Human Anatomy and Physiology - The Skeleton

The Skeleton

• The skeletal system consists of:
  • Bones
  • Cartilages
  • Joints
  • Ligaments
• Mostly bone, with cartilage in isolated areas.
• Ligaments connect bones and reinforce joints.
• The skeleton accounts for 20\% of body mass.
• Two major divisions:
  • Axial skeleton
  • Appendicular skeleton

Axial Skeleton

• Consists of 80 bones divided into three major regions:
  • Skull
  • Vertebral column
  • Thoracic cage
• Functions:
  • Forms longitudinal axis of body
  • Supports head, neck, and trunk
  • Protects brain, spinal cord, and thoracic organs

The Skull

• Most complex bony structure in body.
• Formed by two sets of bones:
  • Cranial bones (cranium):
    • Enclose the brain in the cranial cavity.
    • Provide sites of attachment for head and neck muscles.
  • Facial bones:
    • Form framework of face.
    • Contain cavities for special sense organs for sight, taste, and smell.
    • Provide openings for air and food passage.
    • Secure teeth.
    • Anchor facial muscles used for facial expression.
  • Most skull bones are flat and firmly locked together (except for mandible).
    • Joints are called sutures.
    • Have a serrated, saw-tooth appearance.

Overview of Skull Geography

• Facial bones form anterior aspect, with cranium forming the rest of skull.
• Cranium is divided into a vault and a base.
  • Cranial vault (calvaria) forms superior, lateral, and posterior portion of skull, as well as forehead.
  • Cranial base forms inferior aspect of skull.
    • Internally, base is divided into three “steps,” or fossae: anterior, middle, posterior fossae.
    • Brain sits within these fossae, enclosed by cranium vault.
    • Area referred to as cranial cavity.
• Cranium also contains other cavities:
  • Middle and internal ear cavities
  • Nasal cavity
  • Orbits that house eyeballs
• Skull has 85 named openings.
  • Foramina, canals, fissures
  • Provide passageways for spinal cord, major blood vessels, and the 12 cranial nerves

Cranium

• Comprised of eight cranial bones:
  • Frontal bone
  • Parietal bones (two—left and right)
  • Occipital bone
  • Temporal bones (two—left and right)
  • Sphenoid bone
  • Ethmoid bone

Frontal Bone

• Shell-shaped bone forms anterior portion of cranium.
  • Vertical part, called squamous region, is also known as the forehead.
  • Inferior portion ends at supraorbital margins.
    • Area underneath eyebrows
  • Forms superior wall of the orbits and most of anterior cranial fossa.
    • Supraorbital foramen (notch) allows supraorbital artery and nerve to pass to forehead.
  • Glabella is area of frontal bone between orbits.
    • Frontal sinuses located just lateral to glabella

Parietal Bones and Sutures

• Two large parietal bones form most of superior and lateral aspects of cranial vault.
• Four sutures mark articulations of parietal bones with frontal, occipital, and temporal bones:
  • Coronal suture: between parietal bones and frontal bone
  • Sagittal suture: between right and left parietal bones
  • Lambdoid suture: between parietal bones and occipital bone
  • Squamous (squamosal) sutures: between parietal and temporal bones on each side of skull

Occipital Bone

• Forms most of skull’s posterior wall and posterior cranial fossa.
• Articulates with parietal, temporal, and sphenoid bones.
  • Foramen magnum: “large hole” through which brain connects with spinal cord.
    • Flanked by pair of occipital condyles that articulate with 1st vertebra
  • Hypoglossal canal allows cranial nerve XII to pass through
  • External occipital protuberance: protrusion just superior to foramen magnum
  • External occipital crest: ridges that are site of attachment for ligamentum nuchae
  • Superior and inferior nuchal lines: site of attachment for many neck and back muscles

