Complete Topic List: Gross Anatomy of the Human Skeleton

SECTION 1 - Introduction & General Osteology

1.1 Overview of the Skeleton

• Definition and functions of the skeleton (support, protection, movement, mineral storage, hematopoiesis)
• Division of the skeleton: axial vs. appendicular skeleton
• Total number of bones in the adult (206) vs. the neonate (~270-300)
• Anatomical position and standard planes (sagittal, coronal, transverse)
• Anatomical terms of location and direction

1.2 Classification of Bones

• By shape: long, short, flat, irregular, sesamoid, accessory/sutural (Wormian) bones
• By developmental origin: membranous vs. cartilaginous (endochondral) bones
• By position: axial vs. appendicular

1.3 Gross Structure of a Long Bone

• Diaphysis, epiphyses, metaphysis
• Epiphyseal (growth) plate - structure and closure times
• Articular cartilage (hyaline)
• Periosteum: structure, layers (fibrous and osteogenic/cambium), attachments
• Endosteum
• Medullary (marrow) cavity
• Nutrient foramen and nutrient artery
• Compact (cortical) bone vs. cancellous (trabecular/spongy) bone
• Haversian systems (osteons): Haversian canal, Volkmann's canals, lamellae, lacunae, canaliculi

1.4 Bone Marrow

• Red marrow (hematopoietically active) - distribution in adults vs. children
• Yellow marrow (fatty, inactive)
• Sites of active red marrow in the adult: vertebrae, sternum, ribs, iliac crest, skull diploe, proximal femur/humerus
• Clinical relevance: bone marrow aspiration sites, bone marrow transplantation

1.5 Bone Development (Osteogenesis)

• Intramembranous ossification: flat bones of the skull vault, mandible, clavicle
• Endochondral ossification: long bones, base of skull, vertebrae
• Primary ossification centers (diaphyseal)
• Secondary ossification centers (epiphyseal) - appearance and fusion times
• Bone modeling vs. bone remodeling
• Remodeling cycle: osteoclast resorption, osteoblast formation
• Wolff's Law

1.6 Blood Supply & Nerve Supply of Bone

• Nutrient artery (principal supply to diaphysis)
• Metaphyseal and epiphyseal arteries
• Periosteal arteries
• Importance of blood supply in fracture healing
• Nerve supply: periosteum richly innervated (pain-sensitive); compact bone sparsely innervated

1.7 Bone Markings & Surface Features

• Processes/projections: condyle, epicondyle, head, neck, tuberosity, tubercle, trochanter, crest, spine, ramus, coronoid, coracoid, mastoid
• Depressions and openings: fossa, groove/sulcus, notch, foramen, canal, meatus, sinus, fissure

1.8 Fractures (Gross Anatomy Perspective)

• Classification: closed vs. open, complete vs. incomplete
• Types: transverse, oblique, spiral, comminuted, greenstick (children), stress/fatigue, pathological, avulsion, compression
• Fracture healing stages: hematoma, soft callus, hard callus, remodeling
• Clinical correlates: Colles', Pott's, hip fractures, rib fractures

SECTION 2 - Joints (Arthrology)

2.1 Classification of Joints

• By structure: fibrous, cartilaginous, synovial
• By function/mobility: synarthrosis, amphiarthrosis, diarthrosis

2.2 Fibrous Joints

• Sutures: serrate, squamous, plane; found in the skull; synostosis in age
• Syndesmoses: interosseous membranes (radius-ulna, tibia-fibula), stylohyoid ligament
• Gomphoses: teeth in their sockets (periodontal ligament)

2.3 Cartilaginous Joints

• Primary (synchondroses): epiphyseal plate, spheno-occipital synchondrosis, first sternocostal joint; permit growth, then ossify
• Secondary (symphyses): pubic symphysis, intervertebral discs, manubriosternal joint; fibrocartilage, allow limited movement

