Logan Steele
The thumb's metacarpophalangeal (MCP) joint has a full range of motion of about 60 degrees, which is almost completely flexion. The muscles that produce flexion of the thumb MCP joint are the flexor pollicis brevis and the flexor pollicis longus muscle. The palmar ligament, which contains two sesamoid bones, is also present in the thumb MCP joint and helps prevent hyperextension. The deep transverse metacarpal ligaments provide stability to the MCP joints during grip functions.
| Characteristics | Values |
|---|---|
| Full range of motion | 60° |
| Ligaments | palmar ligament, deep transverse metacarpal ligaments |
| Muscles that produce flexion | flexor pollicis brevis, flexor pollicis longus |
| Muscles that produce axial rotation | flexor pollicis brevis, abductor pollicis brevis |
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What You'll Learn
- The thumb MCP joint has a full range of motion of about 60 degrees
- The palmar ligament prevents MCP joint hyperextension
- Flexor pollicis brevis and longus muscles produce thumb flexion
- Axial rotation is produced by flexor pollicis brevis and abductor pollicis brevis
- Gamekeeper's thumb is an injury to the ulnar collateral ligament of the MCP joint
The thumb MCP joint has a full range of motion of about 60 degrees
The metacarpophalangeal (MCP) joints are the articulations where the fingers and thumb attach to the hand. These joints are vital to the hand's functional capabilities, enabling gripping, pinching, bending, straightening, and moving together or spreading apart the fingers. The MCP joints' normal range of motion is 90-100 degrees of flexion and 30-45 degrees of extension.
Abduction and adduction in the MCP joints are followed by movements in the corresponding carpometacarpal joints. Axial rotation is crucial for the MCP joint of the thumb and occurs during opposition. This rotation can be active or passive, with active axial rotation produced by the simultaneous action of flexor pollicis brevis and abductor pollicis brevis muscles.
Flexion of the thumb is primarily produced by flexor pollicis brevis, aided by flexor pollicis longus muscle. Extension of the thumb (from a flexed position) is mainly produced by the extensor pollicis brevis, with some assistance from the extensor pollicis longus muscle. The palmar ligament, or palmar/volar plate, is a dense fibrocartilaginous thickening located on the palmar aspect of the MCP joint capsule. Its main function is to prevent hyperextension of the MCP joint.
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The palmar ligament prevents MCP joint hyperextension
The thumb's metacarpophalangeal (MCP) joint is enveloped by a loose fibrous capsule, strengthened by collateral metacarpophalangeal ligaments. The palmar metacarpophalangeal ligament replaces the capsule on its anterior aspect. The palmar ligament contains two sesamoid bones, which articulate with palmar facets on the thumb metacarpal head.
The palmar ligament's main function is to prevent hyperextension of the MCP joint. The deep transverse metacarpal ligaments are narrow fibrous bands that run across the palmar aspect of the second to fifth MCP joints, connecting them together. They are situated anterior to interossei muscles and posterior to lumbricals. Their palmar surfaces are connected to the digital slips of the central palmar aponeurosis.
The MCP joints' movements include flexion, extension, adduction, abduction, circumduction, and limited rotation. The full range of motion for the thumb MCP joint is 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.
The palmar ligament plays a crucial role in maintaining the stability of the MCP joint during grip functions. Its presence helps prevent hyperextension, ensuring that the MCP joint moves within a safe range of motion, and avoiding potential injury or dislocation.
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Flexor pollicis brevis and longus muscles produce thumb flexion
The thumb's metacarpophalangeal (MCP) joint has a full range of motion of about 60 degrees, which is almost completely flexion. The movement in this joint is limited by the ligamentous structures that surround it and antagonistic muscles. The thumb MCP joint's primary function is axial rotation, which is produced by the simultaneous action of the flexor pollicis brevis and abductor pollicis brevis muscles.
The palmar ligament in the thumb contains two sesamoid bones, which articulate with palmar facets on the thumb metacarpal head. This ligament's main function is to prevent hyperextension of the MCP joint. The deep transverse metacarpal ligaments are narrow fibrous bands that run across the palmar aspect of the second to fifth MCP joints, connecting them together. They are situated anterior to interossei muscles and posterior to lumbricals.