Temporal Bones

• Paired bones that make up inferolateral aspects of skull and parts of cranial base.
• Three major regions:
  • Squamous: zygomatic processes articulate with zygomatic bone to form zygomatic arch and mandibular fossa makes up part of temporomandibular joint
  • Tympanic: surround external acoustic meatus (external ear canal)
  • Petrous: houses middle and internal ear cavities
    • Makes up part of the middle cranial fossa
    • Several foramina penetrate petrous region:
      • Jugular foramen allows passage of three cranial nerves
      • Carotid canal: passageway for internal carotid artery
      • Foramen lacerum: jagged opening covered by cartilage in living human
      • Internal acoustic meatus and styloidmastoid foramen: cranial nerve passageways
    • Mastoid and styloid processes: areas for attachment of several neck and tongue muscles

Clinical Note: Mastoiditis

• Mastoid process contains cavities (sinuses) called mastoid air cells.
• Mastoiditis can develop if a middle ear infection spreads into mastoid process area.
• Mastoid air cells are separated from brain by a very thin bony plate, increasing chances that the infection could spread to brain.

Sphenoid Bone

• Complex, bat-shaped bone.
• Keystone bone that articulates with all other cranial bones.
  • Sphenoidal sinuses found within body of sphenoid.
  • Body also includes sella turcica prominence that includes hypophyseal fossa area enclosing the pituitary gland.
• Contains three pairs of processes:
  • Greater wings
  • Lesser wings
  • Pterygoid processes
• Contains several foramina:
  • Optic canals: allow passage of optic nerves
  • Superior orbital fissure: cranial nerve passage
  • Foramen rotundum and foramen ovale: also passageways for cranial nerves
  • Foramen spinosum: opening for arteries

Ethmoid Bone

• Deepest skull bone.
• Superior part formed by paired cribriform plates that also form roof of nasal cavity and floor of anterior cranial fossa.
  • Crista galli: triangular process that is point of attachment for brain’s dura mater covering.
  • Perpendicular plate: forms superior part of nasal septum and is flanked by lateral masses that contain sinuses called ethmoidal air cells.
    • Lateral masses extend medially to form superior and middle nasal conchae.
  • Orbital plates contribute to medial wall of orbits.

Sutural Bones

• Tiny, irregularly shaped bones that appear within sutures.
• Significance is unknown, as not everyone has these.

Facial Bones

• Facial skeleton is made up of 14 bones, 12 of which are paired (mandible and vomer are single).
  • Mandible
  • Maxillary bones (2)
  • Zygomatic bones (2)
  • Nasal bones (2)
  • Lacrimal bones (2)
  • Palatine bones (2)
  • Vomer
  • Inferior nasal conchae (2)

Mandible

• Largest, strongest bone of face.
  • U-shaped lower jawbone made up of body (chin) and two upright rami.
    • Mandibular angle: point where rami and chin meet
    • Coronoid process: superior end of rami serves as insertion point for large temporalis muscle
    • Condylar process: posterior to coronoid forms part of temporomandibular joint
    • Mandibular notch: separates processes
  • Body consists of alveolar process that contains sockets for teeth and mandibular symphysis ridge
  • Foramina include mandibular (for nerves) and mental foramina (for nerves and blood vessels)

Maxillary Bones (Maxillae)

• Medially fused to form upper jaw and central facial skeleton.
  • Upper teeth held in alveolar processes.
  • Anterior nasal spine forms just below nose.
  • Palatine process forms two-thirds of hard palate.
  • Frontal process: forms lateral bridge of nose.
  • Zygomatic processes articulate with zygomatic bones.
  • Maxillary sinuses: flank nasal cavity laterally.
  • Openings for nerves and blood vessels include:
    • Inferior orbital fissure
    • Infraorbital foramen
    • Incisive fossa and canal

Zygomatic Bones

• Form cheekbones and inferolateral margins of orbits.
• Articulate with zygomatic processes of temporal, frontal, and maxillary bones.

Nasal Bones

• Form bridge of nose.
• Articulate with frontal, maxillary, and ethmoid bones.
• Attach to cartilage that forms tip of nose.

Lacrimal Bones

• Form medial walls of orbits.
• Articulate with frontal, maxillary, and ethmoid bones.
• Lacrimal fossa that houses lacrimal sac allows passageway for tears to drain.

