The Pelvis at the Bedside: Landmarks, Examinations and Needles
Every other article in this section built the pelvis out of bone, muscle, vessel and nerve. This one puts your hands on it. Almost nothing in the pelvis can be seen, and almost everything important in it can be felt — through a finger, through a needle, through the resistance of a catheter that has reached a bend it cannot take. The whole clinical craft of the pelvis rests on a handful of bony points that a trained finger can find in seconds, and on knowing exactly which structure hides behind each one. Learn those points and the pelvis stops being a dark box: it becomes a map you can read in the dark, with your fingertips.
It is two in the morning and the delivery room is quiet in the way that busy rooms become quiet when everyone knows their job. The obstetrician slides two fingers into the vagina and, without looking at anything, walks them laterally and backwards until they stop against a hard little point of bone on each side. She says a number out loud — the station — and everyone in the room adjusts their expectations of the next hour to it. A moment later the same two fingers guide a needle along their own length, to a spot a centimetre medial and below that point of bone, and inject. Within minutes the mother's perineum is numb, although she still feels every contraction exactly as before. Nothing on a screen told the obstetrician any of this. One bony spine, the size of the tip of your little finger, gave her the progress of the labour, the target for the needle, and the reason the block would take away one pain and leave the other.
The bones you can find with your fingers
Surface anatomy is not a list of bumps; it is a list of doors, each opening onto something you cannot see. Run your hands down from the waist and the first ridge you meet is the ILIAC CREST, and its highest point lies at the level of the body of the L4 vertebra — the single most useful vertebral level in medicine, because the line joining the two crests (the intercristal or TUFFIER'S LINE) is how an anaesthetist finds the right interspace without an X-ray. About 5 cm behind the anterior end of the crest is the ILIAC TUBERCLE, the widest point of the pelvis and the landmark of the transtubercular plane (L5). The crest ends in front at the ANTERIOR SUPERIOR ILIAC SPINE (ASIS): the attachment of the inguinal ligament and sartorius, the outer end of the line on which McBurney's point is measured, and one of the two fixed points from which limb length is measured. In the midline in front lies the PUBIC SYMPHYSIS, and 2–3 cm lateral to it the PUBIC TUBERCLE — the point that decides a hernia, since an inguinal hernia emerges above and medial to it and a femoral hernia below and lateral. Sitting down, you rest your weight on the ISCHIAL TUBEROSITIES, which are the lateral angles of the perineal diamond and the origin of the hamstrings; behind, the SACRUM can be traced to the SACRAL HIATUS, a gap felt between the two sacral cornua about 5 cm above the tip of the COCCYX, which itself is palpable only from behind or through the rectum. These are the same bones dissected in the hip bone and bony pelvis — the difference is that here you meet them through skin.
The ischial spine: the most useful point in the pelvis
One landmark outranks all the others, and it cannot be reached from outside at all: the ISCHIAL SPINE, felt through the lateral vaginal wall or through the rectum, roughly at four and eight o'clock, a hard prominence with a taut cord — the SACROSPINOUS LIGAMENT — running backwards from it to the sacrum. Four separate clinical worlds meet on this one point of bone. First, it is the attachment of the sacrospinous ligament, which divides the greater from the lesser sciatic foramen and is the anchor used in sacrospinous fixation for vault prolapse. Second, the interspinous distance (about 10–11 cm) is the narrowest diameter of the whole birth canal, so the spines define the mid-pelvis. Third, the level of the spines is ZERO STATION: the descent of the fetal head is reported in centimetres above (minus) or below (plus) an imaginary line between them, the single number that tells a labour ward whether anything is happening, as set out in the anatomy of childbirth. Fourth, and the reason a needle goes anywhere near it, the pudendal nerve and the internal pudendal vessels leave the greater sciatic foramen, hook backwards around the ligament exactly at the spine, and re-enter the pelvis through the lesser foramen — the anatomy detailed in the pudendal nerve. Find the spine and you have found the nerve.