2.4 Synovial Joints

• General structure: joint cavity, synovial membrane, synovial fluid, articular capsule (fibrous + synovial layers), articular cartilage
• Accessory structures: intra-articular discs/menisci, labra, bursae, tendon sheaths
• Blood supply and nerve supply to joints (Hilton's Law)
• Classification by shape/movement: plane, hinge (ginglymus), pivot (trochoid), condyloid (ellipsoid), saddle (sellar), ball-and-socket (spheroid)
• Degrees of freedom of movement
• Movements: flexion/extension, abduction/adduction, rotation, circumduction, supination/pronation, inversion/eversion, dorsiflexion/plantarflexion, opposition/reposition

2.5 Degenerative and Clinical Joint Concepts

• Osteoarthritis - joint space narrowing, osteophytes
• Rheumatoid arthritis - pannus formation
• Joint replacement (arthroplasty): hip, knee

SECTION 3 - Axial Skeleton

3.1 Skull

3.1.1 Overview

• Bones of the skull (22 bones: 8 cranial + 14 facial)
• Neurocranium vs. viscerocranium (splanchnocranium)
• Sutures of the skull: coronal, sagittal, lambdoid, squamous, metopic
• Fontanelles: anterior (bregmatic), posterior, sphenoidal, mastoid - timing of closure
• Foramina of the skull and structures passing through them

3.1.2 Bones of the Cranium

• Frontal bone: squama, supraorbital margin, orbital plates, frontal sinuses, glabella, nasion
• Parietal bones (×2): parietal eminence, parietal foramina, superior/inferior temporal lines
• Occipital bone: squama, basilar part, lateral parts, foramen magnum, occipital condyles, hypoglossal canals, external occipital protuberance, nuchal lines, clivus, jugular processes
• Temporal bones (×2): squamous, petrous, tympanic, mastoid parts; external auditory meatus, mastoid process, mastoid air cells, styloid process, stylomastoid foramen, jugular fossa, carotid canal, internal auditory meatus, petrous ridge
• Sphenoid bone: body, lesser wings, greater wings, pterygoid processes, sella turcica, pituitary fossa, optic canals, superior orbital fissure, foramen rotundum, foramen ovale, foramen spinosum, foramen lacerum
• Ethmoid bone: cribriform plate, crista galli, perpendicular plate, superior/middle conchae, ethmoidal labyrinths, ethmoidal air cells

3.1.3 Norma Views of the Skull

• Norma verticalis (from above): bregma, lambda, pterion, asterion
• Norma frontalis (from front): orbital margins, nasal bones, piriform aperture, zygomatic bones
• Norma lateralis (from side): temporal fossa, infratemporal fossa, pterion (H-shaped), zygomatic arch
• Norma occipitalis (from behind): lambda, external occipital protuberance, inion
• Norma basalis/inferior (from below): hard palate, choanae, pterygoid plates, occipital condyles, mandibular fossa

3.1.4 Cranial Fossae (Internal Base of Skull)

• Anterior cranial fossa: frontal bones, cribriform plate, lesser wings of sphenoid; contents - frontal lobes
• Middle cranial fossa: greater wings of sphenoid, temporal bone; sella turcica, foramina (rotundum, ovale, spinosum, lacerum); contents - temporal lobes, pituitary gland
• Posterior cranial fossa: occipital bone, petrous temporal; foramen magnum, jugular foramen, hypoglossal canal, internal auditory meatus; contents - brainstem, cerebellum

3.1.5 Facial Bones

• Maxillae (×2): body, frontal/zygomatic/palatine/alveolar processes, maxillary sinus (largest paranasal sinus)
• Zygomatic bones (×2): temporal process, zygomatic arch (with temporal bone)
• Nasal bones (×2)
• Lacrimal bones (×2): lacrimal groove, nasolacrimal canal
• Palatine bones (×2): horizontal and perpendicular plates; contribute to hard palate, floor of nose, medial orbital wall
• Inferior nasal conchae (×2): largest, most inferior nasal turbinate; separate bones
• Vomer: forms inferior part of nasal septum
• Mandible: body, ramus, symphysis menti, mental foramen, alveolar process, angle, condylar process, coronoid process, mandibular notch, mandibular foramen, lingula, mylohyoid line