Palatine Bones

• L-shaped bones made from two bony plates.
  • Horizontal plate: completes posterior one-third of hard palate
  • Perpendicular plate: forms part of posterolateral walls of the nasal cavity and a small part of the orbits

Vomer

• Plow-shaped bone; forms part of nasal septum.

Inferior Nasal Conchae

• Paired bones that form part of lateral walls of nasal cavity.
• Largest of three pairs of conchae.
  • Ethmoid bone forms other two pairs.

The Hyoid Bone

• Not a bone of skull.
• Lies in anterior neck inferior to mandible.
• Only bone in body that does not articulate directly with another bone.
  • Anchored by ligaments
• Acts as a movable base for tongue and site of attachment for muscles of swallowing and speech.

Special Characteristics of the Orbits

• Cavities that encase eyes and lacrimal glands.
• Sites of attachment for eye muscles.
• Formed by parts of seven bones:
  • Frontal, sphenoid, zygomatic, maxilla, palatine, lacrimal, and ethmoid.

Special Characteristics of Nasal Cavity

• Formed by parts of several bones.
  • Roof: cribriform plates of ethmoid
  • Lateral walls: superior and middle conchae of ethmoid, perpendicular plates of palatine and Inferior nasal conchae
    • Spaces between conchae called meatuses
    • Conchae increase turbulence of air flow
  • Floor: processes of palatine and maxillary bones
  • Nasal septum
    • Bony posterior formed by vomer and perpendicular plate of ethmoid
    • Anterior formed by septal cartilage

Special Characteristics of Paranasal Sinuses

• Formed from five skull bones: frontal, sphenoid, ethmoid, and paired maxillary bones.
• All contain mucosa-lined, air-filled spaces.
• Functions:
  • Warm and humidify air
  • Help to lighten skull
  • Enhance resonance of voice

The Vertebral Column - General Characteristics

• Extends from skull to pelvis
• Also called spine or spinal column
• Functions to transmit weight of trunk to lower limbs, surround and protect spinal cord, provide attachment points for ribs and muscles
• Flexible curved structure contains 26 irregular bones called vertebrae in five major regions

Regions and Curvatures

• Regions: ~28² long vertebral column broken into five major regions:
  • Cervical: consists of 7 vertebrae
  • Thoracic: 12 vertebrae
  • Lumbar: 5 vertebrae
  • Sacrum: one bone, formed from fusion of several bones, articulates with hip
  • Coccyx: also fused bones that form terminus of column
• Curvatures: four main curves in the column help to increase resilience and flexibility of spine
  • Cervical and lumbar curvatures
    • Concave posteriorly
  • Thoracic and sacral curvatures
    • Convex posteriorly
• Ligaments: along with trunk muscles, help support vertebral column
  • Anterior and posterior longitudinal ligaments: continuous bands from neck to sacrum that run down front and back of spine
    • Support and prevent hyperextension (backward) or hyperflexion (forward) bending
  • Ligamentum flavum: connects adjacent vertebrae
  • Short ligaments: connect each vertebra to those above and below
• Intervertebral discs
  • Cushionlike pad sandwiched between vertebrae that act as shock absorbers
  • Composed of two parts
    • Nucleus pulposus
      • Inner gelatinous nucleus
      • Gives disc its elasticity and compressibility
    • Anulus fibrosus
      • Outer collar composed of collagen and fibrocartilage
      • Limits expansion of nucleus pulposus when compressed

Clinical Note: Herniated Discs

• Severe physical trauma to spine may result in one or more herniated (prolapsed) discs
• Usually involves rupture of anulus fibrosus, resulting in protrusion of nucleus pulposus, which can press on spinal cord or nerves, causing numbness or excruciating pain
• Treatment: exercise, massage, heat, painkillers, or surgical intervention if non-surgical treatments are not successful

