Chapter 8 - Pectoral Girdle

Division and Structure of the Appendicular Skeleton

• Definition and Function of the Appendicular Skeleton

  • Primary function: Enable body movement, manipulation of objects, and locomotion.

  • Structural components: Includes all bones of the upper limbs, lower limbs, and the girdles (pectoral and pelvic) that attach the limbs directly to the axial skeleton.

  • Functional contrast:

  • Axial skeleton: Forms the central longitudinal axis of the body (head, neck, trunk) and provides protection for central organs.

  • Appendicular skeleton: Extends from the central axis to provide mobility.

• Quantitative Breakdown of the Human Skeleton

  • Total adult skeletal bone count: $206$ bones.

  • Total axial skeleton bone count: $80$ bones.

  • Cranium: $8$ bones

    • The part of the skull that encloses and protects the brain

  • Facial bones: $14$ bones

  • Hyoid bone: $1$ bone

    • A small, U-shaped bone located at the front of he neck

  • Auditory ossicles: $6$ bones

  • Vertebral column: $26$ bones

    • A flexible chain of bones that extends from the base of the skull to the tailbone

  • Sternum: $1$ bone

    • The long, flat, T-shaped bone located at the center front of the chest

  • Ribs: $24$ bones

  • Total appendicular skeleton bone count: $126$ bones ($63$ bones per side).

• Upper Limb Skeletal Division ($32$ Bones per Limb / $64$ Bones Total)

  • Pectoral (Shoulder) Girdle: $2$ bones per side ($4$ total)

  • Clavicle: $2$ ($1$ per side)

  • Scapula: $2$ ($1$ per side)

  • Free Upper Limb: $30$ bones per side ($60$ total)

  • Humerus (Arm): $2$ ($1$ per side)

  • Ulna (Forearm): $2$ ($1$ per side)

  • Radius (Forearm): $2$ ($1$ per side)

  • Carpals (Wrist): $16$ total ($8$ per wrist)

    • Proximal row: Scaphoid ($2$), Lunate ($2$), Triquetrum ($2$), Pisiform ($2$)

    • Distal row: Trapezium ($2$), Trapezoid ($2$), Capitate ($2$), Hamate ($2$)

  • Metacarpals (Palm): $10$ total ($5$ per hand)

  • Phalanges (Hand/Digits): $28$ total ($14$ per hand)

    • Proximal phalanges: $10$ ($5$ per hand)

    • Middle phalanges: $8$ ($4$ per hand; absent in digit $1$ / thumb)

    • Distal phalanges: $10$ ($5$ per hand)

• Lower Limb Skeletal Division ($31$ Bones per Side including Pelvic Girdle / $62$ Bones Total)

  • Pelvic (Hip) Girdle: $2$ bones total ($1$ per side)

  • Hip (Coxal) bone: $2$ total (each formed by the fusion of the ilium, ischium, and pubis in early adolescence)

  • Free Lower Limb: $30$ bones per side ($60$ total)

  • Femur (Thigh): $2$ ($1$ per side)

  • Patella (Kneecap): $2$ ($1$ per side)

  • Tibia (Leg): $2$ ($1$ per side)

  • Fibula (Leg): $2$ ($1$ per side)

  • Tarsals (Ankle/Foot): $14$ total ($7$ per foot)

    • Calcaneus ($2$), Talus ($2$), Navicular ($2$), Cuboid ($2$), Medial cuneiform ($2$), Intermediate cuneiform ($2$), Lateral cuneiform ($2$)

  • Metatarsals (Instep): $10$ total ($5$ per foot)

  • Phalanges (Toes): $28$ total ($14$ per foot)

    • Proximal phalanges: $10$ ($5$ per foot)

    • Middle phalanges: $8$ ($4$ per foot; absent in hallux / big toe)

    • Distal phalanges: $10$ ($5$ per foot)

Osteology of the Pectoral Girdle

• Overview of the Pectoral Girdle

  • Composed of two pairs of bones: two clavicles and two scapulae.

