Anatomy of the Pelvic Girdle
- 1 Introduction
- 2 Osteology of the Pelvis
- 3 Ligaments of the Pelvis
- 4 Muscles of the Pelvis
- 5 References
The term "pelvis" is used to identify the area between the abdomen and the lower extremities. It can be divided into the greater pelvis and the lesser pelvis. The pelvis consists of the sacrum, the coccyx, the ischium, the ilium, and the pubis. The structure of the pelvis supports the contents of the abdomen while also helping to transfer the weight from the spine to the lower limbs. During gait, the joints within the pelvis work together to decrease the amount of force transferred from the ground and lower extremities to the spine and upper extremities.
Osteology of the Pelvis
The pelvic bones are:
- Two innominate bones, which consist of the:
- The inlet to the pelvic canal is at the level of the sacral promontory and superior aspect of the pubic bones.
- The outlet is formed by the pubic arch, ischial spines, sacrotuberous ligaments, and the coccyx.
- The enclosed space between the inlet and outlet is called the true pelvis, with the plane of the inlet being at right angles to the plane of the outlet.
- The female true pelvis differs from the male in being shallower, having straighter sides, a wider angle between the pubic rami at the symphysis, and a proportionately larger pelvic outlet.
- Gynecoid/genuine pelvis
- the brim is round, wider, and both ischial spines are less prominent this allows easy baby delivery.
- Android pelvis
- like a heart-shaped brim with narrow pelvic cavity than presented in gynecoid one, get narrower at the supra-pubic arch, and both ischial spines are prominent. During delivery, she needs to take an active role.
- Anthropoid pelvis
- oval brim, slightly narrower pelvic cavity than above with larger outlet diameter.
- Platypelloid pelvis
- shallow pelvic cavity, and decreased antero-posterior diameter, broad outlet, during labour there will be difficult for the baby to enter the pelvis at the beginning.
- Gynecoid/genuine pelvis
- In women, the pelvis houses the uterus, tubes, ovaries and vagina.
There are three articulations within the pelvis:
- Inferiorly between the sacrum and the coccyx
- Posteriorly between the sacrum and each ilium (sacroiliac (SI) joint)
- Anteriorly between the pubic bodies (pubic symphysis)
Symphysis Pubis Joint
- non-synovial amphiarthrodial joint
- inter-pubic fibrocartilage disc
- less form closure than sacroiliac joint
For more information on the sacroiliac joint, read this Physiopedia page: Sacroiliac Joint
- at apex of sacrum and coccyx
- amphiarthrodial joint between the base of the coccyx (concave) and the sacral apex (convex)
- Synovium present occasionally
- sacrococcygeal disc present
- slightly moveable joint, but movement decreases with age
Ligaments of the Pelvis
- from the tip of the transverse process of L5 to posterior aspect of the inner lip of iliac crest
- 2 main bands attach to the pelvis
- Lower band - attaches to base of sacrum, contiguous with anterior sacroiliac ligament
- Upper band - attaches to iliac crest anterior to the sacro-iliac articulation, contiguous with lumbodorsal fascia
- Strengthens the lumbosacral joint
- Anterior relationship with psoas major
- Posterior relationship with muscles in vertebral groove such a multifidus and erector spinae
- Superior relationship with quadratus lumborum
Lateral Lumbosacral Ligament
- partially continuous with the lower border of the iliolumbar ligament
- from the lower border of L5 transverse process to the ala of the sacrum
- intermingles with anterior sacroiliac ligament
- consists of bundles of fibres of varying strength
- Sacrotuberous Ligament
- from sacrum to tuberosity of the ischium
- PSIS to the 4th and 5th transverse tubercle of the sacrum and the lateral inferior border of the sacrum and coccyx
- the free concave border is an attachment for obturator fascia
- directly continuous with the long head of biceps femoris
- the posterior surface of the ligament is also the origin of gluteus maximus
- Sacrospinous Ligament
- Ventral/Anterior sacroiliac ligament
- from the anterolateral aspect of the sacrum to the auricular surface of the ilium
- Dorsal/Posterior sacroiliac ligament
- The upper portion (short posterior sacroiliac ligament) - from 1st and 2nd transverse tubercles of the sacrum to the tuberosity of ilium
- The lower portion (long posterior sacroiliac ligament) - from 3rd transverse tubercle of the sacrum to the posterior superior iliac spine (PSIS)
