Chapter 8: The Appendicular Skeleton

Appendicular Skeleton

Overview

The appendicular skeleton includes:

  • Upper and lower limb bones.
  • Bones of the hands and feet.
  • Bones that anchor the limbs to the axial skeleton.

Axial vs. Appendicular Skeletons

  • Axial Skeleton: Forms the central axis of the body.
    • Includes the skull, vertebral column, and thoracic cage.
  • Appendicular Skeleton:
    • Includes the pectoral and pelvic girdles.
    • Limb bones.
    • Bones of the hands and feet.

Pectoral Girdle

The pectoral girdle attaches the upper limb to the axial skeleton (sternum).

  • Consists of the clavicle and the scapula.

Scapula

  • Features:
    • Acromion: Process at the lateral end of the spine.
    • Coracoid process:Anterior projection
    • Superior border
    • Suprascapular notch
    • Superior Angle
    • Supraspinous fossa: Area above the spine on the posterior side.
    • Infraspinous fossa: Area below the spine on the posterior side.
    • Glenoid cavity: Articulates with the humerus.
    • Spine: Prominent ridge on the posterior side.
    • Subscapular fossa: Large depression on the anterior (deep) side.
    • Lateral border
    • Medial border
    • Inferior angle

Humerus and Elbow Joint

The humerus is the single bone of the upper arm region.

  • Articulates with the radius and ulna bones of the forearm to form the elbow joint.

Ulna and Radius

  • Ulna: Located on the medial side of the forearm.
  • Radius: Located on the lateral side of the forearm.
  • Interosseous membrane: Connects the ulna and radius.

Bones of the Wrist and Hand

  • Carpal Bones: Eight carpal bones form the base of the hand.
    • Arranged in proximal and distal rows of four bones each.
  • Metacarpal Bones: Form the palm of the hand.
  • Phalanx Bones: Form the thumb and fingers.

Radiograph of Hand Bones

  • Carpal bones form the base of the hand.

Carpal Tunnel

  • Passageway for nine muscle tendons and a major nerve to enter the hand from the anterior forearm.
  • Walls and floor formed by the U-shaped grouping of the carpal bones.
  • Roof formed by the flexor retinaculum (a strong ligament that anteriorly unites the bones).

Hand During Gripping

  • During tight gripping, the fourth and fifth metacarpal bones are pulled anteriorly.
  • Increases contact between the object and the medial side of the hand, improving the firmness of the grip.

Fractures of the Humerus and Radius

  • Falls or direct blows can result in fractures of the surgical neck or shaft of the humerus.
  • Falls onto the elbow can fracture the distal humerus.
  • Colles fracture: Fracture of the distal radius; most common forearm fracture.

Pelvis

The pelvic girdle attaches the lower limb to the axial skeleton through articulation with the sacrum.

  • Formed by a single hip bone.
  • The right and left hip bones, plus the sacrum and the coccyx, together form the pelvis.

Hip Bone

  • Consists of three regions:
    • Ilium: Large, fan-shaped superior portion.
    • Ischium: Posteroinferior portion.
    • Pubis: Anteromedial portion.

Ligaments of the Pelvis

  • Posterior sacroiliac ligament: Supports the sacroiliac joint.
  • Sacrospinous ligament: Spans the sacrum to the ischial spine.
  • Sacrotuberous ligament: Spans the sacrum to the ischial tuberosity.
  • Sacrospinous and sacrotuberous ligaments contribute to the formation of the greater and lesser sciatic foramens.

Male and Female Pelvis

The female pelvis is adapted for childbirth.

  • Broader.
  • Larger subpubic angle.
  • Rounder pelvic brim.
  • Wider and more shallow lesser pelvic cavity than the male pelvis.

Femur and Patella

The femur is the single bone of the thigh region.

  • Articulates superiorly with the hip bone at the hip joint.
  • Articulates inferiorly with the tibia at the knee joint.
  • The patella only articulates with the distal end of the femur.

The Q-Angle

  • Measure of the amount of lateral deviation of the femur from the vertical line of the tibia.
  • Adult females have a larger Q-angle due to their wider pelvis than adult males.

Tibia and Fibula

  • Tibia: Larger, weight-bearing bone located on the medial side of the leg.
  • Fibula: Slender bone of the lateral side of the leg; does not bear weight.

Bones of the Foot

  • Divided into three groups:
    • Tarsal bones: Form the posterior foot (seven bones).
    • Metatarsal bones: Form the mid-foot (five bones).
    • Phalanges: Form the toes.

Limb Development

  • Limb buds are visible in an embryo at the end of the seventh week of development.

Clubfoot

  • Common deformity of the ankle and foot present at birth.
  • Most cases are corrected without surgery, and affected individuals will grow up to lead normal, active lives.