--- module: 079-01 language: en chapter: 79 title: "Pelvic, Perineal, Reproductive, and Urinary Anatomy" module_title: "Bony pelvis, pelvic walls, pelvic floor, fascia, vessels, and nerves" source_sha256: 9c9d535ecc3a354d904f9cb1ce4a8a860f759a97720d5b1a3a8dcd7a0cf1fe14 --- # Bony pelvis, walls, floor, fascia, vessels, and nerves ## The pelvic ring ### Hip bone: ilium, ischium, pubis fused at acetabulum ### Symphysis anteriorly, sacroiliac joints posteriorly #### Closed ring: one break, look for another ### Brim separates greater from lesser pelvis #### Inlet in plane of brim #### Outlet: pubic arch, tuberosities, sacrotuberous, coccyx ### Sacrospinous, sacrotuberous ligaments #### Convert notches into foramina #### Resist sacral rotation ### Sacroiliac joint: synovial front, posterior syndesmosis #### Weight wedges sacrum between ilia ### Ring injury by force and stability #### AP compression opens symphysis and sacroiliac #### Lateral compression buckles hemipelvis #### Vertical shear disrupts posterior support #### Bleeding from bone, venous plexuses, arteries #### Assess urethra, bladder, rectum, plexus, vessels ### Symphysis: secondary cartilaginous joint #### Pregnancy widening modest, trauma destabilises ## Dimensions and variation ### Inlet, midpelvis, outlet influence childbirth #### No single measurement predicts birth mechanics #### Moulding, position, soft tissue, uterine force ### Sex-associated average differences overlap #### Age, ancestry, stature, activity, nutrition #### Answer a clinical question, not identity ### Obstetric conjugate not directly measurable #### Diagonal conjugate estimates it ### Interspinous distance: midpelvic transverse ## Lateral and posterior walls ### Lateral: obturator membrane, obturator internus #### Obturator canal to medial thigh ### Posterior: sacrum, coccyx, piriformis, ligaments ### Piriformis divides greater sciatic foramen #### Superior gluteal vessels and nerve above #### Sciatic, inferior gluteal, pudendal below ### Pudendal nerve curves round ischial spine #### Enables nerve block #### Vulnerable in childbirth and surgery ## Pelvic diaphragm ### Levator ani and coccygeus with fascia ### Puborectalis, pubococcygeus, iliococcygeus ### Puborectalis sling at anorectal junction #### Keeps anorectal angle at rest #### Relaxes during defecation ### Levator supports viscera, resists pressure ### Hiatus: urethra, vagina, anorectal canal #### Necessary weak region, changes with loading ### Sacral plexus branches, pudendal to sphincters ### Excess tone: pain, voiding difficulty ### Weakness: prolapse, incontinence ## Endopelvic fascia and support ### Parietal fascia on walls, visceral on organs ### Loose planes permit filling and dissection #### Also transmit vessels and spread ### Cardinal, uterosacral: cervix and upper vagina ### Puboprostatic, pubovesical: bladder neck ### Perineal body: central fibromuscular node #### Injury weakens posterior wall and continence ### Prolapse: multi-component support failure #### Descent does not map perfectly to symptoms #### Repair integrated support, not one defect ## Internal iliac vessels ### Posterior division: iliolumbar, lateral sacral, superior gluteal ### Anterior division: viscera, perineum, gluteal region ### Extensive anastomoses across midline ### Uterine artery crosses above ureter ### Corona mortis crosses superior pubic ramus ### Valveless venous plexuses #### Communicate with vertebral plexus #### Collapse poorly, bleeding diffuse ## Somatic and autonomic nerves ### Sacral plexus on piriformis #### Masses, childbirth, surgery affect many nerves ### Sympathetics via hypogastric plexuses ### Pelvic splanchnic nerves S2 to S4, parasympathetic ### Pudendal nerve S2 to S4, somatic #### Do not confuse despite shared roots ### Pelvic pain line #### Above: sympathetic, thoracolumbar levels #### Below: parasympathetic, sacral levels ## Pelvic spaces ### Retropubic space: surgical access ### Paravesical, pararectal: vessels, nerves, ureters ### Presacral: autonomic plexus, vessels ### Extraperitoneal bleeding spreads widely ### Infection and tumour follow fascial planes ### Imaging defines sidewall, floor, peritoneum, ureter