Anatomy and Radiography of the Radius, Ulna, and Distal Humerus

Forearm Anatomy: Radius and Ulna Bone Groups

  • Upper Limb Bone Groups: Second group of bones; include the radius and ulna.

  • Anatomic Orientation:

    • Radius: Lateral aspect of the forearm.

    • Ulna: Medial side of the forearm.

  • Articulation Points:

    1. Proximal Radioulnar Joint.

    2. Distal Radioulnar Joint.

  • Functional Movement: Facilitates wrist and hand rotation, e.g., pronation.

Detailed Structures of the Distal Forearm and Wrist Joint

  • Styloid Processes: Projections at distal ends of radius and ulna.

  • Radial Styloid Process: On thumb side, protrudes more distally.

  • Ulnar Notch: Depression on the distal radius where the ulnar head fits.

  • Head of the Ulna: Near wrist, visible during pronation.

  • Joint Involvement: Radius is shorter and directly involved in the wrist.

Detailed Structures of the Proximal Forearm and Elbow Joint

  • Head of the Radius: Proximal end at elbow, round appearance.

  • Neck of the Radius: Constricted area below the head.

  • Radial Tuberosity: Rough process below the neck.

  • Body (Shaft): Midportion of radius and ulna.

  • Ulna Characteristics: Longer bone, forms elbow joint.

  • Bony Processes of Ulna:

    • Olecranon Process: Palpable on posterior elbow.

    • Coronoid Process: Beaklike process on proximal ulna.

    • Coronoid Tubercle: Medial edge of the coronoid process.

  • Ulna Notches:

    • Trochlear Notch: Concave depression articulating with humerus.

    • Radial Notch: Where radius articulates at proximal ulna.

Functional Mechanics of Pronation

  • Functional Mechanics of Pronation: Radius rotates, ulna stays stationary.

Anatomy of the Distal Humerus

  • Humeral Condyle: Distal end of humerus, divided articular portions.

  • Trochlea: Medial condyle, spool-shaped, articulates with ulna.

  • Trochlear Sulcus: Depression in trochlea.

  • Capitulum: Lateral condyle, articulates with radius.

  • Epicondyles:

    • Medial: Larger on medial side.

    • Lateral: Smaller above capitulum.

Fossae and Soft Tissue of the Distal Humerus

  • Fossae and Soft Tissue:

    • Coronoid Fossa: Receives coronoid process at flexion.

    • Radial Fossa: Receives radial head at flexion.

    • Olecranon Fossa: Receives olecranon during arm extension.

Radiographic Evaluation of the True Lateral Elbow

  • Positioning Requirements: Requires an accurate lateral position with exactly 90ext°90^{ ext{°}} flexion.

  • Criteria for Evaluation (Three Concentric Arcs):

    1. First Arc: The smallest arc, representing the trochlear sulcus.

    2. Second Arc: The intermediate arc, appearing as a double line representing the outer ridges of the capitulum (smaller ridge) and the trochlea (larger medial ridge).

    3. Third Arc: The largest arc, representing the trochlear notch of the ulna.

  • Alignment Indicators: In a true lateral position, the epicondyles are directly superimposed and appear proximal to the circular trochlear sulcus. If rotation occurs, these arcs will not be symmetrically aligned, and the joint space will not be optimally open.