Overview
This lecture covers the key anatomical structures of the elbow joint as seen on MRI, including bones, muscles, tendons, ligaments, and nerves, and highlights important normal variants and imaging signs.
Bones of the Elbow Joint
- The elbow joint consists of the humerus (upper arm), radius (lateral forearm), and ulna (medial forearm).
- Distal humerus features: lateral and medial epicondyles, trochlea (articulates with ulna), and capitellum (articulates with radius).
- Main joints: radio-capitellar (radius/capitellum), ulno-humeral (ulna/trochlea), proximal radio-ulnar (radius/ulna pivot).
- Key bone landmarks: radial head, neck, shaft, and tuberosity (biceps brachii insertion); olecranon (posterior ulna), trochlear notch, coronoid process (anterior ulna), and ulnar tuberosity (brachialis insertion).
Muscles and Tendons
- Main elbow flexors: biceps brachii (attaches to radial tuberosity), brachialis (attaches to ulnar tuberosity).
- Main elbow extensor: triceps brachii (attaches to olecranon).
- Common extensor tendon (lateral epicondyle): gives rise to wrist and finger extensors (e.g., extensor carpi ulnaris, extensor digitorum).
- Common flexor tendon (medial epicondyle): origin for flexor-pronator muscles (e.g., pronator teres, flexor carpi radialis, palmaris longus).
- Tendons lie superficial to ligaments at the elbow.
Ligaments of the Elbow
- Medial (ulnar) collateral ligament: anterior, posterior, and transverse bands; anterior band is main stabilizer against valgus stress.
- Lateral (radial) collateral ligaments: radial collateral ligament, lateral ulnar collateral ligament, and annular ligament (encircles radius).
- Annular ligament secures the radial head for pivot motion.
- Ligaments provide joint stability; injury to anterior bundle is common in throwing athletes.
Nerves of the Elbow
- Ulnar nerve: passes posterior to the medial epicondyle ("funny bone"), enters forearm via cubital tunnel.
- Radial nerve: wraps around humerus laterally and divides into superficial (sensory) and deep (motor/posterior interosseous) branches at the elbow.
- Median nerve: passes through the anterior elbow (cubital fossa) into forearm.
Imaging Signs and Normal Variants
- Olecranon and coronoid fossae contain fat pads; displacement suggests joint effusion ("sail sign").
- Trochlear ridge creates a normal gap in cartilage at the trochlear notch—do not confuse with pathology.
- Posterior aspect of capitellum has no cartilage—normal finding.
- Perineural fat aids in nerve identification on MRI.
Key Terms & Definitions
- Olecranon — bony prominence of the proximal ulna (elbow tip).
- Capitellum — rounded lateral part of distal humerus articulating with radius.
- Trochlea — spool-shaped medial part of distal humerus articulating with ulna.
- Annular ligament — encircles radial head, stabilizing proximal radio-ulnar joint.
- Cubital tunnel — groove behind medial epicondyle where the ulnar nerve passes.
Action Items / Next Steps
- Review elbow radiograph anatomy if unsure about bony landmarks.
- Prepare for next week’s lecture on the foot and ankle, starting with radiographs.