Surface projections: what lies where
The adult pelvis hides its contents so well that anything you can feel through the abdominal wall is, by definition, abnormal or pregnant. The EMPTY BLADDER lies entirely within the bony pelvis and cannot be palpated or percussed; as it fills beyond roughly 300 mL it rises out of the pelvis as a smooth midline swelling arising from behind the symphysis, dull to percussion, which you cannot get below — and in acute retention it may reach the umbilicus. (In infants the bladder is an abdominal organ even when empty, which is why a baby's bladder is palpable and easily punctured.) The NON-PREGNANT UTERUS is likewise impalpable abdominally; the pregnant uterus first becomes palpable above the symphysis at about 12 WEEKS, reaches the umbilicus at about 20 WEEKS, and the xiphisternum at about 36. The great vessels project onto the same wall: the AORTA BIFURCATES at the level of L4 — the intercristal line, a little below and left of the umbilicus — and each COMMON ILIAC ARTERY divides into external and internal in front of the SACROILIAC JOINT, which is why the internal iliac and its branches are pelvic, not abdominal, surgery. The ureters cross the pelvic brim at that same bifurcation, a fact every pelvic surgeon carries into every operation.
The vaginal examination, done properly
It is called BIMANUAL because one hand alone can reach nothing: the pelvic organs must be trapped between two. Two gloved fingers enter the vagina while the flat of the other hand presses the lower abdomen downwards and backwards; the organs are palpated in the space between them, because a retroverted uterus, an ovary or a mass in the pouch of Douglas is otherwise simply out of reach. Proceed in a fixed order and nothing is missed. The CERVIX is found first: its consistency (firm like the tip of the nose when not pregnant, soft like the lips in pregnancy), the OS (a dimple in the nullipara, a transverse slit after childbirth), and whether moving it hurts — CERVICAL EXCITATION TENDERNESS, which means peritoneal irritation and, in a woman with a positive pregnancy test, an ectopic pregnancy until proven otherwise. Then the UTERUS: size (measured in weeks of pregnancy, a fibroid uterus being described the same way), position (anteverted in most, retroverted in perhaps a fifth), regularity and MOBILITY — a uterus fixed by endometriosis or malignancy is a serious finding, as discussed in the uterus and uterine tubes. Then the FORNICES: the lateral fornices lead the fingers onto the ischial spines and, beyond them, onto any ADNEXAL MASS; a normal ovary is palpable in slim women only. Finally the POSTERIOR FORNIX, which is separated from the POUCH OF DOUGLAS by little more than the thickness of vaginal wall and peritoneum — nodules felt through it suggest endometriosis or peritoneal deposits, and a bulge suggests fluid, blood or an abscess in the lowest part of the peritoneal cavity. Every one of these examinations requires explanation, verbal consent, privacy and a chaperone recorded by name; the anatomy is the smaller half of the skill.
The rectal examination, done properly
Inspect first — fissures, fistulae, prolapsed piles and skin tags are seen, not felt — then introduce a lubricated finger and read the anal canal in a fixed sequence. TONE at rest is the internal sphincter (smooth muscle, sympathetic); tone on SQUEEZE is the external sphincter and puborectalis (somatic, pudendal), and asking the patient to squeeze is the only bedside test of that nerve. ANTERIORLY in the male lies the PROSTATE: two lateral lobes with a MEDIAN SULCUS between them, normally the size of a chestnut, firm and rubbery. Benign hyperplasia gives a smooth, symmetrically enlarged gland with the sulcus preserved; carcinoma gives a hard, craggy, asymmetrical gland with the sulcus obliterated, and it is palpable precisely because cancer favours the PERIPHERAL zone that lies against the rectum, while hyperplasia arises in the transition zone around the urethra — the zonal anatomy of the prostate and seminal vesicles made clinical by a fingertip. Anteriorly in the female the CERVIX is felt through the rectal wall and is often mistaken by beginners for a tumour. POSTERIORLY lie the coccyx and sacrum; laterally the ischial spines and the ischiorectal fossae, where an abscess is exquisitely tender. A boggy, tender, hot swelling felt anteriorly or above suggests a collection in the pouch of Douglas or a pelvic appendix, and the classic teaching that it may cause diarrhoea and urinary frequency comes from the abscess resting on rectum and bladder. Finally, feel deliberately for a rectal MASS, note the level and whether it is fixed, and look at the glove.
