The Vertebral Column, Thoracic Cage, and Appendicular Skeleton

7.3 The Vertebral Column and Thoracic Cage

The Vertebral Column (Spine)

The vertebral column is a flexible, supportive structure composed of 33 vertebrae, providing the main axial support for the body and protecting the spinal cord.

• Regions of the Vertebral Column:

  • 7 cervical vertebrae (neck)

  • 12 thoracic vertebrae (upper back, each articulates with a rib)

  • 5 lumbar vertebrae (lower back)

  • 5 fused sacral vertebrae (form the sacrum, articulate with pelvic bones)

  • 3-5 fused coccygeal vertebrae (form the coccyx, tailbone)

• Intervertebral Foramen: Spaces between most unfused vertebrae, allowing passage of spinal nerves.

• Spinal Curvatures:

  • Primary Curvatures: Thoracic and sacral (convex, present in fetal development)

  • Secondary Curvatures: Cervical and lumbar (concave, develop after birth to allow upright posture)

• Clinical Correlations:

  • Scoliosis: Lateral curvature (C or S-shaped), can be congenital, neuromuscular, or idiopathic (most common)

  • Lordosis: Exaggerated lumbar/cervical curvature ("swayback")

  • Kyphosis: Exaggerated thoracic curvature ("hunchback")

Common Features of Vertebrae

• Body (Centrum): Main weight-bearing structure, anteriorly placed

• Vertebral Foramen: Canal for spinal cord, posterior to body

• Pedicles and Laminae: Form the vertebral arch; pedicles project from body, laminae complete the arch posteriorly

• Articular Processes: Superior and inferior, with smooth facets covered in hyaline cartilage for articulation

• Transverse Processes: Lateral projections for muscle attachment

• Spinous Process: Posterior projection, palpable along the back

Regional Vertebral Differences

• Cervical Vertebrae (C1–C7):

  • Transverse foramina for vertebral arteries/veins

  • Oval bodies, large triangular vertebral foramina

  • Short, often forked spinous processes (except C7, which is prominent and not forked)

  • C1 (Atlas): No body or spinous process; articulates with occipital condyles ("yes" motion)

  • C2 (Axis): Dens (odontoid process) projects superiorly; allows "no" motion

• Thoracic Vertebrae (T1–T12):

  • Heart-shaped bodies, circular vertebral foramina

  • Long, inferiorly pointing spinous processes

  • Costal facets for rib articulation

• Lumbar Vertebrae (L1–L5):

  • Largest, heaviest; kidney-shaped bodies

  • Thick, posteriorly pointing spinous processes

  • Flattened triangular vertebral foramina

• Sacrum: 5 fused vertebrae, forms posterior pelvic wall; articulates with pelvic bones at auricular surfaces

• Coccyx: 3–5 fused vertebrae, forms the tailbone

Intervertebral Discs

• Located between vertebrae (23 total, from C2–C3 to L5–S1)

• Composed of:

  • Nucleus Pulposus: Gel-like center for shock absorption

  • Anulus Fibrosus: Outer fibrocartilage ring, holds nucleus pulposus and vertebrae together

The Thoracic Cage

The thoracic cage protects vital organs and supports the shoulder girdle and upper limbs.

• Components: Sternum, 12 pairs of ribs, thoracic vertebrae

• Sternum:

  • Manubrium: Superior part, with suprasternal and clavicular notches

  • Body: Largest part, attachment for ribs 2–7

  • Xiphoid Process: Inferior tip, initially cartilage, ossifies by age 40

• Ribs: 12 pairs

  • True Ribs (1–7): Attach directly to sternum via own costal cartilage

  • False Ribs (8–12): Do not attach directly to sternum

    • 8–10: Vertebrochondral, attach to cartilage of rib 7

    • 11–12: Floating (vertebral), no anterior attachment

  • Each rib has a head (with articular facets), neck, tubercle (articulates with vertebral transverse process), angle, and shaft

  • Ribs 1, 10–12: Attach to only one vertebra; floating ribs lack tubercles

7.4 Bones of the Pectoral Girdle and Upper Limb (Appendicular Skeleton)

Pectoral Girdle

The pectoral girdle anchors the upper limb to the axial skeleton and allows for a wide range of motion.

