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The structure involved in cephalopelvic disproportion at the level of inlet is the pelvic inlet. Ischial tuberosity does not form a boundary of the pelvic inlet.

Boundaries of the pelvic inlet:

• Posterior - sacral promontory
• Lateral - arcuate line on the inner surface of the ilium and the pectineal line on the superior ramus.
• Anterior - pubic symphysis

Boundaries of the pelvic outlet:

• Posterior - tip of the coccyx
• Lateral - ischial tuberosities and the inferior margin of the sacrotuberous ligament
• Anterior - pubic arch

Clinical significance:

Cephalopelvic disproportion can occur when any of the inlet or outlet diameters are shortened by more than 0.5 cm, thus leading to the fetal head not getting engaged during labor. A primigravida presenting with a non-engaged head at term should raise suspicion of a contracted pelvis and cephalopelvic disproportion.

The marked muscle is the piriformis muscle.

• Origin:
• The anterior surface of the sacrum
• The posterior inferior iliac spine
• The capsule of the sacroiliac joint
• Sacrotuberous ligament
• Insertion - greater trochanter of the femur.
• Action - lateral rotation of the thigh in extension and abduction of the thigh in the flexed position

The muscle forms the posterolateral wall of the pelvic cavity. The sciatic nerve is closely related to the muscle and it passes through the muscle fibres or below the muscle.

Clinical significance:

Piriformis syndrome is a clinical condition characterized by the compression of the sciatic nerve by the piriformis muscle. This can occur due to inflammation of the piriformis muscle. The patient will present with pain along the distribution of the sciatic nerve which is also known as sciatica.

The following image shows relationship of sciatic nerve with the piriformis.

Obturator internus with its fascia forms the anterolateral wall of the true pelvis. Muscles forming walls of the true pelvis:

• Anterolateral wall - obturator internus and the fascia over its upper and inner (pelvic) surface.
• Posterolateral wall - piriformis
• Floor - levator ani and coccygeus

The given case scenario and image is suggestive of uterine prolapse which occurs due to weakness of the levator ani muscle. Ischiococcygeus is not a part of the levator ani. It is a separate muscle that lies at the posterosuperior part of the pelvis and is not a part of the supports of the uetrus.

The levator ani forms a large portion of the pelvic floor. It is composed of three separate paired muscles:

• Pubococcygeus - this starts from the posterior part of the pubis and runs lateral to the urethra and it' spinchter while passing through the pelvic floor.
• Puborectalis - This muscle starts from the ischiopubic rami and runs medial to pubococcygeus and iliococcygeus to terminate posterior to the rectum at anorectal junction.
• Iliococcygeus - This muscle is placed posterior most as a triangular musculotendinous sheet where the apex is attached to the tip of the ischial spine and the base is attached to the lateral margin of coccyx and the fifth sacral segment.

The levator ani muscle arises from condensations of the obturator fascia which forms the tendinous arch of the levator ani.

The vaginal, urethral, and rectal lumen are occluded by the contraction of the levator ani and relaxation of the muscle is needed for defecation and urination.

The pubococcygeus and puborectalis parts of the levator ani help maintain the tone of the rectum as well as create the anorectal angle.

The anterior division of the internal iliac artery gives rise to the internal pudendal artery.

The internal iliac artery is the major artery of the pelvis. At the superior border of the greater sciatic foramen in the pelvis, it divides into anterior and posterior trunks.

Branches of the anterior trunk of internal iliac artery:

• Obturator artery
• Superior vesical artery
• Inferior vesical artery
• Inferior gluteal artery
• Middle rectal artery
• Vaginal artery (in females)
• Uterine artery (in females)
• Internal pudendal artery

Branches of the posterior trunk of internal iliac artery:

• Iliolumbar artery
• Lateral sacral arteries
• Superior gluteal artery

The lateral boundary of Hesselbach's triangle is formed by the inferior epigastric artery. It originates from the external iliac artery.

