Radius bone

The radius is one of the two long bones in the forearm, positioned on the lateral side of the ulna. It plays a crucial role in the movement of the wrist and elbow and serves as an attachment site for multiple muscles. Understanding its anatomy is essential for diagnosing and managing upper limb injuries.

Anatomy of the Radius

Proximal End

The proximal end of the radius includes several important structures:

• Head of radius: A disc-shaped structure that articulates with the capitulum of the humerus and the radial notch of the ulna.
• Neck of radius: A constricted region just distal to the head that connects the head to the radial tuberosity.
• Radial tuberosity: A bony prominence on the medial side for the attachment of the biceps brachii tendon.

Body (Shaft) of Radius

The shaft of the radius extends from the neck to the distal end and has the following features:

• Surfaces: Anterior, posterior, and lateral surfaces, each providing attachment points for muscles.
• Borders: Anterior, posterior, and interosseous borders which serve as attachment lines for muscles and the interosseous membrane.

Distal End

The distal end of the radius contributes to the wrist joint and has several key landmarks:

• Ulnar notch: A concave surface that articulates with the head of the ulna to form the distal radioulnar joint.
• Styloid process: A lateral projection that provides attachment for ligaments stabilizing the wrist.
• Dorsal tubercle: Acts as a pulley for extensor tendons of the wrist.

Articulations

Proximal Radioulnar Joint

The head of the radius articulates with the radial notch of the ulna, forming the proximal radioulnar joint. This pivot joint allows rotation of the radius for pronation and supination of the forearm.

Distal Radioulnar Joint

The distal radioulnar joint is formed by the articulation between the ulnar notch of the radius and the head of the ulna. It facilitates rotational movements of the forearm and stabilizes the wrist during hand motions.

Wrist Joint (Radiocarpal Joint)

The distal radius articulates with the proximal row of carpal bones, primarily the scaphoid and lunate. This joint enables wrist flexion, extension, radial and ulnar deviation, and contributes to overall hand mobility.

Muscle Attachments

Flexor Muscles

The radius serves as an attachment site for several flexor muscles that assist in forearm and hand movements:

• Flexor pollicis longus: Attaches to the anterior surface of the radius and flexes the thumb.
• Pronator teres: Inserts onto the lateral aspect of the radius, aiding in forearm pronation.
• Flexor digitorum superficialis: Originates partly from the anterior border of the radius, contributing to finger flexion.

Extensor Muscles

Several extensor muscles attach to the radius or use it as a landmark for tendon passage:

• Brachioradialis: Attaches to the lateral distal radius and assists in elbow flexion.
• Supinator: Wraps around the proximal radius and facilitates supination of the forearm.
• Extensor carpi radialis longus and brevis: Insert near the distal radius, enabling wrist extension and radial deviation.

Other Attachments

The interosseous membrane connects the radius to the ulna along the interosseous border. This fibrous sheet provides stability to the forearm and serves as an attachment site for additional muscles and ligaments.

Blood Supply and Innervation

Arterial Supply

The radius receives arterial blood from multiple sources to maintain bone viability:

• Radial recurrent artery supplying the proximal radius
• Branches from the radial and interosseous arteries supplying the shaft and distal end
• Periosteal vessels supporting cortical bone and muscle attachments

Venous Drainage

Venous blood from the radius follows the arteries, draining into the radial, interosseous, and brachial veins. This ensures efficient removal of metabolic waste from bone and surrounding tissues.

Nervous Supply

Innervation of the radius primarily involves the periosteum, which is sensitive to pain. Sensory fibers from the radial, median, and ulnar nerves transmit nociceptive information. Muscles attached to the radius are innervated according to their respective nerves, coordinating forearm and hand movements.

Development and Ossification

Embryological Origin

The radius develops from mesenchymal condensations within the lateral plate mesoderm of the upper limb bud during early embryogenesis. This process initiates the formation of a cartilaginous model, which later undergoes ossification to form the mature bone.

Ossification Centers

The radius has distinct ossification centers that contribute to its growth:

• Primary center: Located in the shaft, appears during the seventh week of fetal life, responsible for longitudinal growth.
• Secondary centers: Appear at the proximal and distal ends postnatally, contributing to epiphyseal growth and shaping of the bone ends.

