Pelvic Anatomy

Pelvic anatomy is a high-yield area for finals, especially in obstetrics, gynaecology, urology, and general surgery. You need to understand the bony pelvis for childbirth and fracture management, the pelvic floor for continence and prolapse, and the visceral relationships for surgical safety. The pelvis is divided into the 'Greater (False) Pelvis' (above the pelvic brim) and 'Lesser (True) Pelvis' (below the brim). The pelvic brim is a key anatomical landmark, defining the pelvic inlet. The pelvic floor is a muscular diaphragm crucial for supporting pelvic viscera and maintaining continence. Key viscera include the bladder, rectum, and reproductive organs, which differ significantly between sexes.

The bony pelvis, comprising the two hip bones, sacrum, and coccyx, forms a protective basin. Its morphology varies by sex, impacting obstetric outcomes. The pelvic inlet (brim) and outlet are crucial for understanding labour mechanics. The pelvic floor, primarily the Levator Ani, acts as a dynamic sling, supporting organs against gravity and intra-abdominal pressure. Its integrity is vital for continence. Autonomic innervation to the pelvic viscera dictates function: parasympathetics (S2-S4 pelvic splanchnics) promote micturition and erection, while sympathetics (T10-L2) inhibit these and facilitate ejaculation. The pudendal nerve (S2-S4) provides somatic sensation to the perineum and motor control to the external anal and urethral sphincters, making it key for voluntary continence. The ureters enter the pelvis at the common iliac artery bifurcation, running retroperitoneally to the bladder, a course that puts them at risk during pelvic surgery.

Pelvic floor dysfunction is a common presentation, leading to stress urinary incontinence, faecal incontinence, or pelvic organ prolapse (e.g., cystocele, rectocele, uterine prolapse). Understanding the anatomy of the Pouch of Douglas is vital as it's the most dependent part of the peritoneal cavity, prone to fluid accumulation (e.g., in ruptured ectopic pregnancy, ascites), and accessible via culdocentesis. Ectopic pregnancies most commonly occur in the fallopian tubes. Prostate cancer, often arising in the peripheral zone, is palpable on digital rectal examination. During gynaecological surgery, particularly hysterectomy, the ureter is highly vulnerable to injury when clamping the uterine artery ('water under the bridge'). Pelvic fractures, especially 'open book' fractures, can cause life-threatening haemorrhage due to damage to the rich internal iliac venous plexus. For obstetricians, knowledge of pelvic diameters and planes is fundamental for assessing the progress of labour and predicting potential difficulties.

For pelvic pathology, transvaginal (TVS) or transabdominal ultrasound (TAS) is often the first-line imaging modality for assessing uterine, ovarian, and bladder pathology. MRI pelvis is the gold standard for detailed soft tissue imaging, crucial for staging gynaecological and rectal cancers, and assessing complex pelvic floor dysfunction. Cystoscopy allows direct visualisation of the bladder and urethra. Urodynamic studies are essential for investigating the causes of urinary incontinence and voiding dysfunction. Digital rectal examination (DRE) is a key clinical investigation for assessing the prostate in males and the posterior pelvic floor/rectum in both sexes. Speculum and bimanual examination are vital for assessing female pelvic organs and identifying prolapse.

Pelvic floor muscle training (Kegel exercises) is the first-line conservative management for mild to moderate stress urinary incontinence and pelvic organ prolapse. Surgical interventions range from prolapse repair (e.g., sacrocolpopexy, colporrhaphy) to hysterectomy for uterine pathology or cancer. Pelvic fractures require urgent stabilisation, often with a pelvic binder, and may necessitate angiographic embolisation or surgical fixation for severe haemorrhage. Management of pelvic pain or dysfunction often involves a multidisciplinary approach.