The external iliac artery is the main artery of the lower limb. Its branches are:

• Deep circumex iliac
• Inferior epigastric
• Small branches to psoas major and nearby lymph nodes
• Femoral artery
• Clinical significance:

Apart from being a landmark in hernia surgery, the inferior epigastric artery contributes to the corona mortis. This is an anastomosis between the common iliac, internal iliac, obturator, inferior epigastric, and external iliac vessels. Iatrogenic injury in this region leads to torrential hemorrhage.

The median sacral vein is a tributary of the common iliac vein.

Tributaries of common iliac vein:

• Median sacral veins
• Iliolumbar vein
• Lateral sacral veins (occasionally)

Tributaries of internal iliac vein:

• Superior and inferior gluteal veins
• Internal pudendal vein
• Obturator vein
• Lateral sacral veins (usually)
• Middle rectal vein
• Vesical veins
• Uterine and vaginal veins
• Tributaries of external iliac vein:
• Inferior epigastric vein
• Deep circumex iliac vein
• Pubic vein

Clinical Note: Agenesis of the external iliac vein has been reported in association with Klippel–Trenaunay syndrome.

The structure marked in red is the ischial spine and the pudendal nerve is related to it.

The pudendal nerve originates from the sacral plexus S2-S4. It exits out of the pelvis by passing through the greater sciatic foramen. It then enters the perineum below the pelvic floor by passing around the ischial spine. The ischial spine is used as a landmark for pudendal nerve block.

The sacrospinous ligament does not form an anatomical boundary of the perineum. The perineum is a diamond-shaped region that overlies the pelvic outlet.

Boundaries of perineum:

• Anteriorly: Pubic symphysis and its arcuate ligament.
• Posteriorly: Coccyx
• Anterolaterally: Ischiopubic rami and the ischial tuberosities.
• Posterolaterally: Sacrotuberous ligaments

An imaginary line joining the ischial tuberosities (the inter-ischial line) divides the perineum into an anterior urogenital triangle and a posterior anal triangle.

The urogenital triangle faces downwards and forwards and has the following structures: In males:

• Scrotum
• The root of the penis
• In females:
• Mons pubis
• Labia with the vestibule

The anogenital triangle faces downwards and backwards and has the following structures common to both males and females:

• Anal canal with its sphincters
• Ischioanal fossa with its contents

Colle's fascia prevents the extravasation of the urine from spreading into the thigh and anal triangle.

Scarpa's fascia is continuous with the superficial fascia of the scrotum and becomes the Colles' fascia. In women, it continues into the labia majora and is continuous with the fascia of the perineum. Colle's fascia has the following attachments:

• Posterior - perineal membrane. It prevents the extravasation of fluids such as blood, pus, or urine into the anal triangle.
• Lateral - ischiopubic rami and fascia lata along Holden's line. This line extends from the pubic tubercle laterally for 8 cm. It prevents the extravasation of fluids into the thigh.

Option A: Camper's fascia is the superficial fatty layer of the superficial fascia of the abdomen. Option B: Scarpa's fascia is the deep membranous layer of the superficial fascia of the abdomen. Option C: Buck's fascia is the deep fascia of the penis

Clinical significance:

When a urethral injury occurs, urine can extravasate into the superficial perineal pouch, penis, scrotum, labia majora and the anterior abdominal wall.

Bulbourethral glands are not a content of the superficial perineal pouch. They are located in the deep perineal pouch.

The superficial perineal pouch is a potential space between the perineal membrane above and the membranous layer of perineal fascia (Colle's fascia) below.

