Anatomy: The Upper Limb & Scapula

Overview of the Upper Limb

• The upper limb, also known as the upper extremity, extends from the shoulder joint to the fingertips.
• It includes the shoulder, arm, forearm, wrist, and hand.
• There are 64 bones in the upper limbs.
• The bones of the upper limbs include the:
  • Scapula (2): One on each side of the upper back
  • Clavicle (2): One on each side of the upper chest
  • Humerus (2): One in each upper arm
  • Radius (2): One in each forearm
  • Ulna (2): One in each forearm
  • Carpals (16): 8 in each wrist
  • Metacarpals (10): 5 in each hand
  • Phalanges (28): 14 in each hand (fingers and thumbs)

The Scapula

• Also known as the shoulder blade.
• It is a triangular, flat bone, serving as a site for muscle attachments.
• It articulates with the humerus at the glenohumeral joint.
• It articulates with the clavicle at the acromioclavicular joint.
• It connects the upper limb to the trunk.

Costal (Anterior) Surface of the Scapula

• The costal surface faces the ribcage.
• A large, concave depression covering most of its surface called the subscapular fossa is present.
• The subscapularis (rotator cuff muscle) originates from this fossa.
• Originating from the superolateral surface of the costal scapula is the coracoid process, a hook-like projection lying just underneath the clavicle.
• The pectoralis minor, coracobrachialis, and the short head of the biceps brachii attach to the coracoid process.

Lateral Surface

• The lateral position of the scapula refers to its position on the rib cage.
• Normally, the scapula lies flat against the rib cage, with its medial border (the edge closest to the spine) aligned with the spinous processes of the thoracic vertebrae.

Posterior surface

• Faces outwards and serves as a site of origin for most of the rotator cuff muscles of the shoulder.
• It is marked by the:
  • Spine, which is the most prominent feature of the posterior scapula, runs transversely, and divides the surface into two.
  • Acromion, which is a projection of the spine that arches over the glenohumeral joint and articulates with the clavicle at the acromioclavicular joint.
  • Infraspinous fossa, which is the area below the spine of the scapula, displays a convex shape, and is where the infraspinatus muscle originates.
  • Supraspinous fossa, which is smaller and more convex in shape than the infraspinous fossa.
  • The supraspinatus muscle originates from this area.

Muscles Attached to the Scapula

• Posterior Muscles:
  • Trapezius: Attaches to the posterior surface and the external occipital protuberance, superior nuchal line, and spinous processes of C7-T12.
  • Rhomboids: Attaches to the posterior surface and the spinous processes of T2-T5 (Rhomboid major) and C7-T1 (Rhomboid minor).
  • Supraspinatus: Attaches to the supraspinous fossa on the posterior surface.
  • Infraspinatus: Attaches to the infraspinous fossa on the posterior surface.
  • Teres minor: Attaches to the axillary border on the posterior surface.
• Anterior Muscles:
  • Subscapularis: Attaches to the subscapular fossa on the anterior surface.
  • Pectoralis minor: Attaches to the coracoid process on the anterior surface.
  • Serratus anterior: Attaches to the costal surface on the anterior surface.
• Lateral Muscles:
  • Deltoid: Attaches to the spine and acromion process on the lateral surface.
  • Teres major: Attaches to the inferior angle on the lateral surface.
• Medial Muscles:
  • Levator scapulae: Attaches to the superior angle and neck on the medial surface.
  • Omohyoid: Attaches to the superior border on the medial surface.
  • Rhomboids: Attaches to the medial border and the spinous processes of T2-T5 (Rhomboid major) and C7-T1 (Rhomboid minor).
• Inferior Muscles:
  • Teres major: Attaches to the inferior angle.
  • Latissimus dorsi: Attaches to the inferior angle and has a broad aponeurosis that attaches to the spinous processes of the lower thoracic vertebrae.
• Muscles Attached provide movement, stability, and support to the scapula and entire upper limb.

Clinical Relevance: Fractures of the Scapula

• Scapula fractures are relatively uncommon and usually indicate severe chest trauma.
• They are frequently seen in high-speed road collisions, crushing injuries, or sports injuries.
• Fractured scapulae typically do not require fixation because the surrounding muscle tone holds the pieces in place for healing.

Clavicle (Collarbone)

• The clavicle is a slender, S-shaped bone.
• Facing forward, the medial aspect is convex, and the lateral aspect is concave.
• The clavicle consists of a sternal (medial) end, a shaft, and an acromial (lateral) end.

Sternal (Medial) End of the Clavicle

• The sternal end contains a large facet for articulation with the manubrium of the sternum at the sternoclavicular joint.
• The inferior surface of the sternal end is marked by a rough oval depression for the costoclavicular ligament (a ligament of the SC joint).

