Joints of the Pelvis

Pelvis structure

Basin or bowl shaped, right and left hip bones with sacrum wedged between

Joints of pelvis

Two hip joints, pubic symphysis, two sacroiliac joints

Orientation of pelvis

asis and pubic tubercle line up in same coronal plane, inferior tip of sacrum/base of coccyx lies just superior to pubic symphysis in transverse plane, right and left asis line up in transverse plane, pelvis brim faces anteriorly, acetabulum is directed inferolaterally

Functions of pelvis

Support and protect pelvis viscera and lower abdominal viscera, provides bony support for birth canal, provides extensive muscle attachment sites, supports weight of head/trunk/upper limbs, allows for weight transfer

Pelvic inlet

Pubic crest, pectineal line, arcuate line, sacral alar and promontory

True pelvis

Any structure inferior to pelvic inlet

False pelvis

Any structure superior to pelvic inlet

Pelvic outlet

Apex of coccyx, ischial tuberosities, pubic symphysis (inferior edge)

Male pelvis

Heart shaped inlet, ischial tuberosities close together, prominent sacral promontory, smaller sub pubic angles, narrow alar of ilium

Female pelvis

Round shaped inlet, ischial tuberosities further apart, less prominent sacral promontory, greater sub pubic angles, wider alar of ilium

Pubic symphysis joint

Secondary cartilaginous joint between symphyseal surfaces of pubic bones, fibrocartilage disc supported by ligaments, limited movement - exception during pregnancy

Sacroiliac joint classification

Anteriorly = synovial, multiaxial plane, posteriorly = fibrous joint - due to massive interosseous ligaments, limited movement with a large amount of stability

Auricular surface of pelvis

Smooth in infants, develops a series of complementary ridges and depressions with age, interlock and aid joint stability, joint cavity obliterated with advancing age

Sacroiliac joint surfaces

Articular surfaces (synovial part) = auricular surface of ilium and auricular surface of sacrum, tuberosities for fibrous part of joint

Anterior sacroiliac ligaments

Anterior sacroiliac ligament, iliolumbar ligament, interosseous sacroiliac ligament

Posterior sacroiliac ligament

Posterior sacroiliac ligament (long and short fibres), sacrotuberous ligament, sacrospinous ligament

Weight transfer in pelvis

From trunk to lower limb, weight to femurs when standing, weight to ischial tuberosities when sitting

Weight transfer through pelvis

Sacrum pushed down into space between innominate bones, wedging of sacrum and interlocking of ridged articular surfaces increases stability, sacroiliac ligaments resists tendency of ilia to move laterally, prevents sacrum from omv

Weight transfer through pelvis (torsional force)

Superior sacrum tends to rotate forwards between innominate bones, resisted by sacrotuberous and sacrospinous ligaments, limits posterior rotation of the lower sacrum