Appendicular Skeleton Overview

Appendicular Skeleton

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

Pectoral Girdle

• Two lateral sides, each containing a clavicle and a scapula
• Clavicle is the collarbone (anterior)
• Scapula is the shoulder blade (posterior)
• Provides structural support to the shoulder region

Clavicle

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

Scapula

• Triangular flat bone forming the posterior portion of the pectoral girdle
• Acromion is the "high point" of the shoulder
• Acromion articulates with the clavicle at the acromioclavicular joint
• Spine is a thick ridge extending inferiorly and medially from the acromion
• Coracoid process is a lateral and superior projection, point of attachment for arm/chest muscles and ligaments
• Glenoid cavity is a depression accommodating the humeral head

Upper Limbs

• Comprised of 30 bones in three regions: humerus (proximal), radius and ulna (forearm), carpals + metacarpals + phalanges (wrist and hand)

Humerus

• Humeral head is the large rounded epiphysis, articulating with the glenoid cavity to form the glenohumeral joint

Ulna

• Medial and longest of the forearm bones
• Head of the ulna is at the distal portion, joined to the wrist by fibrocartilage
• Olecranon is a projection at the proximal end, the bony part of the elbow

Radius

• Lateral bone of the forearm, shorter than the ulna
• Head of the radius is located at the proximal end, articulating with the humerus and ulna
• Distal end articulates with the ulna and carpals

Radius and Ulna Connection

• Joints at the epiphyses (two proximal joints for the elbow, one distal joint for the wrist)
• Interosseous membrane: fibrous connective tissue joining the diaphysis

Carpals

• Carpus or wrist formed by the distal radioulnar joint + radiocarpal joints
• Scaphoid is the most frequently fractured wrist bone

Metacarpals

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

Phalanges

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

Pelvic Girdle

• Functions: joins lower limbs to the axial skeleton, stabilizes the axial skeleton during lower limb movement, protects reproductive, digestive, and excretory organs

Coxal (Hip) Bones

• Two hip bones fan out laterally from the sacrum
• Subdivided into three regions: ilium, ischium, and pubis

Ilium

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

Ischium

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

Pubis

• Forms the anterior and inferior portion of the pelvic girdle
• Pubic symphysis is the 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

• 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, with the rim forming the pelvic brim
• Pelvic brim divides the pelvis into superior and inferior portions
• False pelvis is the portion superior to the pelvic brim
• True pelvis is the portion inferior to the pelvic brim

Pelvic Axis

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

Male and Female Pelves

• Male pelvis has a smaller pelvic brim and false pelvis, a pubic arch less than 90 degrees, and the pelvic inlet is heart-shaped.
• Female pelvis has a larger pelvic brim and false pelvis, a pubic arch greater than 90 degrees, and the pelvic inlet is oval-shaped.

Lower Limb

• Comprised of 30 bones in 4 regions: femur (thigh), patella (kneecap), tibia and fibula (lower leg), 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 is the large round proximal epiphysis
• Neck of the femur is the constricted portion just distal to the head
• Medial and lateral condyles are distal knobby projections, articulating with the tibia and patella

Patella

• Sesamoid bone
• Articulates with the femur and tibia
• 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 is a large anterior and proximal projection, point of attachment for the patellar ligament
• At the distal end:
  • Medial malleolus articulates with the talus, forming the medial bony "ankle bone"

Fibula

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

Tibia and Fibula Connection

• Joints at epiphyses (proximal and distal tibiofibular joints)
• Interosseous membrane joining the diaphyses

Tarsus

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

Tarsals

• Both are located in the posterior portion of the foot
• Talus articulates with the fibula to form the lateral malleolus
• Calcaneus is the largest and strongest tarsal, forming the heel bone

Summary

• The upper limbs are attached to the axial skeleton at the pectoral girdle
• The lower limbs are attached to the axial skeleton at the pelvic girdle
• The 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.