The metacarpus forms the intermediate segment of the hand, connecting the wrist to the fingers. This critical anatomical region consists of five metacarpal bones that create the framework of the palm and provide essential support for hand movements.
In the dorsal (posterior) view of the left hand shown in the image, the metacarpal bones are highlighted in yellow, clearly distinguishing them from the carpal bones above and the phalanges below. Understanding the metacarpus is fundamental for medical professionals, as it serves as a crucial connection point for numerous tendons, ligaments, and muscles that enable the complex movements and functions of the human hand.
Labeled Parts of the Metacarpus
Metacarpus – The metacarpus consists of five long bones that form the intermediate part of the skeleton of the hand between the carpus (wrist) and the phalanges (fingers). These cylindrical bones are numbered from the thumb side (radial) to the little finger side (ulnar) as first through fifth metacarpals.
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Ext. Carpi Radialis Longus – This muscle extends from the lateral supracondylar ridge of the humerus to the base of the second metacarpal. It functions primarily to extend the wrist and assists in radial deviation (bending the wrist toward the thumb side).
Ext. Carpi Radialis Brevis – This muscle originates from the lateral epicondyle of the humerus and inserts at the base of the third metacarpal bone. It works in conjunction with the longus to extend the wrist and provide radial deviation.
Ext. Carpi Ulnaris – This extensor muscle runs along the ulnar side of the forearm and attaches to the base of the fifth metacarpal. It functions to extend and adduct the wrist (moving the hand toward the ulnar side).
Ext. Pollicis Brevis – This small muscle originates from the posterior surface of the radius and inserts on the base of the proximal phalanx of the thumb. It extends the thumb at the carpometacarpal and metacarpophalangeal joints.
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Ext. Pollicis Longus – This longer thumb extensor muscle arises from the posterior surface of the ulna and inserts on the base of the distal phalanx of the thumb. It functions to extend all joints of the thumb.
Ext. Digitorum Communis – This muscle extends from the lateral epicondyle of the humerus to the middle and distal phalanges of the four fingers. It serves as the primary extensor of the four fingers at the metacarpophalangeal and interphalangeal joints.
Ext. Digiti Communis – This extensor muscle helps extend the fingers at the metacarpophalangeal and interphalangeal joints, working in coordination with the extensor digitorum communis.
Ext. Indicis Proprius – This specialized extensor muscle extends the index finger independently from the other fingers. It originates from the posterior surface of the ulna and inserts into the extensor expansion of the index finger.
Phalanges – These are the bones that form the fingers. Each finger (digits 2-5) has three phalanges (proximal, middle, and distal), while the thumb has only two phalanges (proximal and distal).
1st Row – The proximal row of phalanges articulates with the metacarpal bones proximally and the middle phalanges distally. These bones are critical for gripping and fine motor control of the fingers.
2nd Row – The middle phalanges articulate with the proximal phalanges proximally and the distal phalanges distally. These bones are absent in the thumb, which has only proximal and distal phalanges.
3rd Row – The distal phalanges form the tips of the fingers and are characterized by their flattened, spatulate distal ends. These bones support the fingernails and are crucial for precise tactile functions.
Head – The head of each metacarpal bone is the rounded distal end that articulates with the proximal phalanx of the corresponding digit. This convex surface allows for flexion, extension, and limited lateral movement of the fingers.
Body – The shaft or body of each metacarpal bone is slightly curved, with the concavity facing anteriorly. This design provides structural integrity to the hand while allowing for the attachment of various interosseous muscles.
Base – The base of each metacarpal is the proximal, expanded portion that articulates with the carpal bones and adjacent metacarpal bases. The configuration of these articulations contributes significantly to the flexibility and stability of the hand.
Carpus – This region comprises eight small bones arranged in two rows that form the wrist joint. The carpus articulates with the radius and ulna proximally and the metacarpals distally, serving as an important transition zone between the forearm and hand.
Anatomy and Function of the Metacarpus
Structure and Arrangement
The metacarpus is the intermediate segment of the hand consisting of five metacarpal bones arranged in a slightly curved, fan-like formation. These bones create the skeletal framework of the palm, with each metacarpal having a distinct shape and function based on its position. The metacarpal bones are long bones with a proximal base, an intermediate shaft (body), and a distal head. The bases articulate with the distal row of carpal bones, forming the carpometacarpal joints.