The flexor pollicis brevis and flexor pollicis longus muscles produce thumb flexion. The flexor pollicis brevis is the primary muscle responsible for flexion of the thumb MCP joint, with assistance from the flexor pollicis longus. The flexor pollicis brevis muscle is also involved in the active axial rotation of the MCP joint, along with the abductor pollicis brevis.
The close-packed position of the thumb MCP joint is maximum opposition, while the open-packed or resting position is slight flexion. The capsular pattern of the MCP joints generally allows for more limitation of flexion than extension. Additionally, accessory movements in the thumb MCP joint include accessory rotation, anteroposterior translation of metacarpals or phalanges, and lateral translation of metacarpals or phalanges.
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Axial rotation is produced by flexor pollicis brevis and abductor pollicis brevis
Axial rotation is a movement that occurs during opposition of the thumb MCP joint. This rotation can be active or passive. Active axial rotation is produced by the simultaneous action of flexor pollicis brevis and abductor pollicis brevis muscles. The flexor pollicis brevis is a small, narrow muscle that originates from the flexor retinaculum of the wrist and the ulnar side of the metacarpal bone. It flexes and rotates the thumb, bending it towards the small finger. The abductor pollicis brevis, on the other hand, pulls the thumb away from the index finger. Together, these muscles contract to produce axial rotation of the thumb MCP joint.
The thumb MCP joint has a full range of motion of about 60 degrees, which is almost completely flexion. The movements in this joint are limited by ligamentous structures and antagonistic muscles. The thumb MCP joint's main function is to provide stability during grip functions. The palmar ligament, for instance, prevents hyperextension of the MCP joint.
The flexor pollicis brevis is part of the thenar muscle group, which forms the muscle bulk on the thumb side of the hand. This muscle group is responsible for complex movements of the thumb, especially fine motor functions. The abductor pollicis brevis is also part of the thenar muscle group and plays a crucial role in hand functions.
In rare cases, individuals may be born with bilateral congenital absence of the flexor pollicis brevis and abductor pollicis brevis muscles, resulting in thenar atrophy. This condition can lead to mild disability in bilateral thumb abduction and opposition, but some individuals may refuse surgical treatment if they experience only mild hand dysfunction.
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Gamekeeper's thumb is an injury to the ulnar collateral ligament of the MCP joint
The thumb metacarpophalangeal (MCP) joint has a range of motion of about 60 degrees, which is almost completely flexion. The palmar ligament in the thumb contains two sesamoid bones, which articulate with palmar facets on the thumb metacarpal head. The palmar ligament prevents hyperextension of the MCP joint. The MCP joints are stabilised by the deep transverse metacarpal ligaments, which are narrow fibrous bands that run across the palmar aspect of the second to fifth MCP joints, connecting them together.
The flexor pollicis brevis and abductor pollicis brevis muscles produce axial rotation in the MCP joint. The flexor pollicis brevis also produces flexion in the MCP joint, aided by the flexor pollicis longus muscle.
Ulnar collateral ligament injuries can be classified as partial, complete, or chronic tears. Patients with this injury may experience swelling and tenderness at the first MCP joint, along with instability or laxity. Diagnosis of this condition can be challenging as it is often accompanied by damage to other hand structures. Physical examination combined with imaging procedures such as X-rays or MRI scans is typically used for diagnosis. Treatment options depend on the severity of the injury, with mild injuries treated through physical therapy and severe ruptures or tears requiring surgical intervention.
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Frequently asked questions
The thumb MCP joint flexion is produced by flexor pollicis brevis, with support from flexor pollicis longus muscle.
The thumb MCP joint has a range of motion of about 60 degrees, which is mostly flexion.
The palmar ligament in the thumb MCP joint contains two sesamoid bones and its main function is to prevent hyperextension of the MCP joint.
The close-packed position of the thumb MCP joint is maximum opposition, while the open-packed or resting position is slight flexion.
Gamekeeper's thumb is an injury to the ulnar collateral ligament of the MCP joint of the thumb, often caused by falling on an outstretched hand with an abducted thumb. Treatment depends on the severity, with mild injuries treated with physical therapy and complete ruptures requiring surgery.