Clavicle Shaft

• It acts as a point of origin and attachment for several muscles including the deltoid, trapezius, subclavius, pectoralis major, sternocleidomastoid, and sternohyoid.

Acromial (Lateral) End of the Clavicle

• The acromial end houses a small facet for articulation with the acromion of the scapula at the acromioclavicular joint.
• Serves as an attachment point for the conoid tubercle and the trapezoid line.
  • Conoid tubercle: The attachment point of the conoid ligament, the medial part of the coracoclavicular ligament.
  • Trapezoid line: The attachment point of the trapezoid ligament, the lateral part of the coracoclavicular ligament.
• The coracoclavicular ligament is a very strong structure, effectively suspending the weight of the upper limb from the clavicle.

Muscles Attached to the Clavicle

• Superior Surface:
  • Trapezius: Attaches to the lateral third of the clavicle.
  • Deltoid: Attaches to the anterior surface of the lateral third of the clavicle.
• Inferior Surface:
  • Subclavius: Attaches to the groove on the inferior surface of the clavicle.
  • Pectoralis major: Attaches to the anterior surface of the medial two-thirds of the clavicle.
• Medial End:
  • Sternocleidomastoid: Attaches to the medial end of the clavicle.
• Lateral End:
  • Deltoid: Attaches to the anterior surface of the lateral third of the clavicle.
  • Trapezius: Attaches to the lateral third of the clavicle.

Clinical Relevance: Fracture of the Clavicle

• The clavicle transmits forces from the upper limb to the axial skeleton.
• Size makes it susceptible to fracture.
• The most common mechanism of injury is falling onto the shoulder or an outstretched hand.
• When the clavicle is arbitrarily divided into thirds:
  • 15% of fractures occur in the lateral third
  • 80% occur in the middle third
  • 5% occur in the medial third.
• After a fracture, the lateral end of the clavicle is displaced inferiorly by the weight of the arm and displaced medially by the pectoralis major.
• The medial end is pulled superiorly by the sternocleidomastoid muscle.
• Management of a clavicular fracture can be conservative (e.g., sling immobilization) or operative (e.g., open reduction and internal fixation).
• The supraclavicular nerves lie in close proximity to the clavicle and are occasionally sacrificed during a surgical repair, resulting in a numb patch over the upper chest and shoulder.

The Humerus

• It is the long bone of the upper limb, extending from the shoulder to the elbow.
• The proximal aspect of the humerus articulates with the glenoid fossa of the scapula, forming the glenohumeral joint.
• Distally, at the elbow joint, the humerus articulates with the head of the radius and the trochlear notch of the ulna.

Proximal Region

• The proximal humerus is marked by a head, anatomical neck, surgical neck, greater and lesser tuberosity, and intertubercular sulcus.
• The upper end of this bone consists of the head, which faces medially, upwards, and backwards, and is separated from the greater and lesser tuberosities by the anatomical neck.
• The greater tuberosity is located laterally on the humerus and has anterior and posterior surfaces.
• It serves as an attachment site for three of the rotator cuff muscles: the supraspinatus, infraspinatus, and teres minor attaching to superior, middle, and inferior facets, respectively.
• The lesser tuberosity is much smaller and more medially located on the bone, only has an anterior surface providing attachment for the last rotator cuff muscle, the subscapularis.
• A deep groove separates the two tuberosities, called the intertubercular sulcus.
• The tendon of the long head of the biceps brachii emerges from the shoulder joint and runs through this groove.
• The edges of the intertubercular sulcus are known as lips.
• Pectoralis major, teres major, and latissimus dorsi insert on the lips of the intertubercular sulcus.
• The surgical neck extends from just distal to the tuberosities to the shaft of the humerus.
• The axillary nerve and circumflex humeral vessels lie against the bone there.

Clinical Relevance: Surgical Neck Fracture

• The surgical neck is the place to get it.
• It is a direct blow to the area, or the result of falling on an outstretched hand.
• Axillary Nerve Injury from surgical neck of the humerus fracture damages the deltoid and teres minor muscles, impairing abduction and sensation over the lower deltoid.

The Humerus Shaft

• It connects the proximal end (near the shoulder) to the distal end (near the elbow).
• Proximal end: The shaft begins just below the head of the humerus.
• Distal end: The shaft ends just above the condyles of the humerus.
• Anterior surface: The front surface of the shaft is smooth and convex.
• Posterior surface: The back surface of the shaft has a longitudinal ridge, known as the deltoid tuberosity, where the deltoid muscle attaches.
• Medial border: The medial border of the shaft is thin and smooth.
• Lateral border: The lateral part of the shaft is thicker and more prominent.
• Spiral groove: This runs along the posterior surface of the shaft, housing the radial nerve, and the profunda brachii artery.

