Upper Limb Study Notes

THE UPPER LIMB

Overview

  • Focus on the Brachial (Arm) Region: Bones and Muscles

Objectives

  • Identify key structures and bone markings of the upper limb, including:

    • Clavicle

    • Humerus

  • Differentiate left from right anatomy of the upper limb.

  • Explain how the humerus articulates with radius and ulna.

  • Identify anterior and posterior arm muscles along with their actions.

  • Discuss implications of a rupture of the biceps tendon.

The Clavicle

  • Definition: The clavicle, also known as the collarbone, is a critical bone that connects the upper limb to the trunk.

  • Bone Structure and Features:

    • Medial Two-Thirds:

    • Convex anteriorly.

    • Enlarged and triangular sternal end which articulates with the manubrium of the sternum at the sternoclavicular (SC) joint.

    • Lateral Third:

    • Flattened and concave anteriorly.

    • Flat acromial end articulates with the acromion of the scapula at the acromioclavicular (AC) joint.

    • Curvature:

    • The distinct curvatures give the clavicle an elongated capital 'S' appearance, which increases its resilience.

  • Function:

    • Acts as a moveable strut supporting the scapula and free limb, maximizing their freedom of motion by keeping them away from the trunk.

    • Forms a bony boundary for the cervico-axillary canal, protecting the neurovascular bundle serving the upper limb.

  • Notable Features:

    • Conoid Tubercle near acromial end.

The Humerus

  • Overview: The humerus is the largest bone in the upper limb and has several key articulations.

  • Articulations:

    • Articulates with the scapula at the glenohumeral joint.

    • Articulates with the radius and ulna at the elbow joint.

  • Head Structure:

    • Spherical Head:

    • Fits into the glenoid cavity of the scapula.

  • Neck Structure:

    • Anatomical Neck: Grooved region surrounding the head, separating it from the greater and lesser tubercles.

    • Surgical Neck:

    • A narrower region distal to the head; commonly fractured.

  • Tubercles:

    • Greater and Lesser Tubercles:

    • Provide muscular attachment and leverage for scapulohumeral muscles.

  • Intertubercular Sulcus:

    • Also known as the bicipital groove, it separates the tubercles, providing a protected path for the long head of the biceps muscle tendon.

Shaft of the Humerus

  • Key Features:

    • Deltoid Tuberosity: Located laterally, serves as the attachment site for the deltoid muscle.

    • Radial Groove: Situated posteriorly, channels the radial nerve and profunda brachii artery as they pass anterior to the long head of the triceps brachii muscle.

Distal End of Humerus

  • Condyle Structure:

    • Composed of the trochlea, capitulum, olecranon fossa, coronoid fossa, and radial fossa.

  • Articular Surfaces:

    • Capitulum: Lateral surface for articulation with the head of the radius.

    • Trochlea: Medial spool-shaped region for articulation with the proximal ulna.

  • Fossae: (Hollows)

    • Coronoid Fossa: Anteriorly located; receives the coronoid process of the ulna during full elbow flexion.

    • Radial Fossa: Superior to the capitulum, accommodates the head of the radius during full flexion.

    • Olecranon Fossa: Posteriorly located; houses the olecranon of the ulna in elbow extension.

Muscles of the Anterior Arm

  • Muscle Actions:

    • Biceps Brachii:

    • Functions to supinate the forearm and flex the forearm when in a supine position. Its short head helps resist shoulder dislocation.

    • Coracobrachialis:

    • Aids in flexing and adducting the arm. Also contributes to resisting shoulder dislocation.

    • Brachialis:

    • Responsible for flexing the forearm regardless of arm position.

Muscles of the Posterior Arm

  • Muscle Actions:

    • Triceps Brachii:

    • Serves as the primary extensor of the forearm. The long head as well helps resist dislocation of the humerus during adduction.

    • Anconeus:

    • Aids the triceps in extending the forearm and stabilizes the elbow joint.

Rupture of the Tendon of Long Head of Biceps Brachii

  • Cause and Mechanism:

    • Often results from wear and tear of an inflamed tendon that shifts in the intertubercular sulcus.

    • Typically seen in individuals over 35 years of age.

    • The tendon usually tears from its attachment at the supraglenoid tubercle of the scapula.

  • Symptoms:

    • Characterized by a notable snap or pop upon rupture.

    • Leads to a condition known as "Popeye deformity," where the detached muscle belly forms a ball near the center of the distal anterior arm.