  • Functions to attach the free upper limb to the axial skeleton at the sternoclavicular joint.

  • Lacks a direct posterior bony attachment to the axial skeleton; the scapula is held against the thoracic cage primarily by muscles, allowing exceptionally high mobility at the expense of structural stability.

    • Bony attachment = bones directly connecting to other bones.

    • The scapula does NOT directly connect by bone to the vertebral column or ribs.

      • Instead, the scapula sits on the back of your rib cage and is held there mainly by muscles.

      • Front:
        Clavicle → Sternum
        ✅ Direct bone-to-bone connection

      • Back:
        Scapula → rib cage/vertebral column
        ❌ No direct bone-to-bone connection

    • Thoracic cage = your rib cage

      • Your scapula sits on the back of your rib cage.

      • But there isn't a joint directly connecting the scapula to the ribs.

      • Instead, muscles hold the scapula against the rib cage

      • That's why you can move your shoulder blade around so much.

      • Your shoulder blade is mostly held in place by muscles rather than being locked into the skeleton by a strong bony joint.

    • Because the scapula isn't tightly attached to the skeleton by bones:

      More mobility → less stability

• The Clavicle (Collarbone)

  • S-shaped long bone located anteriorly in the superior thorax horizontally above the first rib.

    • Anteriorly → Toward the front of your body.

    • Superior thorax → The upper part of your chest.

    • It runs roughly side-to-side across your upper chest.

    • The clavicle sits above your first rib.

  • Sternal End (Medial End): Round, blunt, triangular extremity that articulates with the manubrium of the sternum to form the sternoclavicular (SC) joint.

    • Extremity just means end.

    • Sternal → Related to the sternum (breastbone).

    • Medial → Closer to the middle of your body.

    • Manubrium = the upper part of the sternum.

  • Acromial End (Lateral End): Broad, flattened extremity that articulates with the acromion of the scapula to form the acromioclavicular (AC) joint.

    • Lateral → Farther from the middle of your body.

    • Wider and flatter than the inner end.

  • Conoid Tubercle: Distinct projection located on the inferior aspect of the lateral/acromial end; serves as an attachment site for the conoid part of the coracoclavicular ligament.

    • The conoid tubercle is a small bump on the underside of the outer end of the clavicle.

    • The coracoclavicular ligament isa strong pair of bands that connects the collarbone (clavicle) to a hook-like bony projection on the shoulder blade

  • Costal Tuberosity (Impression for Costoclavicular Ligament): Rough impression located on the inferior surface of the medial/sternal end; serves as the attachment site for the costoclavicular ligament anchoring the clavicle to the first rib.

    • An impression is basically a roughened/depressed area on the bone.

• Clinical Implications: Clavicle Fractures

  • Biomechanical susceptibility: The clavicle's double-curved S-shape is structured to transmit force from the upper limb to the axial skeleton, but it does not resist longitudinal compression well.

    • Longitudinal = along the length of the bone.

    • Compression = being pushed/squeezed from both ends.

    • Because of its curved shape, the clavicle can bend/buckle under certain forces, making it susceptible to fracture.

  • Common injury mechanism: Direct force applied to the shoulder, direct blow to the mid-shaft (middle of clavicle), or falling on an outstretched hand (FOOSH).

    • FOOSH: Body → arm → hand hits ground

      • The force travels up the arm toward the shoulder, potentially breaking the clavicle.

• Common site of fracture: The middle third (junction of the middle and lateral thirds) is the weakest region of the bone.

  • Medial ⅓ | Middle ⅓ | Lateral ⅓

• Structural strength of joints: The sternoclavicular joint ligaments are structurally stronger than the clavicle shaft; thus, stress typically breaks the bone rather than dislocating the SC joint.

  • The ligaments around this joint are very strong.

  • The clavicle shaft, however, is relatively more vulnerable.

  • Strong ligament + weaker bone

    → The bone breaks before the SC joint dislocates.

