension, and the role of ligaments in joint stability. Test your understanding of these crucial anatomical concepts.
