Distal Humerus Anatomy

Distal Humerus

• The distal humerus is the expanded distal end of the humerus, divided into medial and lateral parts.
• The trochlea is the medial condyle, shaped like a pulley or spool, articulating with the ulna.
• It features two outer margins and a smooth depressed center (trochlear sulcus)
• The capitulum is the lateral condyle, articulating with the radial head.
• It means "little head", and you can remember it by associating it with "cap" being on top of "head" .
• The lateral epicondyle is a small projection on the lateral aspect of the distal humerus above the capitulum.
• The medial epicondyle is larger and located on the medial edge of the distal humerus.
• The coronoid fossa is an anterior depression that receives the coronoid process.
• The radial fossa is another anterior depression, more lateral than the coronoid fossa, that receives the radial head.
• The olecranon fossa is a posterior depression that receives the olecranon process when the arm is fully extended.

Joints

• The elbow joint is the articulation between the distal humerus, proximal radius, and proximal ulna.
• The proximal radioulnar joint is the articulation between the proximal radius and ulna, allowing for rotation of the forearm.

Fat Pads

• Anterior fat pad - Visible on lateral elbow projection, located anterior to the elbow joint.
• Posterior fat pad - Usually not visible unless trauma present or the elbow isn't flexed correctly.
• Supinator fat stripe - May indicate a radial head or neck fracture.

True Lateral Elbow

• The elbow should be flexed 90 degrees.
• There are three concentric arcs:
  • 1st and smallest - Trochlear sulcus
  • 2nd - Capitulum (smallest) and Trochlea (largest)
  • 3rd - Trochlear notch of the ulna

Medial Oblique (Internal) AP Projection - Elbow

• Best visualizes the coronoid process of the ulna and the trochlea.
• 40 SID
• Arm fully extended
• Pronate hand into a natural palm-down position then rotate the arm internally till the distal humerus/anterior elbow is rotated 45 degrees.
• CR perpendicular to IR, directed to the mid-elbow joint.
• Radial head and neck should be superimposed and centered over the proximal ulna.

Lateral (Lateromedial) Projection - Elbow

• 40 SID
• Seat patient at end of table, with elbow flexed 90 degrees.
• Drop shoulder so it is on the same plane as forearm.
• Rotate hand & wrist into true lateral position (thumb up).
• CR perpendicular to IR, directed to mid-elbow joint.
• Three concentric arcs are visible.

Special Projections - Elbow

Trauma Axial Laterals (Coyle Method) - Elbow

• 40 SID, two projections:
  • Axial Lateromedial Projection - Visualizes radial head best.
  • Axial Mediolateral Projection: Coronoid process best visualized.

Axial Lateromedial Projection – Elbow (Radial Head)

• Clinical indications: fractures and dislocations of the radial head.
• Elbow flexed 90 degrees if possible, hand pronated.
• CR angled 45 degrees towards shoulder, centered to the radial head, mid-elbow joint.
• Joint space between the radial head and capitulum is open, radial head, neck, and tuberosity are free of superposition.

Axial Mediolateral Projection - Elbow (Coronoid Process)

• Clinical indications: fractures and dislocations of the coronoid process.
• Elbow flexed only 80 degrees, hand pronated.
• CR angled 45 degrees from shoulder, centered to the mid-elbow joint.
• Anterior portion of the coronoid appears elongated, but in profile, joint space between coronoid process and trochlea should be open, and the radial head and neck should be superimposed by ulna.

Radial Head Laterals - Elbow

• Clinical indications: occult (hidden) fractures of the radial head or neck.
• 40 SID
• Arm flexed 90 degrees.
• Upper extremity & shoulder all on the same plane.
• Four projections:
  • Supinate hand and externally rotate as far as patient can tolerate.
  • Place hand in true lateral.
  • Pronate hand.
  • Internally rotate hand as far as patient can tolerate.
• CR perpendicular to IR and directed at radial head.
• Radial tuberosity should be visualized in different positions.

Common Pathologies

• Osteomyelitis is an infection of the bone or bone marrow, which can be caused by bacteria introduced through trauma or surgery.
• Bursitis is the inflammation of bursae, fluid-filled sacs surrounding joints, leading to pain and limited movement.
• Osteopetrosis is a rare genetic condition characterized by abnormally dense bone (marble bone).

Positioning

AP Elbow

• CR perpendicular to IR and directed to the mid-elbow joint.
• Hand is positioned in a natural palm-down position.
• Mid-elbow joint is found near the center of the humeral epicondyles.

Partial Flexion Elbow Projection

• -Performed when the patient cannot fully extend their elbow.
• Center the CR to the mid-elbow joint.
• Flex patient's arm 80-90 degrees.
• Two images are recommended: - One image with the CR perpendicular, and - One image with the CR angled 10-15 degrees cephalically.

Medial/Internal Oblique Elbow

• Best demonstrates the coronoid process.
• The hand is pronated and rotated internally 45 degrees.

Lateral Elbow

• Elbow is flexed 90 degrees.
• The shoulder and elbow are on the same plane.
• CR perpendicular to IR, directed to the mid-elbow joint.
• Mid-elbow joint is found near the center of the humeral epicondyles.
• Three concentric arcs should be visualized.

Coyle Method

• Axial Lateromedial Projection: Visualizes radial head, CR is angled 45 degrees towards shoulder.
• Axial Mediolateral Projection: Visualizes coronoid process; CR is angled 45 degrees towards shoulder.
• The hand is pronated for both.