Maximus Gage
The metacarpophalangeal (MCP) joints are situated between the metacarpal bones and the proximal phalanges of the fingers. MCP joints allow for flexion, extension, abduction, adduction, circumduction, and limited rotation of the digit. The muscles of the forearm and hand are responsible for all MCP joint movements. The extensor tendon, which passes the joint, is crucial for MCP extension, as it generates torque and carries force. Axial rotation is particularly important for the MCP joint of the thumb, allowing for opposition.
| Characteristics | Values |
|---|---|
| Type of Joint | Multiaxial diarthrodial-condyloid joint |
| Location | Between the metacarpal bones and the proximal phalanges of the fingers |
| Number of Joints | 5, one for each digit |
| Planes of Motion | 2 |
| Range of Motion | About 60° |
| Muscles Involved | Forearm and hand muscles, including flexor pollicis brevis, abductor pollicis brevis, extensor pollicis longus, extensor indicis, extensor digitorum, extensor digiti minimi, flexor digitorum profundus, flexor pollicis longus, dorsal interossei, abductor digiti minimi, lumbricals, and interossei |
| Ligaments | Deep transverse metacarpal ligaments, collateral ligaments, triangular ligament, transverse retinacular ligament, oblique retinacular ligament |
| Tendons | Extensor tendon, flexor tendon, intrinsic tendons |
| Bones | Metacarpal bones, proximal phalanges |
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What You'll Learn
The extensor tendon and extension force
The extensor tendon plays a crucial role in the extension of the metacarpophalangeal (MCP) joints, which are situated between the metacarpal bones and the proximal phalanges of the fingers. The dorsal surfaces of these joints are covered by the expansions of the extensor tendons, along with loose areolar tissue that connects the deep surfaces of the tendons to the bones.
The extension of the MCP joint is achieved through the torque generated by the extensor tendon as it passes the joint, carrying a force and possessing an extension moment arm. This torque enables the MCP joint to extend, allowing movements such as straightening the fingers or thumb. The extensor tendon is crucial in this process, as it transmits the force required for extension.
The MCP joint's range of motion, particularly in the thumb, is limited by ligamentous structures and antagonistic muscles. The axial rotation of the thumb MCP joint is of particular importance, with active rotation directed medially and passive rotation possible in either direction. The simultaneous action of specific muscles, such as the flexor pollicis brevis and abductor pollicis brevis, contributes to active axial rotation.
Extensor tendon injuries can significantly impact the extension of the MCP joints. These injuries often result from deep cuts, overstretching, or blunt trauma to the dorsal side of the hand or fingers. Symptoms of extensor tendon injuries include the inability to extend one or more joints of the finger or wrist and abnormal finger or wrist posture at rest. Treatment for extensor tendon injuries can be challenging, and some patients may experience long-term stiffness or impaired function despite extensive therapy.
Additionally, conditions such as extensor tendinitis can affect the function of the extensor tendon. Extensor tendinitis is characterised by inflammation or irritation of the extensor tendons, often caused by repetitive motions or overuse. It can lead to pain and difficulty in moving the hands or fingers, and treatment typically involves rest, avoidance of aggravating activities, and various therapies.
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Forearm and hand muscles
The metacarpophalangeal (MCP) joints are situated between the metacarpal bones and the proximal phalanges of the fingers. MCP joints are of the condyloid kind, formed by the reception of the rounded heads of the metacarpal bones into shallow cavities on the proximal ends of the proximal phalanges. The full range of motion for the thumb MCP joint is about 60 degrees, which is almost completely flexion. Axial rotation is most important for the MCP joint of the thumb and occurs during opposition. All the movements of the MCP joints are performed by the muscles of the forearm and hand.
The forearm is the section of the upper limb from the elbow to the wrist, and its bony structure is formed by the radius and ulna. The forearm muscles are divided into two compartments: the anterior flexor compartment and the posterior extensor compartment. These compartments contain twenty muscles that act on the elbow and wrist joints, as well as carpometacarpal, metacarpophalangeal, and interphalangeal joints of the hand. The forearm muscles enable complex movements of the arm, wrist, and fingers.
The intrinsic muscles function to move the forearm by pronating and supinating the radius and ulna. The extrinsic muscles flex and extend the digits of the hand. One muscle, the brachioradialis, traverses the elbow joint, running from the arm to the wrist, helping to flex the elbow. The biceps are the main supinator of the forearm, helping to rotate the palm up and down.
The deep muscles of the anterior forearm are the flexor pollicis longus, flexor digitorum profundus, and pronator quadratus. This muscle group is associated with pronation of the forearm, flexion of the wrist, and flexion of the fingers. The flexor digitorum superficialis is the only muscle of the intermediate compartment. It can be classed as a superficial muscle, but in most individuals, it lies between the deep and superficial muscle layers. The muscle splits into four tendons at the wrist, which travel through the carpal tunnel and attach to the base of the middle phalanx of the four digits. The flexor digitorum superficialis bends the middle joint of each finger (except the thumb).
