General Features of the Pelvis

General Functions of the Pelvis

·       Bear the weight of the upper body when sitting or standing.

·       Transfer weight from the axial to the lower appendicular skeleton for standing and walking.

·       Provide attachment for the powerful muscles of locomotion and posture.

·       It contains the pelvic viscera (inferior parts of the urinary tracts and the internal reproductive organs) and inferior abdominal viscera (intestines).

·       Birth canal in women expands for the passage of the fetus.

Walls of the Pelvis

·       Anterior Wall: Pubic bone; Pubic symphysis

·       Lateral Wall: Hip bone below the pelvic inlet; Obturator membrane; Obturator internus muscle (Refer slides for OAIN)

·       Posterior Wall: Sacrum and coccyx; Piriformis muscle (Refer slides for OAIN)

Membranes and Ligaments of the Pelvis

·       Obturator Membrane: Fibrous sheet that almost completely encloses the obturator foramen. Leaves a small gap (Obturator canal) for the passage of the obturator nerve and vessels.

·       Sacrotuberous and Sacrospinous ligaments

·       Sacrotuberous - Strong ligament extending from the lateral part of the sacrum and coccyx to the ischial tuberosity.

·       Sacrospinous Ligament - Strong ligament extending from the lateral part of the sacrum and coccyx to the ischial spine.

·       Functions: The sacrotuberous and sacrospinous ligaments prevent the lower end of the sacrum and coccyx from being rotated upward at the sacroiliac joint by the weight of the body. They also convert the greater and lesser sciatic notches into the greater and lesser sciatic foramina.

General Features of the Pelvis and definitions of common terminology

·       Borders of the Pelvis

o   Pelvic Inlet (Superior pelvic aperture, Pelvic brim)

§  Pubic symphysis and crest

§  Arcuate and pectineal lines (pecten pubis)

§  Sacral promontory

o   Pelvic Outlet (Inferior pelvic aperture)

§  Pubic symphysis

§  Ischiopubic ramus

§  Ischial tuberosities

§  Sacrotuberous ligaments

§  Coccyx

·       Pelvic Diaphragm - Separates pelvis from the perineum below.

·       Pubic Tubercles and the ASIS - are located on the same vertical plane in the anatomical position.

Sex Differences of the Pelvis:

·       The sexual differences of the male and female pelvis are due mainly to the heavier build and larger muscles of men and to the adaptation of the female pelvis for childbearing.

·       Therefore, the male pelvis is heavier and thicker and has more prominent bone markings and the female pelvis is wider, shallower, and has a larger pelvic inlet and outlet.

·       Major differences can be seen in:

o   Shape of the Pelvic Inlet

o   Density of bone

o   Shape and size of pelvic cavity

o   Subpubic Angles

o   Shape and size of Sacrum

The Pelvic Fascia:

·       Parietal Pelvic Fascia:

o   Continuous above with the endo-abdominal fascia lining the abdominal wall.

o   Named according to the underlying muscle (e.g., Obturator internus fascia)

o   Note:  Arcus Tendinous - Thickening of the obturator internus fascia, important as the origin of a large portion of the levator ani muscle.

·       Visceral Pelvic Fascia - looser connective tissue investing the pelvic viscera (e.g., bladder, vagina, uterus, rectum).

·       Subperitoneal Pelvic Fascia:

o   Continuation of the extraperitoneal fascia from the abdomen into the pelvis.

o   Special thickenings of the fascia form ligaments. Ex: Females - Pubovesical ligaments, Transverse cervical ligaments (Cardinal ligaments, Mackenrodt’s ligament), Sacrouterine ligament

·       All ligaments blend medially with the visceral fascia of either the prostate, bladder, vagina or cervix and laterally with the parietal pelvic fascia.