Think of the pelvis as a cellar with no windows and two service hatches. You will never see inside it, but you can put an arm through either hatch and feel the whole room. The vaginal hatch opens onto the front and middle of the cellar — cervix, uterus, adnexa, the spines on each side. The rectal hatch opens onto the back and the far wall — prostate or cervix in front of you, sacrum and coccyx behind, ischiorectal fossae to the sides. Between them, almost nothing in the pelvis is out of reach of a trained hand. And the lowest corner of the cellar, where anything spilled inevitably collects, sits directly behind a single thin partition at the back of the vaginal hatch: the posterior fornix and the pouch of Douglas. That is why a needle passed through that one partition has, for a century, been the fastest way to find out whether the cellar is full of blood.
Catheters: the urethra as a road with two bends
Almost every difficulty with a catheter is a difficulty of anatomy, not of technique. The FEMALE urethra is about 4 cm long, straight, and opens in the vestibule between the clitoris and the vaginal orifice — a catheter passes with no resistance at all, and the commonest error is entering the vagina by mistake. The MALE urethra is about 20 cm and has two curves: a fixed PREPUBIC curve as it turns up under the symphysis, and a mobile PENILE curve. Lifting the penis vertically abolishes the second curve and turns the road into one gentle bend, which is exactly why the textbook instruction is to hold the penis upright and on stretch as the catheter goes in. Resistance is met at three predictable places — the external meatus (the narrowest point of all), the BULBOMEMBRANOUS JUNCTION where the urethra pierces the perineal membrane and the external sphincter, and the bladder neck in a man with a large prostate. At the membranous urethra the correct response is gentle steady pressure and asking the patient to breathe out or to try to pass urine, because that relaxes a voluntary sphincter; force there creates a false passage into the corpus spongiosum and a great deal of blood. Never inflate the balloon until urine is seen, and in a man always advance to the hilt first: the parts and calibre of the passage are set out in the urethra. And never re-place a foreskin that was retracted for the procedure and left behind the glans — that is how paraphimosis is caused in hospital.
When the urethral route fails, the bladder itself offers a door — but only when it is full. The empty bladder is a pelvic organ, shielded by the pubic bones and covered by peritoneum with coils of small bowel lying on top of it. As it distends it rises out of the pelvis and, crucially, it STRIPS THE PERITONEUM UPWARDS off the anterior abdominal wall, so that a strip of bladder comes to lie directly against the wall with no peritoneum and no bowel in between. That strip is the whole basis of SUPRAPUBIC CATHETERISATION: the needle or trocar is passed in the MIDLINE, about two finger-breadths (roughly 2–3 cm) above the symphysis pubis, aimed slightly downwards, into a bladder that has been confirmed distended by percussion or ultrasound. A bladder that is not distended has not stripped the peritoneum, and the same needle enters the peritoneal cavity and the bowel — which is why an undistended bladder, previous lower abdominal surgery with adhesions, and known or suspected bladder cancer are the classic contraindications. The relations that make this safe are those of the urinary bladder.
