Dominic Stone
The metacarpophalangeal joints (MCP) are situated between the metacarpal bones and the proximal phalanges of the fingers. These joints allow for movements of flexion, extension, abduction, adduction, and circumduction. The muscles responsible for MCP flexion include the flexor pollicis brevis, flexor pollicis longus, flexor digitorum superficialis, flexor digitorum profundus, lumbricals, and flexor digiti minimi brevis. The third palmar interosseous, abductor digiti minimi, and small lumbrical muscles are also involved in MCP flexion. Understanding the anatomy of the MCP joints and their associated muscles is essential for diagnosing and treating injuries, such as gamekeeper's thumb, which involves damage to the ulnar collateral ligament of the MCP of the thumb.
| Characteristics | Values |
|---|---|
| Type of joint | Condyloid |
| Joint stabilizers | Extrinsic musculotendinous units and intrinsic joint elements of capsule and collateral ligaments |
| Joint movement | Flexion, extension, abduction, adduction, circumduction, and limited rotation |
| Muscles of flexion | Flexor pollicis brevis, flexor pollicis longus, flexor digitorum superficialis, flexor digitorum profundus, lumbricals, flexor digiti minimi brevis, third palmar interosseous, abductor digiti minimi, flexor digiti minimi, small lumbrical |
| Axial rotation | Co-contraction of flexor pollicis brevis and abductor pollicis brevis |
| Ulnar nerve palsy | Loss of active ring and little DIP joint flexion and wrist flexion |
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What You'll Learn
- The thumb MCP joint's full range of motion is about 60 degrees
- The small finger has a large intrinsic contribution due to the hypothenar muscles
- The muscles of flexion and extension include the Extensor tendons
- The MCP joint is formed by the metacarpal bones and the proximal phalanges
- The MCP joint allows for extension, flexion, abduction, adduction, and rotation
The thumb MCP joint's full range of motion is about 60 degrees
The metacarpophalangeal (MCP) joints are situated between the metacarpal bones and the proximal phalanges of the fingers. They are of the condyloid kind, which means they are formed by the reception of the rounded heads of the metacarpal bones into shallow cavities on the proximal ends of the proximal phalanges. The movements that occur in these joints are flexion, extension, abduction, adduction, and circumduction.
The MCP joints are most prominent when making a fist and they facilitate anything that requires opening or closing the hand. They help us grip, pinch, bend or straighten, and move together or spread apart the fingers. The MCP joints' normal range of motion values is 90-100 degrees of flexion and 30-45 degrees of extension.
The thumb MCP joint has a full range of motion of about 60 degrees, which is almost completely flexion. The movements in this axis are limited by ligamentous structures that surround the joint and antagonistic muscles. The full range of motion in this axis is around 25-30 degrees, which belongs mostly to abduction. These movements are limited mainly by the shape and width of the metacarpal head and by collateral ligaments. When the MCP joints are flexed, neither abduction nor adduction can occur, largely due to the arrangement of the collateral ligaments.
Flexion of the thumb is mainly produced by flexor pollicis brevis, aided by flexor pollicis longus muscle. Extension of the thumb (from the flexed position) is mainly produced by the extensor pollicis brevis, with some help from extensor pollicis longus muscle.
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The small finger has a large intrinsic contribution due to the hypothenar muscles
The human hand is a complex structure, with various muscles, joints, and bones working together to allow for a wide range of movements. One of the key joints in the hand is the metacarpophalangeal (MCP) joint, which is situated between the metacarpal bones and the proximal phalanges of the fingers. This joint allows for movements such as flexion, extension, abduction, adduction, and circumduction.
The small finger, or the fifth digit, has a unique muscular structure at its base known as the hypothenar eminence. This fleshy part is formed by four hypothenar muscles, which are intrinsic muscles located within the hand itself. These muscles include the opponens digiti minimi, the abductor digiti minimi, and two others. The hypothenar muscles are similar in name and organisation to the thenar muscles, which are located at the base of the thumb.
The small finger has a large intrinsic contribution to MCP joint flexion due to the presence of these hypothenar muscles. The larger moment arms of the hypothenar muscles enable this increased contribution. The hypothenar muscles contract to produce motion in the little finger, including flexion and rotation. For example, the opponens digiti minimi rotates the metacarpal of the little finger towards the palm, while the abductor digiti minimi abducts the little finger.
The ulnar nerve innervates the hypothenar muscles, and any compromise of this nerve can lead to symptomatic changes in the hypothenar eminence. Ulnar nerve repair requires a thorough understanding of its course to prevent atrophy and loss of function in the region. The hypothenar muscles are crucial for fine motor movements and work in conjunction with the thenar muscles to provide opposition between the little finger and the thumb.
