Anatomy of the Pelvic Girdle

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Introduction

File:Interactive pelvis - pelvis and perineum - L8F36.jpg

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:

• Sacrum
• Coccyx
• Two innominate bones, which consist of the:
  • Ischium
  • Ilium
  • Pubis

• 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.
• 
  The shape of the female bony pelvis can be classified into four broad categories: gynecoid, anthropoid, android, and platypelloid.
  • Gynecoid/genuine pelvis
    • the brim is round, more 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.
• In women, the pelvis houses the uterus, tubes, ovaries and vagina.

Joint Articulations

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)

Other articulations:

The pelvis and femur articulate via the acetabulum

Symphysis Pubis Joint

• non-synovial amphi-arthrodial joint
• inter-pubic fibrocartilage disc
• less form closure than sacro-iliac joint

Sacroiliac Joint

• 
  diarthrodial joint
• held together by fibrous capsule and synovial fluid
• slightly moveable joint

For more information on the sacroiliac joint, read this Physiopedia page: Sacroiliac Joint

Sacrococcygeal 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

Iliolumbar Ligament

• 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 sacro-iliac articulation, contiguous with lumbodorsal fascia
• Strengthens the lumbo-sacral 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 lower border or 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

Ischio-sacral Ligaments

• Sacrotuberous Ligament
  • from sacrum to tuberosity of the ischium
  • PSIS to the 4th and 5th transversus tubercle of the sacrum and the lateral inferior border of the sacrum and coccyx
  • free concave border is attachment for obturator fascia
  • directly continuous with the long head of biceps femoris
  • posterior surface of ligament is also origin of gluteus maximus
• Sacrospinous Ligament
  • from the ischial spine to lateral margins of the sacrum
  • triangular in shape
  • broad base connected to sacrum and the coccyx
  • narrow section connected to the ischial spine
  • closely connected to coccygeus muscle

Sacroiliac Ligaments

• 
  Ventral/Anterior sacroiliac ligament
  • from antero-lateral aspect of the sacrum to 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

Sacrococcygeal Ligaments

• 
  Ventral/Anterior sacrococcygeal ligament
  • 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

Inguinal Ligament

• 
  runs from the ASIS to the pubic tubercle
• formed by the aponeurosis of the external oblique
• continuous with fascia lata of the thigh
• Superficial inguinal ring:
  • 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 ring

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:

Adductor brevis	Adductor longus	Adductor magnus	Biceps femoris - long head	Coccygeus
Erector Spinae	External oblique	Gluteus maxiumus	Gluteus medius	Gluteus minimus
Gracilis	Iliacus	Inferior gemellus	Internal oblique	Latissimus dorsi
Levator ani	Multifidus	Obturator internus	Obturator externus	Pectineus
Levator ani	Piriformis	Psoas minor	Pyramidalis	Quadratus femoris
Quadratus lumborum	Rectus abdominis	Rectus femoris	Sartorius	Semimembranosus
Semitendonosus	Sphincter urethrae	Superficial transverse perineal ischiocavernous	Superior gemellus	Tensor fascia lata
Transversus abdominus

Muscles of the Hip

• Gluteus maximus
  • primary stabilising muscle of the sacroiliac joint
  • often inhibited in people with low back pain, pelvic girdle pain or sacroiliac joint dysfunction
• 
  Gluteus medius
• Gluteus minimus
• Piriformis
• Superior gemellus
• Obturator Internus
• Inferior gemellus
• Quadratus femoris
• Iliopsoas
  • composed of psoas major and iliacus
  • primarily hip flexor
  • may assist in anterior pelvic tilt
  • also functions as external rotator of the hip
  • acts as pelvic and hip stabiliser, especially during single-leg stance
  • important to consider iliopsoas during any pelvic rehabilitation

Pelvic Floor Myology

Pelvic Floor

Pelvic Floor Muscles

Sacral and Coccygeal Plexus

Layer One - Urogenital Triangle

• Bulbocavernosus
• Ischiocavernosus
• 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.

• 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)
• Coccygeus
• Piriformis
• Obturator internus
• Arcus tendinous of 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.