Needles, blocks and the segments they must reach
The PUDENDAL NERVE BLOCK is the purest example of surface anatomy turned into treatment. Transvaginally, two fingers walk laterally to the ischial spine, a guarded needle is passed along them, and local anaesthetic is injected just MEDIAL and INFERIOR to the spine, where the nerve is crossing the sacrospinous ligament. It anaesthetises the S2–S4 territory: the perineum, the lower vagina, the vulva and the anal margin — enough for an instrumental delivery, an episiotomy and its repair, or a perineal tear. It does NOT touch the pain of uterine contraction, because that is visceral pain travelling with sympathetic fibres to T10–L1, an entirely different set of segments. That single fact explains why a labouring woman with a good pudendal block still feels every contraction, and why an epidural — which floods the epidural space and can cover both territories — is a different order of analgesia. NEURAXIAL anaesthesia is governed by one hard rule: the spinal cord ends at L1/L2 in the adult, so a SPINAL needle, which must pierce the dura, is placed BELOW that at L3/L4 or L4/L5, identified from Tuffier's intercristal line. Cover T10–L1 for the first stage of labour, S2–S4 for the second, and up to T4 for caesarean section — which is why a woman for caesarean is tested to the nipple line and often feels pressure and nausea as the peritoneum is handled. A CAUDAL block takes the same epidural space by a different door, through the sacral hiatus between the sacral cornua, used for perineal and paediatric surgery and beloved of anaesthetists precisely because the hiatus is a landmark you can feel.
A 24-year-old woman arrives collapsed, pale and cold, with six weeks of amenorrhoea, sudden lower abdominal pain and shoulder-tip pain. Before ultrasound existed, the next step was CULDOCENTESIS: a needle passed through the POSTERIOR VAGINAL FORNIX, which is separated from the rectouterine pouch of Douglas by only the vaginal wall and peritoneum, into the lowest part of the peritoneal cavity in an upright woman. Non-clotting blood in the syringe meant haemoperitoneum, and in this setting a ruptured ectopic pregnancy — straight to theatre. Ultrasound and quantitative hCG have almost entirely replaced the procedure, but the anatomy it exploited has not moved an inch: it is the same route by which a pelvic abscess in the pouch of Douglas is drained transvaginally today, and the same reason that a bulging, tender posterior fornix in a febrile woman is a finding you act on. The shoulder-tip pain, incidentally, comes from blood irritating the diaphragmatic peritoneum and being referred along the phrenic nerve to C4 — the pelvis announcing itself at the neck.
The prostate is the one pelvic organ whose two biopsy routes are chosen by anatomy and infection, not by convenience. TRANSRECTAL biopsy passes the needle through the rectal wall — the shortest route to the peripheral zone, and the traditional one — but every pass carries rectal flora directly into the prostate and the bloodstream, so the feared complication is sepsis, increasingly with quinolone-resistant organisms. TRANSPERINEAL biopsy passes through prepared perineal skin instead, avoiding the rectum entirely; infection rates fall close to zero and access to the anterior prostate is better, at the cost of needing more anaesthesia and a slightly higher rate of urinary retention. Same gland, same needle, two different bacterial neighbourhoods on the way in. It is the cleanest demonstration in the pelvis that a route is never chosen on distance alone.
- Palpable landmarks and their uses: iliac crest (highest point = L4, Tuffier's intercristal line for neuraxial blocks), iliac tubercle (transtubercular plane, L5), ASIS (inguinal ligament, McBurney's line, limb length), pubic symphysis and pubic tubercle (inguinal hernia above and medial, femoral below and lateral), ischial tuberosity (weight-bearing in sitting, lateral angle of the perineum), sacral hiatus and coccyx (caudal block).
- The ISCHIAL SPINE, felt vaginally or rectally, is the key point of the pelvis: attachment of the sacrospinous ligament, narrowest (interspinous) diameter of the birth canal at about 10–11 cm, ZERO STATION for fetal descent, and the point where the pudendal nerve and internal pudendal vessels hook round — hence the target of a pudendal block.
- Surface projections: the empty bladder is impalpable and becomes a dull midline suprapubic swelling only above roughly 300 mL; the uterus is palpable abdominally at about 12 weeks of pregnancy and reaches the umbilicus at about 20; the aorta bifurcates at L4 and each common iliac artery divides in front of the sacroiliac joint, where the ureter crosses the pelvic brim.
- Bimanual vaginal examination in order: cervix (consistency, os, excitation tenderness), uterus (size in weeks, position, mobility), fornices (ischial spines laterally, adnexal masses), posterior fornix (nodules or a bulge = the pouch of Douglas).