Contents of superficial perineal pouch:

Males

Root of the penis

Common to both Urethra

Females

Body of the clitoris

Males Common to both Females

Muscles:Two corpora cavern osaCorpora spongiosa

Perineal nerve branches:Post erior scrotumBulb of penis

Perineal artery branches:Post erior scrotal arteryBranches of the penile artery

The duct of the bulbourethral gland

Muscles:Superficial transvers e perineiIschiocavernosusBul bocavernosus

Perineal nerve: muscular bra nches

Perineal artery branches:Tra nsverse perineal branch

Bulbs of vestibule

Perineal nerve branches:Labi aBulbs of vestibule

Perineal artery branches:Post erior labial arteryBranches of the clitoral artery

Greater vestibular gland and its ducts

The root of the penis consists of two crura and one bulb. It is a content of the superficial perineal pouch.

The deep perineal pouch is used to describe the space enclosed between the endopelvic fascia and the perineal membrane and includes the following contents:

Males

Nerves: Dorsal nerve of penis

Arteries:Penile arteryOrigin of the branches of the penile artery

Bulbourethral glands

Common to both

Muscles:Deep transverse peri neiSphincter urethrae

Arteries:Origin of the urethra l artery

Urethra

Females

Nerves: Dorsal nerve of clitor is

Arteries:Clitoral arteryOrigin of the branches of the artery of clitoris

The internal anal sphincter is not involved in the formation of the perineal body.

The perineal body is a fibromuscular structure present in the midline at the junction between the anal and urogenital triangle. It attaches to various muscles in the pelvis:

• Anterior - superficial and deep transverse perinei, bulbospongiosus
• Posterior - external anal sphincter
• Superior - puborectalis, pubovaginalis and the rectovaginal septum

It is continuous with the perineal membrane and the superficial perineal fascia. In males, it continues as the perineal raphe, and in females, it is attached to the posterior commissure and the introitus.

The following image shows the perineal body and its muscular attachments.

The lateral boundaries of the ischioanal fossa are formed by obturator internus(with its fascia).

The ischioanal fossa is a wedge-shaped space on either side of the anal canal in the anorectal triangle. It has a pad of fat. The boundaries include:

• Anterior: Posterior border of perineal membrane
• Posterior: Gluteus maximus muscle, Sacrotuberous ligament
• Lateral: Ischial tuberosity, Obturator internus
• Medial: Sphincter ani externus, Pelvic diaphragm (levator ani).
• Clinical significance:

Ischioanal fossa provides a relatively bloodless field during resection of anal cancers, therefore it is an important surgical plane.

The Alcock's (pudendal) canal is formed by the fascia of the obturator internus muscle.

It is formed by connective tissue binding the vessels and nerve to the medial surface of the fascia covering obturator internus.

Contents of the pudendal canal:

• Internal pudendal artery and vein
• Pudendal nerve
• Clinical significance:
• Infiltration of a local anesthetic around the trunk of the pudendal nerve at the level of the
• ischial spine results in analgesia of the lower vagina, posterior perineum, and vulva.
• Pudendal neuralgia can occur due to compression of pudendal nerve in the pudendal canal.

The structure related to the anterior surface of the affected bone i.e. the proximal femur is the intertrochanteric line. It is present at the junction of the neck and shaft of the femur.

The femur can be divided into:

• Proximal femur - consists of the head, neck, greater and lesser trochanters. The intertrochanteric line is present on the anterior surface at the junction of the neck and shaft of the femur. The intertrochanteric crest is present on the posterior surface.
• Shaft of the femur - consists of linea aspera (bony crest present on the posterior surface),
• gluteal tuberosity, and pectineal line.
• Distal femur - consists of the medial condyle, lateral condyle, intercondylar fossa, and patellar surface.

The images given below shows the anatomy of the femur bone.

Spiral fractures of long bones such as femur or humerus in a child suggest an external application of a twisting force. This is highly suspicious of non-accidental trauma. The probable diagnosis is battered baby syndrome.

The normal angle of the neck of the femur to the shaft is approximately 125°. This is known as neck-shaft angle or angle of inclination.

This facilitates the movement at the hip joint, enabling the limb to move freely.

