Skeletal System Comprehensive Study Notes

Skeletal System: Comprehensive Study Notes

  • Course context: KINE 3600 – Bones and the Skeletal System (University of Virginia). Key terms introduced early: Axial skeleton, Appendicular skeleton, Costal cartilage, Articular cartilage.
  • Week focus reminders: planes and axes of motion, names of common motions, directional terms; review bones of the human skeleton; use Complete Anatomy for Introduction, Bones, Bones of Upper/Lower Extremity, Joints lectures.

Functions of the Skeletal System

  • Primary roles
    • Stability of limbs and thorax
    • Attachment site for muscles and ligaments
    • Protection of vital structures
    • Blood cell production: continuous supply of new blood cells
    • Mineral reservoir (calcium, phosphate, etc.)

Bone Shapes and Major Classifications

  • Main shapes/classes
    • Long bones
    • Short bones
    • Flat bones
    • Irregular bones
    • Sesamoid bones
  • Examples (from slides):
    • Long bone example: Humerus
    • Short bone example: Carpals (e.g., in the hand)
    • Flat bone example: Parietal bone
    • Irregular bone example: Vertebra
    • Sesamoid bone example: Patella

Macroscopic Structure of Long Bones

  • Key regions
    • Epiphysis (proximal/distal ends, contains articular cartilage)
    • Metaphysis (wider portion adjacent to epiphysis, where growth occurs in children)
    • Diaphysis (shaft)
  • Associated features
    • Articular cartilage (hyaline cartilage on joint surfaces)
    • Periosteum (outer fibrous layer; provides blood supply and growth/repair capacity)
    • Endosteum (inner lining of medullary cavity)
    • Medullary canal/cavity (marrow cavity; contains bone marrow)
    • Growth plate (epiphyseal plate; site of longitudinal growth in children)
    • Nutrient vessels and nutrient foramen (entries point for blood supply)
  • Growth and remodeling interfaces
    • Epiphyseal plate allows lengthwise growth during development; once fused, growth in length ceases (epiphyseal line remains)

Other Bone Types (Illustrative Examples)

  • Short bones: Carpal bones of the hand
  • Flat bones: Parietal bone of the skull
  • Irregular bones: Vertebrae
  • Sesamoid bones: Patella (kneecap)

General Landmarks on Bones

  • Common anatomical landmarks and terms:
    • Condyle, Crest, Epicondyle, Facet, Fissure, Foramen, Fossa, Head, Line, Malleolus, Neck, Notch, Process, Protuberance, Ramus, Sinus, Spine, Sulcus, Trochanter, Tubercle, Tuberosity, Trochlea

Bone Tissue: Structural and Functional Levels

  • Structural levels
    • Cortical (Compact) bone
    • Trabecular (Cancellous/spongy) bone
  • Structural differences
    • Cortical bone: solid, dense; contains medullary cavity; makes up ~80extextpercent80 ext{ extpercent} of the skeleton; slow turnover; contains osteons (Haversian systems)
    • Trabecular bone: porous; lattice-like trabeculae; higher turnover; lighter weight; supports red marrow production
  • Functional differences
    • Cortical: provides strength for weight-bearing and attachment sites; maximum strength in the diaphysis
    • Trabecular: provides lightweight scaffolding; distributes stress along trabeculae; located in ends of long bones and in vertebrae
  • Structural hierarchy
    • Primary (immature, woven, bundle) bone vs Secondary (mature, lamellar) bone
    • Osteons (Haversian systems) are the functional units of cortical bone
  • Regional proportions (illustrative)
    • Cortical bone constitutes ~80extextpercent80 ext{ extpercent} of the skeleton; deeper, shaft regions
    • Trabecular bone is more metabolically active and found predominantly at the ends of long bones and in the vertebrae

Bone Cells: Types and Roles

  • Osteocytes: mature bone cells
    • Functions: maintain bone tissue, ion exchange, mechanosensation
  • Osteoblasts: bone-forming cells
    • Location: a layer under the endosteum and periosteum
    • Do not undergo mitosis; synthesize bone matrix; mineralize matrix
    • Respond to mechanical stress by increasing activity; secrete osteocalcin
  • Osteoclasts: bone-resorbing cells
    • Break down bone matrix during remodeling
  • Osteogenic (osteoprogenitor) cells: undifferentiated cells from which osteoblasts derive

Microstructure of Compact and Spongy Bone

  • Compact bone microarchitecture
    • Osteon (Haversian system): functional unit
    • Haversian canal (central canal): contains blood vessels and nerves
    • Lamellae: concentric rings around the canal
    • Lacunae: small cavities housing osteocytes
    • Canaliculi: tiny channels linking lacunae
  • Vascular channels
    • Haversian canals (vertical/longitudinal)
    • Volkmann’s canals (transverse/horizontal): connect osteons and supply blood/nerve access
  • Interactions with periosteum and endosteum
    • Nutrient vessels enter via nutrient foramina and supply the inner bone; periosteum supplies outer layers