• Assessment protocol:

  • In addition to assessing local bone pain and deformity, full neurovascular and circulatory status of the affected upper limb must be performed.

    • Check whether the nerves supplying the arm are functioning normally

    • Check whether blood is flowing properly through the arm

  • Posterior displacement of bone fragments can compress or puncture the underlying subclavian artery and subclavian vein, or injure branches of the brachial plexus.

    • Remember that important structures are located behind/below the clavicle.

    • Subclavian artery: Carries oxygenated blood toward the upper limb.

    • Subclavian vein: Carries blood back toward the heart.

    • Brachial plexus: A network of nerves that supplies the upper limb.

• The Scapula (Shoulder Blade)

  • Large, triangular, flat bone situated on the posterior thoracic wall spanning between the $2\text{nd}$ and $7\text{th}$ (or $8\text{th}$) ribs.

  • Surfaces and Fossae:

    • Subscapular Fossa: Broad, concavity covering the entire anterior (costal) surface; origin for the subscapularis muscle.

    • Spine of the Scapula: Prominent ridge crossing obliquely across the upper portion of the posterior surface.

    • Supraspinous Fossa: Concavity superior to the scapular spine; origin for the supraspinatus muscle.

    • Infraspinous Fossa: Broad concavity inferior to the scapular spine; origin for the infraspinatus muscle.

  • Borders:

    • Superior Border: Thin, short superior margin.

    • Medial (Vertebral) Border: Long margin running parallel to the vertebral column.

    • Lateral (Axillary) Border: Thick margin facing toward the armpit.

  • Angles:

    • Superior Angle: Junction of the superior and medial borders.

    • Inferior Angle: Distinct bottom apex junction of medial and lateral borders.

    • Lateral Angle: Junction containing the glenoid cavity.

  • Specific Landmarks:

    • Acromion: Flattened, expanded lateral process continuous with the scapular spine; articulates with the acromial end of the clavicle.

    • Coracoid Process: Hook-like projection extending anteriorly and laterally from the superior border; site of attachment for pectoralis minor, coracobrachialis, short head of biceps brachii, and coracoclavicular ligaments.

    • Glenoid Cavity (Glenoid Fossa): Shallow, oval socket at the lateral angle that articulates with the head of the humerus.

    • Suprascapular Notch: Indentation along the superior border medial to the base of the coracoid process; converted into a foramen by the superior transverse scapular ligament.

    • Spinoglenoid Notch: Notch located at the lateral base of the scapular spine connecting the supraspinous and infraspinous fossae.

    • Supraglenoid Tubercle: Small roughness superior to the glenoid cavity; origin for the long head of the biceps brachii muscle.

    • Infraglenoid Tubercle: Rough area inferior to the glenoid cavity; origin for the long head of the triceps brachii muscle.

• Clinical Importance: Suprascapular Nerve Trapping

  • Innervation source: Suprascapular nerve arises from the ventral rami of spinal nerves $C_5$ and $C_6$.

  • Anatomical course: Passes through the suprascapular notch beneath the superior transverse scapular ligament (while the suprascapular artery passes superior to the ligament).

  • Motor distribution: Supplies the supraspinatus muscle (initiates arm abduction) and infraspinatus muscle (lateral rotation of the arm).

  • Compression syndrome: Neural compression can occur within the notch due to repetitive overhead motion, anatomical ligament hypertrophy, or local paralabral ganglion cysts.

  • Clinical manifestation: Burning shoulder pain, muscular weakness in abduction and external rotation, and eventual visible muscle atrophy in the supraspinous and infraspinous fossae.

Articulations and Joints of the Pectoral Girdle and Upper Limb

• Sternoclavicular (SC) Joint

  • Bones involved: Sternal end of clavicle, manubrium of sternum, and first costal cartilage.

  • Joint classification: Structural: Synovial joint (saddle joint functionally operating as plane and pivot); Functional: Freely movable (diarthrosis).

  • Primary movements: Elevation, depression, protraction, retraction, and axial rotation of the clavicle.