3.1.6 Orbit

• Seven bones forming the orbit: frontal, sphenoid, ethmoid, lacrimal, maxilla, palatine, zygomatic
• Walls: roof, floor, medial wall (thinnest - "lamina papyracea"), lateral wall (strongest)
• Openings: optic canal, superior orbital fissure, inferior orbital fissure, nasolacrimal canal

3.1.7 Nasal Cavity and Paranasal Sinuses

• Boundaries of the nasal cavity
• Nasal septum: vomer and perpendicular plate of ethmoid
• Lateral wall: superior, middle, inferior conchae; meatuses and their drainage
• Paranasal sinuses: maxillary, frontal, ethmoidal (anterior, middle, posterior), sphenoidal - openings and clinical significance

3.1.8 Temporomandibular Joint (TMJ)

• Type: modified hinge/bicondylar synovial joint
• Articular surfaces: condylar head of mandible + mandibular fossa/articular tubercle of temporal bone
• Intra-articular disc (divides into upper and lower compartments)
• Movements: depression/elevation, protraction/retraction, lateral excursion
• Ligaments: lateral (temporomandibular), sphenomandibular, stylomandibular

3.2 Vertebral Column

3.2.1 Overview

• 33 vertebrae at birth: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral (fused), 4 coccygeal (fused)
• Adult: 26 bones (7C + 12T + 5L + 1 sacrum + 1 coccyx)
• Curvatures: lordosis (cervical, lumbar) - secondary; kyphosis (thoracic, sacral) - primary
• Clinical conditions: scoliosis, kyphosis (pathological), lordosis (pathological), Scheuermann disease

3.2.2 A Typical Vertebra

• Body (centrum): weight-bearing; superiorinferior endplates
• Vertebral arch: 2 pedicles + 2 laminae
• Vertebral foramen (all together form vertebral canal)
• Processes: 2 transverse, 1 spinous, 4 articular (2 superior, 2 inferior)
• Superior and inferior vertebral notches - form intervertebral foramina
• Facet (zygapophyseal) joint orientation by region

3.2.3 Regional Characteristics

• Cervical vertebrae (C1-C7):
  • Small body, bifid spinous process (C3-C6), triangular foramen, transverse foramina (vertebral artery C1-C6)
  • C1 (Atlas): no body, no spinous process, anterior and posterior arches, lateral masses, articular facets for occipital condyles (atlanto-occipital joint - nodding)
  • C2 (Axis): dens (odontoid process) - pivot for atlas; atlanto-axial joint - rotation ("no" movement)
  • C7 (Vertebra prominens): long non-bifid spinous process - landmark
  • Uncovertebral joints (of Luschka) - unique to cervical spine
• Thoracic vertebrae (T1-T12):
  • Costal facets on body (demifacets) and transverse processes; heart-shaped body; round foramen; long downward-sloping spinous process
• Lumbar vertebrae (L1-L5):
  • Kidney-shaped body (largest); small round foramen; horizontal spinous process (can palpate); no transverse foramina or costal facets; mamillary and accessory processes
• Sacrum:
  • 5 fused vertebrae; triangular; promontory; ala; auricular surface (for sacro-iliac joint); anterior and posterior sacral foramina; sacral canal; sacral hiatus; median sacral crest; sacral cornua
• Coccyx:
  • 3-5 fused rudimentary vertebrae; coccygeal cornua; articulates with sacrum; attachment for gluteus maximus, coccygeus, anococcygeal ligament

3.2.4 Intervertebral Discs (IVDs)

• Fibrocartilaginous secondary cartilaginous joints
• Nucleus pulposus: gelatinous core, remnant of notochord; resists compression
• Annulus fibrosus: concentric collagen lamellae; resists tension
• No disc between C0-C1, C1-C2; thickest in lumbar region
• Clinical: disc herniation (prolapsed disc, "slipped disc") - posterolateral most common; nuclear sequestration
• Schmorl's nodes (vertical herniation into vertebral body)