• When the angle is gt; 135°, the condition is known as coxa valga
• When the angle is lt; 120°, the condition is known as coxa vara
• The image given below shows the normal neck-shaft angle of femur.

The given clinical scenario is suggestive of slipped capital femoral epiphysis (SCFE). Linea aspera of the affected bone i.e. femur gives attachment to:

• Adductor longus
• Intermuscular septa
• Short head of biceps femoris.

Linea aspera is the roughened ridges of bone present on the posterior surface of the femoral shaft. It is made of medial and lateral edges.

Proximally:

• Medial edge is continuous as spiral line
• Lateral edge is continuous as gluteal tuberosity
• Distally:
• Medial border is continuous as medial supracondylar line
• Lateral border is continuous as lateral supracondylar line
• Surface between the medial and lateral supracondylar line is the popliteal surface
• The image given below shows posterior surface of the femur.

The arterial supply to the femoral head is mostly by the medial circumflex femoral artery.

The blood supply of the femoral head is derived from an arterial ring (trochanteric anastomosis) around the neck of the femur constituted by:

• Medial and lateral circumflex femoral arteries, branches of profunda femoris artery
• Superior and inferior gluteal vessels (minor contributions)

In the fetus and early postnatal period, the medial and lateral circumflex femoral arteries contribute equally. Whereas in the later life the supply from the lateral circumflex femoral artery diminishes and it is mainly supplied by two major arteries of the medial circumflex femoral arteries.

A small acetabular branch of the obturator artery also reaches the head, through the ligament of the head of the femur. However, it is a minor source.

The image given below shows the blood supply of the head of the femur:

The second perforating branch of the profunda femoris artery is the nutrient artery to the femur.

The following table shows bones of the lower limb and their nutrient arteries:

Bones of the Lower li mb

Femur Tibia Fibula

Nutrient arteries

2ndperforating branch of the profunda femoris

Branch of posterior tibial art ery

Peroneal artery, a branch of posterior tibial artery

The secondary ossification centres of the distal end of the femur appear at the 9th

month (full-term) of intrauterine life. They form the condyles and epicondyles of the femur. Femur ossifies from one primary centre and four secondary centres:

• Primary centre appears in the midshaft in the seventh week of the prenatal period
• The secondary ossification centres appear at the following sites:
• Distal end of the femur during ninth month of intrauterine life
• Head of the femur during six months after birth
• Greater trochanter during the fourth year
• Lesser trochanter between twelfth and fourteenth year

The patella is an example of sesamoid bone, which is formed within the tendon of the quadriceps femoris muscle.

It is triangular in shape and lies in the patellofemoral groove. The apex is directed inferiorly which gives attachment to the patellar ligament and the base is directed superiorly which gives attachment to the quadriceps femoris muscle.

Its convex anterior surface is perforated by numerous nutrient vessels and is separated from the skin by a prepatellar bursa. Its posterior surface has an oval articular area crossed by a smooth vertical ridge that fits into the intercondylar groove. This ridge divides the patellar articular area into medial and lateral facets. These facets articulate with the corresponding condyles of the femur.

Important sesamoid bones:

• Patella - largest sesamoid bone in the tendon of quadriceps femoris.
• Pisiform - tendon of flexor carpi ulnaris.
• Fabella - lateral head of the gastrocnemius.
• Two sesamoid bones can be found in the first metacarpal within the tendons of flexor pollicis brevis and adductor pollicis.
• Two sesamoid bones can be found in the first metatarsophalangeal articulation within the double tendon of flexor hallucis brevis.

The apex of the tibial triangular area is formed by tibial tuberosity.

The tibial triangular area is a small area present in front of the anterior condylar surface. The apex is directed downwards and is formed by tibial tuberosity and the base is continuous with the anterior condylar surfaces of the tibia.

The tibial tuberosity gives attachment to the patellar ligament and is divided into distal rough and proximal smooth regions. The distal region is palpable and is separated from the skin by

the infrapatellar bursa.