PHTY100 Lecture Notes - Lecture 11: Pelvic Outlet, Pelvic Inlet, Pelvic Cavity
The Pelvis
11.1 Orientate the pelvis in the anatomical position
In the anatomical position –
• ASIS and the pubic tubercles are in the same coronal plane
• inferior coccyx and superior pubic symphysis in the same horizontal plane
• the left and right ASIS are in the same transverse plane
• pelvic brim faces anteriorly
11.2 State the functions of the pelvis
•houses and protects the pelvic contents
•supports the weight of the head, trunk and arms
•allows for weight transference from trunk to lower limb
•supports the birth canal and provides an exit for the foetus
•provides extensive muscle attachment sites
11.3 Identify and classify the joints of the pelvis:
•Pubic symphysis
•a fibrocartilaginous joint between the two medial symphyseal surfaces of the pubic bones
•supported by ligaments
•Sacroiliac joints
•synovial, plane joint
•between the auricular surface of the ilium and the corresponding surface of the sacrum
•joint surfaces are smooth in infants, but develop a series of complementary ridges and
depressions with age, more marked in male than female
11.4 State the movements available at, and identify and state the mechanical function(s) of
each of the ligaments of the joints of the pelvis:
•Pubic symphysis
•little to no movement between bones
•Sacroiliac joint
•small magnitude gliding and rotation movements
anterior rotation of superior sacrum - nutation
anterior rotation of inferior sacrum -
counternutation
•Sacrospinous ligament
•Sacrotuberous ligament
•Sacroiliac ligament (dorsal and ventral)
•Interrosseous sacroiliac ligament
•Iliolumbar ligament
11.5 Describe the different forces acting on the
joints of the pelvis and explain the mechanisms
which ensure their stability
Weight transfer through pelvis:
Sacrum is pushed down into the space between the
innominate bones (shear force) - wedging of sacrum
between the ilia and interlocking of the irregularity of the
articular surfaces. Sacroiliac ligaments restrict tendency of ilia
to move laterally. Superior sacrum tends to rotate
forward between the innominate bones (torsional force) -
resisted by the sacrotuberous and sacrospinous ligaments.
Function: prevent the posterior rotation of the lower sacrum
associated with weight bearing.
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