• Acromioclavicular (AC) Joint

  • Bones involved: Acromial end of clavicle and acromion of scapula.

  • Joint classification: Structural: Synovial plane (gliding) joint; Functional: Freely movable (diarthrosis).

  • Primary movements: Small gliding and rotational movements of the scapula on the clavicle during movement of the shoulder.

• Glenohumeral (Shoulder) Joint

  • Bones involved: Head of the humerus and glenoid cavity of the scapula.

  • Joint classification: Structural: Synovial ball-and-socket joint; Functional: Freely movable (diarthrosis).

  • Primary movements: Flexion, extension, abduction, adduction, medial rotation, lateral rotation, and circumduction.

  • Structural features:

  • Glenoid Labrum: A ring of fibrocartilage attached to the margin of the glenoid cavity that deepens the socket by approximately $50\%$ to improve stability without limiting mobility.

  • Articular Capsule: Envelopes the joint from the circumference of the glenoid cavity to the anatomical neck of the humerus.

  • Supporting Ligaments: Coracohumeral ligament, superior/middle/inferior glenohumeral ligaments, transverse humeral ligament, and coracoacromial ligament.

  • Protective Bursae: Synovial-lined fluid sacs that minimize friction between moving surfaces. Include the subacromial bursa, subcoracoid bursa, and subscapular bursa.

• Detailed Appendicular Joints Reference Table

  • Sternoclavicular: Synovial (plane/pivot); Gliding, limited movements in nearly every direction.

  • Acromioclavicular: Synovial (plane); Gliding and rotation of scapula on clavicle.

  • Radioulnar: Synovial (pivot); Rotation of forearm (pronation/supination).

  • Wrist (Radiocarpal): Synovial (condyloid); Flexion, extension, abduction, adduction, circumduction of wrist.

  • Intercarpal: Synovial (plane), except midcarpal joint which has saddle characteristics; Gliding plus movement during wrist flexion/extension.

  • Carpometacarpal: Synovial (saddle) at thumb (digit $1$); Synovial (plane) at remaining digits ($2-5$).

  • Metacarpophalangeal (MCP): Synovial (condyloid); Flexion, extension, abduction, adduction, circumduction.

  • Interphalangeal (IP): Synovial (hinge); Flexion and extension.

  • Sacroiliac: Synovial (plane); Slight gliding (increases during pregnancy).

  • Pubic Symphysis: Cartilaginous (symphysis); Slight movements (increases during pregnancy).

  • Tibiofibular: Synovial (plane) proximally; Fibrous (syndesmosis) distally.

  • Intertarsal: Synovial (plane/saddle); Inversion and eversion of foot.

  • Tarsometatarsal: Synovial (plane); Slight gliding.

Functional Biomechanics and Scapular Movements

• Functional Role of the Pectoral Girdle Musculature

  • Stabilizes the scapula against the thoracic wall to provide a stable foundation for muscles originating on the scapula that act on the humerus.

  • Dynamic scapular movements position the glenoid cavity in space, significantly expanding the overall functional range of motion of the upper extremity (e.g., full elevation/abduction of the arm above head height requires upward rotation of the scapula).

• Types of Scapular Movements

  • Elevation: Superior movement of the scapula (e.g., shrugging shoulders).

  • Depression: Inferior movement of the scapula (e.g., pulling shoulders down).

  • Protraction (Abduction): Lateral and anterior movement of the scapula away from the vertebral column (e.g., reaching forward, pushing, poor posture).

  • Retraction (Adduction): Medial and posterior movement of the scapula toward the vertebral column (e.g., pulling shoulder blades together, good posture).

  • Superior (Upward) Rotation: Movement of the inferior angle laterally and superiorly, directing the glenoid cavity upward (necessary for full arm abduction).

  • Inferior (Downward) Rotation: Movement of the inferior angle medially and inferiorly, directing the glenoid cavity downward.

• Summary Table of Prime Movers for Scapular Actions

  • Elevation: Trapezius (superior part), Levator scapulae, Rhomboid major, Rhomboid minor.