- Interosseous sacroiliac ligament- lies deep to posterior SI ligament and runs between the tuberosities of the sacrum and ilium
- from the anterior surface of sacrum to the front of the coccyx; continuation of the anterior longitudinal ligament of the spine
- Dorsal sacrococcygeal ligament
- Deep portion - from the inside sacral canal at the 5th sacral segment to the dorsal surface of the coccyx; continuation of the posterior longitudinal ligament of the spine
- Superficial portion - from free margin of sacral hiatus to dorsal surface of the coccyx; corresponds with the ligamentum flavum of the spine
- Lateral sacrococcygeal ligament
- from the inferior lateral angle of the sacrum to the transverse process of the 1st coccygeal vertebra
Pubic Symphysis Ligaments
- Superior pubic ligament - runs between pubic tubercles
- Inferior pubic ligament (aka arcuate pubic ligament) - runs between inferior pubic rami and blends with the fibrocartilaginous disc of the pubic symphysis
- Anterior pubic ligament
- Posterior pubic ligament - a membranous structure which blends with periosteum
- formed by the aponeurosis of the external oblique
- continuous with fascia lata of the thigh
- Superficial inguinal ring:
- the exit of the inguinal canal
- inguinal nerve
- genitofemoral nerve
- spermatic cord (males)
- round ligament (females)
- palpable under normal conditions
- dilated in athletic pubalgia
- inguinal hernia - abdominal contents may protrude through the ring
- the exit of the inguinal canal
Muscles of the Pelvis
There are 36 muscles that attach to the sacrum or innominates. The purpose of these muscles is primarily to provide stability to the joint not to produce movement.
Muscles that attach to the sacrum or innominates are:
Muscles of the Hip
- Gluteus maximus
- Gluteus minimus
- Superior gemellus
- Obturator Internus
- Inferior gemellus
- Quadratus femoris
- composed of psoas major and iliacus
- primarily hip flexor
- may assist in anterior pelvic tilt
- also functions as an external rotator of the hip
- acts as a pelvic and hip stabiliser, especially during single-leg stance
- important to consider iliopsoas during any pelvic rehabilitation
Muscles of the Back
- Quadratus Lumborum
- may play a role in functional scoliosis as a result of its attachments
Muscles of the Abdomen and Groin
- Rectus Abdominis
- External and Internal Obliques
- Transverse Abdominis
- Femoral Triangle
Muscles of the Abdominal Canister
Pelvic Floor Myology
Layer One - Urogenital Triangle
- Superficial transverse perineal
- External anal sphincter
Layer Two - Urogenital Diaphragm
The urogenital diaphragm, also called the triangular ligament, is a strong, muscular membrane that occupies the area between the symphysis pubis and ischial tuberosities and stretches across the triangular anterior portion of the pelvic outlet. The urogenital diaphragm is external and inferior to the pelvic diaphragm.
- The urethral sphincter (sphincter urethrae)
- Compressor urethrae
- Sphincter urethral vaginalis
- Deep transverse perineal
- Perineal membrane
Layer Three - Pelvic Diaphragm
The pelvic diaphragm is a wide but thin muscular layer of tissue that forms the inferior border of the abdominopelvic cavity. Composed of a broad, funnel-shaped sling of fascia and muscle, it extends from the symphysis pubis to the coccyx and from one lateral sidewall to the other.
- Levator Ani Muscle (pubococcygeus aka pubovisceral, pubovaginalis, puboanalis, puborectalis, iliococcygeus)
- Obturator internus
- Arcus tendinous of the levator ani
- Arcus tendinous fasciae pelvis
Perineal Body - a fibromuscular structure located between the vagina/testicles and the anus, attaching to the sides of the ischiopubis rami by the deep transverse perineal muscle. It is known as the central tendon of the pelvis because many pelvic floor structures intersect with the perineum at this structure.
For more information read this Physiopedia page on Pelvic Floor Anatomy
- Contributes to the health of the pelvic girdle by "pistoning" motion in produces in abdominal "canister"
- Attaches to 11th & 12th ribs and the costal cartilages 7 to 10, xiphoid process and lumbar vertebrae
- Centrally via R and L crura of the central tendon
- L1-3 intervertebral discs
- Physiological sphincter of the oesophagus
- The inferior surface of the pericardium
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