Anatomy of the Human Wrist: Bones, Joints, Muscles, Ligaments, and Functions

Anatomy of the Human Wrist

The wrist is a complex joint that connects the forearm to the hand and allows for a wide range of movements such as flexion, extension, abduction, and rotation. It is essential for grip, dexterity, and overall hand function.

1. Bones of the Wrist

The wrist consists of eight small carpal bones arranged in two rows:

• Proximal row (from thumb to little finger):

  1. Scaphoid
  2. Lunate
  3. Triquetrum
  4. Pisiform

• Distal row (from thumb to little finger): 5. Trapezium
  6. Trapezoid
  7. Capitate
  8. Hamate

These bones articulate with the radius (forearm bone) and the metacarpal bones (hand bones) to form the wrist joint.

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2. Joints of the Wrist

• Radiocarpal joint: Connects the radius with the proximal row of carpal bones.
• Midcarpal joint: Lies between the proximal and distal rows of carpal bones.
• Distal radioulnar joint: Allows rotation of the forearm, essential for pronation and supination.

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3. Ligaments of the Wrist

Ligaments provide stability to the wrist:

• Palmar ligaments: Support the front of the wrist.
• Dorsal ligaments: Support the back of the wrist.
• Radial and ulnar collateral ligaments: Stabilize the wrist on the thumb (radial) and little finger (ulnar) sides.

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4. Muscles Affecting the Wrist

The wrist itself has no intrinsic muscles, but its movements are controlled by muscles of the forearm:

• Flexors (anterior forearm) – allow bending of the wrist:

• Flexor carpi radialis
• Flexor carpi ulnaris
• Palmaris longus

Extensors (posterior forearm) – allow straightening of the wrist:

• Extensor carpi radialis longus & brevis
• Extensor carpi ulnaris

• Abductors and adductors (radial and ulnar deviation):

• Abductor pollicis longus
• Extensor pollicis brevis

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5. Nerves of the Wrist

• Median nerve: Passes through the carpal tunnel; controls flexion and sensation in the thumb, index, middle, and part of the ring finger.
• Ulnar nerve: Runs along the little finger side; controls some flexors and intrinsic hand muscles.
• Radial nerve: Innervates wrist extensors.

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6. Blood Supply

• Radial artery and ulnar artery provide blood to the wrist and hand.
• Form superficial and deep palmar arches in the hand.

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7. Functions of the Wrist

• Enables flexion and extension of the hand.
• Allows side-to-side movement (abduction and adduction).
• Supports fine motor skills and gripping.
• Acts as a shock absorber during weight-bearing activities.

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Blood Supply of the Human Wrist

The wrist is a complex joint that connects the forearm to the hand. To sustain its constant movements and functional demands, the wrist requires a rich vascular supply. This is primarily provided by the radial and ulnar arteries, which branch from the brachial artery in the forearm and contribute to the formation of arterial arches that ensure continuous blood flow.

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Main Arteries Involved

1. Radial Artery

• The radial artery originates from the brachial artery at the level of the elbow and travels down the lateral (thumb) side of the forearm.
• At the wrist, it runs superficially near the styloid process of the radius, making it easily palpable (commonly used for pulse measurement).
• Branches at the wrist include:
  • Superficial palmar branch: contributes to the superficial palmar arch.
  • Dorsal carpal branch: helps form the dorsal carpal arch.

2. Ulnar Artery

• The ulnar artery also arises from the brachial artery and runs along the medial (little finger) side of the forearm.
• At the wrist, it passes superficially through the Guyon’s canal along with the ulnar nerve.
• Branches at the wrist include:
  • Superficial palmar branch: forms the main part of the superficial palmar arch.
  • Dorsal carpal branch: contributes to the dorsal carpal arch.

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Formation of Arterial Arches

The radial and ulnar arteries communicate extensively at the wrist and hand level through anastomoses, forming arterial arches that provide collateral circulation.

1. Superficial Palmar Arch

   • Primarily formed by the ulnar artery.
   • Completed on the lateral side by the superficial palmar branch of the radial artery.
   • Supplies most of the fingers through the common and proper palmar digital arteries.

2. Deep Palmar Arch

   • Mainly formed by the radial artery.
   • Completed medially by the deep branch of the ulnar artery.
   • Supplies the deep structures of the palm and thumb.

3. Dorsal Carpal Arch

   • Formed by dorsal carpal branches of both radial and ulnar arteries, along with contributions from the anterior and posterior interosseous arteries.
   • Provides blood to the dorsal aspect of the wrist and hand.

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Physiological Importance

• The vascular network of the wrist ensures a continuous and reliable blood flow even if one artery is temporarily compressed or damaged.
• The arches and interconnections act as collateral circulation, protecting the hand and wrist from ischemia.
• Oxygen and nutrient delivery is essential for the integrity of bones, ligaments, tendons, muscles, and nerves of the wrist.

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Clinical Relevance

1. Pulse Examination

   • The radial artery at the wrist is the most common site for measuring pulse due to its superficial position.

2. Allen’s Test

   • A clinical test used before radial artery cannulation or graft harvesting (e.g., for coronary artery bypass). It evaluates the adequacy of collateral circulation between radial and ulnar arteries.

3. Vascular Injury

   • Trauma to the wrist can damage either artery, but the presence of arterial arches often preserves blood supply. Severe injuries, however, may compromise circulation and require surgical repair.

4. Arterial Cannulation and Access

   • The radial artery is commonly used for arterial blood gas sampling and catheter insertion due to its accessibility.

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Conclusion

The blood supply of the wrist is a finely organized system primarily involving the radial and ulnar arteries. Through their branches and interconnections, these arteries form arterial arches that ensure robust and redundant circulation. This network not only sustains the functional demands of the wrist and hand but also provides important clinical access points for diagnosis and treatment. Understanding this vascular arrangement is crucial for clinicians, surgeons, and anyone studying human anatomy.