  • Common Causes of Rupture:

    • Can result from forceful arm flexion against resistance, often encountered in weightlifting.

    • Frequently related to chronic tendonitis, with repetitive overhead motions in activities like swimming and baseball leading to tendon tearing.

References

  • Moore, Keith L. (2018). Influence: Clinically Oriented Anatomy. Wolters Kluwer E-books

THE UPPER LIMB

Antebrachial (Forearm) Region: Bones and Muscles

Objectives

  • Identify the bones that form the antebrachium (forearm).

  • Discuss the ulna’s articulation with the humerus.

  • Identify the bone markings of both ulna and radius.

  • Discuss fractures associated with the ulna and radius, with a focus on the Colles fracture.

  • Outline the flexor muscles of the forearm and their actions.

  • Outline the extensor muscles of the forearm and their actions.

  • Discuss pronator syndrome.

Introduction to the Upper Limb: Antebrachial Bones

  • Ulna

    • Description: The ulna is the stabilizing bone of the forearm and is notable for being the medial and longer of the two forearm bones.

    • Anatomy: The proximal end of the ulna is more massive and specialized for articulation with the humerus at the elbow and with the head of the radius laterally.

  • Radius

    • Description: The radius is the lateral and shorter of the two forearm bones.

    • Anatomy: The proximal end features a short head, neck, and a medially directed tuberosity that is integral for movement.

    • Articulation: The smooth superior aspect of the discoid head is concave, facilitating articulation with the capitulum of the humerus during flexion and extension of the elbow joint.

Ulna

  • Articulation with the Humerus

    • Prominent Projections:

    1. Olecranon

      • Location: Projects proximally from the posterior aspect of the ulna.

      • Function: Forms the point of the elbow and serves as a lever for extension of the elbow; part of the trochlear notch.

    2. Coronoid Process

      • Location: Projects anteriorly from the ulna.

    • Radial Notch: This is the area where the radial head articulates with the ulna.

  • Functional Characteristics

    • The articulation of the ulna with the humerus mainly permits flexion and extension at the elbow joint, with minimal abduction and adduction during forearm pronation and supination.

    • Tuberosity: Located inferior to the coronoid process, it serves as an attachment point for the brachialis muscle's tendon.

    • Shaft Structure: The shaft is thick and cylindrical at the proximal end but tapers distally.

    • Distal End: The small disc-like head of the ulna features a small conical ulnar styloid process, which does not reach the wrist and therefore does not participate in the wrist (radiocarpal) joint.

Radius

  • Articulations

    • The radial head articulates with the radial notch of the ulna, covered by articular cartilage.

    • The neck of the radius represents a constriction distal to the head, with the oval radial tuberosity located below the medial part of this neck, marking the proximal end.

  • Functionality

    • Radial Tuberosity: Serves as the attachment point for the tendon of the biceps brachii muscle.

    • Shaft Characteristics: The radius gradually enlarges distally, with the medial aspect forming the ulnar notch for the head of the ulna, while the lateral aspect becomes ridge-like, terminating at the distal styloid process of the radius.

Fractures of the Radius & Ulna / Colles Fracture

  • Colles Fracture

    • Common among older individuals and athletic adults, typically resulting from severe trauma.

    • Characteristics: Direct injury usually leads to transverse fractures occurring at the same level, frequently in the mid third of the bones.

    • Isolated fractures: Fractures of either radius or ulna can occur independently.

    • Associated Risk: Due to the tight binding of the bones via the interosseous membrane, a fracture in one bone often results in dislocation of the nearby joint.

Muscles of the Forearm

Anterior (Flexor) Muscles of the Forearm - Superficial Layer

  • Pronator Teres: Function - Pronates and flexes the forearm at the elbow.

  • Flexor Carpi Radialis: Function - Flexes and abducts the hand at the wrist.

  • Palmaris Longus: Function - Flexes the hand at the wrist and tenses the palmar aponeurosis. (Note: This muscle is absent in 10%-20% of the population.)

  • Flexor Carpi Ulnaris: Function - Flexes and adducts the hand at the wrist.

Anterior (Flexor) Muscles of the Forearm - Intermediate Layer

  • Flexor Digitorum Superficialis: Function - Flexes middle phalanges at the proximal interphalangeal joints of the middle four digits; it also flexes proximal phalanges at the metacarpophalangeal joints when engaged more strongly.