Clinical Note: Abnormal Spinal Curvatures

• Abnormal spinal curvatures can be congenital or result from disease, poor posture, or unequal pull of muscles on spine
• Scoliosis: abnormal lateral rotation of spine, most often in thoracic region, which may lead to breathing difficulties
• Kyphosis (hunchback): is abnormal dorsal thoracic curvature common in people with osteoporosis, tuberculosis of spine, rickets, or osteomalacia
• Lordosis (swayback): is accentuated lumbar curvature that can result from disease but is also seen in men with pot bellies and in pregnant women

General Structure of Vertebrae

• All have common structural pattern consisting of:
  • Body (centrum), the anterior weight-bearing region
  • Vertebral arch composed of:
    • Two pedicles: short pillars form sides of arch
    • Two laminae: fused, flattened plates form posterior arch
  • Vertebral foramen: enclosure formed by body and vertebral arch coming together
  • Vertebral canal: series of vertebral foramina
  • Intervertebral foramina: lateral openings between vertebrae for passage of spinal nerves
• Vertebrae have seven processes:
  • Spinous process: projects posteriorly
  • Transverse processes (2): project laterally
  • Superior articular processes (2): protrude superiorly
  • Inferior articular processes (2): protrude inferiorly

Regional Vertebral Characteristics

Cervical Vertebrae

• C1 to C7: smallest, lightest vertebrae
• C3 to C7 share following features:
  • Oval-shaped body
  • Exception: C7 spinous processes are split (bifid)
  • Large, triangular vertebral foramen
  • Transverse foramen found in each transverse process for artery passageways
  • C7 is vertebra prominens; large and can be felt through skin, so used as a landmark
• C1 (atlas) and C2 (axis) have unique features
  • Atlas (C1)
    • No body or spinous process
    • Consists of anterior and posterior arches, and two lateral masses
    • Superior surfaces of lateral masses articulate with occipital condyles
      • Occipital condyles “carry” skull
      • Movement for nodding head “Yes”
  • Axis (C2)
    • Has body and processes like other vertebrae
    • Major feature is knoblike dens that projects superiorly into anterior arch of atlas
      • Dens is the “missing” body of atlas
    • Dens is a pivot for rotation of atlas
      • Movement allows side to side rotation for saying “No”

Thoracic Vertebrae

• T1 to T12 increase in size and articulate with ribs
• Unique characteristics:
  • Body is heart shaped with two small demifacets that articulate with ribs
    • T10 to T12 have only single facet, not two
  • Vertebral foramen is circular
  • Long, sharp spinous process points inferiorly
  • Transverse processes have transverse costal facets that articulate with ribs (except T11, T12)
  • Location of articular facets allows rotation of this area of spine

Lumbar Vertebrae

• L1 to L5 "small of back"; receives most stress, so bodies are massive
• Other characteristics:
  • Short, thick pedicles and laminae
  • Flat, hatchet-shaped spinous processes point posteriorly
  • Vertebral foramen is triangular
  • Orientation of articular facets locks lumbar vertebrae together to prevent rotation

Sacrum

• Triangular bone shapes posterior wall of pelvis; made from five fused vertebrae (S1–S5)
  • Superior articular process articulates with L5
  • Articulates inferiorly with coccyx and laterally with hip bones via its auricular surfaces, forming sacroiliac joints
  • Sacral promontory: anterosuperior margin
  • Transverse ridges mark lines of fusion
  • Anterior sacral foramina: lie at lateral ends of ridges; act as openings for nerves and vessels
  • Alae: winglike expansions
  • Median sacral crest: roughened bumps on posterior midline and lateral sacral crest; roughened area seen laterally on posterior side
  • Posterior sacral foramina: large openings for sacral spinal nerves
  • Sacral canal: continuation of vertebral canal
  • Sacral hiatus: large opening at end of canal

Coccyx

• Tailbone formed from three to five fused vertebrae; articulates superiorly with sacrum
  • Very little function

Thoracic Cage

• Composed of:
  • Thoracic vertebrae posteriorly
  • Sternum and costal cartilages anteriorly
  • Ribs laterally
• Functions
  • Protects vital organs of thoracic cavity
  • Supports shoulder girdles and upper limbs
  • Provides attachment sites for muscles of neck, back, chest, and shoulders

