Pelvis and Perineum

• Greater pelvis

  • Protects the lower abdominal viscera
• Lesser pelvis


  • Provides the skeletal framework for both the pelvic cavity and the perineum; both being separated by the pelvic diaphragm
• Components of the pelvis

  • Bony pelvis
  • Pelvic joints
  • Pelvic ligaments
  • Pelvic muscles, fascia, walls, vessels & nerves
• Bony pelvis


  Composed of four bones: Two pelvic bones, Sacrum, Coccyx
• Hip bone


  • Composed of three parts: Ilium, Ischium, Pubis. The two hip bones articulate with each other anteriorly at the symphysis pubis and posteriorly with the sacrum at the sacroiliac joints.
• Obturator foramen


  • Large foramen inferior to the acetabulum
• Posterior margin of the hip bone

  • Marked by two notches separated by the ischial spine: Greater sciatic notch, Lesser sciatic notch
• Ilium


  • The upper flattened part. It has: Iliac crest, Anterior iliac spines(superior & inferior), Posterior iliac spines(superior & inferior), Auricular surface(articulates with sacrum), Iliopectineal line
• Ischium


  • Has the following: Body, Ischial spine, Ischial tuberosity, Ischial ramus
• Pubis


  • Has the following: Body which has pubic crest & pubic tubercle, Superior and inferior rami
• Sacrum


  • Consists of five rudimentary vertebrae fused together. It articulates above with the 5th lumbar vertebra, below with the coccyx, and laterally with the two iliac bones to form the sacroiliac joints. It has the following: Sacral promontory, Ala, Sacral canal, Sacral hiatus, Anterior and posterior sacral foramina
• False pelvis


  The part of the pelvis above the pelvic brim, which forms part of the abdominal cavity
• True pelvis


  The part of the pelvis below the pelvic brim
• False pelvis


  • Bounded by: Anteriorly - lower part of the anterior abdominal wall, Laterally - Iliac fossae and the iliacus, Posteriorly - L5 & S1 vertebrae
• True pelvis


  • Bounded by the pelvic surfaces of the hip bones, sacrum, and coccyx. Limited inferiorly by the musculofascial pelvic diaphragm. It has an inlet, an outlet, and a cavity.
• Pelvic inlet/brim


  • Anteriorly - Symphysis pubis, Posteriorly - Promontory of sacrum, ala of sacrum, Laterally - Ileopectineal (arcuate) lines
• Pelvic outlet


  • Anteriorly - Symphysis pubis, Posteriorly - Coccyx, Anterolaterally - ischiopubic ramus, Posterolaterally - Sacrotuberous ligament
• Pelvic cavity


  • The space between the inlet and the outlet. It is a short, curved canal, with a shallow anterior wall and a much deeper posterior wall. Has 3 walls & 1 floor
• Anterior pelvic wall


  • Formed primarily by the bodies and rami of the pubic bones and the pubic symphysis
• Lateral pelvic walls


  • Formed by the hip bones and the obturator internus muscles
• Posterior pelvic wall


  • Formed by the sacrum and coccyx, adjacent parts of the ilia, and the S-I joints; piriformis muscle covers the area
• Piriformis


  • Origin: Pelvic surface of the middle 3 sacral vertebrae, Insertion: Greater trochanter of the femur, Action: Lateral rotator of the femur at the hip joint, Nerve supply: Sacral plexus
• Obturator internus


  • Origin: Inner surface of the obturator membrane and the hip bone, Insertion: It leaves the pelvis through the lesser sciatic foramen to be inserted into the greater trochanter of the femur, Action: Lateral rotator of the femur at the hip joint, Nerve supply: Nerve to obturator internus
• Pelvic floor/diaphragm


  • Formed by the funnel shaped pelvic diaphragm – consists of the levator ani and coccygeus muscles and their fascia. Stretches between the pubis anteriorly and the coccyx posteriorly and from one lateral pelvic wall to the other. It is incomplete anteriorly to allow passage of the urethra in males and the urethra and the vagina in females.
• Types/shapes of female pelvis


