Appendicular Skeleton Notes

Appendicular Skeleton

• The appendicular skeleton comprises 126 bones primarily involved in body movements.
• It includes the bones of the upper and lower limbs and the girdles that attach them to the axial skeleton.

Introduction

• The appendicular skeleton consists of approximately 126 bones, compared to around 80 in the axial skeleton.
• Bones of the limbs include the upper limbs and pectoral girdle, as well as the lower limbs and pelvic girdle.
• The primary function of the appendicular skeleton is movement and locomotion.
• Lower limbs are adapted for bearing weight, while upper limbs are more specialized for a large range of motion.

Pectoral (Shoulder) Girdle

• The pectoral (shoulder) girdles consist of two clavicles and two scapulae.
• Ligaments such as the coracoclavicular and costoclavicular ligaments support the pectoral girdle.
• Joints include the acromioclavicular and glenohumeral joints.

Clavicle

• The clavicle (collarbone) is S-shaped.
• The medial (sternal) end articulates with the manubrium of the sternum.
• The lateral (acromial) end articulates with the acromion of the scapula.

Scapula

• Key features of the scapula include the coracoid process, glenoid cavity, and acromion.
• The scapula also features the suprascapular notch, superior angle, supraspinous fossa, spine, infraspinous fossa, subscapular fossa, medial border, lateral border, and inferior angle.

Upper Limb (Extremity)

• The humerus is the bone of the arm.
• Proximally, the humerus articulates with the scapula; distally, it articulates with the radius and ulna.
• Specifically, the trochlea articulates with the ulna, and the capitulum articulates with the radius.

Humerus

• Notable features of the humerus include the greater and lesser tubercles, intertubercular groove (sulcus), anatomical neck, head, surgical neck, deltoid tuberosity, body (shaft), lateral supracondylar ridge, radial fossa, capitulum, olecranon fossa, coronoid fossa, medial epicondyle, trochlea, lateral epicondyle, and olecranon fossa.

Radius and Ulna

• The ulna and radius are the two bones of the forearm.
• The radius is lateral (thumb side), and the ulna is medial.
• The olecranon and coronoid process at the proximal end of the ulna form the trochlear notch, which wraps around the trochlea of the humerus, creating the elbow joint.

Proximal Articulations

• The ulna articulates with the trochlea.
• The radius articulates with the capitulum.

Carpal Bones

• The carpal bones consist of 8 small bones connected by ligaments, arranged in two rows of four bones each.
• The proximal row includes the scaphoid, lunate, triquetrum, and pisiform, which articulate with the distal radius and ulna.
• The distal row includes the trapezium, trapezoid, capitate, and hamate, which articulate with the metacarpals.

Palm and Digits

• The palm and back of the hand are made up of five metacarpals, numbered I through V (or 1–5) starting with the thumb.
• The bases of the metacarpals articulate with the distal carpals, while their heads articulate with the proximal phalanges.
• The phalanges are the bones of the digits, with a total of 14 per hand/foot.
• The thumb (pollex) has 2 phalanges (proximal and distal), while the other four fingers each have 3 phalanges (proximal, middle, and distal).

Pelvic (Hip) Girdle

• The pelvic girdle is composed of two hip bones that articulate with the sacrum posteriorly.
• Each hip bone is made up of three individual bones: ilium, ischium, and pubis.
• The two hip bones articulate anteriorly at the pubic symphysis, with a disc of fibrocartilage between them.

Ilium, Ischium, and Pubis

• Key features include the iliac crest, iliac fossa, anterior superior iliac spine, anterior inferior iliac spine, posterior superior iliac spine, posterior inferior iliac spine, arcuate line, greater sciatic notch, ischial spine, lesser sciatic notch, ischial body, ischial tuberosity, obturator foramen, superior ramus of pubis, pubic tubercle, pubic body, articular surface of pubis (at pubic symphysis), inferior ramus of pubis, ischial ramus, and ischiopubic ramus.

Acetabulum

• The head of the femur articulates with the acetabulum of the hip bone, forming a ball-and-socket joint.
• The acetabulum is composed of parts of all three bones that make up the hip bone (ilium, ischium, and pubis).

Male and Female Pelves

• The male and female pelves differ in several ways.
• The bones of the male pelvis are usually larger and heavier.
• The bones of the female pelvis are structured to meet the requirements of pregnancy and childbirth.
• The female pelvis is wider and shallower than that of the male.

Femur

• The femur is the longest, heaviest, and strongest bone in the body.
• The proximal end (head) inserts into the acetabulum of the hip bone.
• The distal end articulates with the tibia and patella.

Patella

• The patella is a triangular bone that develops in the quadriceps tendon.
• Its posterior surface articulates with the femur.

Tibia and Fibula

• The lower leg consists of the tibia and fibula.
• The proximal end of the tibia articulates with the femur.
• The distal end of the tibia articulates with the talus bone of the ankle.
• The tibial tuberosity on the anterior surface is the point of attachment for the patellar ligament.

Tarsal Bones

• The tarsus contains 7 tarsal bones.
• These are the talus, calcaneus, navicular, 3 cuneiforms, and the cuboid.

Talus and Calcaneus

• These bones form part of the ankle and heel, respectively.

Metatarsal Bones

• The metatarsus is made up of 5 metatarsal bones.
• Just like the metacarpals, they are numbered I through V (1–5) starting with the big toe.
• They make up the sole and dorsal surface of the foot.
• The proximal ends articulate with the 3 cuneiform bones and the cuboid.
• The distal ends articulate with the proximal phalanges.

Phalanges

• The phalanges are arranged exactly like those of the hand.
• The big toe has a proximal and distal phalanx, and the other toes have a proximal, middle, and distal phalanx.