Pelvis and Acetabulum Anatomy Guide

Osseous Structures/Landmarks:

Pelvis = 2 innominate bones

Innominate bone = 3 united bones; Ilium, Ischium, Pubis

Bony landmarks:

Ilium

-Anterior Superior Iliac Spine (ASIS); lateral edge of inguinal ligament; origin for sartorius, transversus and internal abdominal muscles.

-Anterior Inferior Iliac Spine (AIIS); distal to and less prominent than ASIS; origin for direct head of rectus femoris, iliofemoral ligament (Y ligament of Bigelow).

-Posterior Superior Iliac Spine (PSIS); 4-5 cm lateral to S2 spinous process

-Greater Sciatic Notch

Iliopectineal eminence;

-union of ilium and pubis;

  • Iliopsoas muscle makes groove b/w eminence and AIIS

Acetabulum:

-Anteverted 15 degrees, obliquely oriented/abducted 45 degrees.

-Articular surface: thickened posterosuperior (wt bearing), deficient inferiorly, acetabular or cotyloid notch bound by transverse acetabular ligament.

-Hip joint:

  • ball and socket
  • deepened by fibrocartilaginous labrum

Ischial Tuberosity

Obturator Fossa


Ligaments:

Sacrospinous – anterior sacrum to ischial spine, inferior border of greater sciatic foramen, superior border of lesser sciatic foramen

Sacrotuberous – inferior border of lesser sciatic foramen

Hip capsule: Iliofemoral ligament (Y ligament of Bigelow=strongest in the body=AIIS to intertrochanteric line), Ischiofemoral ligament (posterior), pubofemoral ligament (anterior).

Ligamentum Teres: apex of cotyloid notch, attaches to fovea of femoral head, arterial branch of posterior division of obturator artery to femoral head (less sig in adults)

Iliolumbar – Ilium to L5 TP, causes avulsion of L5 TP

Spaces:

Greater Sciatic Foramen

-Borders: greater sciatic notch, sacrospinous ligament

-Contents: piriformis, sciatic nerve, superior gluteal vv and n.

Lesser Sciatic Foramen

-Borders: sacrospinous ligeamnt, sacrotuberous ligament

-Contents: short external rotators (obturator internus, superior and inferior gemelli)

Obturator Foramen

-obturator n

Femoral triangle

-Borders: pectineus mc, sartorius mc, inguinal ligament.

-Contents: lat to med = NAVL (femoral n, a, v, lymphatics)

Joints:

Sacroiliac joint – diarthrodial, posterior SI/anterior SI/interosseus ligaments

Pubic Symphysis – fibrocartilaginous disc, superior and arcuate pubic ligaments

Hip joint - See Acetabulum in Osseus section

Muscle Groups:

-Mc; Origin/Insertion/Nerve/Roots (division)

Hip Flexors

-Iliacus; Iliac fossa/Lesser Trochanter/Femoral/L2-4 (P)

-Psoas; TP L1-L5/Lesser Trochanter/Femoral/L2-L4 (P)

-Pectineus; Pectineal line (pubis)/Pectineal line (femur)/Femoral/L2-L4 (P)

-Rectus Femoris; AIIS (direct head) + Acetab rim (reflected head)/patella/Femoral/L2-L4 (P)

-Sartorius; ASIS/Prox medial tibia/Femoral/L2-L4 (P)

Hip Adductors

-Posterior Adductor Magnus; Inferior pubic ramus and ischial tuberosity/Linea aspera and adductor tubercle/Obturator (P) and sciatic (tibial)/L2-L4 (A)

-Adductor longus; Anterior pubic ramus/linea aspera/Obturator (A)/L2-L4 (A)

-Adductor brevis; Inferior pubic ramus/linea aspera and pectineal line/Obturator (P)/L2-L4 (A)

-Gracilis; Inferior symphysis and pubic arch/prox medial tibia/Obturator (A)/L2-L4 (A)

Hip External Rotators

-Gluteus Maximus; Posterior gluteal line (Ilium)/ITB and gluteal sling (femur)/Inferior gluteal/L5-S2 (P)

