Appendicular: The pelvic girdle and bony pelvis

Pelvic girdle definition

The pelvic girdle is formed by a pair of hip bones (os coxae) that attach the lower limbs to the axial skeleton.

Bony pelvis definition

The bony pelvis consists of the two os coxae, the sacrum, and the coccyx.

Pelvic girdle function

The pelvic girdle provides stability, supports body weight, and transfers weight from the axial skeleton to the lower limbs.

Pelvic girdle mobility

The pelvic girdle is largely immobile compared to the pectoral girdle, allowing greater stability for weight-bearing.

Os coxa definition

The os coxa (hip bone) is a large bone forming the pelvic girdle and is also called the innominate bone.

Os coxa development

The os coxa develops from three primary ossification centres: ilium, ischium, and pubis.

Os coxa fusion

In juveniles, the ilium, ischium, and pubis are separate and united by cartilage; in adults, they fuse into one bone.

Regions of os coxa

The three regions of the os coxa are the ilium, ischium, and pubis.

Acetabulum definition

The acetabulum is a deep, cup-shaped cavity formed by the convergence of ilium, ischium, and pubis.

Acetabulum articulation

The acetabulum articulates with the head of the femur to form the hip joint.

Obturator foramen definition

The obturator foramen is a large opening between the pubis and ischium inferior to the acetabulum.

Obturator foramen function

The obturator foramen allows passage of nerves and blood vessels to the lower limb.

Ilium position

The ilium is the large, superior, fan-shaped region of the hip bone.

Iliac crest

The iliac crest is the broad, curved superior border of the ilium.

Greater sciatic notch

The greater sciatic notch is a large posterior indentation allowing passage of structures such as the sciatic nerve.

Iliac spines definition

The ilium has four iliac spines: anterior superior, anterior inferior, posterior superior, and posterior inferior.

Anterior superior iliac spine (ASIS)

The ASIS is located at the anterior end of the iliac crest and is a key palpable landmark.

Auricular surface

The auricular surface is a roughened area of the ilium that articulates with the sacrum.

Auricular meaning

The term "auricular" refers to an ear-like shape.

Sacroiliac joint

The auricular surface of the ilium articulates with the sacrum to form the sacroiliac joint.

Ischium position

The ischium forms the posteroinferior region of the hip bone.

Ischial tuberosity

The ischial tuberosity is a large, roughened projection that supports body weight when sitting and serves as a hamstring attachment site.

Ischial ramus

The ischial ramus extends anteriorly and joins the inferior pubic ramus.

Ischiopubic ramus

The ischial ramus and inferior pubic ramus fuse to form the ischiopubic ramus.

Pubis position

The pubis forms the anterior portion of the hip bone.

Pubic body

The pubic body is the central portion of the pubis.

Symphyseal surface

The symphyseal surface is an oval medial surface that articulates with the opposite pubis.

Pubic symphysis

The pubic symphysis is a cartilaginous joint joining the left and right pubic bones.

Inferior pubic ramus

The inferior pubic ramus extends laterally and joins the ischial ramus.

Superior pubic ramus

The superior pubic ramus extends from the pubic body toward the ilium.

Hip joint type

The hip joint is a synovial ball-and-socket joint.

Hip joint articulation

The hip joint is formed between the acetabulum and the head of the femur.

Pelvic joint classification

Pelvic joints include synovial joints (hip, sacroiliac) and cartilaginous joints (pubic symphysis).

Sacroiliac joint classification

The sacroiliac joint is a strong, largely immobile synovial joint.

Pubic symphysis classification

The pubic symphysis is a cartilaginous joint allowing slight movement (amphiarthrosis).

Joint classification overview

Joints are classified structurally as fibrous, cartilaginous, or synovial.

Functional classification of joints

Joints are classified as synarthrosis (immovable), amphiarthrosis (slightly movable), or diarthrosis (freely movable).

Synovial joint definition

Synovial joints have a joint cavity and allow free movement.

Cartilaginous joint definition

Cartilaginous joints are joined by cartilage and allow limited movement.

Hip joint movement

The hip joint allows flexion, extension, abduction, adduction, rotation, and circumduction.

Flexion definition

Flexion decreases the angle between bones.

Extension definition

Extension increases the angle between bones.

Abduction definition

Movement away from the midline.

Adduction definition

Movement toward the midline.

Rotation definition

Movement around a longitudinal axis.

Circumduction definition

A circular movement combining multiple movements.