The first metacarpal, supporting the thumb, is shorter and more mobile than the others, allowing for opposition of the thumb to the fingers. This unique mobility is essential for precision grip and fine motor skills. The second and third metacarpals are firmly attached to the carpus, providing stability to the hand. The fourth and fifth metacarpals have progressively more mobility, enhancing the hand’s adaptability when gripping objects of various shapes and sizes.
Biomechanical Significance
The metacarpus serves as a crucial mechanical link in the kinetic chain of the upper limb. The arrangement of the metacarpal bones creates both longitudinal and transverse arches across the palm, which:
- Enhance the hand’s ability to conform to different objects
- Provide stability during gripping actions
- Allow for efficient force distribution across the palm
- Support the soft tissues of the hand, including nerves and blood vessels
The metacarpophalangeal joints, formed between the metacarpal heads and the proximal phalanges, are condyloid (ellipsoid) joints that permit flexion, extension, abduction, adduction, and circumduction. These joints are reinforced by collateral ligaments and connected to the extensor mechanism of the hand, which is clearly visible in the dorsal view shown in the image.
Muscular Attachments and Movements
The metacarpus serves as an attachment site for multiple intrinsic and extrinsic hand muscles:
- The interossei muscles (both dorsal and palmar) attach between the metacarpals and are responsible for finger abduction and adduction
- The extensor tendons cross over the dorsal surface of the metacarpals before inserting on the phalanges
- The opponens muscles attach to the first and fifth metacarpals, facilitating opposition movements
The extrinsic extensor muscles highlighted in yellow and labeled in the image are particularly important for metacarpal function:
- They stabilize the wrist during finger movements
- Enable extension of the hand at the wrist joint
- Contribute to radial and ulnar deviation of the hand
- Work antagonistically with flexor muscles to produce controlled movements
Clinical Significance of the Metacarpus
Common Injuries and Conditions
The metacarpal bones are frequently subject to injury, particularly during punching or falling on an outstretched hand. Common injuries include:
- Boxer’s fracture – a fracture of the neck of the fifth metacarpal
- Bennett’s fracture – an intra-articular fracture at the base of the first metacarpal
- Rolando’s fracture – a comminuted fracture at the base of the first metacarpal
- Metacarpal shaft fractures – may be transverse, spiral, or comminuted
Additionally, the metacarpus can be affected by various pathological conditions:
- Rheumatoid arthritis often affects the metacarpophalangeal joints
- Osteoarthritis can develop in the carpometacarpal joint of the thumb
- Dupuytren’s contracture affects the palmar fascia but can lead to metacarpophalangeal joint contractures
Diagnostic and Surgical Considerations
When examining the metacarpus, clinicians assess:
- Alignment of the metacarpal bones
- Integrity of the metacarpophalangeal joints
- Function of the extensor tendons passing over the dorsum of the hand
- Intrinsic muscle function
Surgical approaches to the metacarpus typically involve:
- Dorsal approaches for extensor tendon repairs and metacarpal fracture fixation
- Careful attention to the extensor tendons shown in the image
- Preservation of the dorsal interossei muscles
- Consideration of the metacarpal arches during reconstruction
Understanding the detailed anatomy of the metacarpus as shown in the dorsal view image is essential for accurate diagnosis, appropriate treatment planning, and successful surgical outcomes in hand conditions.
Conclusion
The metacarpus represents a remarkable example of evolutionary adaptation, providing humans with the structural foundation for our advanced manual dexterity. As illustrated in the dorsal view image, the complex arrangement of metacarpal bones, their articulations, and the associated extensor tendons highlights the intricate design that enables precision movements. Medical professionals working with hand conditions must possess a thorough understanding of metacarpal anatomy, as the restoration of proper metacarpal structure and function is essential for maintaining the hand’s ability to perform its diverse roles in daily activities, occupational tasks, and expressive movements.
 view of the left hand shown in the image, the metacarpal bones are highlighted in yellow, clearly distinguishing them from the carpal bones above and the phalanges below. Understanding the metacarpus is fundamental for medical professionals, as it serves as a crucial connection point for numerous tendons, ligaments, and muscles that enable the complex movements and functions of the human hand.){kind=link}