3.2.5 Joints of the Vertebral Column

• Atlanto-occipital joints: ellipsoid synovial; flexion/extension ("yes" nodding)
• Atlanto-axial joint: median (pivot) + lateral (plane)
• Zygapophyseal (facet) joints: plane synovial; orientation determines movement type
• Ligaments: anterior longitudinal (ALL), posterior longitudinal (PLL), ligamenta flava, interspinous, supraspinous, nuchal ligament (cervical), intertransverse

3.3 Thoracic Cage

3.3.1 Overview and Functions

• Components: 12 thoracic vertebrae, 12 pairs of ribs + costal cartilages, sternum
• Functions: protect thoracic viscera, respiratory mechanics

3.3.2 Sternum

• Three parts: manubrium, body (gladiolus), xiphoid process
• Manubriosternal joint (angle of Louis/sternal angle) - T4/T5 disc level; landmark for 2nd costal cartilage, bifurcation of trachea, aortic arch beginning/ending
• Jugular (suprasternal) notch - T2 level
• Xiphisternal joint - T9 level
• Facets for clavicle and 1st costal cartilage on manubrium
• Clinical: sternal fracture, sternal angle, sternal puncture (bone marrow biopsy)

3.3.3 Ribs

• 12 pairs; classified as: true (1-7, costochondral to sternum directly), false (8-10, joined via costal margin), floating/free (11-12, no anterior attachment)
• Parts of a typical rib (3-9): head (2 facets), neck, tubercle (articular + non-articular), angle, body/shaft, costal groove, anterior end (costal cartilage)
• Atypical ribs: Rib 1 (flat, no costal groove, scalene tubercle, groove for subclavian vessels), Rib 2, Rib 10, Rib 11, Rib 12
• Cervical rib (anomaly) - clinical significance (thoracic outlet syndrome)

3.3.4 Costal Cartilages

• Hyaline cartilage; calcify with age

3.3.5 Joints of the Thoracic Cage

• Costovertebral joints: head of rib with vertebral bodies (costocorporeal) and tubercle with transverse process (costotransverse) - plane synovial joints; radiate and costotransverse ligaments
• Sternocostal (chondrosternal) joints: 1st = primary cartilaginous; 2nd-7th = plane synovial
• Interchondral joints: between costal cartilages 6-10
• Thoracic outlet (superior) and inferior thoracic aperture

SECTION 4 - Appendicular Skeleton

4.1 Pectoral (Shoulder) Girdle

4.1.1 Clavicle

• S-shaped; medial 2/3 convex forward, lateral 1/3 concave forward
• Medial (sternal) end and lateral (acromial) end
• No medullary cavity (membranous ossification)
• Costal tuberosity (costoclavicular ligament), conoid tubercle, trapezoid line (coracoclavicular ligament)
• Most commonly fractured bone; junction of medial 2/3 and lateral 1/3
• Strut mechanism for upper limb

4.1.2 Scapula

• Flat triangular bone; posterior chest wall T2-T7
• Surfaces: anterior (costal/subscapular fossa), posterior (supraspinous + infraspinous fossae divided by spine of scapula)
• Borders: medial (vertebral), lateral (axillary), superior
• Angles: superior, inferior, lateral (glenoid angle)
• Glenoid cavity (fossa) + supraglenoid and infraglenoid tubercles
• Coracoid process: attachment for pectoralis minor, short head of biceps brachii, coracobrachialis
• Acromion process
• Spine of scapula
• Suprascapular notch (bridged by superior transverse scapular ligament - suprascapular nerve passes through; artery over)
• Notch vs. foramen - clinical relevance (suprascapular nerve entrapment)

4.1.3 Sternoclavicular Joint

• Only bony articulation between upper limb and axial skeleton
• Type: saddle (sellar) synovial joint (functionally ball and socket)
• Intra-articular disc
• Ligaments: anterior/posterior sternoclavicular, interclavicular, costoclavicular
• Movements: elevation/depression, protraction/retraction, rotation