Sternum

• Also called the breastbone; consists of three fused bones:
  • Manubrium: superior portion that articulates with clavicular notches and ribs 1 and 2
  • Body: midportion that articulates with costal cartilages of ribs 2 through 7
  • Xiphoid process: inferior end that is site of muscle attachment
    • Not ossified until ~age 40
• Has three important anatomical landmarks:
  • Jugular notch
    • Central indentation in superior border of manubrium
  • Sternal angle
    • Horizontal ridge across front of sternum
  • Xiphisternal joint
    • Point where sternal body and xiphoid process fuse

Clinical Note: Xiphoid Process

• Xiphoid process projects posteriorly in some people.
• A blow to the chest (chest trauma) at the level of the xiphoid process can push process into underlying liver or heart.
• Can cause massive hemorrhaging.
• During CPR, hands must be position midsternum to avoid breaking off xiphoid process and damaging underlying organs

Ribs

• 12 pairs form sides of thoracic cage
• All attach posteriorly to bodies and transverse processes of thoracic vertebrae
  • True (vertebrosternal) ribs (pairs 1–7)
    • Attach directly to sternum by individual costal cartilages
  • False (vertebrochondral) ribs (pairs 8–10)
    • Attach indirectly to sternum by joining costal cartilage of rib above
  • Vertebral (floating) ribs (pairs 11–12)
    • No attachment to sternum
• Main parts of rib:
  • Shaft: flat bone that makes up most of rib
    • Costal groove: houses nerves and vessels
  • Head (posterior end)
    • Articulates with facets (demifacets) on bodies of two adjacent vertebrae
  • Neck: constricted portion beyond head
  • Tubercle: knoblike structure lateral to neck
    • Articulates posteriorly with transverse costal facet of same-numbered thoracic vertebra

The Appendicular Skeleton

• Consists of bones of the limbs and their girdles
  • Pectoral girdle
    • Attaches upper limbs to body trunk
  • Pelvic girdle
    • Attaches lower limbs to body trunk

The Pectoral Girdle

• Consists of clavicles (anteriorly) and scapulae (posteriorly)
  • Attach upper limbs to axial skeleton
  • Provide attachment sites for muscles that move upper limbs
  • Offer great degree of mobility because:
    • Scapulae are not attached to axial skeleton
    • Socket of shoulder joint is shallow and does not restrict movement

Clavicles

• Also called collarbones
  • S-shaped sternal end articulates with sternum medially
  • Flattened acromial end articulates laterally with scapula
  • Anchor muscles and act as braces to hold the scapulae and arms out laterally

Scapulae

• Also called shoulder blades; thin, triangular flat bones on dorsal surface of rib cage, between ribs 2 and 7
• Each scapula has three borders
  • Superior: shortest, sharpest border
  • Medial (vertebral): runs parallel to spine
  • Lateral (axillary): near armpit, ends superiorly in glenoid cavity fossa (shoulder joint)
• Each scapula has three angles where borders meet:
  • Superior angle: between superior and medial
  • Lateral angle: between superior and lateral
  • Inferior angle: between medial and lateral
• Bone features
  • Spine: prominent ridge posteriorly
  • Acromion: lateral projection that articulates with acromial end of clavicle to form acromioclavicular joint
  • Coracoid process: anterior projection that anchors bicep muscle of arm
  • Suprascapular notch: opening for nerves
  • Several large fossae named according to location

The Upper Limb

• 30 bones form skeletal framework of each upper limb
  • Arm
    • Humerus
  • Forearm
    • Radius and ulna
  • Hand
    • 8 carpal bones in the wrist
    • 5 metacarpal bones in the palm
    • 14 phalanges in the fingers