- Rectal examination in order: inspection, resting tone (internal sphincter), squeeze tone (external sphincter and puborectalis — the bedside test of the pudendal nerve), prostate or cervix anteriorly, sacrum and coccyx posteriorly, ischiorectal fossae laterally, any mass, and the glove.
- Prostate on rectal examination: normally chestnut-sized, firm, with a median sulcus. Benign hyperplasia = smooth, symmetrically enlarged, sulcus preserved (transition zone). Carcinoma = hard, craggy, asymmetrical, sulcus lost (peripheral zone — the zone your finger reaches).
Positions, probes and the discipline of describing what you found
The position that gives access is also the position that injures nerves, and the two facts must be learnt together. The LITHOTOMY position — supine, hips flexed and abducted, legs in stirrups — opens the perineum for everything from an episiotomy repair to a transperineal biopsy, and it endangers four nerves. The COMMON FIBULAR nerve is the classic: it winds round the neck of the fibula with only skin over it, and pressure from the lateral bar of the stirrup gives a foot drop that the patient discovers on standing up. Excessive HIP FLEXION or abduction stretches the FEMORAL nerve under the inguinal ligament (weak knee extension, numb anteromedial thigh); over-flexion can stretch the SCIATIC nerve, and the OBTURATOR nerve is at risk from pressure at the pelvic brim. Prolonged lithotomy with the legs above the heart also risks lower limb compartment syndrome — which is why steep or long lithotomy is timed and the legs lowered periodically. Two further practical points. Ultrasound is anatomy at the bedside: a FULL bladder is deliberately used as an acoustic window for a TRANSABDOMINAL pelvic scan, pushing bowel gas out of the way and letting sound through fluid to reach the uterus and adnexa, whereas a TRANSVAGINAL scan needs the bladder EMPTY, because the probe is already past it and a full bladder only displaces the organs away from the transducer. Finally, describe what you find by the CLOCK FACE in the lithotomy position, with 12 o'clock anterior and 6 o'clock posterior — a fissure at six o'clock, a fistula opening at four — because that convention, and only that convention, lets the next clinician find exactly what you found.
A 74-year-old man in acute urinary retention has a bladder palpable to the umbilicus and a distress that no analgesic will touch. A 14 Fr catheter is passed; it stops about 15 cm in and will not advance. The anatomy names the culprit before anyone reaches for another catheter: 15 cm is the bulbomembranous region and the bladder neck, and the two candidates are spasm of the external sphincter or a hypertrophied prostate. The correct sequence is to lift the penis vertically and keep it on stretch, add more lubricant and local anaesthetic gel and wait for it to work, ask the patient to breathe out or bear down, and try a larger, stiffer catheter — counter-intuitive but correct, because a bigger catheter negotiates the prostatic urethra where a small floppy one curls up. Force produces a false passage, torrential bleeding and a urethral stricture months later. If it still will not pass, the answer is not a third attempt but the other door: percussion or ultrasound confirms a distended bladder, and a suprapubic catheter goes in the midline two finger-breadths above the symphysis, through the strip of bladder that has stripped the peritoneum off the abdominal wall. Two routes, one organ, and the choice between them made entirely on anatomy.
- Urethral catheterisation: the female urethra is ~4 cm and straight; the male is ~20 cm with two curves — lift the penis vertically to abolish the mobile penile curve. Resistance is met at the external meatus, the bulbomembranous junction (external sphincter) and the bladder neck; never inflate the balloon before urine is seen, and always replace a retracted foreskin.
- Suprapubic catheterisation is possible only into a DISTENDED bladder that has risen out of the pelvis and stripped the peritoneum off the anterior abdominal wall; enter in the MIDLINE about two finger-breadths above the symphysis. An undistended bladder, previous lower abdominal surgery and suspected bladder cancer are the classic contraindications.
- Pudendal block: transvaginal, needle just medial and inferior to the ischial spine; covers S2–S4 (perineum, lower vagina, vulva, anal margin) but NOT uterine contraction pain, which is visceral and travels to T10–L1.