-Piriformis; Anterior sacrum and sciatic notch/Prox greater trochanter/Piriformis/S1-2 (P)

-Obturator Externus; Ischiopubic rami or obturator membrane/Trochlear fossa/Obturator (A)/L2-L4 (A)

-Oburator Internus; Ischiopubic rami or obturator membrane/Medial Greater Troch (MGT)/Obturator Internus/L5-S2 (A)

-Superior Gemellus; Outer ischial spine/MGT/Obt Int/L5-S2 (A)

-Inferior Gemellus; Ischial tuberostiy/MGT/Obturator femoris/L4-S1 (A)

-Quadratus femoris; Ischial tuberosity/Quadrate line (femur)/Obturator femoris/ L4-S1 (A)

Hip Abductors

-Gluteus Medius; b/w post and ant gluteal lines (Ilium)/GT/Superior gluteal/L4-S1 (P)

-Gluteus Minimus; b/w ant and inf gluteal lines (Ilium)/ant GT/Sup Glut/L4-S1 (P)

-Tensor Fasciae Latae; Ant iliac crest/ITB/Sup Glut/L4-S1 (P)


Nerves:

Lumbosacral Plexus

-Ventral Rami T12-S3

-Anterior surface of quadratus lumborum, deep to or in psoas mc

*Almost all nerves above the hip leave via greater sciatic foramen; sup glut n/a/v above piriformis and everything else below;

-POP’S IQ (nerves lat to med) – pudendal, obturator internus, posterior femoral cutaneous, sciatic, inferior gluteal, quadratus femoris

-Pudendal and obturator internus nerves leave greater sciatic but re-enter via the less sciatic foramen

Iliohypogastric / 1 L.
Ilioinguinal / 1 L.
Genitofemoral / 1, 2 L.
Dorsal divisions.
Lateral femoral cutaneous / 2, 3 L.
Femoral / 2, 3, 4 L.
Ventral divisions.
Obturator / 2, 3, 4 L.
Accessory obturator / 3, 4 L.


Iliohypogastric Nerve (L1)

-emerges from the upper part of the lateral border of the Psoas major, and crosses obliquely in front of the Quadratus lumborum to the iliac crest

-perforates the posterior part of the Transversus abdominis, near the crest of the ilium

-divides between that muscle and the Obliquus internus abdominis into a lateral and an anterior cutaneous branch

Ilioinguinal Nerve (L1)

-emerges from the lateral border of the Psoas major just below the iliohypogastric passing obliquely across the Quadratus lumborum and Iliacus

-perforates the Transversus abdominis, near the anterior part of the iliac crest

-communicates with the iliohypogastric nerve between the Transversus and the Obliquus internus

-pierces the Obliquus internus, accompanying the spermatic cord through the subcutaneous inguinal ring

-distributed to the skin of the upper and medial part of the thigh, to the skin over the root of the penis and upper part of the scrotum in the male, and to the skin covering the mons pubis and labium majus in the female

-size of this nerve is in inverse proportion to that of the iliohypogastric

Genitofemoral n (L1, L2)

-passes obliquely through the substance of the Psoas major

-emerges from its anteromedial border, close to the vertebral column, opposite the fibrocartilage between the third and fourth lumbar vertebræ

-descends on the surface of the Psoas major, under cover of the peritoneum

-divides into the external spermatic and lumboinguinal nerves

  • occasionally these two nerves emerge separately through the substance of the Psoas.