4.1.4 Acromioclavicular Joint

• Plane synovial joint; articular disc often present
• Coracoclavicular ligament (conoid + trapezoid): primary suspension of upper limb from clavicle
• Acromioclavicular ligament
• Clinical: AC joint dislocation/separation (common in contact sports)

4.2 Upper Limb

4.2.1 Humerus

• Proximal end: head (articulates with glenoid), anatomical neck, greater and lesser tubercles, bicipital groove (intertubercular sulcus), surgical neck (axillary nerve and anterior circumflex humeral artery)
• Shaft: deltoid tuberosity, radial (spiral) groove (radial nerve and profunda brachii artery), medial and lateral supracondylar ridges
• Distal end: capitulum (for radius), trochlea (for ulna), medial and lateral epicondyles, olecranon fossa, coronoid fossa, radial fossa, lateral supraepicondylar ridge
• Medial epicondyle - ulnar nerve ("funny bone")
• Common clinical fractures: surgical neck, shaft (radial nerve), supracondylar (children, anterior interosseous nerve), lateral condyle (children), medial epicondyle (ulnar nerve)

4.2.2 Glenohumeral (Shoulder) Joint

• Ball and socket synovial joint; most mobile, least stable
• Glenoid labrum deepens the socket; glenoid cavity faces anterolaterally and is smaller than humeral head
• Capsule: relatively lax (allows extensive range); reinforced by glenohumeral ligaments (superior, middle, inferior)
• Rotator cuff muscles (SITS): Supraspinatus (most commonly torn), Infraspinatus, Teres minor, Subscapularis
• Long head of biceps tendon passes through joint
• Subcoracoid and subacromial bursae
• Stability: primarily muscular (rotator cuff); bony factors minor
• Dislocation: anterior-inferior most common (axillary nerve and circumflex humeral artery at risk)

4.2.3 Radius

• Lateral bone of forearm
• Proximal end: head (disc-shaped, capitulum), neck, radial tuberosity (biceps brachii insertion)
• Shaft: anterior (flat), interosseous border medially
• Distal end: styloid process (lateral, longer), ulnar notch, dorsal tubercle of Lister
• Colles' fracture (distal radius - "dinner fork deformity"); Smith's fracture (reverse Colles')
• Scaphoid fracture (most common carpal fracture; avascular necrosis risk)

4.2.4 Ulna

• Medial bone of forearm
• Proximal end: olecranon (triceps insertion), coronoid process, trochlear notch (articulates with humerus), radial notch (articulates with radius head)
• Shaft: posterior border (subcutaneous, palpable entire length), interosseous border laterally
• Distal end: head, styloid process (medial, shorter)
• Olecranon bursitis ("student's elbow")

4.2.5 Elbow Joint

• Humeroulnar: hinge synovial (principal weight bearing)
• Humeroradial: ball and socket (modified)
• Proximal radioulnar: pivot synovial
• All within one joint capsule
• Collateral ligaments: medial (ulnar) - anterior, posterior, transverse bands; lateral (radial) - radial collateral, annular, lateral ulnar collateral
• Annular ligament of radius
• Cubitus valgus/varus; carrying angle (normal ~10-15 degrees in males, ~15-20 in females)
• Clinical: pulled elbow (nursemaid's elbow) in children; medial epicondyle avulsion; supracondylar fracture

4.2.6 Radioulnar Joints

• Proximal (pivot synovial): annular ligament retains radial head
• Distal (pivot synovial): articular disc (triangular fibrocartilage/TFCC)
• Interosseous membrane: connects radius and ulna shafts; oblique cord
• Movements: pronation and supination (radius rotates around ulna)

4.2.7 Wrist (Radiocarpal) Joint

• Ellipsoid (condyloid) synovial
• Proximal articular surface: radius + articular disc
• Distal articular surface: proximal row carpals (scaphoid, lunate, triquetrum); pisiform excluded
• Movements: flexion/extension, abduction (radial deviation)/adduction (ulnar deviation)
• Intercarpal joints (midcarpal joint)

