Regional Anatomy 2

Demonstrate a general understanding of the concept of 'Anatomical Ring' structures.

• Identify main bones, bony features, joints and ligaments of the

pelvic girdle and explain their function.

• Describe the inlet and outlet of the pelvis.

• Discuss the differences in male and female pelvis

• Inlet: Pomontry > Sacral ala > arcuate line > Pectin pubic > pubic crest > pubic symphysis

• Outlet: Sacrum & coccyx > sacrotubrous ligament > pubic arch > ischial tuberosity

• The ring shape of the pelvis is vulnerable to injuries

• High energy force on once side of the ring always > '# or ligament lesion on opposite site (polo mint)

• Low energy forces e.g oestoporotic / stress or avulsion # would usually lead to break at one point only.

  • Avulsion fractures are common in young athletes aged between 11-16, predominantly in males. They usually occur at the insertion of tendons.

3 bones makes up the pelvis

• Right and left innominate/pelvic bone, sacrum & coccyx

Joints

• Right and left sacroiliac joint - posteriorly joins the pelvic bones to sacrum

• pubic symphysis - anteriorly joins 2 pelvic bones

• Male - heart shaped , acute pubic arch, more prominent ischial spine

• Female - oval inlet, wider pubic arch, less prominent ischial spine

• Secondary cartilaginous joint - between 2 pubic bodies

• Articular surfaces covered by hyaline cartilage and linked across midline by fibrocartilage

• Stabilised by 2 ligaments:

  • superior and inferior pubic ligaments

• Plane synovial joint between L shaped articular facets on lateral surface of sacrum & facets on iliac part of pelvic bone

• Joint has irregular contour and interlocks to resist movement

• Becomes fibrous with age & may ossify

• Stablised by 3 ligaments:

  • Anterior sacro-iliac ligament

  • Posterior sacro-iliac ligament

  • Interosseous sacro-iliac ligament

Sacrotuberous ligament

• Broad based ligament - attached to posterior superior iliac spine, posterior sacroiliac ligament, lateral sacral crest, lateral margins of caudal sacrum & crainal coccyx

• Prevents upward tilting of pelvis, resists shear & flexion

Sacrospinous ligaments

• Resists external rotation

• Attached to ischial spine & lateral margins of sacrum & coccyx anterior to sacrotuberous ligament

• Pudental nerve (supplies perineal sensation & external sphincters) - crosses ischial spine > perineum

Group of ligaments important for pelvic ring stability. Strongest ligaments in the body.

• Interosseous sacroiliac ligaments

  • Resists anterior-posterior translation of pelvis

• Posterior sacroiliac

  • Resists cephalad-caudad displacement of pelvis (up-down)

• Iliolumbar

  • Resists rotation and augment posterior SI ligament

> Common iliac veins join together at L5 making IVC

> Iliac vessels originate from the common iliac system beginning near L4 at the bifurcation of abdominal aorta

• EIA courses anteriorly along pelvic brim - emerging as common femoral artery distal to inguinal ligament

• IIA dives posteriorly near sacro-liac joint - divides into posterior (superior gluteal artery) and anterior (obturator artery) division.

• Corona mortis - a connection between obturator & external iliac artery - located in some on the superior pubic ramus

  • Subject to damage during pelvic # (crown of death)

> Venous plexus in posterior pelvis > 90% of bleed associate with pelvic ring injuries

• Superior hypogastric plexus - plexus of nerves at lower 1/3rd of L5 and upper 1/3rd of S1 vertebra

  • it is retro-peritoneal, lies anterior to bifurcation of AA

  • From this plexus, sympathetic fibres are carried into pelvis through R and L hypogastric nerves.

  • Also contains parasympathetic fibres which arise from pelvic splanchnic nerves (S2-S4) and ascends from inferior hypogastric plexus.

OTA classificaton incorporates mechanism of injury, degree of pelvic instability and site of injury

• Type A: stable injuries with intact posterior pelvic ring and pelvic floor

• Type B: complete disruptions of the anterior pelvic ring but incomplete disruption of the posterior ring

• Type C: rotationally and vertically unstable injuries

Isolated stable pelvic # can occur in lower energy mechanism or sports injuries:

• Acetabular #, pubic ramus #, iliac wing and avulsion #

• List the structures present in the pelvic cavity in males

• Describe pelvic fascia & peritoneal spaces related to the organs

• Explain the anatomy of male pelvic viscera

• correlate the anatomy with clinical findings in pathological conditions

• Parts of GI tract - sigmoid colon, rectum & anal canal

  • Sigmoid colon is completely intraperitoneal - connected to posterior abdominal wall by sigmoid mesocolon

  • Rectum is retroperitoneal (transitions at S3 level) - structures below are located anterior to rectum.

