Appendicular Skeleton Overview

Appendicular Skeleton

• Anchors limbs to the axial skeleton
• Attaches to skeletal muscle

Pectoral Girdle

• Two lateral sides
• Each side: 1 clavicle + 1 scapula
• Clavicle: collarbone (anterior)
• Scapula: shoulder blade (posterior)
• Function: Provides structural support to the shoulder region on the left and right sides of the body

Clavicle

• S-shaped bone
• Makes up the anterior portion of the pectoral girdle
• Joins sternum at the sternoclavicular joint
• Only direct connection between the pectoral girdle and axial skeleton

Scapula

• Triangular flat bone
• Forms posterior portion of the pectoral girdle
• Acromion: “high point” of the shoulder
  • Articulates anteriorly w/ sternum
• Spine: thick ridge extending inferiorly and medially from the acromion
• Coracoid process: lateral and superior projection
  • Point of attachment for muscles and ligaments of arms/chest
• Glenoid cavity: depression accommodating the humeral head

Upper Limbs

• Composed of 30 bones and 3 regions:
  • Humerus (proximal upper limb)
  • Radius and ulna (forearm)
  • Carpals + metacarpals + phalanges (wrist and hand)

Humerus

• Humeral head: large, rounded epiphysis of the humerus
  • Articulates with glenoid cavity of scapula = glenohumeral joint

Ulna

• Medial and longest of the forearm bones
• Head of ulna: distal portion of the bone
  • Joined to the wrist by fibrocartilage
• Olecranon: projection at the proximal end of the ulna
  • Bony part of the elbow

Radius

• Lateral bone of the forearm
• Shorter than the ulna
• Head of the radius: proximal end of the bone
  • Articulates with humerus and ulna
• Distal end articulates with ulna and carpals

Radius and Ulna

• Joined by:
  • Joints at the epiphyses
    • Two proximal joints (elbow)
    • One distal joint (wrist)
  • Interosseous membrane
    • Fibrous connective tissue joining the diaphysis

Carpals

• Carpus or wrist formed by the distal radioulnar joint + radiocarpal joints
• Scaphoid: only broken bone in majority of wrist fractures

Metacarpals

• Intermediate to the carpals and phalanges
• Prominent heads = "knuckles"
• Numbered 1-5, thumb to little finger

Phalanges

• Bones of the digits
• Most distal bones of the upper limb
• Thumb = pollex
• Numbered 1-5, thumb to little finger

Pelvic Girdle

• Functions:
  • Joins lower limbs to the axial skeleton
  • Stabilizes the position of the axial skeleton during lower limb movement
  • Protects organs of the reproductive, digestive, and excretory systems

Coxal (Hip) Bones

• Two hip or coxal bones fan out laterally from the sacrum
  • 1. Ilium
  • 2. Ischium
  • 3. Pubis

Ilium

• Acetabulum: depression accommodating the femoral head
• Iliac crest: superior and lateral border of the coxal bones
• Sciatic notch: nestles the longest nerve in the body: sciatic nerve
• Sacroiliac joint: portion of ilium joining the sacrum

Ischium

• Forms the inferior and posterior portion of the pelvic girdle
• A portion of the ischium forms the acetabulum
• "Butt bones"

Pubis

• Forms the anterior and inferior portion of the pelvic girdle
• Pubic symphysis: anterior joining of the two coxal bones (held together by fibrocartilage)
• Pubic arch: lies inferior to the pubic symphysis (the angle formed by the inferior joining of the coxal bones)

Obturator Foramen

• The largest foramen in the body
• Allows for rotation and abduction
• Provides passage for blood vessels and nerves

True vs. False Pelves

• Pelvis can be thought of like a bowl
• Pelvic brim: rim of the bowl dividing the pelvis into a superior and inferior portion
• False pelvis: portion superior to the pelvic brim
• True pelvis: portion inferior to the pelvic brim

Pelvic Axis

• Pelvic inlet: superior opening defined by the pelvic brim
• Pelvic outlet: inferior opening of the true pelvis
• Pelvic axis: imaginary line drawn from the centre of the inlet to the centre of the outlet

Male vs. Female Pelves

• Male and female pelves are different!
• There is a difference in the size of the pelvic brim and false pelvis, a greater than 90 degrees pubic arch is a sign of a female pelvis.

Lower Limb

• Composed of 30 bones in 4 regions:
  • The femur (thigh)
  • The patella (kneecap)
  • The tibia and fibula (lower leg)
  • The tarsals, metatarsals, and phalanges of the foot (tarsus or ankles and feet)

Femur

• Longest, strongest and heaviest bone in the body
• Joins the pelvic girdle at the acetabulum
  • Head of the femur: large round proximal epiphysis
  • Neck of the femur: constricted portion just distal to the head (location of hip "breaks")
  • Medial and lateral condyles: distal knobby projections (articulate with the tibia and patella)

Patella

• Sesamoid bone
• Articulates with the femur and tibia
• Functions:
  • Protects the knee joint
  • Stabilizes tendon position when the knee is bent
  • Increases the leverage of the quadriceps femoris muscle

Tibia

• Longer bone of the lower leg
• Tibial tuberosity: large anterior and proximal projection
  • Point of attachment for the patellar ligament
• Distal end of the tibia:
  • Medial malleolus: articulates with the talus (a tarsal)
    • Forms medial bony "ankle bone"

Fibula

• Smaller bone of the lower leg (lateral)
• Only articulates with the tibia and talus (tarsal)
• Fibulotalar joint:
  • Forms lateral "ankle bone"
  • Called the lateral malleolus

Tibia and Fibula

• Joined by:
  • Joints at the epiphyses
    • Proximal and distal tibiofibular joints
  • Interosseous membrane
    • Joins diaphyses

Tarsus

• Composed of seven tarsals
• Metatarsals are numbered 1-5 medial to lateral
• Phalanges are numbered 1-5 by digit (like the hand)
  • The big toe is the hallux

Tarsals

• Located in the posterior portion of the foot
• Talus: articulates with the fibula to form the lateral malleolus
• Calcaneus: largest and strongest tarsal (forms the heel bone)

Summary

• Upper limbs are attached to the axial skeleton at the pectoral girdle
• Lower limbs are attached to the axial skeleton at the pelvic girdle
• Limbs move around articulations or joints formed at bone-bone contacts
• The appendicular skeleton stabilizes the axial skeleton so that muscles can move the limbs.