Humerus

• Only bone of the arm; the largest and longest bone of upper limb
  • Articulates superiorly with glenoid cavity of scapula
  • Articulates inferiorly with radius and ulna
• Bone features
  • Head: proximal end that fits into glenoid cavity of scapula
  • Anatomical neck: slight constriction inferior to head
  • Greater tubercle is separated from lesser tubercle by the intertubercular sulcus
    • Sites of attachment of rotator cuff muscles
  • Surgical neck: most frequently fractured part of humerus
  • Deltoid tuberosity: about midway down shaft; site of deltoid muscle attachment
  • Radial groove: carries radial nerve
  • Trochlea: distal hourglass-shaped condyle
  • Capitulum: distal ball-like condyle
  • Medial and lateral epicondyles: points of muscle attachment
  • Medial and lateral supracondyle ridges
  • Fossae: coronoid, olecranon, and radial

Forearm - Ulna

• Two parallel bones form forearm skeleton: ulna and radius
  • Proximal ends articulate with humerus and each other
  • Distally articulate with each other at the radioulnar joint
  • Interosseous membrane connects radius and ulna along their entire length
• Ulna
  • Medial bone in forearm
  • Forms major portion of elbow joint with humerus
  • Bone features
    • Olecranon and coronoid processes: grip trochlea of humerus, forming hinge joint
      • Processes separated by trochlear notch
    • Radial notch: articulates with head of radius
    • Ulnar head: knoblike distal portion
    • Ulnar styloid process: ligament attachment

Forearm - Radius

• Lateral bone in forearm
• Bone features:
  • Head: articulates with capitulum of humerus and radial notch of ulna
  • Radial tuberosity: anchors biceps
  • Ulnar notch: articulates with ulna
  • Radial styloid process: anchors ligaments

Clinical Note: Colles’ Fracture

• Colles’ fracture: break in distal end of radius
• Very common fracture because person falling attempts to break fall with outstretched hands

Hand - Carpus, Metacarpus and Phalanges

• Bones of the hand include carpus, metacarpus, and phalanges
• Carpus (wrist): eight bones in two rows
  • Proximal row: lateral to medial
    • Scaphoid, lunate, triquetrum, and pisiform
  • Distal row: lateral to medial
    • Trapezium, trapezoid, capitate, and hamate
  • Only scaphoid, lunate, and triquetrum form wrist joint
• Metacarpus (palm)
  • Five metacarpal bones (I to V from thumb to little finger) form the palm
    • Bases articulate with carpals, and heads articulate with proximal phalanges
• Phalanges (fingers)
  • Fingers (digits): numbered I to V starting at thumb (pollex)
  • Digit I (pollex) has two bones: no middle phalanx
  • Digits II to V have three bones: distal, middle, and proximal phalanx

Clinical Note: Carpal Tunnel Syndrome

• Median nerve and tendons travel through carpal tunnel
  • Tunnel formed by ligaments through wrist
• Carpal tunnel syndrome can occur from overuse and inflammation of tendons, which can compress median nerve, causing tingling and numbness

The Pelvic Girdle

• Also called hip girdle; is formed by 2 hip bones (coxal bones, or os coxae) and sacrum
  • Attach lower limbs to axial skeleton with strong ligaments
  • Transmit weight of upper body to lower limbs
  • Support pelvic organs
  • Less mobility but more stability than shoulder joint
• Three fused bones form coxal bone
  • Ilium, ischium, and pubis
  • Deep socket, acetabulum, formed at point of fusion receives head of femur

Ilium

• Superior region of coxal bone
  • Auricular surface articulates with sacrum (sacroiliac joint)

Ischium

• Posteroinferior part of hip bone

Pubis

• Anterior portion of hip bone
  • Pubis joins at pubic symphysis joint
• Superior region of hip bone
  • Consists of body and winglike ala
    • Iliac crests: thickened superior margin of ala
    • Iliac crest ends at anterior superior iliac spine and posterior superior iliac spine
  • Greater sciatic notch: sciatic nerve passage
  • Gluteal surface contains three ridges: posterior, anterior, and inferior gluteal lines
  • Iliac fossa: concavity on ala
  • Auricular surface articulates with sacrum
  • Arcuate line: defines pelvic brim
• Posteroinferior part of hip bone
  • Consists of body and ramus
  • Three important markings:
    • Ischial spine
    • Lesser sciatic notch
    • Ischial tuberosity
• V-shaped anterior portion of hip bone
  • Consists of the body and superior and inferior pubic rami
  • Anterior border forms the pubic crest
  • Lateral end forms pubic tubercle
  • Obturator foramen: large opening formed by rami and body
  • Pubic bones join at pubic symphysis
  • Pubic arch (subpubic angle): formed by rami; main difference between male and female pelves