  • Depression: Trapezius (inferior part), Pectoralis minor, Serratus anterior (lower part).

  • Protraction / Abduction: Serratus anterior (principal driver), Pectoralis minor.

  • Retraction / Adduction: Trapezius (middle part principal), Rhomboid major, Rhomboid minor.

  • Upward Rotation: Serratus anterior (principal driver), Trapezius (upper fibers).

  • Downward Rotation: Rhomboid major, Rhomboid minor, Levator scapulae.

Musculature of the Pectoral Girdle and Upper Arm

• Classification Scheme of Pectoral Girdle and Shoulder Muscles

  • Category I: Anterior Thoracic Muscles (Move the Pectoral Girdle)

  • Category II: Posterior Thoracic Muscles (Move the Pectoral Girdle)

  • Category III: Axial Muscles Attached to Humerus

  • Category IV: Scapular Muscles Attached to Humerus (including Rotator Cuff)

• Category I: Anterior Thoracic Muscles

  • Pectoralis Minor

  • Action: Protracts and depresses scapula; helps elevate ribs during forced inhalation when scapula is fixed.

  • Origin: Anterior surfaces of ribs $3-5$.

  • Insertion: Coracoid process of scapula.

  • Innervation: Medial pectoral nerve ($C_8-T_1$).

  • Serratus Anterior

  • Action: Prime mover in scapula protraction; superiorly rotates scapula (directs glenoid cavity superiorly); holds scapula flat against chest wall.

  • Origin: External margins of ribs $1-8$ (or $9$).

  • Insertion: Anterior surface of the medial border of scapula.

  • Innervation: Long thoracic nerve ($C_5-C_7$).

  • Subclavius

  • Action: Stabilizes and depresses clavicle.

  • Origin: Rib $1$ (at costal cartilage junction).

  • Insertion: Inferior surface of clavicle.

  • Innervation: Nerve to subclavius ($C_5-C_6$).

• Category II: Posterior Thoracic Muscles

  • Levator Scapulae

  • Action: Elevates scapula; inferiorly rotates scapula (pulls glenoid cavity inferiorly).

  • Origin: Transverse processes of $C_1-C_4$ vertebrae.

  • Insertion: Superior angle and superior part of medial border of scapula.

  • Innervation: Cervical nerves ($C_3-C_4$) and dorsal scapular nerve ($C_5$).

  • Rhomboid Major

  • Action: Elevates, retracts (adducts), and inferiorly rotates scapula.

  • Origin: Spinous processes of $T_2-T_5$ vertebrae.

  • Insertion: Medial border of scapula from spine to inferior angle.

  • Innervation: Dorsal scapular nerve ($C_5$).

  • Rhomboid Minor

  • Action: Elevates, retracts (adducts), and inferiorly rotates scapula.

  • Origin: Spinous processes of $C_7-T_1$ vertebrae.

  • Insertion: Medial border of scapula superior to the spine.

  • Innervation: Dorsal scapular nerve ($C_5$).

  • Trapezius

  • Action:

    • Superior fibers: Elevate and superiorly rotate scapula.

    • Middle fibers: Retract (adduct) scapula.

    • Inferior fibers: Depress scapula.

  • Origin: Occipital bone (superior nuchal line), ligamentum nuchae, spinous processes of $C_7-T_{12}$.

  • Insertion: Clavicle (lateral third), acromion process, and spine of scapula.

  • Innervation: Accessory nerve ($CN\,XI$) (motor).

• Category III: Axial Muscles Attached to the Humerus

  • Latissimus Dorsi ("Swimmer's Muscle")

  • Action: Prime mover of arm extension; adducts and medially rotates arm.

  • Origin: Spinous processes of $T_7-T_{12}$, ribs $8-12$, iliac crest, thoracolumbar fascia.

  • Insertion: Intertubercular groove (bicipital groove) of humerus.

  • Innervation: Thoracodorsal nerve ($C_6-C_8$).