Distal Region

• The lateral and medial borders of the distal humerus form medial and lateral supraepicondylar ridges.
• The lateral supraepicondylar ridge is more roughened, providing the origin site of the forearm extensor muscles.
• Extracapsular projections of bone are immediately distal to the supraepicondylar ridges.
• Both medial and lateral epicondyles can be palpated at the elbow, with the medial being larger and extending more distally.
• The ulnar nerve passes in a groove on the posterior aspect of the medial epicondyle where it is palpable.
• Distally, the trochlea is located medially and extends onto the posterior aspect of the bone.
• Lateral to the trochlea is the capitulum, which articulates with the radius.
• Located on the distal portion are the coronoid, radial, and olecranon fossae, accommodating forearm bones during flexion/extension.

Muscles Attached to the Humerus

• Anterior Muscles:
  • Pectoralis major: Attaches to the anterior surface of the greater tubercle.
  • Teres major: Attaches to the anterior surface of the lesser tubercle.
  • Brachialis: Attaches to the anterior surface of the shaft.
  • Brachioradialis: Attaches to the lateral surface of the shaft.
• Posterior Muscles:
  • Teres minor: Attaches to the posterior surface of the greater tubercle.
  • Supraspinatus: Attaches to the superior facet of the greater tubercle.
  • Infraspinatus: Attaches to the middle facet of the greater tubercle.
  • Triceps brachii: Attaches to the posterior surface of the olecranon process.
  • Anconeus: Attaches to the posterior surface of the lateral epicondyle.
• Lateral Muscles:
  • Deltoid: Attaches to the deltoid tuberosity on the lateral surface.
  • Extensor carpi radialis longus: Attaches to the lateral surface of the shaft.
  • Extensor carpi radialis brevis: Attaches to the lateral surface of the shaft.
• Medial Muscles:
  • Subscapularis: Attaches to the lesser tubercle.
• Distal Muscles:
  • Brachialis: Attaches to the coronoid process and the tuberosity of the ulna.
  • Extensor carpi ulnaris: Attaches to the posterior surface of the lateral epicondyle.
  • Extensor digitorum: Attaches to the posterior surface of the lateral epicondyle.
  • Extensor digiti minimi: Attaches to the posterior surface of the lateral epicondyle.

Clinical Relevance: Supracondylar Fracture

• It is a fracture of the distal humerus just above the elbow joint.
• Typically transverse or oblique, and the most common mechanism of injury is falling on an outstretched hand.
• More common in children than adults.
• Brachial artery damage may occur either directly, or via swelling following the trauma.
• Ischaemia can cause Volkmann’s ischaemic contracture which is uncontrolled flexion of the hand.
• Damage to the anterior interosseous, ulnar, and radial nerves can also affect the function of the limb.
• The Gartland classification is used for these fractures including;
  • Type 1: minimally displaced.
  • Type 2: displaced with but with an intact posterior cortex.
  • Type 3: completely off-ended.
• Type 1 Injuries can be managed conservatively with an above elbow cast, whereas types 2 and 3 typically require surgical fixation with crossed, bi-cortical k-wires.

The Radius

• It is a long bone in the forearm.
• The radius lies laterally and parallel to the ulna.
• It pivots around the ulna to produce movement at the proximal and distal radio-ulnar joints.

The Proximal Region

• The proximal end of the radius articulates in both the elbow and proximal radioulnar joints.
• Landmarks include:
  • Radial Head: Shaped like a disc and has a concave articulating surface – thicker medially.
  • Radial Neck: Area below the head.
  • Radial Tuberosity: Bony projection where the bicep attaches.

The Radius Shaft

• Long, thin, cylindrical part of the bone that connects the proximal end (near the elbow) to the distal end (near the wrist).
• Landmarks include:
  • A thin, rough edge that runs along the medial side of the shaft providing attachment for the interosseous membrane runs between the interosseous border
  • Smooth rounded edge along the anterior surface
  • A smooth, rounded edge along the posterior surface
  • Smooth, rounded edge along the lateral border

Distal Region of the Radius

• Radial shaft expands to form a rectangular end.
• Styloid process projects distally on the lateral side.
• On the medial surface, the ulnar notch (concavity) articulates with the head of ulna.
• The surface has facets for articulation with scaphoid and lunate carpal bones to make up the wrist joint

The Attached Muscle

• Anterior
  • Flexor Pollicis Longus
  • Pronator Teres attaches laterally
  • Pronator Quadratus, distally
• Posterior:
  • Extensor Pollicis Brevis + Longus
  • Abductor Pollicis Longus
• Lateral Side:
  • Brachioradialis
• Proximal, from Radial Tuberosity
  • Biceps Brachii

Radius - Common Fractures

• Colles: The distal radius breaks when someone falls on outstretched hand
• Radial Head - falling on outstretched arm causes head to compress capitulum of humerus
• Smith – break from falling onto back of the hand causing distal fragment to protrude

THE ULNA

• The ulna is a long bone found in the forearm.
• Lies medially and parallel to the Radius, the ulna acts as a stabilizing bone as the Radius moves.

