Anatomy Notes: Appendicular Skeleton and Lower Limbs

Ulna and Radius

• Ulna (medial): Forms the hinge joint of the elbow.

• Radius (lateral): Facilitates forearm rotation.

Appendicular Skeleton

Pectoral Girdle

• Each girdle consists of:

  • Clavicle: Collar bone (S-shaped).

  • Scapula: Shoulder blade (triangular shape, often isosceles).

• Major Roles:

  • Supports the arms by attaching them to the body.

  • Positions the shoulder joints.

  • Enables arm movement.

Scapulae (Shoulder Blades)

• Triangular shape: Broad and flat.

• Articulates with the humerus and clavicle.

• Possesses three sides.

Skeleton of Upper Limbs

• Consists of bones of:

  • Arms (shoulder to elbow).

  • Forearms: Radius (thumb side) and Ulna (pinky side).

  • Wrists: 8 carpal bones total.

  • Hands: 5 metacarpals and 14 phalanges.

Humerus

• The only bone in the arm.

• Position: Proximal to the shoulder, distal to the hand.

Forearm (Antebrachium)

• Consists of two long bones: radius and ulna.

• Interosseous Membrane:

  • A fibrous sheet made of dense connective tissue.

  • Connects the lateral margin of the ulna to the radius (analogous to the connection between the tibia and fibula).

  • inter = in between.

  • osseous = bones.

  • Roles:

    • Stabilizes bones.

    • Provides a site for muscle attachment.

    • Facilitates forearm rotation, including pronation/supination and flexion/extension.

Metacarpals

• I: Lateral, thumb (pollex).

• II: Index finger.

• III: Middle finger.

• IV: Ring finger.

• V: Medial, little finger.

• Total number of bones in the hand: 14.

Ulna

• Olecranon: Proximal end; point of the elbow.

  • “Part of the elbow that we feel.”

  • Movements at elbow joints: flexion and extension.

• Head of ulna (ulnar head):

  • Located at the distal end (near the wrist).

  • Movements of hand/wrists.

  • The radius is denser than the ulna.

Radius

• Head of the radius: At the proximal end (elbow).

• Ulnar notch: At the distal end (near the wrist).

• Role of radius:

  • Stabilizes the forearm, enabling a large range of motion.

  • Movements: flexion, extension, and rotation.

  • Works in conjunction with the ulna, connected by a fibrous sheet.

Eight Carpal Bones

Proximal Row

• Scaphoid: On the lateral side (thumb).

• Lunate: Next to the scaphoid; articulates with the radius.

• Triquetrum: Articulates with the pisiform.

• Pisiform: Sesamoid bone, located on top of the triquetrum.

Distal Row

• Trapezium: Articulates with the first metacarpal.

• Trapezoid: Articulates with the second metacarpal.

• Capitate: Articulates with the third metacarpal.

• Hamate: Has a hook-like projection called the hamulus.

Function of Carpal Bones

• Allow the wrist to bend and twist, enabling:

  • Flexion.

  • Extension.

  • Abduction (radius).

  • Adduction (ulna).

Pelvic Girdle

• Consists of two hip bones, each featuring the obturator foramen (located between the pubis and ischium; the largest foramen in the body).

• Each hip bone comprises:

  • Ilium: The largest of the three parts; supports body weight when standing or walking. The iliac crest can be easily palpated (“feel”).

  • Ischium: Features the ischial tuberosities (“sit bones”).

  • Pubis: Includes the pubic symphysis, which joins the two hip bones.

  • Acetabulum: The meeting point of the ilium, ischium, and pubis; also where the femur connects with the pelvic girdle.

    • Type of joint: ball and socket joint.

• Women: possess wider and more shallow (childbirth-related adaptation) pelvises; the coccyx is more outward.

• Distinction between the true and false pelvis:

  • True pelvis: located below the pelvic brim.

  • False pelvis: located above the pelvic brim.

Phalanges

• Pollex (thumb):

  • Has two phalanges (proximal and distal).

• Each of the other four fingers:

  • Has three phalanges (proximal, middle, distal).

Pelvis

• Composed of:

  • Hip bones.

  • Sacrum.

  • Coccyx.

True Pelvis

• Contains the bladder, reproductive organs, and rectum.

• Inferior to the pelvic brim.

• Encloses the pelvic inlet (baby passes through during childbirth).

False Pelvis

• Supports the abdominal organs and intestines.

• Superior to the pelvic brim.

Pelvic Outlet

• The fetus passes through during childbirth.

• Lower opening of the true pelvis.

Perineum

• Located below the pelvic outlet.

• Role: Supports the external genitalia and anus.

Lower Limbs

• Function: support body weight and facilitate movement.

• Movement activities: maintaining posture, standing, walking, running, crawling, lifting, jumping, climbing, and squatting.

Bones of Lower Limbs

• Femur.

• Patella.

• Tibia.

• Fibula.

• Tarsals.

• Metatarsals.

• Phalanges.

Leg Definition

• The distal portion of the limb (from knee to ankle).

Femur

• Longest and heaviest bone in the body.

• Head (epiphysis):

  • Articulates with the hip bone at the acetabulum.

• Neck:

  • Joins the shaft (longest part of the femur, diaphysis) at an angle of approximately $125$$$125$$ degrees.

  • Angle of inclination: varies based on age, sex, and genetics; affects running and walking efficiency.

Patella

• Plural: patellae.

• Shape: Sesamoid shaped.

• Location: Anterior to the knee joint.

• Quadriceps Femoris:

  • Four muscles attach to the base of the patella:

    • Rectus femoris.

    • Vastus lateralis.

    • Vastus medialis.

    • Vastus intermedius.

Bones of the Leg

• Tibia and Fibula (tibia is larger and more dense).

• Bound by the interosseous membrane.

Tibia

• Large, medial, weight-bearing bone of the leg.

• Medial position: Tibia is medial to the body (inner side of the body).

• Joins the femur at the knee and the talus at the ankle.

Fibula

• Smaller bone located laterally (head articulates with the tibia).

• Roles:

  • Supports the tibia.

  • Attachment site for muscles.

  • Provides stability for movements such as:

    • Inversion (foot inward).

    • Eversion (foot outward).

    • Plantarflexion (toes down).

• Lateral Malleolus:

  • Distal/lateral end (malleolus articulates with the ankle).

Tarsal Bones

• Talus: Located on top of the foot, between the tibia and fibula.

• Calcaneus: Transfers weight from the talus to the ground; main connection between the leg and the foot.

• Navicular.

• Cuboid: Articulates with the calcaneus and metatarsals.

• 3 Cuneiform Bones: Articulate with the 1st, 2nd, and 3rd metatarsals and the navicular bone.

Metatarsals

• I: Big toe (hallux); medial.

• II: Second toe.

• III: Third toe.

• IV: Fourth toe.

• V: Little toe; lateral.

Anatomical Position

• Pollex (thumb): Lateral (in supine position with palms facing forward).

• Hallux (big toe): Medial (in prone position with foot facing downward).

Phalanges

• 14 bones of the toes.

• Hallux (great toe):

  • Has two phalanges (proximal and distal).

Clinical Relevance

• Bunion: A bony bump at the base of the hallux.

  • Occurs at the metatarsophalangeal joint.

  • Causes:

    • Improper footwear.

    • Predisposition/genetics.