  • Pectoralis Major

  • Action: Prime mover of arm flexion; adducts and medially rotates arm.

  • Origin: Medial clavicle, costal cartilages of ribs $2-6$, body of sternum.

  • Insertion: Lateral lip of intertubercular groove of humerus.

  • Innervation: Lateral pectoral nerve ($C_5-C_7$) and medial pectoral nerve ($C_8-T_1$).

• Category IV: Muscles Originating on the Scapula Acting on the Humerus

  • Deltoid

  • Action:

    • Anterior fibers: Flex and medially rotate arm.

    • Middle fibers: Prime mover of arm abduction (past first $15$ degrees).

    • Posterior fibers: Extend and laterally rotate arm.

  • Origin: Acromial end of clavicle, acromion, and spine of scapula.

  • Insertion: Deltoid tuberosity of humerus.

  • Innervation: Axillary nerve ($C_5-C_6$).

  • Coracobrachialis

  • Action: Adducts and flexes arm (synergistic to pectoralis major).

  • Origin: Coracoid process of scapula.

  • Insertion: Middle medial shaft of humerus.

  • Innervation: Musculocutaneous nerve ($C_5-C_6$).

  • Teres Major

  • Action: Extends, adducts, and medially rotates arm.

  • Origin: Inferior lateral border and inferior angle of scapula.

  • Insertion: Lesser tubercle and medial lip of intertubercular groove of humerus.

  • Innervation: Lower subscapular nerve ($C_5-C_6$).

  • Triceps Brachii (Long Head)

  • Action: Extends and adducts arm at shoulder joint; extends forearm at elbow joint.

  • Origin: Infraglenoid tubercle of scapula.

  • Insertion: Olecranon process of ulna.

  • Innervation: Radial nerve ($C_5-C_7$).

  • Biceps Brachii (Long Head)

  • Action: Flexes arm at shoulder joint; flexes and supinates forearm at elbow joint.

  • Origin: Supraglenoid tubercle of scapula.

  • Insertion: Radial tuberosity and bicipital aponeurosis.

  • Innervation: Musculocutaneous nerve ($C_5-C_6$).

• Rotator Cuff Muscle Group (SITS)

  • Functional mechanics: Form a musculotendinous cuff surrounding the glenohumeral joint to fuse with the joint capsule, dynamically reinforcing and centering the head of the humerus inside the shallow glenoid cavity during movement.

  • Subscapularis

  • Action: Medially rotates arm.

  • Origin: Subscapular fossa of scapula.

  • Insertion: Lesser tubercle of humerus.

  • Innervation: Upper and lower subscapular nerves ($C_5-C_6$).

  • Supraspinatus

  • Action: Abducts arm (initiates first $15$ degrees of abduction before deltoid takes over).

  • Origin: Supraspinous fossa of scapula.

  • Insertion: Greater tubercle of humerus.

  • Innervation: Suprascapular nerve ($C_5-C_6$).

  • Infraspinatus

  • Action: Adducts and laterally rotates arm.

  • Origin: Infraspinous fossa of scapula.

  • Insertion: Greater tubercle of humerus.

  • Innervation: Suprascapular nerve ($C_5-C_6$).

  • Teres Minor

  • Action: Adducts and laterally rotates arm.

  • Origin: Upper dorsal lateral border of scapula.

  • Insertion: Greater tubercle of humerus.

  • Innervation: Axillary nerve ($C_5-C_6$).

Review Questions and Self-Assessment

• Multiple Choice Questions

  • Question 1: Which two bones form the pectoral girdle on each side of the body?

  • A. Humerus and scapula

  • B. Clavicle and scapula

  • C. Clavicle and sternum

  • D. Scapula and humerus

  • Answer: B — Clavicle and scapula.

  • Question 2: The pectoral girdle is part of which division of the skeleton?

  • A. Axial skeleton

  • B. Appendicular skeleton

  • C. Vertebral skeleton

  • D. Thoracic skeleton

  • Answer: B — Appendicular skeleton.