Compact Bone vs Spongy Bone: Visual Summary

  • Compact bone: dense, organized into osteons; outer shell of bones
  • Spongy bone (trabecular/cancellous): porous; contains red marrow in many bones; trabeculae align along lines of stress
  • Lacunae, lamellae, and canaliculi are present in both forms, enabling osteocyte communication

Blood and Nerve Supply of Bone

  • Nutrient artery system
    • Nutrient artery enters via a nutrient foramen; provides blood for marrow, cancellous bone, and deep compact tissue
  • Metaphyseal-epiphyseal arteries
    • Supply blood to joints and the ends of long bones
  • Periosteum innervation
    • Rich sensory nerve endings; important for pain sensing and remodeling signals

Yellow Marrow and Red Marrow

  • Yellow marrow
    • Typically found inside the medullary cavity of long bones
    • High fat content; can serve as an energy reserve
  • Red marrow
    • Produces red blood cells, white blood cells, and platelets; found in red marrow spaces within trabecular bone
  • Mood of marrow distribution changes with age and metabolic demands

Bone Growth and Development: Ossification Processes

  • Two primary processes

    • Intramembranous ossification (membrane bone formation)
    • Endochondral ossification (cartilage replacement)

  • Intramembranous Ossification

    • Occurs in fetus; undifferentiated mesenchymal cells differentiate into osteoblasts
    • Osteoblasts deposit organic matrix that mineralizes to form bone
    • Flat bones (e.g., cranial bones) are typical sites
    • Key concept: direct transformation from mesenchyme to bone without a cartilage intermediate

  • Endochondral Ossification

    • Cartilage model formed in the fetus; bone replaces cartilage postnatally
    • Esigned by primary and secondary ossification centers
    • Primary ossification center forms in the diaphysis; secondary centers form in epiphyses
    • Growth continues via the epiphyseal (growth) plate until fusion and formation of the epiphyseal line
    • Periosteal bud invades the diaphysis; formation of a bone collar around the diaphysis
    • Cartilage calcifies and is progressively replaced by bone tissue
    • Medullary cavity forms as osteoclasts resorb cartilage and trabeculae from inside
    • Result: bone lengthening occurs from center toward the ends; diameter/width increases by appositional growth on the outside while internal remodeling occurs

  • Endochondral ossification diagrammatic steps (summary from slides)

    • Step 1: Fetal hyaline cartilage model develops
    • Step 2: Cartilage calcifies; periosteal bone collar forms around diaphysis
    • Step 3: Primary ossification center forms in the diaphysis
    • Step 4: Blood vessels invade; secondary ossification centers form in the epiphyses
    • Step 5: Bone replaces cartilage except articular cartilage and epiphyseal plates; spongy bone forms; medullary cavity enlarges
    • Step 6: Epiphyseal plates ossify, forming the epiphyseal line once growth ceases
    • Notation: Hyaline cartilage model; periosteal bud; developing periosteum; developing bone collar; epiphyseal plate

Growth Plate Dynamics and Epiphyseal Closure

  • Epiphyseal plate (growth plate) separation from epiphysis and metaphysis allows growth in length during development
  • Closure results in epiphyseal line; growth in length stops over time
  • Hormonal control (growth factors and hormones) modulates growth during development

Bone Modeling vs Remodeling

  • Bone modeling: shaping and growth during development (intramembranous and endochondral processes contribute to bone size and shape)
  • Bone remodeling: lifelong turnover via activation of osteocytes, resorption by osteoclasts, and formation by osteoblasts
  • Wolff’s Law: bone adapts to the loads under which it is placed; remodeling along lines of greatest stress → specific adaptations to imposed demands
  • Remodeling rate: approximately 10extextpercent10 ext{ extpercent} per year under normal conditions

Aging and the Skeletal System

  • Peak bone density timing

    • Females: peak around age 1818 years
    • Males: peak around age 2020 years

  • Peak bone density approximately around age 3030 years

  • After age 3030: Resorption exceeds formation, leading to bone loss

  • Menopause and bone loss

    • Significant increase in resorption due to lower estrogen levels
    • Similar risk can occur in younger women with amenorrhea or oligomenorrhea

  • Bone mineral density (BMD) thresholds

    • Osteopenia: BMD between −1.0-1.0 and −2.5-2.5 standard deviations below the young adult mean
    • Osteoporosis: BMD more than −2.5-2.5 standard deviations below the young adult mean

