Functional Anatomy of the Elbow

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Elbow Structure

Three bones makes up the elbow joint: the distal end of humerus and the proximal ends of ulna and radius. The ulna and the radius are both forearm bones which form the wrist joint at their distal end.

The distal end of humerus includes the medial and lateral columns, medial and lateral epicondyles, and two articular surfaces:

• Medial and lateral columns
  • The distal end of the medial column includes the medial epicondyle with the insertion of forearm flexor muscles and the medial humeral trochlea
  • The distal end of the lateral column includes the capitellum and more proximally the lateral epicondyle with the insertion of the forearm extensor muscles
• Medial and lateral epicondyles
  • A large medial epicondyle is a bony projection located at the distal end of the medial supracondylar ridge of the humerus
  • A smaller lateral epicondyles located at the at the distal end of the lateral supracondylar ridge of the humerus. It is curved forward, and provides attachment point for the radial collateral ligament, and serves as the origin of the supinator and some forearm extensor muscles.
• Articular surfaces
  • Medially located trochlea articulates with the ulna
  • Laterally located capitellum articulates with radius

The proximal radius consists of the radial head, neck and tuberosity:

• The radial head is cylindrical which articulates with the capitellum of the humerus. The head rotates within the annular ligament to produce supination and pronation of the forearm.
• The neck and tuberosity support the head and provide points of attachments for supinator brevis and biceps brachii

The proximal ulna

• Olecranon process articulates with with distal humerus via trochlea and olecranon fossa
• The projection of the medial margin is called sublime tubercle, which serves as an insertion for the ulnar collateral ligament

Bones, Articulations and Kinematics of the Elbow

Mobility and stability of the elbow joint is necessary for daily functions, sports , and recreational activities. Static stabilisers provide elbow stability via ulnohumeral articulation, the medial collateral ligament and the lateral ulnar collateral ligament. Dynamic stabilisers include all muscles crossing the elbow joint that provide joint compressive forces.

Bones and Articulations

Bones	Articulations	Characteristics	Key palpation points
Humerus Ulna	Humeroulnar joint	made up of the trochlear groove on the humerus and the trochlear notch on the ulna.
Humerus Radius	Humeroradial joint	made up of the capitulation of the humerus and the head of the radius
Radius Ulna	Radioulnar joint

Elbow Kinematics

When assessing elbow flexion and extension, the variation between individuals must be considered. It includes individuals with joint hyperlaxity who may hyperextend by over 10 degrees or bodybuilders who may flex only up to 130 degrees due to their muscle bulk. According to Morrey et al., activities of daily living including dressing and hygiene require 140 degrees of elbow flexion, while 15 degrees of flexion is needed to tie a shoe. In general, most of the activities of daily living can be completed with 30 to 130 degrees of available elbow flexion, 50 degrees of forearm pronation, and 50 degrees of forearm supination.For daily tasks performances, these ranges are required in a dominant upper extremity as the dominant forearm is in pronation. Reduction in elbow pronation range of motion can be compensated to by shoulder abduction in some tasks performance. However there is no effective compensation mechanism for loss of elbow supination.

Joint	Type of joint	Plane of movement	Motion	Kinematics	Closed pack position	Open pack position
Humeroulnar joint	Hinge joint	Saggital	Flexion Extension	Flexion:135 degrees Extension:0 degrees
Humeroradial joint	Pivot joint	Saggital Transverse	Flexion/Extension Pronation/supination	Pronation:80 degrees Supination: 85 degrees
Radioulnar joint	Synovial Note: it is functionally a pivot joint, allowing for rotation motion between the radius and the ulna (radius rotates on the ulna)	Transverse	Pronation Supination

Ligaments of the Elbow

Key ligaments	Origin	Insertion	Action/role	Key palpation points
Ulnar collateral ligament or medial collateral ligament Anterior bundle: anterior, central and posterior bands Posterior bundle Transverse segment	Anteroinferior aspect of the medial epicondyle	Proximal aspect of the ulna	The anterior band of the anterior bundle is taut throughout the arc of motion and is a primary static stabilizer of the elbow. The posterior bundle is taut only in flexion as it attaches posterior to the sagittal axis of rotation. The transverse segment has the least contribution to elbow stability.
Radial collateral ligament or lateral collateral ligament	Lateral epicondyle	The annular ligament	Provides stabilisation for the radial head
Annular ligament	The anterior margin of the lesser sigmoid notch	The posterior margin of the lesser sigmoid notch
Quadrate ligament

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