  • Gynecoid
  • Anthropoid
  • Android
  • Platypelloid
• Gynecoid pelvis


  • Typical female pelvis found in 50% of women. Rounded—slightly oval inlet, Straight pelvic sidewalls with roomy pelvic cavity, Good sacral curve, Ischial spines are not prominent, Pubic arch is wide
• Anthropoid pelvis


  • Found in 25% white women & 50% nonwhite. Pelvic brim APD > TD, Long & narrow pelvic canal with long sacrum, Straight pelvic sidewalls
• Android pelvis


  • Typical male pelvis found in 1/3 white women 1/6 non-white. Pelvic brim is heart shaped, Pelvis funnels from above downwards (convergent sidewalls), Narrow pubic arch, Prominent spines
• Platypelloid pelvis


  • Found in 3% of women. Pelvic brim TD >>> APD, Kidney shape, Sacral promontory pushed forwards
• Pubic symphysis


  • Secondary cartilagenous joint. Articular surface of medial aspect of body of pubis. Covered with hyaline articular cartilage. Disc of fibro-cartilage in between. A cavity may develop in the disc but it is not lined with synovial membrane. There is normally very little movement at the pubic symphysis, except during the latter months of pregnancy.
• Lumbosacral joints


  • Formed between vertebra L5 and the sacrum. Consist of: Two zygapophysial joints are between the inferior and superior articular processes, Intervertebral disc that joins the bodies of vertebrae LV and SI. Reinforced by: Iliolumbar ligament, lumbosacral ligament.
• Sacroiliac joints


  • Synovial joints. Stabilized by: Anterior sacro-iliac ligament, Interosseous sacro-iliac ligament(strongest), Posterior sacro-iliac ligament, Sacrotuberous and Sacrospinous ligaments.
• Pelvic ligaments


  • Sacrotuberous
  • Sacrospinous
  • Sacroiliac & Sacrococcygeal
  • Cardinal ligament
  • Lateral ligament of the rectum
  • Waldyer's fascia
• Pubic symphysis


  Secondary cartilagenous joint, articular surface of medial aspect of body of pubis, covered with hyaline articular cartilage, disc of fibro-cartilage in between, a cavity may develop in the disc but it is not lined with synovial membrane, there is normally very little movement at the pubic symphysis, except during the latter months of pregnancy
• Lumbosacral joints


  Formed between vertebra L5 and the sacrum, consist of two zygapophysial joints between the inferior and superior articular processes, intervertebral disc that joins the bodies of vertebrae LV and SI, reinforced by iliolumbar ligament and lumbosacral ligament, synovial joints
• Sacroiliac joints


  Each sacro-iliac joint is stabilized by the anterior sacro-iliac ligament, interosseous sacro-iliac ligament (strongest), posterior sacro-iliac ligament, sacrotuberous and sacrospinous ligaments
• Pelvic ligaments


  • Sacrotuberous
  • Sacrospinous
  • Sacroiliac & Sacrococcygeal
  • Cardinal ligament
  • Lateral ligament of the rectum
  • Waldyer's fascia
• Pelvic muscles


  • Iliacus & psoas (above the brim)
  • Obturator internus & its fascia (sidewalls)
  • Pyriformis (posterior wall)
  • Levator ani & coccygeus (pelvic floor)
• Levator ani muscle


  Wide thin sheet-like muscle, consists of three parts - pubococcygeus, puborectalis and iliococcygeus, originates from the body of the pubis, tendinous arch of the obturator fascia and the ischial spine, inserts into the perineal body, coccyx, anococcygeal ligament, walls of the prostate or vagina, rectum and anal canal, innervated by the nerve to levator ani from S4 and the inferior anal (rectal) nerve from S2-S4 and the coccygeal plexus, helps to support the pelvic viscera, acting together they raise the pelvic floor and assist the abdominal muscles in forced expiration activities
• Levator ani muscle parts


  • Pubococcygeus
  • Iliococcygeus
  • Puborectalis