  • Question 3: Which end of the clavicle articulates with the manubrium of the sternum?

  • A. Acromial end

  • B. Lateral end

  • C. Sternal end

  • D. Conoid end

  • Answer: C — Sternal end.

  • Question 4: The acromial end of the clavicle articulates with which structure?

  • A. Coracoid process

  • B. Acromion of the scapula

  • C. Head of the humerus

  • D. Manubrium

  • Answer: B — Acromion of the scapula.

  • Question 5: Which structure of the scapula forms the shallow socket for the head of the humerus?

  • A. Acromion

  • B. Coracoid process

  • C. Glenoid cavity

  • D. Supraspinous fossa

  • Answer: C — Glenoid cavity.

  • Question 6: Which feature helps you recognize the posterior surface of the scapula?

  • A. Subscapular fossa

  • B. Spine of the scapula

  • C. Glenoid labrum

  • D. Coracoid ligament

  • Answer: B — Spine of the scapula.

  • Question 7: The spine of the scapula separates which two fossae?

  • A. Subscapular and supraspinous fossae

  • B. Supraspinous and infraspinous fossae

  • C. Glenoid and subscapular fossae

  • D. Superior and inferior fossae

  • Answer: B — Supraspinous and infraspinous fossae.

  • Question 8: The suprascapular nerve passes through which structure of the scapula?

  • A. Glenoid cavity

  • B. Acromion

  • C. Suprascapular notch

  • D. Coracoid process

  • Answer: C — Suprascapular notch.

  • Question 9: Which two muscles are supplied by the suprascapular nerve?

  • A. Deltoid and teres major

  • B. Supraspinatus and infraspinatus

  • C. Trapezius and rhomboid major

  • D. Pectoralis minor and serratus anterior

  • Answer: B — Supraspinatus and infraspinatus.

  • Question 10: Which joint is formed between the head of the humerus and the glenoid cavity?

  • A. Acromioclavicular joint

  • B. Sternoclavicular joint

  • C. Glenohumeral joint

  • D. Costoclavicular joint

  • Answer: C — Glenohumeral joint.

  • Question 11: Why does the shoulder joint have a large range of motion but relatively less bony stability?

  • A. The humeral head is very small

  • B. The glenoid cavity is shallow

  • C. The clavicle is very short

  • D. The scapula is fused to the ribs

  • Answer: B — The glenoid cavity is shallow.

  • Question 12: What is the main function of the glenoid labrum?

  • A. To produce shoulder movement

  • B. To deepen the glenoid cavity and improve stability

  • C. To attach the clavicle to the sternum

  • D. To reduce blood flow around the joint

  • Answer: B — To deepen the glenoid cavity and improve stability.

• Free-Response Assessment Questions

  • Question 13: A patient shrugs their shoulders. What movement of the scapula is occurring, and name one muscle that can produce this movement.

  • Answer: Elevation of the scapula. Muscles that produce this action include the upper trapezius, levator scapulae, rhomboid major, or rhomboid minor.

  • Question 14: A patient reaches both arms forward as if pushing something away. What scapular movement is occurring, and which muscle is a major mover for this action?

  • Answer: Protraction (abduction) of the scapula. The prime mover for this action is the serratus anterior muscle.

  • Question 15: A patient falls directly onto the shoulder and fractures the clavicle. Besides assessing pain, what important assessment should the healthcare provider perform, and why?

  • Answer: Assess distal circulation and full neurovascular status of the upper limb. This is critical because displaced bone fragments from a fractured clavicle can injure or compress the underlying subclavian artery, subclavian vein, or brachial plexus nerves.

  • Question 16: A patient has difficulty raising the arm and reports weakness around the shoulder. Compression of the suprascapular nerve is suspected. Which two muscles may be affected?

  • Answer: Supraspinatus and infraspinatus muscles. Compression of the suprascapular nerve impairs motor function to both muscles, causing weakness in initial arm abduction and external rotation.