Lateral femoral cutaneus n (LFCN) (L2, L3)

-emerges from the lateral border of the Psoas major about its middle, and crosses the Iliacus obliquely, toward the anterior superior iliac spine

-passes under the inguinal ligament and over the Sartorius muscle into the thigh

-divides into two branches

  • anterior branch becomes superficial about 10 cm. below the inguinal ligament
  • posterior branch pierces the fascia lata, and subdivides into filaments which pass backward across the lateral and posterior surfaces of the thigh, supplying the skin from the level of the greater trochanter to the middle of the thigh

Femoral n (L2, L3, L4)

-lies b/w iliacus and psoas mcs

-muscle branches; iliacus, psoas, quadriceps (rectus, vastus lateralis, medialis, intermedialis)

-largest branch of the lumbar plexus

-descends through the fibers of the Psoas major, emerging from the muscle at the lower part of its lateral border, and passes down between it and the Iliacus, behind the iliac fascia

-then runs beneath the inguinal ligament, into the thigh, and splits into an anterior and a posterior division

-under the inguinal ligament, it is separated from the femoral artery by a portion of the Psoas major

- within the abdomen the femoral nerve gives off small branches to the Iliacus, and a branch which is distributed upon the upper part of the femoral artery

Obturator n (L2, L3, L4)

-injured by retractors behind transverse acetabular ligament and anterior inferior acetabular screws

-muscle branches;

  • ant div – obturator externus,
  • post div - adductor brevis, longus, magnus (dual innervation), gracilis

-descends through the fibers of the Psoas major, and emerges from its medial border near the brim of the pelvis

-passes behind the common iliac vessels, and on the lateral side of the hypogastric vessels and ureter, which separate it from the ureter, and runs along the lateral wall of the lesser pelvis, above and in front of the obturator vessels, to the upper part of the obturator foramen

-enters the thigh, and divides into an anterior and a posterior branch, which are separated at first by some of the fibers of the Obturator externus, and lower down by the Adductor brevis

  • Anterior branch (ramus anterior)
  • leaves the pelvis in front of the Obturator externus and descends in front of the Adductor brevis, and behind the Pectineus and Adductor longus
  • at the lower border of the latter muscle it communicates with the anterior cutaneous and saphenous branches of the femoral nerve, forming a kind of plexus., descends upon the femoral artery, to which it is finally distributed
  • near the obturator foramen the nerve gives off an articular branch to the hipjoint
  • behind the Pectineus, it distributes branches to the Adductor longus and Gracilis, and usually to the Adductor brevis, and in rare cases to the Pectineus
  • receives a communicating branch from the accessory obturator nerve when that nerve is present
  • Posterior branch
  • pierces the anterior part of the Obturator externus, and supplies this muscle
  • passes behind the Adductor brevis on the front of the Adductor magnus, where it divides into numerous muscular branches which are distributed to the Adductor magnus and the Adductor brevis when the latter does not receive a branch from the anterior division of the nerve
  • Articular branch for the knee-joint is sometimes absent
  • either perforates the lower part of the Adductor magnus, or passes through the opening which transmits the femoral artery, and enters the popliteal fossa
  • then descends upon the popliteal artery, as far as the back part of the knee-joint, where it perforates the oblique popliteal ligament, and is distributed to the synovial membrane

Accessory Obturator Nerve (n. obturatorius accessorius) (L3, L4)

-present in about 29 per cent. of cases

-descends along the medial border of the Psoas major, crosses the superior ramus of the pubis, and passes under the Pectineus, where it divides into numerous branches

  • one supplies the Pectineus, penetrating its deep surface
  • another distributed to the hip-joint
  • third communicates with the anterior branch of the obturator nerve

Sciatic n (L4-S3)

-anterior preaxial tibial div, posterior postaxial peroneal div (short head of biceps mc)

-muscle branches; semitendinosis, semimembranosus, biceps femoris, adductor magnus (dual innervation)

Superior Gluteal n (L4, L5)

-enters the gluteal regioin through the upper margin of the greater sciatic notch, just superior to the piriformis muscle

-courses with superior gluteal artery between gluteus medius and minimus

-muscle branches; gluteus medius,, gluteus minimus, tensor fascia lata

Inferior Gluteal n (L5, S1, S2)

-passes from the pelvis below the piriformis muscles in the greater sciatic foramen

-enters the deep surface of the gluteus maximus muscle

-muscle branches; gluteus maximus

Pudendal n (S2, S3, S4)

-passes between the piriformis and coccygeus muscles and leaves the pelvis through the lower part of the greater sciatic foramen.