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Axial rotation
Active axial rotation is produced by the simultaneous action of the flexor pollicis brevis and abductor pollicis brevis muscles. This type of rotation is always directed medially. Passive axial rotation, on the other hand, can be directed in either direction. The MCP joints of the index, long, ring, and small fingers also exhibit passive axial rotation, with the ring and small finger MCP joints showing significantly greater ranges of supination.
The MCP joints have a full range of motion of about 60 degrees, which is almost completely flexion. This range of motion is limited by the ligamentous structures surrounding the joint and antagonistic muscles. The primary movements of the MCP joints are flexion, extension, abduction, adduction, circumduction, and limited rotation. These joints are enveloped by a loose fibrous capsule and are stabilised by collateral ligaments, which consist of proper collateral and accessory collateral ligaments.
The extension of the MCP joint is a topic of interest in the Journal of Hand Surgery, where it is suggested that the extension is achieved through the action of the sagittal bands and the extensor tendon. The extensor tendon, along with some loose areolar tissue, covers the dorsal surfaces of the MCP joints. The extensor tendon passes the joint, carrying a force and possessing an extension moment arm, thus generating torque to extend the MCP joint.
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Flexion and extension
The metacarpophalangeal (MCP) joints are situated between the metacarpal bones and the proximal phalanges of the fingers. The MCP joint is also known as "the knuckle". Each MCP joint has two planes of motion, allowing flexion, extension, abduction, adduction, circumduction, and limited rotation of the digit. All the movements of the MCP joints are performed by the muscles of the forearm and hand.
The muscles of flexion and extension are as follows: Arthritis of the MCP is a distinguishing feature of rheumatoid arthritis, unlike osteoarthritis, which affects the distal interphalangeal joint. In many quadrupeds, especially horses and other large animals, the MCP joint is referred to as the "fetlock", which corresponds to the "second" or "mid-finger" knuckle of the human hand.
The dorsal surfaces of the MCP joints are covered by expansions of the extensor tendons, along with some loose areolar tissue that connects the deep surfaces of the tendons to the bones. The extensor mechanism at the MCP joint level consists of the extensor tendon, sagittal bands, and volar plate. The sagittal bands are part of a complex extensor retinacular system that includes various ligaments.
Extension of the MCP joint is accomplished through the extensor tendon passing the joint, carrying a force and possessing an extension moment arm. The fibres of the sagittal band extend from the extensor hood to the palmar plate. This mechanism is important to understand when making clinical decisions related to injuries and repairs of the extensor tendon and sagittal bands.
The intrinsic muscles and tendons are palmar to the joint axis of rotation, allowing them to flex the MCP joints and extend the interphalangeal (IP) joints. The full range of motion for the thumb MCP joint is about 60 degrees, which is almost completely flexion. The axial rotation of the MCP joint of the thumb is most important and can be active or passive.
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Arthritis and injury
The metacarpophalangeal (MCP) joints are situated between the metacarpal bones of the hand and the proximal phalanges of the fingers. MCP joints allow the fingers to move in multiple directions, including bending, straightening, spreading apart, and moving together. They are important for pinching and gripping.
Arthritis of the MCP joint is a common condition, especially in the thumb and index finger, due to the stress of pinching. MCP joint arthritis can cause pain, swelling, stiffness, and difficulty in performing tasks such as gripping and opening jars. The condition can lead to a weakening of the hands and a tendency to drop objects.
Osteoarthritis (OA), also known as wear-and-tear arthritis, is a common form of arthritis affecting the MCP joint. It causes inflammation, loss of cartilage, pain, and a reduction in mobility and function. OA typically affects individuals over the age of 50. Post-traumatic arthritis is a type of osteoarthritis that develops following an injury to the joint. Rheumatoid arthritis (RA) is another type of arthritis that can affect the MCP joints, causing joint swelling and deformity.
Infections, particularly after a cut, puncture, or animal bite, can also lead to MCP joint arthritis by introducing bacteria into the joint and causing rapid cartilage injury. Arthritis in the MCP joint can be identified through X-rays, which reveal a narrowing of the space between the bones, indicating cartilage loss. Blood tests and imaging studies may also be used to confirm the diagnosis and distinguish the type of arthritis.
Treatment options for MCP joint arthritis include non-surgical methods such as activity modification, oral and topical anti-inflammatory medications, splinting, cortisone injections, and physical therapy. In more severe cases, surgery may be considered, including joint replacement or fusion.
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Frequently asked questions
Metacarpophalangeal joints (MCP) are the joints situated between the metacarpal bones and the proximal phalanges of the fingers.
The MCP joints allow for flexion, extension, abduction, adduction, circumduction and limited rotation of the digit.
The muscles involved in extending the MCP joints include the extensor pollicis longus, extensor indicis, extensor digitorum, extensor digiti minimi, and the extrinsic tendon extensor system.
The extensor tendon passes the MCP joint, carrying a force and possessing an extension moment arm, which generates torque to extend the joint.
The MCP joint of the thumb has a full range of motion of about 60 degrees, which is almost completely flexion. Axial rotation is also particularly important for the MCP joint of the thumb.
