Carpus – Anatomy, Function and Conditions
The carpus (wrist) is the bony foundation of the wrist joint, consisting of eight small bones. It connects the forearm to the hand and enables a wide range of movements.
Things worth knowing about "Carpus"
The carpus (wrist) is the bony foundation of the wrist joint, consisting of eight small bones. It connects the forearm to the hand and enables a wide range of movements.
What is the Carpus?
The carpus, commonly referred to as the wrist, is the proximal segment of the hand that forms the bony framework of the wrist joint. It consists of eight small, irregularly shaped bones arranged in two rows. Together, these bones create a stable yet flexible connection between the forearm and the metacarpal bones of the hand.
Anatomy and Structure
The eight carpal bones are organized into two rows:
Proximal Row (closer to the forearm)
- Scaphoid bone (Os scaphoideum) – the largest bone in the proximal row and the most commonly fractured carpal bone
- Lunate bone (Os lunatum) – crescent-shaped, situated centrally in the wrist
- Triquetrum bone (Os triquetrum) – located on the ulnar (little finger) side of the wrist
- Pisiform bone (Os pisiforme) – a small, pea-shaped bone classified as a sesamoid bone
Distal Row (closer to the fingers)
- Trapezium bone (Os trapezium) – articulates with the first metacarpal bone of the thumb
- Trapezoid bone (Os trapezoideum) – the smallest bone in the distal row
- Capitate bone (Os capitatum) – the largest of all carpal bones
- Hamate bone (Os hamatum) – recognized by its distinctive hook-shaped projection (hamulus)
Functions of the Carpus
The carpus serves several important biomechanical roles:
- Movement transmission: It enables flexion (bending), extension (straightening), radial and ulnar deviation (side-to-side tilting), and circumduction (circular motion) of the hand.
- Force distribution: The arrangement of the bones distributes mechanical forces evenly across the wrist, protecting joints and ligaments from excessive stress.
- Protection of nerves and tendons: The carpal bones form the floor and walls of the carpal tunnel, a narrow passage through which the median nerve and several flexor tendons travel to the hand.
Common Conditions and Injuries
Scaphoid Fracture
The scaphoid fracture is the most frequent carpal bone fracture, typically caused by a fall onto an outstretched hand. It can be challenging to diagnose because it may not be visible on standard X-rays immediately after injury. Delayed diagnosis and treatment can lead to avascular necrosis (bone death due to disrupted blood supply), a serious complication.
Carpal Tunnel Syndrome
Carpal tunnel syndrome occurs when the median nerve becomes compressed within the carpal tunnel at the level of the carpus. Typical symptoms include tingling, numbness, and pain in the thumb, index, and middle fingers, often worsening at night. Treatment options range from conservative measures (wrist splints, physiotherapy, corticosteroid injections) to surgical release of the carpal tunnel.
Lunate Necrosis (Kienbock Disease)
Kienbock disease involves the avascular necrosis of the lunate bone, believed to result from repetitive microtrauma or vascular insufficiency. It presents with wrist pain, swelling, and reduced range of motion. Treatment depends on the stage of the disease and may include immobilization, surgical revascularization, or partial wrist fusion.
Carpal Instability
Ligament tears or sprains in the wrist can lead to carpal instability, in which the normal alignment of the carpal bones is disrupted. This results in pain, loss of grip strength, and an increased risk of developing wrist osteoarthritis over time.
Diagnosis
Several imaging techniques are used to evaluate the carpus:
- X-ray: First-line imaging for suspected fractures or deformities
- Magnetic Resonance Imaging (MRI): Provides detailed visualization of soft tissues, ligaments, and early-stage bone necrosis
- Computed Tomography (CT): Used for precise assessment of complex fractures
- Wrist Arthroscopy: A minimally invasive procedure allowing both diagnosis and treatment of joint pathologies
Treatment
Treatment of carpal conditions depends on the type and severity of the injury or disease:
- Conservative treatment: Immobilization with a cast or splint, physiotherapy, and anti-inflammatory medications
- Surgical treatment: Screw fixation for fractures, ligament reconstruction for instability, denervation, or partial wrist fusion (arthrodesis) for advanced arthritis
References
- Drake R.L., Vogl A.W., Mitchell A.W.M. - Gray's Anatomy for Students. 4th edition. Elsevier, Philadelphia, 2019.
- Standring S. (Ed.) - Gray's Anatomy: The Anatomical Basis of Clinical Practice. 42nd edition. Elsevier, Edinburgh, 2020.
- World Health Organization (WHO) - International Classification of Diseases (ICD-11), Musculoskeletal Disorders Chapter, 2019. Available at: https://icd.who.int
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