Kin 3305 EXam 2 part 3

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The four bones that relate to the function of the elbow and forearm complex

1) scapula

2) distal humerus

3) ulna

4) radius


Scapula – has three bony features that are important to the muscles of the elbow

- Coracoid process – serves as the proximal attachment for the short head of the biceps

- Supraglenoid tubercle – serves as the proximal attachment for the long head of the biceps

- Infraglenoid tubercle – marks the proximal attachment for the long head of the triceps


Radius – only the radius interacts with wrist joint

- The radial head is shaped like a wide disc on the proximal end of the radius

- The superior surface of the radial head consists of a shallow, cup-shaped depressed called the fovea that articulates with the capitulum of the humerus, forming the humeroradial joint

- The radial tuberosity, is an enlarged ridge of bone located on the anterior-medial aspect of the proximal radius

  • The primary distal attachment for the biceps brachii

Radius (cont.)

- The distal end of the radius is wide and flat with two notable structures: the styloid process and the ulnar notch

  • The styloid process is the pointed (and easily palpated) projection of bone off the distal lateral radius
  • The ulnar notch is a small depression on the medial side of the distal radius that articulates with the ulnar head, forming the distal radioulnar joint


- The olecranon process is the large, blunt, proximal top of the ulna commonly referred to as the elbow bone

  • The rough posterior surface of the olecranon process is the distal attachment for the triceps muscles

- The trochlear notch is the large, jaw-like curvature of the proximal ulna that articulates with the trochlea (of the humerus), forming the humeroulnar joint


Ulna (cont.)

- The coronoid process strengthens the articulation of the humeroulnar joint by firmly grabbing the trochlea of the humerus

- Slightly inferior and lateral to the trochlear notch is the radial notch, which articulates with the head of the radius to form the proximal radioulnar joint


Ulna (cont.)

- Ulnar tuberosity – gives insertion to a part of the brachialis

- Antebrachial interosseous membrane (between bones) – fibrous sheet that connects the interosseous margins of the radius and the ulna

- Ulnar head

- Located distally, the styloid process is a pointed projection of bone that arises from the ulnar head

  • Both of these structures can be palpated on the ulnar side of the dorsum of the wrist, with the forearm fully pronated

Elbow joint (general features)

- The humeroulnar joint provides most of the structural stability to the elbow as a whole

- The humeroradial joint is formed by the ball-shaped capitulum of the humerus articulating with the bowl-shaped fovea of the radius

- The primary function of the collateral ligaments is to limit excessive varus and valgus deformations of the elbow

  • The medial collateral ligament is most often injured during attempts to catch oneself from a fall

Supporting structures of the elbow joint

- Medial collateral ligament – contains fibers that attach proximally to the medial condyle and distally to the medial aspects of the coronoid and olecranon processes

  • Provide stability primarily by resisting cubitus valgus
  • This ligament is also called the ulnar collateral ligament

- Lateral collateral ligament – originates on the lateral epicondyle and ultimately attaches to the lateral aspect of the proximal forearm

  • These fibers provide stability to the elbow by resisting cubitus varus
  • This ligament is also referred to as the radial collateral ligament

Elbow joint (kinematics)

- From the anatomic position, elbow flexion and extension occur in the sagittal plane about a medial-lateral axis of rotation, which courses through both epicondyles

  • The range of motion at the elbow normally spans from 5 degrees beyond extension and 145 degrees of flexion

Forearm (general features)

- The forearm is composed of the proximal and distal radioulnar joints

  • These joints are located at the proximal and distal ends of the forearm

- Pronation and supination occur as a result of motion at each of these two joints

  • In full supination, the radius and ulna lie parallel to one another
  • However, in full pronation, the radius crosses over the ulna

- Pronation and supination involve the radius rotating around a relatively fixed ulna


Supporting structures of the proximal and distal radioulnar joints

- Annular ligament – a thick circular band of CT that wraps around the radial head and attaches to either side of the radial notch of the ulna

  • This ring-like structure holds the radial head firmly against the ulna, allowing it to spin freely during supination and pronation

- Interosseous membrane – helps bind the radius to the ulna; serves as a site for muscular attachments, and as a mechanism to transmit forces proximally through the forearm