• Parts of urinary tract - bladder and urethra

  • Bladder is the most anterior viscera in pelvic cavity

• Reproductive system - prostate, seminal vesicles & ducts

  • Prostate is located inferior to bladder - beginning at neck of urethra which penetrates the prostate > underneath pubic none > penis

    
    

The parietal peritoneum reflects on the superior surface of the bladder > descends into posterior surface > anterior surface of the rectum.

• This reflection forms the Rectovesical pouch

• Either side of the rectum are gutters - these are the pararectal fossae.

Pic: superior view

1. The peritoneum around this area of the abominal wall is attached loosly - this is to allow bladder to expand up when it is full.

2. The peritoneum then reflects to cover superficial surface of the badder creating supravesical fossa around 2

1. It descends posteriorly, then 5. laterally forms folds over the ureters & deferense

1. Refects from bladder & seminal glands > rectum = creates rectovesical pouch.

Membranous fascia and the endopelvic fascia

-> Pelvic fascia forms a CT layer between pelvic viscera (internal organs) & the skeletal muscles forming lateral walls & floor of pelvis.

-> Membranous fascia also divided into:

• Parietal pelvic fascia (covers pelvic muscles of floor & lateral wall) - Obturator fascia (obturator internus), pririformis fascia (piriformis muscle), superior fascia over pelvic diaphragm (levator ani) and presacral fascia (in from of sacrum)

• Visceral pelvic fascia (covers pelvic organs)

-> Endopelvic fascia

• fills the subperitoneal space between the parietal & visceral membranous fascia > stronger condensation that support rectum & urinary bladder in men.

• Condensations can be in the form of ligaments > supports & holds organs to pelvic wall

• Superiorly – urinary bladder

• Inferiorly – deep perineal pouch & external urethral sphincter

• Anteriorly – Pubic symphysis (this is the rectopubic space, containing the vesical venous plexus which drains the bladder, the prostatic venous plexus, draining the prostate and the dorsal vein of penis, draining the penis)

• Posteriorly – seminal vesicle, end of vas deferens, and rectum

• Laterally – levator ani (pelvic diaphragm) + prostatic venous plexus

Note: Prostate is penetrated by urethra & ejaculatory ducts (formed by union of ~30 glands) which pass into prostatic urethra. Within prostatic urethra, there is prostatic utricle which is a rudimentary uterus.

This divides the prostate into number of zones:

• Central zone - located behind the prostatic urethra, pierced by the left and right ejaculatory ducts

• Transitional zone - surrounding the prostatic urethra. Its the site of BPH

• Anterior fibromuscular zone - this zone is devoid of glandular tissue, contains only fibromuscular stroma

• Peripheral zone - constitutes the periphery of the prostate. Its where Ca prostate originates

Blood supply

• Inferior vesicle artery (branch of internal iliac artery) - supplies inferior part of the bladder, prostate & seminal vesicle.

  • Some supply comes from middle & inferial rectal + pudental arteries

• Venous return is via prostatic venous plexus on either side of prostate > drains into inferior vesicle vein > IVC

  • This plexus have communication with bladder & internal vertebral plexus which is located around lumbar vertebrae - 1st mets from prostate Ca goes to lumbar vertebrae due to this communication.

Cavernous nerves

• These nerves are resposible for blood flow necessary for erection

• Inferior hypogastric plexus (pelvic plexus) is a paired autonomic plexus - gives raise to prostatic plexus (male) & uterovaginal plexus (femae)

• The inferior hypogastric plexus lies on the anterior surface of the rectum & gives branches to the prostate, bladder, urethra, seminal glands, rectum, and corpora cavernosa (bodies of the penis) via the cavernous nerves.

  • This plexus is ANS supplying both sympathetic & parasympathetic innervation to pelvic structures

• The cavernous nerves continue downwards, lying posterolateral to the prostate. They may be injured during radical prostatectomy, resulting in impotence

Note: Vas deference start from the tail of epidimis at posterior testicles. It croses above the terminal of the ureter > joins the seminal vesicle (both lie superior to prostate gland) to form ejaculation duct

• Produce an alkaline secretion that forms part of the semen

• This secretion is important in reproduction as it neutralise the acidic environment of the female vagina.