• Clavicle: S-shaped bone with medial (sternal) end articulating with manubrium (sternoclavicular joint) and lateral (acromial) end with scapula (acromioclavicular joint); acts as a brace for the shoulder

• Scapula: Triangular bone on posterior thoracic cage (ribs 2–7)

  • Features: Coracoid process (anterior), subscapular fossa, glenoid cavity (shoulder joint), spine (posterior), supraspinous and infraspinous fossae, acromion (articulates with clavicle)

Upper Limb Bones

• Humerus: Only bone of the arm (brachium)

  • Proximal: Head (articulates with glenoid cavity), anatomical neck, greater and lesser tubercles, intertubercular sulcus, surgical neck

  • Shaft: Deltoid tuberosity (deltoid muscle attachment), radial groove

  • Distal: Medial/lateral epicondyles, capitulum (lateral), trochlea (medial), radial/coronoid/olecranon fossae

• Forearm (Antebrachium): Radius (lateral) and ulna (medial), connected by interosseous membrane

  • Radius: Proximal head (articulates with capitulum), neck, radial tuberosity (biceps attachment), ulnar notch (distal), styloid process (lateral wrist)

  • Ulna: Proximal trochlear notch, olecranon (elbow), coronoid process, radial notch, distal head, styloid process (medial wrist)

• Carpals (Wrist): 8 short bones in two rows

  • Proximal (lateral to medial): Scaphoid, lunate, triquetrum, pisiform

  • Distal (lateral to medial): Trapezium, trapezoid, capitate, hamate

• Metacarpals (Hand): 5 long bones, each with base, shaft, and head (knuckles)

• Phalanges (Fingers): 14 total; each finger has proximal, middle, and distal phalanges except the thumb (pollex), which has only proximal and distal

7.5 Bones of the Pelvic Girdle and Lower Limb

Pelvic Girdle and Pelvis

The pelvic girdle supports the lower limb and protects pelvic organs. The pelvis is formed by the sacrum, coccyx, and two pelvic (hip) bones.

• Pelvic Inlet: Oval opening formed by pelvic brim (boundary between greater/false and lesser/true pelvis)

• Pelvic Outlet: Inferior boundary of the lesser pelvis

• Pelvic Bone (Os Coxae): Fusion of ilium, ischium, and pubis

  • Acetabulum: Deep socket for femur head (hip joint)

  • Obturator Foramen: Large anterior opening for nerves and vessels

• Ilium: Superior part; features ala (wing), iliac crest, anterior/posterior superior/inferior iliac spines, greater sciatic notch, iliac fossa, auricular surface, arcuate line, gluteal surface (muscle attachment)

• Ischium: Posteroinferior; ischial body and ramus, ischial spine, lesser sciatic notch, ischial tuberosity (bears weight when sitting)

• Pubis: Anteroinferior; superior/inferior rami, pubic body, pubic symphysis (fibrocartilage joint), pubic arch (sexually dimorphic)

Male vs. Female Pelvis

Feature	Male	Female
Greater pelvis	Narrow	Wide
Sacrum	Long, narrow	Short, wide
Coccyx	Less moveable	More moveable, posterior
Pelvic inlet	Narrow, heart-shaped	Wide, oval
Acetabula	Closer, more lateral	Farther apart, more anterior
Pubic arch angle	<90°	90–100°
Ischial tuberosities	Point medially	Point laterally

Lower Limb Bones

• Femur (Thigh): Largest, strongest bone; head (articulates with acetabulum), fovea capitis (ligament attachment), neck (weakest part), greater/lesser trochanters, intertrochanteric line/crest, linea aspera (posterior shaft), medial/lateral epicondyles and condyles (knee joint), intercondylar fossa, patellar surface

• Patella: Sesamoid bone in quadriceps tendon, protects knee joint

• Leg: Tibia (medial, weight-bearing) and fibula (lateral, slender)

  • Tibia: Medial/lateral condyles (articulate with femur), intercondylar eminence (ligament attachment), tibial tuberosity (patellar ligament), anterior crest (shin), medial malleolus (ankle)

  • Fibula: Head (proximal), lateral malleolus (distal, ankle), stabilizes ankle joint

• Ankle and Foot:

  • Tarsals (7): Talus (ankle joint), calcaneus (heel), navicular, medial/intermediate/lateral cuneiforms, cuboid

  • Metatarsals (5): Base, shaft, head; first metatarsal often has sesamoid bones (turf toe risk)

  • Phalanges (14): Toes 2–5 have proximal, middle, distal; hallux (great toe) has proximal and distal only

  • Foot Arches: Medial longitudinal (calcaneus to metatarsals I–III), lateral longitudinal (calcaneus to metatarsals IV–V), transverse (across distal tarsals and metatarsal bases); support and distribute body weight

Example: Clinical Application

• Boxer's Fracture: Fracture of the metacarpal bones, commonly from punching

• Sesamoiditis (Turf Toe): Inflammation of sesamoid bones under first metatarsal due to repetitive stress

Additional info: The vertebral column and appendicular skeleton are essential for movement, support, and protection of vital organs. Understanding their structure aids in diagnosing musculoskeletal disorders and injuries.