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The muscles of flexion and extension include the Extensor tendons
The human body contains two types of skeletal muscles: flexors and extensors. These muscles work in tandem to facilitate movement at the joints. Flexor muscles contract, pulling bones closer together and reducing the angle at the joint, resulting in flexion. Extensor muscles, on the other hand, contract to straighten joints and increase the angle at a joint.
The Extensor tendons cover the dorsal surfaces of the MCP joints, along with some loose areolar tissue that connects the deep surfaces of the tendons to the bones. The extensor digitorum muscle, which originates from the lateral epicondyle of the humerus, is responsible for extending the four medial fingers in their MCP and interphalangeal joints. It also aids in wrist extension.
The intrinsic muscles also contribute significantly to MCP joint flexion, particularly in the middle, ring, and small fingers. The small finger has a large intrinsic contribution due to the larger moment arms of the hypothenar muscles. Additionally, muscles such as the third palmar interosseous, abductor digiti minimi, flexor digiti minimi, and small lumbrical contribute to MCP joint flexion.
In summary, the muscles of flexion and extension, including the Extensor tendons, are essential for the movement and stability of the MCP joints. They work in coordination with intrinsic muscles to enable flexion, extension, and other movements of the fingers and wrist.
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The MCP joint is formed by the metacarpal bones and the proximal phalanges
The MCP, or metacarpophalangeal, joint is formed by the metacarpal bones and the proximal phalanges of the fingers. It is a diarthrodial joint, meaning it allows a wide range of motion, including extension, flexion, abduction, adduction, and rotation. The MCP joint is critical for functional hand motion, allowing us to grip and perform precise movements with our fingers.
The shape of the MCP joint is unique due to the non-spherical shape of the metacarpal head, creating what is known as the ""cam effect." This shape results in a greater distance from the axis of rotation of the metacarpal head to the base of the proximal phalanx during flexion compared to extension. The collateral ligaments play a crucial role in maintaining joint stability by dynamically changing their length relative to the fixed joint axis.
The muscles responsible for MCP joint flexion include the flexor pollicis brevis, flexor pollicis longus, flexor digitorum superficialis, flexor digitorum profundus, lumbricals, and flexor digiti minimi brevis. These muscles work together to produce the flexion movement at the MCP joint, allowing us to bend our fingers.
Additionally, the intrinsic tendons, including the lumbricals and interossei, form lateral bands along the proximal phalanx. These lateral bands slide dorsally and volarly during finger flexion and extension, respectively, contributing to the overall movement of the MCP joint. The stability of the MCP joint during grip functions is also maintained by the deep transverse metacarpal ligaments, which run across the palmar aspect of the second to fifth MCP joints.
Injuries to the MCP joint, such as ligamentous tears or trauma, can result in stiffness and a decreased range of flexion. Prolonged immobilization of the MCP joint in extension may further restrict motion. However, maintaining the MCP joints in flexion during immobilization can provide a greater chance of recovering motion.
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The MCP joint allows for extension, flexion, abduction, adduction, and rotation
The MCP, or metacarpophalangeal, joint is a diarthrodial joint that is critical for functional hand motion. It allows for extension, flexion, abduction, adduction, and rotation. The MCP joints are situated between the metacarpal bones and the proximal phalanges of the fingers.
Flexion and extension are considered the primary movements of the MCP joint. Active flexion has a range of motion of approximately 90 degrees, while extension ranges from 10 degrees in the index finger to 30 degrees in the little finger. The full range of motion for the thumb MCP joint is about 60 degrees, which is almost completely flexion.
The muscles that produce MCP joint flexion include the third palmar interosseous, the abductor digiti minimi, the flexor digiti minimi, and the small lumbrical. The intrinsic tendons (lumbricals and interossei) form along each lateral surface of the finger, allowing the intrinsics to flex the MCP joints and extend the IP.
Abduction and adduction movements in the MCP joints are very limited and cannot be performed while the fingers form a fist. These movements are restricted when the MCP joints are flexed, largely due to the arrangement of the collateral ligaments. Abduction and adduction in the MCP joints are always followed by movements in the corresponding carpometacarpal joints.
Axial rotation is most important for the MCP joint of the thumb and is produced by the simultaneous action of flexor pollicis brevis and abductor pollicis brevis muscles. Low ulnar paralysis can result in a significant loss of hand dexterity and strength, including a loss of the normal pattern of finger flexion.
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Frequently asked questions
MCP joints, or metacarpophalangeal joints, are situated between the metacarpal bones and the proximal phalanges of the fingers. They are critical for functional hand motion.
The muscles involved in MCP flexion include the flexor pollicis brevis, flexor pollicis longus, flexor digitorum superficialis, flexor digitorum profundus, lumbricals, flexor digiti minimi brevis, and flexor digiti minimi.
Yes, injuries to the MCP joints can result in decreased motion and stiffness. One common injury is called "Gamekeeper's thumb," which involves damage to the ulnar collateral ligament of the MCP of the thumb. This can occur when falling onto an outstretched arm with an abducted thumb.