4.2.8 Carpus (Carpal Bones)

• 8 bones in 2 rows (mnemonic: "Some Lovers Try Positions That They Cannot Handle")
• Proximal row: Scaphoid, Lunate, Triquetrum, Pisiform
• Distal row: Trapezium, Trapezoid, Capitate (largest), Hamate (hook of hamate - ulnar nerve + artery)
• Carpal tunnel: transverse carpal ligament (flexor retinaculum) - contents and carpal tunnel syndrome
• Anatomical snuffbox: floor is scaphoid; tenderness = scaphoid fracture

4.2.9 Metacarpals (×5) and Phalanges

• Metacarpal: base, shaft, head ("knuckles"); 1st is shortest and most robust
• 14 phalanges: 2 in thumb (proximal, distal), 3 in each finger (proximal, middle, distal)
• Interphalangeal joints: hinge synovial

4.2.10 Hand Joints

• Carpometacarpal (CMC) joints: 1st CMC (trapezio-metacarpal) = saddle joint (thumb opposition); 2nd-5th = plane joints
• Metacarpophalangeal (MCP) joints: condyloid synovial; flexion/extension, abduction/adduction
• Proximal interphalangeal (PIP) and Distal interphalangeal (DIP): hinge synovial
• Collateral ligaments of interphalangeal joints; volar plates

4.3 Pelvic Girdle

4.3.1 Hip (Coxal) Bone (Os Coxa)

• Formed by three bones fused at Y-shaped triradiate cartilage at acetabulum (fuses age ~16-18)
• Ilium: iliac crest (anterior/posterior superior and inferior iliac spines), iliac fossa, auricular surface, iliopubic eminence
• Ischium: body, ischial spine, lesser sciatic notch, ischial tuberosity (sit on it; hamstrings origin), ischial ramus, greater sciatic notch
• Pubis: body, superior and inferior pubic rami, pubic crest, pubic tubercle, pecten pubis (pectineal line), obturator foramen (largest foramen in the body), obturator groove
• Acetabulum: lunate surface (articular), acetabular notch, acetabular fossa (non-articular, contains fat pad and ligamentum teres)

4.3.2 Bony Pelvis

• Pelvic inlet (superior aperture): sacral promontory → ala → arcuate line → pecten pubis → pubic symphysis
• Pelvic outlet (inferior aperture): coccyx → sacrotuberous ligament → ischial tuberosity → inferior pubic ramus → pubic symphysis
• True pelvis (lesser pelvis) vs. false pelvis (greater pelvis)
• Pelvic axis and inclination
• Sex differences in the pelvis: android (male) vs. gynecoid (female); obstetric significance

4.3.3 Pubic Symphysis

• Secondary cartilaginous joint (fibrocartilaginous disc)
• Superior and inferior (arcuate) pubic ligaments
• Clinical: diastasis pubis in pregnancy; osteitis pubis

4.3.4 Sacroiliac Joint

• Synovial + syndesmosis (interosseous sacroiliac ligaments)
• Very strong; anterior, posterior, and interosseous sacroiliac ligaments
• Accessory ligaments: iliolumbar, sacrospinous, sacrotuberous
• Sciatic foramina: greater (piriformis, sciatic nerve, superior gluteal, etc.) and lesser (obturator internus, pudendal nerve)
• Minimal movement (nutation/counternutation); important in force transmission

4.3.5 Hip (Coxofemoral) Joint

• Ball and socket synovial; very stable
• Acetabular labrum deepens socket; transverse acetabular ligament bridges notch
• Femoral head: two thirds of a sphere; fovea capitis (ligamentum teres femoris - carries artery to femoral head, clinically variable)
• Articular capsule: spans from acetabular rim to intertrochanteric line anteriorly, intertrochanteric crest posteriorly
• Ligaments: iliofemoral (Y-ligament of Bigelow - strongest in body), pubofemoral, ischiofemoral
• Zona orbicularis (circular fibers of capsule)
• Movements: flexion/extension, abduction/adduction, medial/lateral rotation, circumduction
• Dislocation: posterior (most common) - sciatic nerve at risk

