PHTY100 Lecture Notes - Lecture 11: Iliac Crest, Erector Spinae Muscles, Gluteus Medius Muscle
11. The pelvis
• Closed osteoarticular ring
o 4 bones
• 2x innominates
• Sacrum
• Coccyx
o 4 joints
• 2x sacroiliac
• Public symphysis
• Sacrococcygeal
• Male and female pelvis
o Inlet shape - round in female, heart shape in male
o Ischial spines everted in female
o Sacral promontory more prominent in male
o Sub-pubic angles greater in female
o Alar of the ilium wider in female
• 11.1 Orientate the pelvis in the anatomical position
o ASIS and the pubic tubercles are in the same coronal plane
o Inferior coccyx and superior pubic symphysis in the same horizontal plane
o The left and right ASIS are in the same transverse plane
o Pelvic brim faces anteriorly
• 11.2 State the functions of the pelvis
o Static postures: Pelvis houses and protects the pelvic contents; supports weight
of the head, trunk and arms; allows for weight transference from trunk to lower
limb, provides extensive muscle attachment sites.
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o Gait: Pelvic rotation during swing phase helps to position the foot forward. Pelvic
tilt downward on swing leg assists with shortening of leg.
o Pregnancy & childbirth: Pelvis supports the birth canal and provides exit for fetus.
• 11.3 Identify and classify the joints of the pelvis:
o pubic symphysis
• A fibrocartilaginous joint between the two medial symphyseal surfaces of the
pubic bones
• Supported by ligaments
o sacroiliac joints
• Synovial, plane joint
• Small gliding movements
• As we get older - lose movements
▪ Grooves, ridges, etc. form to lock bones together as we gain weight
• Weight-bearing joint
• Wedge shape of both bones allows for a stronger force to jam the bones into
each other for stability
• 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
▪ Complementary ridges and depressions interlock and aid joint stability
▪ Cavity obliterated with advancing age
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• 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:
o pubic symphysis
• Little to no movement between bones
▪ Exception is in pregnancy when the fibres soften under the influence of
hormones associated with pregnancy
o sacroiliac joint
• Movements
▪ Small magnitude gliding and rotation movements
• Anterior rotation of superior sacrum - nutation
• Anterior rotation of inferior sacrum - counternutation
• sacrospinous ligament
▪ Ischial spine to the sacrum
▪ Limit nutation
▪ Stabilizes sacrum on innominate by preventing forward tilting of
sacral promontory
• sacrotuberous ligament
▪ Ischial tuberosity to the sacrum
▪ Act like a sling to limit inferior displacement of the sacrum
▪ Stabilizes sacrum on innominate by preventing forward tilting of
sacral promontory
• sacroiliac ligaments (dorsal and ventral)
▪ Fibres arranged to resist downward movement of sacrum on ilium
▪ Dorsal
• Superficial to interosseous sacroiliac ligament
• Long
• Allow more movement
• Short
▪ Ventral
• Broad sheet of ligamentous material
• Fills the gap/indent
• interosseous sacroiliac ligament
▪ Short fibres
▪ Posterior sacrum to posterior ilium
• iliolumbar ligament
▪ Passes inferiorly and laterally from L5 to iliac crest
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Document Summary
The pelvis, closed osteoarticular ring, 4 bones, 2x innominates. Sacrum: coccyx, 4 joints, 2x sacroiliac, public symphysis. Inlet shape - round in female, heart shape in male. Little to no movement between bones: exception is in pregnancy when the fibres soften under the influence of hormones associated with pregnancy sacroiliac joint, movements. Small magnitude gliding and rotation movements: anterior rotation of superior sacrum - nutation, anterior rotation of inferior sacrum - counternutation sacrospinous ligament. Stabilizes sacrum on innominate by preventing forward tilting of sacral promontory sacrotuberous ligament. Ischial tuberosity to the sacrum: act like a sling to limit inferior displacement of the sacrum. Stabilizes sacrum on innominate by preventing forward tilting of sacral promontory sacroiliac ligaments (dorsal and ventral) Fibres arranged to resist downward movement of sacrum on ilium: dorsal, superficial to interosseous sacroiliac ligament, long, allow more movement, short, ventral, broad sheet of ligamentous material, fills the gap/indent interosseous sacroiliac ligament.
