Overview
This lecture covers the anatomy of the elbow joint as seen on radiographs, key anatomical features, relevant ligaments, and methods for assessing proper alignment and common pathologies.
Elbow Joint Anatomy
- The elbow consists of three bones: humerus (arm), radius (lateral forearm), and ulna (medial forearm).
- There are three joints: ulnar-humeral (hinge: flexion/extension), radiohumeral (pivot: supination/pronation), and proximal radioulnar (pivot).
- The distal humerus features the lateral and medial epicondyles, capitellum (lateral), and trochlea (medial).
- The radius includes the radial head, neck, shaft, and radial tuberosity (biceps insertion).
- The ulna includes the olecranon (posterior), coronoid process (anterior), trochlear notch (articulates with trochlea), and radial notch.
Elbow Radiographic Features
- Always examine the shafts of the long bones for lesions or fractures before focusing on the joint.
- Key fossae: olecranon fossa (posterior, accommodates olecranon), coronoid fossa (anterior, accommodates coronoid process), and radial fossa (for radial head).
- Fat pads fill fossae: anterior, posterior, and radial; their displacement may signal joint effusion.
Ligament Complexes
- Medial collateral ligament: anterior band (medial epicondyle to coronoid), posterior band (medial epicondyle to olecranon), and Cooper’s/transverse ligament (olecranon to coronoid).
- Lateral collateral ligament: annular ligament (encircles radial head), lateral ulnar collateral ligament (ulna to lateral epicondyle), and radial collateral ligament (lateral epicondyle to annular ligament).
Assessing Elbow Alignment
- Anterior humeral line: drawn along the anterior humeral cortex, should intersect the middle third of the capitellum; abnormal in supracondylar fractures.
- Radiocapitellar line: drawn through the radial neck, should intersect the capitellum; abnormal in radial head dislocation.
- Misalignment of these lines indicates possible fracture or dislocation.
Common Pathologies and Signs
- Supracondylar fracture: anterior humeral line does not intersect the capitellum.
- Radial head dislocation: radiocapitellar line does not intersect the capitellum.
- “Sail sign”: visible anterior and posterior fat pads due to joint effusion (often from fracture).
Key Terms & Definitions
- Capitellum — rounded lateral part of distal humerus, articulates with radial head.
- Trochlea — spool-shaped medial part of distal humerus, articulates with ulna.
- Olecranon — proximal posterior part of ulna, forms elbow tip.
- Coronoid process — anterior projection of ulna, fits in coronoid fossa during flexion.
- Annular ligament — wraps around radial head, stabilizes proximal radioulnar joint.
- Sail sign — radiographic sign of joint effusion visible as displaced fat pads.
Action Items / Next Steps
- Review the ossification centers of the elbow.
- Prepare for upcoming lecture on elbow MRI anatomy.