4.4 Lower Limb

4.4.1 Femur

• Longest and strongest bone
• Proximal: head (fovea capitis), neck, greater and lesser trochanters, intertrochanteric line (anterior) and crest (posterior), quadrate tubercle, trochanteric fossa
• Shaft: linea aspera (medial and lateral lips), pectineal line, gluteal tuberosity; nutrient foramen
• Distal: medial and lateral condyles, intercondylar notch/fossa, medial and lateral epicondyles, adductor tubercle, popliteal surface
• Neck-shaft angle (angle of inclination): ~126 degrees; coxa valga (>130) and coxa vara (<120)
• Angle of anteversion (~10-15 degrees)
• Clinical: hip fracture types (intracapsular - subcapital, transcervical; extracapsular - intertrochanteric, subtrochanteric); femoral shaft fractures

4.4.2 Patella

• Largest sesamoid bone; embedded in quadriceps tendon
• Triangular (apex inferior); articular surface (medial and lateral facets for femur)
• Functions: increases mechanical advantage of quadriceps; protects knee joint
• Patellar dislocation (lateral); patella fracture (transverse most common)

4.4.3 Tibia

• Medial and larger bone of leg; weight-bearing
• Proximal: medial and lateral condyles, intercondylar eminence (medial/lateral tubercles - ACL/PCL attachment), tibial plateau, Gerdy's tubercle (iliotibial tract), fibular facet
• Tibial tuberosity (patellar ligament attachment)
• Anterior border (subcutaneous "shin")
• Shaft: triangular; interosseous border laterally
• Distal: medial malleolus, fibular notch, inferior articular surface

4.4.4 Fibula

• Lateral, non-weight-bearing (bears ~17% body weight in some sources)
• Head (apex/styloid process), neck (common fibular/peroneal nerve), shaft, lateral malleolus
• Common fibular nerve wraps around fibular neck (vulnerable to injury)
• Lateral malleolus extends more distally than medial malleolus

4.4.5 Knee Joint

• Most complex joint in the body
• Tibiofemoral joint: two modified condyloid joints (medial + lateral compartments)
• Patellofemoral joint
• Medial and lateral menisci (fibrocartilaginous C-shaped discs): deepen tibial surface, shock absorption, joint nutrition; medial meniscus less mobile (attached to MCL)
• Cruciate ligaments (intra-articular, extrasynovial): ACL (prevents anterior tibial displacement; torn in valgus stress); PCL (prevents posterior displacement; stronger of the two)
• Collateral ligaments: MCL (tibial collateral - broad, attached to medial meniscus); LCL (fibular collateral - cord-like, not attached to lateral meniscus)
• Other structures: popliteus tendon, transverse ligament, posterior meniscofemoral ligament
• Bursae: prepatellar, infrapatellar (superficial + deep), semimembranosus, popliteal (Baker's cyst)
• Locking/unlocking mechanism: lateral condyle finishes rotation before medial → "screw home" mechanism; popliteus unlocks
• Unhappy triad (O'Donoghue): ACL + MCL + medial meniscus

4.4.6 Tibiofibular Joints

• Proximal: plane synovial
• Distal (tibiofibular syndesmosis): fibrous joint; anterior/posterior tibiofibular and interosseous tibiofibular ligaments; essential to mortice stability of ankle
• Interosseous membrane

4.4.7 Ankle (Talocrural) Joint

• Hinge (ginglymus) synovial
• Mortice: formed by medial malleolus + tibial plafond (inferior surface) + lateral malleolus
• Talus: trochlear surface is wider anteriorly (more stable in dorsiflexion)
• Movements: dorsiflexion (tibialis anterior) and plantarflexion (gastrocnemius, soleus)
• Ligaments: medial (deltoid) - superficial and deep parts; lateral (ATFL, CFL, PTFL) - ATFL most commonly torn (ankle sprain)
• Clinical: Pott's fracture (bimalleolar/trimalleolar), ankle sprain