Pelvic Structure and Childbearing

• Pelvis: formed by hip bones, sacrum, and coccyx
• Female pelvis tends to be wider, shallower, lighter, and rounder than male’s
  • Adapted for childbearing
• Pelvic brim (pelvic inlet): continuous oval ridge that runs from pubic crest through arcuate line and sacral promontory
  • False pelvis: superior to pelvic brim
  • True pelvis: inferior to pelvic brim; defines birth canal
    • Pelvic outlet: inferior margin of true pelvis

The Lower Limb

• Carries entire weight of erect body
• Subjected to exceptional forces during jumping or running
• Three segments of lower limb
  • Thigh
  • Leg
  • Foot

Thigh - Femur and Patella

• Femur is largest and strongest bone in the body, making up about one-fourth of person’s height
  • Articulates proximally with acetabulum of hip and distally with tibia and patella
• Patella: sesamoid bone in quadriceps tendon that protects knee joint
• Bone features
  • Fovea capitis: small pit in ball-like head
  • Greater and lesser trochanters: muscle attachment sites
    • Trochanters connected by intertrochanteric line and intertrochanteric crest
  • Gluteal tuberosity blends into linea aspera, which diverges into medial and lateral supracondylar lines
  • Distally, femur ends in lateral and medial condyles that articulate with tibia
  • Medial and lateral epicondyles: sites of muscle attachment
    • Adductor tubercle: medial epicondyle bump
  • Patellar surface: articulates with patella
  • Intercondylar fossa: lies between condyles

Leg - Tibia and Fibula

• Made up of two parallel bones, tibia and fibula
  • Connected by interosseous membrane
• Tibia: medial leg bone that receives weight of body from femur; transmits to foot
• Fibula
  • Not weight bearing; no articulation with femur
  • Several muscles originate from fibula
  • Articulates proximally and distally with tibia
• Bone features
  • Tibia
    • Medial and lateral condyles
    • Intercondylar eminence
    • Tibial tuberosity
    • Anterior border
    • Medial malleolus
    • Fibular notch
  • Fibular:
    • Head
    • Lateral malleolus

Clinical Note: Bimalleolar Fracture

• A bimalleolar fracture is a break in the distal ends of both the tibia and fibula
• It is a common sports injury

Foot - Tarsus, Metatarsals, and Phalanges

• Skeleton of foot includes bones of tarsus, metatarsus, and phalanges
• Tarsus: 7 tarsal bones form posterior half
  • Body weight carried primarily by talus and calcaneus (heel)
    • Calcaneal tuberosity: part that touches ground
    • Sustentacular tali (talar shelf): supports talus
  • Other tarsal bones: cuboid, navicular, and medial, intermediate, and lateral cuneiform bones
• Metatarsals
  • Five metatarsal bones (I to V from hallux to little toe)
  • Enlarged head of metatarsal I forms “ball of the foot”
• Phalanges
  • 14 bones of toes
  • Digit I (hallux, great toe) has two bones: no middle phalanx
  • Digits II to V have three bones: distal, middle, and proximal phalanx
• Arches of the foot
  • Maintained by interlocking foot bones, ligaments, and tendons
  • Allow foot to bear weight
  • Three arches
    • Lateral longitudinal: low curve that elevates lateral part of foot
    • Medial longitudinal: arch curves upwards
    • Transverse: runs obliquely from one side of foot to other

Clinical Note: Flat Foot (Pes Planus)

• Flat foot, or pes planus (or sometimes “fallen arches) may be a congenital condition or may be acquired later in life
• Can also be caused by: increasing age, obesity or high-impact activities
• Wearing proper footwear with good arch support can help prevent problem
  • Orthotic shoe inserts may also help manage symptoms

Developmental Aspects of the Skeleton

Infant Skull

• Infant skull