Other muscles related to pelvic dysfunction

• Psoas
• Rectus abdominus
• Transversus abdominus
  
  

Muscle	Origin	Insertion	Action	Innervation
Bulbospongiosus	perineal body then divides to wrap around vagina	fascia of corpus cavernosa	empties urethra, acts as a sphincter to reduce lumen of vagina and assists erection of clitoris	Deep branch of perineal nerve (branch of pudendal nerve)
Ischiocavernosus	Ischial ramus and tuberosity	Crus of penis or clitoris	Maintains erection of penis or clitoris by compression of outflow veins	Deep branch of perineal nerve (branch of pudendal nerve)
Superficial transverse perineal	Ischial tuberosity	Perineal body	Reinforces action of deep transverse perineal muscle to stabilize perineal body	Deep branch of perineal nerve (branch of pudendal nerve)
External anal sphincter	Perineal body and encircles anal canal	Coccyx	Part of voluntary sphincter of anal canal	Inferior rectal (anal) nerve
Sphincter urethrae	Inferior aspect of pubic ramus and ischial tuberosity	Surrounds urethra; in females, some fibres also enclose the vagina	Controls flow of urine through urethra; also compresses vagina in females	Deep branch of perineal nerve (branch of pudendal nerve)
Compressor urethrae (only in females)	Ischiopubic ramus	Vaginal wall	Compresses ventral wall of the urethra
Sphincter urethral vaginalis (only in females)	Vaginal walls	Ventral surface of urethra	Compresses ventral wall of the urethra
Deep transverse perineal	Inner aspect of ischiopubic ramus	Median raphe (male), perineal body and external anal sphincter	Fixes perineal body, supports the function of levator ani and sphincter urethra	Deep branch of perineal nerve (branch of pudendal nerve)
Perineal membrane (fascial thickening, not a muscle)	Fasical attachments at pubic symphysis	Fascial attachments at ischial spine	Suspensory ligament that provides extra support to prevent descent of perineal body
Levator Ani (Pubococcygeus)	Dorsal surface of pubis and fascia of obturator internus	Anococcygeal body between tip of coccyx and the anal canal	Voluntary spincter of the anal canal	Nerve to levator ani (branches of S4), inferior rectal nerve (from pudendal nerve - S3, S4), coccygeal plexus
Levator Ani (Puborectalis)	Dorsal surface of pubis and  fascia of obturator internus	Unites with its partner to make a U-shaped sling around the rectum	Controls defecation by pulling anorectal junction forward	Nerve to levator ani (branches of S4), branch of pudendal nerve (S2-4)
Levator Ani (Pubovaginalis)				Nerve to levator ani (branches of S4), branch of pudendal nerve (S2-4)
Levator Ani (Iliococcygeus)	Posterior aspect of arcus tendineus levator ani and the ischial spine	Anococcygeal body and the coccyx	Helps to support pelvic viscera and lateral coccyx	Nerve to levator ani (branches of S4), inferior rectal nerve (from pudendal nerve - S3, S4), coccygeal plexus
Ischiococcygeus* (Coccygeus) *some consider this more of a ligament than a muscle	Ischial Spine	Lower two sacral and upper two coccygeal spinal segments, blends with sacrospinous ligament on its external surface	Supports pelvic viscera, flexion of coccyx, stabilizes sacro-iliac joint	Anterior rami of S4 and S5
Piriformis	Pelvic surface of sacrum, passes through greater sciatic foramen	Superior border of the greater trochanter of the femur	Hip external rotation, assist with hip abduction if hip is flexed	Anterior rami of S1 & S2
Obturator Internus	Internal or pelvic surface of the obturator foramen	Medial surface of the greater trochanter of the femur	Hip external rotation, assists with hip abduction if hip is flexed	Nerve to obturator internus (L5, S1, S2)
Arcus tendinous levator ani (fascial thickening, not a muscle)	Fasical attachments at pubic symphysis	Fascial attachments at ischial spine	Suspensory ligament that provides extra support to prevent descent of perineal body
Arcus tendinous fasciae pelvis (fascial thickening, not a muscle)	Fasical attachments at pubic symphysis	Fascial attachments at ischial spine	Suspensory ligament that provides extra support to prevent descent of perineal body

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