Mechanisms of Stress Fractures

  • Mechanism: osteoclast activity exceeds osteoblast activity under increased or rapid loading
  • Contributing factors
    • Rate and type of activity, weight-bearing exercises, sudden increase in training intensity
    • Typical onset after introducing a new program: around 4$-$6 weeks
  • Diagnostic cue: increased bone metabolism at the fracture site (bone scan)

Fractures of the Growth Plate: Salter-Harris Classification

  • Fractures through open growth plates (physes)
  • Types (I–V)
    • Type I: through the growth plate only
    • Type II: through growth plate and metaphysis
    • Type III: through growth plate and epiphysis
    • Type IV: through growth plate, metaphysis, and epiphysis
    • Type V: crush injury of the growth plate
  • Clinical significance: different patterns of growth disturbance and treatment implications
  • Mnemonic aid from slides: “Type I you can’t feel my epiphysis” (contextual mnemonic for Type I) with a common teaching chart showing the five types

Bones of the Skull

  • Major skull bones (listed in various slides):
    • Nasal, Parietal, Frontal, Temporal, Zygomatic, Ethmoid, Maxilla, Mandible
  • Latin nomenclature variants shown on slides (english vs. latin names):
    • os frontale (Frontal), os nasale (Nasal), os parietale (Parietal), os temporale (Temporal), os sphenoidale (Sphenoid), os lacrimale (Lacrimal), os zygomaticum (Zygomatic), os ethmoidale (Ethmoid), maxilla (Maxilla), mandibula (Mandible)
  • Teeth presence noted alongside skull bones

The Spine (Vertebral Column)

  • Vertebral counts
    • Cervical: 7
    • Thoracic: 12
    • Lumbar: 5
    • Sacral: 5 (fused into sacrum in adults)
    • Coccygeal: 4
  • Key differences among vertebrae (a cross-sectional comparison on slides)
    • Cervical vertebrae: features such as transverse foramina; lighter bodies; foramina in transverse processes
    • Thoracic vertebrae: costal facets for rib articulation; long spinous processes
    • Lumbar vertebrae: large vertebral bodies; short, thick spinous processes; robust facets

Rib Cage and Sternum

  • Ribs: 24 ribs in humans
    • True ribs: 1$-$7 (vertebrocostal)
    • False ribs: 8$-$10 (vertebrochondral)
    • Floating ribs: 11––12 (free)
  • Sternum components and landmarks
    • Manubrium, body, xiphoid process
    • Notches and joints: jugular notch, sternal angle (manubriosternal joint), xiphisternal joint
    • Costal cartilages connect the sternum to the ribs

Clavicle, Scapula, and the Shoulder Girdle

  • Clavicle and scapula form the shoulder girdle that connects the upper limb to the axial skeleton
  • Scapula features (examples from slides):
    • Coracoid process, Acromion process, Glenoid fossa
    • Scapular foramina/notches, borders (superior, medial, lateral)
    • Subscapular fossa and other fossae
  • Humerus (upper arm bone) landmarks (anterior and posterior views)
    • Head, greater and lesser tubercles, anatomical neck, surgical neck
    • Deltoid tuberosity (lateral surface)
    • Coronoid fossa, Radial fossa, Olecranon fossa
    • Epicondyles (medial and lateral), Capitulum, Trochlea
    • Nutrient foramen

Forearm: Radius and Ulna

  • Joints and movements
    • Proximal radioulnar joint; annular ligament; axis of rotary movement
    • Distal radioulnar joint
    • Pronation and Supination movements

Carpal Bones (Wrist)

  • Carpal bone list (mnemonic shown in slides): Scaphoid, Lunate, Triquetrum, Pisiform, Trapezium, Trapezoid, Capitate, Hamate
  • Notable clinical relevance: Scaphoid fractures are common and can threaten blood supply if displaced
  • Mnemonics and memory aids can vary (slides show a mnemonic: “Some Lions Test Prey That They Can’t Handle” as a way to recall the eight carpal bones)

The Hand: Metacarpals and Phalanges

  • Metacarpals: 5, numbered I to V from the thumb toward the little finger
  • Phalanges: 14 total; each finger has a proximal, middle, and distal phalanx except the thumb which has only proximal and distal
  • Terms: Phalanx (singular), Proximal, Middle, Distal (positions along the finger)

The Pelvis: Pelvic Girdle

  • Components and regions
    • Ilium, Ischium, Pubis (each half contributes to the acetabulum)
    • Iliac crest, iliac fossa, greater/lesser sciatic notches, posterior superior/inferior iliac spines
    • Pubic symphysis and pubic arch; sacroiliac joint
  • Pelvic spaces
    • Greater (false) pelvis vs Lesser (true) pelvis
  • Pelvic inlet and outlet boundaries defined by pelvic brim

