Chapter 8: Bones of the Lower Limb and Development of the Appendicular Skeleton

The Pelvic Girdle

Also called hip girdle; formed by 2 hip bones (coxal bones, or os coxae) and sacrum

Function of Pelvic Girdle

Attaches lower limbs to axial skeleton with strong ligaments; transmits weight of upper body to lower limbs; supports pelvic organs

Pelvic Girdle Mobility

Less mobility but more stability than shoulder joint

Coxal Bone Composition

Formed by three fused bones: ilium, ischium, and pubis

Acetabulum

Deep socket formed at point of fusion; receives head of femur

Ilium

Superior region of hip bone

Ilium Structure

Consists of body and winglike ala

Iliac Crests

Thickened superior margin of ala

Iliac Crest Ends

Ends at anterior superior iliac spine and posterior superior iliac spine

Greater Sciatic Notch

Passage for sciatic nerve

Auricular Surface

Articulates with sacrum

Arcuate Line

Defines pelvic brim

Ischium

Posteroinferior part of hip bone

Ischial Spine

One of three important markings of ischium

Lesser Sciatic Notch

One of three important markings of ischium

Ischial Tuberosity

One of three important markings of ischium

Pubis

V

Obturator Foramen

Large opening formed by rami and body

Pubic Symphysis

Where pubic bones join

Pubic Arch (Subpubic Angle)

Formed by rami; main difference between male and female pelves

Pelvis

Formed by hip bones, sacrum, and coccyx

Female Pelvis

Wider, shallower, lighter, and rounder than male pelvis; adapted for childbearing

Pelvic Brim (Pelvic Inlet)

Continuous oval ridge running from pubic crest through arcuate line and sacral promontory

Female vs Male Pelvis

Female pelvis is broader, with larger subpubic angle, rounder pelvic brim, and wider, shallower lesser pelvic cavity

The Lower Limb

Carries entire weight of erect body

Lower Limb Forces

Subjected to exceptional forces during jumping or running

Bones per Leg

30

Segments of Lower Limb

Thigh, Leg, Foot

Femur

Largest and strongest bone in the body, about one

Femur Articulation

Proximally with acetabulum of hip; distally with tibia and patella

Patella

Sesamoid bone in quadriceps tendon; protects knee joint

Fovea Capitis

Small pit in head of femur

Greater and Lesser Trochanters

Muscle attachment sites

Intertrochanteric Line and Crest

Connect greater and lesser trochanters

Gluteal Tuberosity

Blends into linea aspera; diverges into medial and lateral supracondylar lines

Femur Condyles

Lateral and medial condyles articulate with tibia

Femur Epicondyles

Medial and lateral sites of muscle attachment

Adductor Tubercle

Bump on medial epicondyle

Patellar Surface

Articulates with patella

Intercondylar Fossa

Lies between condyles

Leg Bones

Made up of two parallel bones, tibia and fibula

Interosseous Membrane

Connects tibia and fibula

Tibia

Medial leg bone; receives body weight from femur and transmits to foot

Fibula

Not weight bearing; no articulation with femur

Fibula Muscles

Several muscles originate from fibula

Fibula Articulations

Articulates proximally and distally with tibia

Pott’s Fracture

Occurs at distal end of fibula, tibia, or both; common sports injury

Foot Skeleton

Includes bones of tarsus, metatarsus, and phalanges

Tarsus

7 tarsal bones form posterior half of foot

Talus and Calcaneus

Bear body weight; calcaneus forms heel

Calcaneal Tuberosity

Part that touches ground

Sustentacular Tali (Talar Shelf)

Supports talus

Other Tarsal Bones

Cuboid, navicular, and medial, intermediate, and lateral cuneiform bones

Metatarsals

Five bones (I–V from hallux to little toe)

Metatarsal I Head

Enlarged; forms “ball of the foot”

Phalanges

14 bones of toes

Hallux (Great Toe)

Two bones; no middle phalanx

Digits II–V

Three bones each: distal, middle, proximal phalanges

Foot Arches

Maintained by interlocking bones, ligaments, and tendons; allow foot to bear weight

Lateral Longitudinal Arch

Low curve; elevates lateral part of foot

Medial Longitudinal Arch

Arch curves upwards

Transverse Arch

Runs obliquely from one side of foot to other

Fallen Arches (Flat Feet)

Result from stress on tendons and ligaments of feet

Causes of Flat Feet

Standing immobile for long periods or running on hard surfaces without arch support

Developmental Aspects of the Skeleton

At birth, cranium is huge relative to face

Cranium Growth

At 9 months, cranium is half the adult size

Mandible and Maxilla

Foreshortened at birth but lengthen with age

Limb Growth

Arms and legs grow faster than head and trunk, leading to adult proportions

Congenital Abnormalities

Appendicular skeleton can suffer from congenital abnormalities

Hip Dysplasia

Occurs in a little over 1% of infants

Hip Dysplasia Cause

Acetabulum forms incompletely or ligaments are loose, allowing head of femur to slip out of socket

Hip Dysplasia Treatment

Splints or harness hold femur in place; surgery may tighten ligaments

Clubfoot

Common deformity of ankle and foot present at birth; most cases corrected without surgery