- Neuraxial blocks: the cord ends at L1/L2, so a spinal is placed at L3/L4 or L4/L5 using Tuffier's intercristal line. Labour needs T10–L1 for the first stage and S2–S4 for the second; caesarean section needs a block to T4. A caudal enters the same epidural space through the sacral hiatus.
- Culdocentesis and transvaginal drainage pass through the posterior fornix into the pouch of Douglas — the lowest point of the peritoneal cavity in the upright woman. Prostate biopsy: transrectal is short but carries sepsis risk; transperineal avoids rectal flora at the cost of more anaesthesia and more retention.
- The lithotomy position endangers the common fibular nerve (stirrup pressure at the fibular neck → foot drop), the femoral nerve (excessive hip flexion), the sciatic and obturator nerves, and — if prolonged — the lower limb compartments. Describe perineal findings by the clock face with 12 o'clock anterior.
- Passing a suprapubic catheter into a bladder that is not clearly distended. Only a full bladder rises out of the pelvis and peels the peritoneum off the abdominal wall; into an empty one the same trocar traverses peritoneum and bowel. Confirm distension by percussion or ultrasound every single time.
- Expecting a pudendal block to relieve labour pain. It anaesthetises the S2–S4 somatic territory of the perineum only; the pain of uterine contraction is visceral and reaches the cord at T10–L1, so the mother will feel every contraction unchanged. Promising otherwise destroys trust at the worst possible moment.
- Using force when a catheter meets resistance at about 15 cm in a man. That point is the bulbomembranous junction and the prostate; the answer is stretch, lubricant, anaesthetic gel, relaxation and a LARGER stiffer catheter — not a smaller one and never force, which creates a false passage and a stricture.
During labour, an obstetrician performs a transvaginal block by palpating a bony prominence on the lateral pelvic wall and injecting local anaesthetic just medial and inferior to it. Which landmark has she used, and what will the block NOT relieve?
- The pelvis is examined through landmarks, not through windows: iliac crest (L4, Tuffier's line), iliac tubercle (L5), ASIS, pubic symphysis and tubercle (the hernia rule), ischial tuberosity, sacral hiatus and coccyx — and, above all, the ischial spine, felt vaginally or rectally.
- The ischial spine carries four meanings at once: the sacrospinous ligament, the narrowest (interspinous) diameter of the birth canal, zero station for fetal descent, and the point where the pudendal nerve hooks round — hence the target of a pudendal block, which covers S2–S4 but never the T10–L1 pain of contractions.
- Examinations are systematic: bimanually per vaginam (cervix, uterus, fornices, posterior fornix and pouch of Douglas) and per rectum (tone at rest and on squeeze, prostate with its median sulcus or the cervix, sacrum, ischiorectal fossae, any mass) — always with explanation, consent, privacy and a documented chaperone.
- Every pelvic procedure is a landmark made useful: catheterisation along a 4 cm straight or 20 cm doubly curved urethra; suprapubic puncture only into a distended bladder that has stripped the peritoneum; spinal below L2 at Tuffier's line with T10–L1, S2–S4 and T4 as the targets of labour and caesarean; caudal through the sacral hiatus; culdocentesis through the posterior fornix; transrectal versus transperineal prostate biopsy; and the lithotomy position, which buys access at the price of the common fibular and femoral nerves.
- Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students — Pelvis and Perineum: surface anatomy and clinical cases.
- Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy — Pelvis and Perineum: surface anatomy, pelvic examination, pudendal and caudal blocks.
- Snell RS. Clinical Anatomy by Regions — Surface anatomy of the pelvis and perineum; catheterisation and suprapubic puncture.
- Last RJ. Last's Anatomy: Regional and Applied — The pelvis: living anatomy and applied topography.
- Netter FH. Atlas of Human Anatomy — Pelvis: bony landmarks, ischial spine and sacrospinous ligament, male and female urethra.
- TeachMeAnatomy — Surface Anatomy of the Pelvis; The Pudendal Nerve; Urethral Catheterisation.