Forearm (kinematics)

- Supination occurs in many functional activities that require the palm to be turned up, such as feeding, washing the face, or holding a bowl of soup

- Pronation is involved with activities such as grabbing an object from a table or pushing up from a chair, which require the palm to be faced down

- Supination and pronation occur as the radius rotates around an axis of rotation that travels from the radial head to the ulnar head

  • The 0-degree or neutral position of the forearm is the thumb-up position

Innervation of muscles

- The musculocutaneous nerve supplies two of the elbow flexors: the biceps brachii and the brachialis

- The radial nerve supplies all of the muscles that extend the elbow and wrist, plus the supinator and the brachioradialis muscles

- The median nerve supplies all the pronators of the forearm, as well as numerous wrist flexor muscles

- The ulnar nerve innervates the flexor carpi ulnaris, as well as most of the intrinsic muscles of the hand


Elbow flexors

- These muscles have a line of force that passes anterior to the elbow’s axis of rotation

- The pronator teres is considered a secondary elbow flexor

- Three of the four flexors also have the potential to pronate or supinate the forearm

  • Any elbow flexor muscle that attaches distally to the radius (versus the ulna) will aso pronate or supinate the forearm

Biceps brachii (3 joint muscle)

(elbow flexor)

(anterior arm)

card image

- Proximal attachment:

  • Long head – supraglenoid tubercle of the scapula
  • Short head – coracoid process of the scapula

- Distal attachment: bicipital tuberosity of the radius

- Innervation: musculocutaneous nerve

Actions: elbow flexion, forearm supination, shoulder flexion


Brachialis (deep to biceps brachii) – “workhouse” of the elbow flexors

(elbow flexor)

(anterior arm)

card image

- Attachments: anterior aspect of the distal humerus & coronoid process of the ulna

- Innervation: musculocutaneous nerve

- Action: elbow flexion



(elbow flexor)

(anterior arm)

card image

- Attachments: lateral supracondylar of the humerus & near the styloid process of the distal radius

- Innervation: radial nerve

- Actions: elbow flexion, pronating or supinating the forearm to the neutral (thumb-up) position


Triceps brachii

(elbow extensor)

(posterior arm)

card image

- Proximal attachment

  • Long head – infraglenoid tubercle of the scapula
  • Lateral head – posterior aspect of the superior humerus, lateral to the radial groove
  • Medial head – posterior aspect of the superior humerus, medial to the radial groove

- Distal attachment: olecranon process of the ulna

- Innervation: radial nerve

- Actions: elbow extension, shoulder extension (long head only)



(elbow extensor)

(posterior arm)

card image

- Attachments: posterior aspect of the lateral epicondyle of the humerus & olecranon process of the ulna

- Innervation: radial nerve

- Action: elbow extension


Forearm supinators and pronators (radio-ulnar joint)

Muscles that supinate or pronate the forearm must meet at least two requirements:

  • 1) the muscles must originate on the humerus or the ulna, or both, and must insert on the radius or the hand
  • 2) the muscles must have a line of force that intersects (versus parallels) the axis of rotation of the forearm joints

Supinators of the forarm

  • The primary supinator muscles are the biceps brachii and the supinator muscle
  • Secondary supinator muscles include the extensor pollicis longus and the extensor indicis


(forearm supinator)

(radio-ulnar joint)

card image

- Attachments: lateral epicondyle of the humerus and spinator crest of the ulna & lateral surface of the proximal radius

- Innervation: radial nerve

- Action: forearm supination


Pronators of the forearm

  • The primary pronator muscles are the pronator teres and the pronator quadratus
  • Secondary pronators are the flexor carpi radialis and the palmaris longus

Pronator teres

(forearm pronator)

(radio-ulnar joint)

card image

- Proximal attachment:

  • Humeral head – medial epicondyle of the humerus
  • Ulnar head – just medial to the tuberosity of the ulna

- Distal attachment: lateral surface of the mid radius

- Innervation: median nerve

- Actions: forearm pronation, elbow flexion


Pronator quadratus

(forearm pronator)

(radio-ulnar joint)

card image

- Attachments: anterior surface of the distal ulna & anterior surface of the distal radius

- Innervation: median nerve

- Action: forearm pronation

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