Lower Limb: Bones of the Leg and Foot

  • The right leg bones (anatomical overview)
    • Femur (thigh bone): head, neck, greater/lesser trochanters, intertrochanteric crest, linea aspera, distal landmarks (medial/lateral condyles, epicondyles)
    • Tibia (shinbone): proximal and distal landmarks; tibial tuberosity; soleal line; intercondylar eminence; medial malleolus
    • Fibula (calf bone): head, neck, lateral malleolus; groove for tendons
  • Intercondylar region and knee joint details
    • Medial and lateral condyles, intercondylar fossa, Gerdy’s tubercle (insertion of iliotibial tract)
  • Foot bones (overview)
    • Tarsals: Talus, Calcaneus, Navicular, Cuboid, Medial/Intermediate/Lateral cuneiforms
    • Metatarsals: five metatarsals
    • Phalanges: proximal, middle, distal; the first digit has two phalanges (proximal and distal) while digits II–V have three
  • Special structures
    • Calcaneal (heel) region and attachment points for tendons (e.g., gastrocnemius/soleus via the calcaneal tendon)

The Tarsals, Metatarsals, and Phalanges: Summary for the Foot

  • Tarsals: Talus, Calcaneus, Navicular, Cuboid, Cuneiforms (Medial, Intermediate, Lateral)
  • Metatarsals: I–V (from the medial to lateral side of the foot)
  • Phalanges: Proximal, Middle, Distal; 5 toes with the 1st toe having 2 phalanges; 2–5 have 3 phalanges each

Bones to Know: Consolidated List for Quick Review

  • Bones of the Skull: Nasal, Parietal, Frontal, Temporal, Zygomatic, Ethmoid, Maxilla, Mandible (teeth associated with the skull)
  • Vertebrae: Distinguishing features between cervical, thoracic, and lumbar types
  • Ribs & Sternum: True, false, and floating ribs; sternum components and joints
  • Clavicle, Scapula, Humerus, Radius, Ulna: Upper limb girdle and bones
  • Ilium, Ischium, Pubis: Pelvis components; hip joint (acetabulum)
  • Femur, Tibia, Fibula: Leg bones
  • Carpals & Tarsals: Names and locations (eight carpal bones; seven tarsal bones)
  • Metacarpals, Metatarsals, Phalanges: Names and counts; regional distribution across hands and feet

Mnemonics and Practical Notes

  • Carpal bones mnemonic (as presented): Some Lions Test Prey That They Can’t Handle
    • Scaphoid, Lunate, Triquetrum, Pisiform, Trapezium, Trapezoid, Capitate, Hamate
  • Clinical relevance: Scaphoid fractures risk avascular necrosis due to distal blood supply patterns; awareness in wrist injuries

Connections to Foundational Principles and Real-World Relevance

  • Wolff’s Law and biomechanics: bone structure reflects mechanical demands; implications for rehabilitation, athletic training, and orthopedic interventions
  • Growth and development: endochondral and intramembranous ossification explain why flat bones (skull) form differently from long bones (limb bones)
  • Aging and bone health: understanding peak density, remodeling balance, and menopause helps interpret risk for osteopenia/osteoporosis and informs prevention strategies
  • Clinical implications of Salter-Harris fractures: growth plate injuries can affect future bone growth; treatment decisions depend on fracture type and involved elements

Equations and Quantitative References (LaTeX)

  • Bone mass remodeling rate (typical): 10\% / \text{yr}
  • Peak bone density timing placeholders (age references): 18years(females),years (females),20 years (males)
  • Peak bone density approximation: around 30 years
  • Osteopenia range: bone mineral density between -1.0andand-2.5 standard deviations below the young adult mean
  • Osteoporosis threshold: bone mineral density less than -2.5 standard deviations below the young adult mean
  • Vertebral counts: 7cervical,cervical,12thoracic,thoracic,5lumbar,lumbar,5sacral,sacral,4$$ coccygeal

Quick Practice Questions (to test comprehension)

  • Identify the primary growth centers in endochondral ossification and describe their roles in diaphyseal and epiphyseal development.
  • Compare and contrast cortical (compact) bone versus trabecular (spongy) bone in terms of structure, turnover, and mechanical function.
  • Explain Wolff’s Law and give a practical example from sports medicine or rehabilitation.
  • List the Salter-Harris fracture types and indicate which involve the growth plate alone versus surrounding bone structures.
  • Name the carpal bones using the mnemonic provided and explain why scaphoid fractures are clinically significant.
  • Describe the flow of blood supply to cortical bone via the nutrient artery and nutrient foramen, and name where these vessels primarily enter the bone.

End of Notes