The Proximal Region of the Ulna

• Articulates with the trochlea of the Humerus proximally.
• Enabling movement relies on specialized bony protuberances to enable muscle attachments
  • Olecranon - large, palpable and projection forming part of the trochlear notch. Triceps Brachii muscle attaches here.
  • Coronoid Process: ridge forming part of trochlear notch projecting anteriorly.
  • Trochlear Notch: Joint from the coronoid Process and Olecranon forms this to enable articulation with the Humerus.
  • Radial Notch: area articulates with the Radius head.
  • Ulna Tuberosity – at point where the coronoid process and ulna join, roughening can be found where Brachialis attaches.

Ulna Shaft

• Long, thin cylindrical section connecting parts of the bone.
• Bony landmarks included:
  • The Interosseous border, found on the lateral side of the shaft for the membrane between it and the radius.
  • The other parts - Medial | Posterior | Anterior Borders – run across the 3 corresponding sides of shaft.

Distal Ulna

• The Diameter is unremarkable and rounded compared to the other Radius and connects to Ulnar styloid process
• Distal Radio-ulnar joint requires that distal surface connects with the ulna notch on the Radius.

Ulna Muscle attachments

• Posterior.
  • Anconeus from Olecranon process .
  • Extensor carpi ulnaris inserts.
  • Abductor pollicis longus inserts nearby the head.
• Anterior-
  • Brachialis to coronoid process
  • ,Flexor digitorum profundus inserts shaft +
    • Flexor Pollicis Longus for anterior Shaft muscles
  • PronatorQuadratus joins on at the distal end of the shaft.

Ulna - Relevant Fractures

• Hitting/trauma causes lone fractures with muscle tone pulling it anteriorly
• Olecranon process causes fracturing.
• Falling on flexed elbow can proximally displace fracture.

Ulna & Radius

• Interosseous membrane joins the ulna to radius.
• Trauma transfers one force to one.
• These are key classical fractures.
  • Monteggia: Ulnar shaft displaced +Radius Proximally. fractures after force to ulna shaft displaces prox of radius by force through it
  • Galeazzi: distal Radius fracture + ulna heads head by distal radio-ulnar joint.

Carpal Bones

• This a group of smaller shaped bones organized into 2 sections - proximal/distal -*Proximal Row. * Distal Row.

  • Scaphoid . Trapezium
  • Lunate Trapezoid
  • Triquetrum Capitate
    • Pisiform(sesamoid bone by surface by flexor carpi ulnaris tendon Hamate

• Arches form due to carpal bones shape, flexor retinaculum forms spans between arch . Carpal Tunnel created.

• • Surface has radio-carpal joint that is joint with the scaphoid/lunate and radius . Next articulation from the distal surface with the metacarpals.

Attachments

• Thenar : Thenar attaches to Trapeziu +1st metacarpal bones as well as *Opponens Pollicis/Flexor Pollicis Brevis ,Abductor Pollicis Brevis.
• Hypothenar Attaches Hamate + 5th Metacarpal. ,*Opponens Digiti Minimi/Flexor Digiti Minimi Brevis/Abductor Digiti Minimi

Other attachments.

• Attaches Extensor Carpi RadialisBrevis + longus on surface of bases 2nd metacarpals. Extensor Carpi Ulnaris joints near base of 5th.

The carpal-Scaphoid Fracture

• falling on hand causes injury
• pain by anatomical snuffbox

Metacarpal Bones

• These join carpal,wrists with the phalanges, fingers
• 5 exist for each digit. List

1. (thumb).
2. (index finger).
3. (middle finger).
4. (ring finger).
5. (little finger).

• Common bone elements include.

1. Base : proximal joins carpals.
2. Shaft : elongate, thin bone.
3. Head : distal,phalangeal articulation

Muscle Attachments

• To metacarpal bone.
  • Thenar on 1st.
  • Hypothenars to 5th.
  • Interosseous. joints.

Phalanges

The bones forming the digits

• *Thumb surface has 1 less phalanx, 2 compared to the typical 3. Proximals , Intermediate,,Distals 14 in total

Bones

• elements joints to them:

1. Base where the metacarp/phalangeal articulations.
2. A basic elognate shaft.
3. Head with another joints phalanx

Muscles

• These elements attach to the joints:

1. Distal - Flexor Digitorum Profundus . 2 Intermediate - Flexor Digitorum Superficialisis. 3 Extensor Digitorums.