4.4.8 Tarsal Bones (×7)

• Talus: no muscle attachments; transmits body weight; head, neck, body; trochlea; posterior process (Stieda's process - can be separate os trigonum)
• Calcaneus: largest tarsal bone; posterior surface (calcaneal/Achilles tendon); sustentaculum tali (supports talus); peroneal tubercle; anterior/middle/posterior facets; tuberosity (heel)
• Navicular: boat-shaped; medial aspect has tuberosity (tibialis posterior insertion); keystone of medial longitudinal arch
• Cuboid: lateral column; peroneal groove (peroneus longus)
• Medial cuneiform (largest), intermediate cuneiform (smallest), lateral cuneiform
• Lisfranc joint (tarsometatarsal joint): clinically important

4.4.9 Metatarsals (×5) and Phalanges

• 1st metatarsal: shortest and widest; two sesamoid bones beneath head
• 5th metatarsal: styloid process (peroneus brevis insertion; fracture site)
• 14 phalanges: same arrangement as hand

4.4.10 Arches of the Foot

• Medial longitudinal arch (talus as keystone): calcaneus, talus, navicular, cuneiforms, 1st-3rd metatarsals; highest arch; spring (plantar calcaneonavicular) ligament, tibialis posterior and anterior, FHL, FDL, plantar fascia
• Lateral longitudinal arch: calcaneus, cuboid, 4th-5th metatarsals; low arch; short plantar ligament
• Transverse arch: across tarsal bones; peroneus longus maintains it
• Pes planus (flat foot) vs. pes cavus (high arch)
• Plantar fascia (plantar aponeurosis): plantar fasciitis

4.4.11 Subtalar (Talocalcaneal) and Other Foot Joints

• Subtalar joint: inversion/eversion of foot
• Transverse tarsal joint (Chopart's joint): talonavicular + calcaneocuboid
• Intertarsal, tarsometatarsal, metatarsophalangeal, and interphalangeal joints

SECTION 5 - Special Topics & Clinical Correlates

5.1 Ossification Centers and Epiphyseal Fusion

• Importance in radiology (growth plate visible on X-ray), forensic age estimation, and medicolegal contexts
• Common clinical: slipped capital femoral epiphysis (SCFE), Osgood-Schlatter disease

5.2 Sesamoid Bones

• Definition; common locations: patella, 2 under 1st metatarsal head, pisiform, fabella
• Sesamoiditis

5.3 Accessory/Supernumerary Bones

• Os trigonum (posterior talus), os naviculare (accessory navicular), Wormian bones (skull)

5.4 Anatomical Variations of Clinical Significance

• Cervical rib, bifid clavicle, bipartite patella, os acromiale, spondylolysis/spondylolisthesis

5.5 Bone as a Metabolic Organ

• Calcium homeostasis: PTH (osteoclast activation), calcitonin (osteoclast inhibition), Vitamin D
• Osteoporosis: reduced bone mass; T-score; DEXA scan; fracture risk (vertebral compression, hip, distal radius)
• Osteomalacia / Rickets: impaired mineralization
• Paget's disease of bone

5.6 Radiological Anatomy of the Skeleton

• Normal bone density and cortical thickness on plain X-ray
• AP and lateral views of key joints
• Common anatomical variants on imaging
• Role of CT (cortical detail) and MRI (marrow, soft tissue, cartilage)

5.7 Developmental and Age-Related Changes

• Fetal cartilaginous skeleton
• Postnatal changes: fontanelle closure, suture closure
• Age-related degenerative changes in joints

SECTION 6 - Surface Anatomy & Landmark Summary

Recommended Study Order

1. General osteology (bone structure, types, development) - builds the language
2. Joints (classification and general principles) - applies to all regions
3. Axial skeleton: skull → vertebral column → thoracic cage
4. Appendicular skeleton: pectoral girdle + upper limb → pelvic girdle + lower limb
5. Special topics + clinical correlates + surface anatomy