• Acidic evironment can also affect the sperm so it helps to neutralise it.

The seminal vesicles have the following relations:

• Anterior - urinary bladder

  Superomedial - ampulla of vas deferens

  Medial - ejaculatory ducts

  Inferior - prostate gland

  Posterior - rectum, rectovasical fascia

-> There are R & L vesicles, lie lateral to vas deferens.

-> Their ducts joins the terminal part of vas deferencs & pierces the posterior aspect of prostate to form 2 ejaculatory ducts

-> Blood supply (same as prostate) is by inferior vesicle artery, nerve supply by inferior hypogastric plexus.

-> Seminal vesicles produce fructose (energy source) & prostaglandin (regulate smooth muscles) - these help the spermatozoa advance.

-> Function - production / contribution to seminal fluid

Beningn prostatic hyperplasia

• Enlargement of glandular tissues of prostate mostly in the transitional zone > compress the prostatic urethra > difficulty / frequency micturation, incomplete emptying of bladder > urgency, dribbling & nocturnia

• Occurs in older men. DRE -> firm & smooth

• Rx: TuRP by inserting cystoscopy via prostatic urethra, incision made, tissue removed to relieve compression

Prostate cancer

• Usually arises from peripheral zone (Adenocarcinoma )= urinary Sx occurs later stage as this zone is far from urethra.

• Sx pelvic or back pain (mets to lumbar spine)

• DRE -> hard, irregular. Bloods -> raised PSA

• Rx: staging, bipsy > radical prostectomy

1. Bladder

2. Vas deference

3. Ejaculating duct

4. Prostate

5. Seminal vesicle

6. 
   

• Both are terminal part of the GIT

• Rectum located in most posterior compartment of pelvis

• It is retroperitoneal = only anterior surface is covered by peritoneum

  • Upper part is covered anterior & laterally, middle is covered anteriorly only by the peritoneum

• Anteriorly it is separated from bladder by seminal vesicles

• Posteriorly it follows the curvature of sacral bone - then it angulate posteriorly to become anal canal forming ano-rectal junction (important for fecal incontinence).

Coronal section of rectum shows number of important features:

• Anorectal line = marks the end of rectum & beginning of anal canal

• The pectinate (dentate) line = marks the anatomical junction between superior part of anal canal (originate from hind gut endoderm) and inferior part (originate from ectoderm)

  • Any pathology above the line is painless, but below the line is painful. Neurovascular supply also differs

• The transverse folds show the 3 lateral curvatures (superior, middle & inferior rectal flexures) of the rectum.

• The Anocutaneous line = marks the junction between the mucosal lining of the anal canal and the stratified keratinised squamous epithelial covering of the skin

The Anal canal has 2 sphincters:

• The internal anal sphincter - deep to the mucosa, surrounds upper 2/3rd anal canal, involuntary

• The external anal sphincter is far superficial and forms part of the pelvic diaphragm

  • Surrounds lower 2/3rd of anal canal, made of skeletal muscles = voluntary control..

-> Anal fissure = tear in the mucosa of the anal canal due to chronic constipation > painful defectation (occurs below dentate line). It is Rx by incision of anal sphincter muscles or relaxation by anaesthetic.

Blood supply comes from 3 rectal arteries:

• Superior anorectal artery - branch of the inferior mesenteric artery

• Middle anorectal artery - branch of the internal iliac artery

• Inferior anorectal artery - branch of the internal pudendal artery

The drainage follows the same pattern, there are 3 veins:

• Superior rectal vein - drains into inferior mesenteric vein which drain into splenic vein and into portal circulation.

  • This makes rectal vein a site of portosystemic anastomosis = get engorged in portal HTN

• Middle rectal vein - drains into internal iliac vein

• Inferior rectal vein - drains into inferior pudendal vein

Lymphatic drainage - follows the blood supply

• Inferior mesenteric lymph nodes

• Internal iliac lymph nodes

• Pararectal lymph nodes

• Makes it a site of portosystemic anastomosis

• These venous plexus are visible at 3, 7 & 9 o’clock during examination when pt lies supine

• The veins get engorged in portal HTN > external haemorrhoids (painful as below dentate line)

• In severe cases, the weight of the engorged venal pleux > partial prolapse of the mucosa throgh the anal cavity > rupture of the veins

• Internal haem results from straining in constipation, pregnancy, straining > increase venous pressure.

  • Internal Haem occurs above the dentate line = painless

• Rx - incision of the mucosa at 3, 7, 9 o’clock & ligation of the veins

Note