Growth and Maturation

The epiphyseal plates of the radius allow longitudinal growth until adolescence. Closure of the distal epiphysis occurs earlier than the proximal epiphysis, resulting in the adult morphology. Proper ossification is essential for normal forearm length and function.

Function

Forearm Movements

The radius plays a crucial role in pronation and supination of the forearm. Its ability to rotate around the ulna enables the hand to turn palm up or palm down, essential for daily activities such as writing, lifting, and manipulating objects.

Load Transmission

The radius bears a significant portion of axial load transmitted from the hand to the forearm. During weight-bearing activities, forces are transferred through the distal radius to the shaft and then to the elbow, with the interosseous membrane distributing some force to the ulna.

Role in Wrist Stability

The distal radius contributes to the stability of the wrist joint by articulating with the carpal bones and providing attachment for ligaments. Its alignment and integrity are critical for smooth wrist motion and effective grip strength.

Clinical Significance

Fractures

The radius is prone to various fractures, often resulting from falls or trauma:

• Colles fracture: Distal radius fracture with dorsal displacement, commonly caused by a fall on an outstretched hand.
• Smith fracture: Distal radius fracture with volar displacement, usually resulting from a fall on a flexed wrist.
• Radial head fractures: Affect the proximal end, impacting forearm rotation and elbow function.

Dislocations

Dislocations can occur at the proximal or distal radioulnar joints. These injuries impair pronation and supination and often require reduction and immobilization.

Congenital and Developmental Disorders

Some conditions affect radius development:

• Madelung deformity: Abnormal growth of the distal radius causing wrist deformity.
• Radial hypoplasia: Underdevelopment of the radius, leading to limb shortening and functional limitations.

Osteoporosis and Bone Diseases

The distal radius is a common site for osteoporotic fractures. Degenerative changes can also affect joint function and grip strength, particularly in the elderly.

Diagnostic Imaging

Imaging modalities used to evaluate the radius include:

• X-ray: First-line imaging for fractures and alignment assessment.
• CT scan: Detailed evaluation of complex fractures.
• MRI: Assessment of soft tissue attachments, bone marrow, and occult fractures.

Surgical and Therapeutic Considerations

Fracture Management

Management of radial fractures depends on type and severity:

• Conservative treatment: Casting or splinting for stable fractures.
• Open reduction and internal fixation: Surgical intervention for displaced or unstable fractures using plates, screws, or pins.

Joint Reconstruction

Reconstruction may be necessary in cases of severe trauma or degenerative disease affecting the proximal or distal radioulnar joints. Procedures aim to restore alignment, stability, and rotational function.

Postoperative Care

After surgical treatment, rehabilitation includes physiotherapy to restore range of motion, strength, and functional use of the forearm and wrist. Regular follow-up imaging ensures proper healing and alignment.

References

1. Gray H, Standring S. Gray’s Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed. London: Elsevier; 2020.
2. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. 8th ed. Philadelphia: Wolters Kluwer; 2018.
3. Palastanga N, Soames R. Anatomy and Human Movement: Structure and Function. 7th ed. London: Elsevier; 2019.
4. Campbell-Walsh Urology. Wein AJ, Kavoussi LR, Partin AW, Peters CA, editors. 12th ed. Philadelphia: Elsevier; 2020.
5. Rockwood CA, Green DP, Bucholz RW, Heckman JD. Rockwood and Green’s Fractures in Adults. 8th ed. Philadelphia: Wolters Kluwer; 2015.
6. Standring S. Handbook of Clinical Anatomy. 2nd ed. London: Elsevier; 2016.
7. Rüedi TP, Murphy WM. AO Principles of Fracture Management. 3rd ed. Stuttgart: Thieme; 2007.
8. Mattox KL, Moore EE, Feliciano DV. Trauma. 9th ed. New York: McGraw-Hill; 2017.
9. Jung SE, Kim JW, Baek GH. Radial fractures: current concepts and treatment. Clin Orthop Surg. 2016;8(2):117-126.
10. DiGiovanni CW, Rothman RH. Upper Extremity Anatomy and Clinical Correlation. Philadelphia: Lippincott Williams & Wilkins; 2014.