Chapter 8 - Appendicular Skeleton

- Part of the skeletal system that allows us to perform a wide variety of movements -

The Appendicular Skeleton 

• Made up primarily of PAIRED bones

• Pectoral girdle (a.k.a shoulder girdle)

  • Attaches the upper limbs to trunk

• Pelvic girdle (a.k.a hip girdle)

  • Attaches the lower limbs to the trunk

• Upper & lower limbs differ in function but share the same structural plan

The Pectoral Girdle

• Consists of clavicle & scapula 

• Function - provides attachment for many muscles that move the upper limb

• Girdle is very light & upper limbs are highly mobile

  • Only clavicle articulates w/ the axial skeleton (manubrim)

  • Socket of the shoulder joint (glenoid cavity) is shallow, making dislocations and other injury types common

Clavicles

• Slender & S-shaped

• Extend horizontally across the superior portion of the thorax

• Acromial (lateral) end is flat

• Sternal (medial) end is rounded/cone shaped

  • Articulates w/ the manubrium of sternum

• Provide attachment for muscles

• Hold the scapulae and arms laterally

• Transmit compression forces from the upper limbs to the axial skeleton

Scapulae

• “Shoulder blade”

• Thin, flat triangular bone

• Located on the dorsal portion of the ribcage, through ribs 2-7

• Head always faces outward, therefore, if the head is facing the right direction, that would be the right scapula

• Coracoid process - anterior projection that attaches the bicep muscle of the arm

• Edges make up 3 different borders

1. Superior border - shortest & sharpest

2. Medial (a.k.a vertebral) border - runs parallel to the vertebral column

3. Lateral - runs to axillary region

• Have 3 angles

1. Superior

2. Inferior

3. Lateral

• Subscapular fossa -  attaches  to rotator cuff muscles

  • Found on anterior side of scapulae

• Supraspinous fossa - superior to the spine of scapulae

• Infraspinous fossa - inferior to the spine of scapulae

The Upper Limb

• 30 bones form each upper limb

• Grouped into bones of the:

  • Arm - (brachium)

  • Forearm (antebrachium)

  • Hand  (manus)

Arm

• Runs between the shoulder and elbow

• Humerus 

  • The only bone of the arm

  • Longest & strongest bone of the upper limb

  • Articulates proximately w/ the scapula at the shoulder

  • Articulates distaley w/ the radius & ulna at the elbow

  • Contains many structures that provide sites for muscle attachment

Structures of the Humerus

• Proximal end

  • Hemispherical head that fits into the glenoid cavity

  • Surgical neck

    • Common fracture site

  • Greater tubercle  

  • Lesser tubercle 

  • Intertubercular sulcus - shallow groove that lies between the 2 tubercles

• Deltoid tuberosity - slight v-shaped roughened area in the middle of the shaft

• Processes on the distal end

  • Capitulum - ball shaped  

  • Trochlea - hourglass shaped, medial to the capitulum

  • Medial & lateral epicondyle

• Coranoid fossa - small depression

  • Only seen anteriorly 

• Olecranon fossa - larger, deeper depression

  • Only seen posteriorly

Attachment Site of Humerus & Bones of Forearm

• Capitulum directly connects to head of radius (lateral bone)

• Trochlea directly connects to head of ulna (medial bone)

  • Trochlear notch makes up majority of the elbow joint

Forearm

• Formed from the radius & ulna

  • Run in inverse orientation

    • Head of radius is found proximaley while head of ulna is found distaley

  • 3 different locations where these 2 bones articulate 

1. Proximal radioulnar joint - between radius and radial notch of the ulna

2. Distal radioulnar joint - between head of the ulna and the ulnar notch of the radius

3. Interosseous membrane - flat ligament

Ulna (medial)

• Slightly longer than the radius

• Main bone responsible for forming the elbow joint with the humerus

  • Hinge joint allows forearm to bend on arm

• Distal end is separated from carpals by fibrocartilage

• Plays little to no role in hand movement

Radius (lateral)

• Distal end directly articulates to carpals

• Plays little to no role in hand movement

• Main contribution to the formation of the wrist joint 

  • Attaches to 2/8 carpal bones

Extended vs. Flexed Elbow Joint

• Fully extended elbow joint shows the olcranon process (belonging to the ulna), fitting into the olecranon fossa of the humerus

• Fully flexed elbow joint, shows the coranoid process on ulna fits into coranoid fossa on humerus

Hand

• Bones:

  • Carpus - wrist

  • Metacarpals - palm

  • Phalanges / phalanx - fingers

Carpus

• Forms the true wrist (the proximal region of the hand)

  • Derived of 8 marble-sized carpal bones

• Arranged in in 2 irregular rows

  • Proximal row from lateral to medial

    • Scaphoi, Lunate, Triquetrium, & Pisiform

  • Distal from from lateral to medial 

    • Trapezium, trapezoid, capitate, and hamate

• A mnemonic to help remember carpals:

  • Sally Left The Party To Take Carmen Home

• Stabilized through ligaments that are attached between the styloid processes of the forearm and the carpals

Metacarpals

• Marked w/ numbers 1-5, moving from the lateral to medial side

  • Metacarpal #1 (thumb) is shortest, but most mobile

• Contains 3 portions; head, shaft, and base

Phalanges

• Pollux (thumb) has no middle phalanx while all other fingers contain proximal, middle & distal phalanges

 Pelvic Girdle 

• Attaches lower limbs to the spine 

• Supports visceral organs

• R and L coxal bone 

  • These alone, form the PELVIC GIRDLE

  • These along w/ the sacrum and coccyx, form the PELVIS

  • Unite to form the pubic symphysis (joint mainly made up of fibrocartilage)

• Pubic arch - Inferior to the pubic symphysis

  • Tells us what gender the pelvis belongs to

• Attaches to axial skeleton through strong ligaments (sacroiliac joint)

  • Auricular surface of the ilium attaches to auricular surface of the sacrum

• Acetabulum - deep socket structure on lateral pelvic surface that holds the head of the femur

  • Have less movement freedom but are more stable than the arm

• Pelvic brim - top outline of the pelvic opening

  • Runing from pubic crest to arcuate line, touching the inferior edge of sacral ala & sacral promontory

• Arcuate line - separates the ala from the body of the ilium

• Iliac crest - superior thickened margin of the ala

  • Ends at the anterior superior iliac spine

• Iliac fossa (medial side) - deep depression running down the ala

• Consists of 3 separate bones in childhood

  • These fuse together once an individual reaches adulthood, but still retain separate names

  • Ilium - Forms a large flaring bone (due to its ala)

  • Ischium 

    • Ischial spine - process that lies posterior to the acetabulum

  • Pubis 

• Obturator foramen - very large opening that very few blood vessels and nerves pass through

True & False Pelves

• Bony pelvis is divided into two regions

  • False (greater) pelvis - bounded by alae of the iliac bones

    • Portion that is superior to the pelvic brim

    • “False” because it does not house any pelvic organs

  • True (lesser) pelvis - inferior to pelvic brim

    • Portion that is inferior to the pelvic brim

    • Forms a bowl containing pelvic organs

• Inferior end is referred to as “pelvic outlet”

Pelvic Structures and Childbearing

The Lower Limb

• Carries the entire weight of the erect body, so bones of the lower limb are thicker and stronger

• Divides into 3 segments

  • Thigh, leg, & foot

Thigh

• Femur - the single bone of the thigh

  • Longest and strongest bone of the body

• Proximal end

  • Ball-shaped head articulate w/ the acetabulum

    • Contains fovea capitis in the center of it

    • Ligament runs from fovea capitis to acetabulum

  • Neck represents the weakest part of the femur

  • Greater trochantar

  • Lesser trochantar

  • Gluteal tuberosity

    • Attaches to buttock muscle 

    • Only visible posteriorly

  • Linea aspera

    • Attachment site for muscles of the thigh

• Distal end

  • Patellar surface

    • Smooth surface that articulates w/ patellar (bone of the kneecap)

  • Condyles - wheel shaped structures on the posterior side

    • Medial condyle

    • Lateral condyle

    • Roll on the flat tibial condyles to form the knee joint

  • Intercondylar fossa - deep depression between the medial and lateral condyles

Leg/Crura

• Refers to the region between the knee and ankle

• Composed of the tibia and fibula

  • Tibia - more massive medial bone of the leg

  • Fibula - stick-like lateral bone of the leg

• 3 points of contact between the tibia and fibula

1. Proximal tibliofibular joint

2. Distal tibliofibular joint

3. Interosseous membrane - flat ligament

The Foot

• Composed of

  • Tarsus, metatarsus, & the phalanges

• Important functions

  • Supports body weight

  • Acts as a level to propel body forward, especially when walking

  • Segmentatino makes foot pliable and adapted to uneven ground

Foot Structure

• Tarsus - composed of 7 tarsal bones

  • Make up the posterior half of the foot

  • Heel bone (calcaenous), ankle bone (talus), cuboid, navicular, lateral cuneform, medial cuneform, intermediate cuneform

    • Trochlea of talus - connects to articular surface of the tibia

• Metatarsus - consists of small long bones labeled 1-5 from medial to lateral

  • First metatarsal (big toe) supports body weight

  • Head

    • Ex) head of metatarsal 1 is the ball of our foot

  • Shaft

  • Base

• Phalanges - 14 phalanges of the toes

  • Smaller and less nimble than those of the fingers

  • Structure and arrangement are similar to the fingers

    • Hallux has no middle phalanx, only proximal and distal

• Facet for lateral malleolus - articulation surface for lateral malleolus of fibula 

Medial malleolus does not have a designated surface to articulate w/ so it rests against the medial aspect of the talus