-crosses the spine of the ischium, and reenters the pelvis through the lesser sciatic foramen

-accompanies the internal pudendal vessels upward and forward along the lateral wall of the ischiorectal fossa, being contained in a sheath of the obturator fascia termed the pudendal canal

-gives off the inferior rectal nerves

-divides into two terminal branches: the perineal nerve, and the dorsal nerve of the penis (males) or the dorsal nerve of the clitoris (in females)

-Innervates the penis and clitoris, bulbospongiosus and ischiocavernosus muscles, and areas around the scrotum, perineum, and anus

Small nerves derived from L4, L5, S1, S2, S3 supply lateral rotators (Piriformis, Gemellus Superior, Obturator Internus, Gemellus Inferior, Obturator Externus, Quadratus Femoris) of thigh except for obturator externus, which is supplied by obturator nerve.



Vessels:

Descending Aorta

Inferior Vena Cava

Common iliac Ay and Vn – branches from aorta at L4, int and ext iliacs come off at S1

Internal Iliac Ay and Vn

-obturator vv; posterior branch supplies transverse acetabular ligament

-superior gluteal vv; near greater sciatic notch

-inferior gluteal vv; supplies g. max, short external rotators

-internal pudendal vv; re-enters pelvis via lesser sciatic foramen

External Iliac Ay and Vn – at risk with anterosuperior acetabular screws, becomes femoral vv after femoral triangle


Surgical Approaches: Recommend Surgical Exposures in Orthopaedicsby Hoppenfeld from LWW

Access to:

-Approach;

  • Eponym/access to/Mc Interval (nerve)/Stuctures at risk/special considerations

Iliac Crest:

-Posterior;

  • none/post crest/G. Max (inf glut) and Latissimus dorsi (thoracodorsal)/Cluneal n, SGA, sciatic n.

-Anterior;

  • TFL/ant crest/G. Med+Min (sup glut) and External abd obliq (segmental)/ASIS, LFCN.

Pubic Symphysis:

-Anterior;

  • none/symphysis/through rectus abdominis muscles/bladder (ID space of Retzius), must ligate sup epigastric vv

Sacroiliac Joint

-Anterior;

  • none/ant SI joint/none (stripping muscles off of ilium)/LFCN, inner wall nutrient vv, sacral nerve roots/tilt table 20 deg away, predrill before osteotomy of iliac crest and ASIS

-Posterior;

  • none/post SI joint, limited ant SI/none (strip G. max and Med off ilium)/inf glut n+ay, sup glut n+ay/detach part of piriformis from greater sciatic notch to reach around and feel anterior surface of SI joint

Acetabulum:

-Posterior;

  • Kocher/post column, lip, dome/split g. max, detach pirif+short ERs/sciatic n, inf glut nvb, sup glut nvb/troch osteotomy for greater exposure

-Ilioinguinal;

  • none/inner (medial) surface of pelvis from SI to symphysis, ant column/not b/w mcs, through lateral abd mcs, isolate spermatic cord or round ligament, isolate iliopsoas mcs, isolate ext iliac nvb in femoral sheath, strip iliacus off ilium/inf epigastic vv must be ligated, spermatic cord or round ligament, LFCN, Femoral n, femoral vv, peritoneum pushed med+sup, bladder

-Iliofemoral;

  • prox extension of Smith-Petersen (ant) approach to hip/ant column, inner and outer table, limited post column/b/w TFL (sup glut) + Sartorius (fem), b/w g. med (sup glut) + rectus fem (fem), strip mcs off inner and outer table/LFCN, asc br lat fem circ ay, femoral n+ay, sup glut n+ay/troch osteotomy to mobilize abductors

References/Sources:

  1. Review of Orthopaedics. 5th Edition. Mark D. Miller. Saunders Elsvier 2008. Philadelphia, PA.
  2. Surgical Exposures in Orthopaedics: The Anatomic Approach. 4th Edition. Stanley Hoppenfeld, Piet deBoer, Richard Buckley. Lippincott Williams and Wilkins 2009. Philadelphia, PA.
  3. anatomy/lumbosacral.htm