A newborn girl is delivered vaginally at term to a healthy 25-year-old G1P1. The pregnancy was uncomplicated. On examination, she was found to have a slight anal invagination, but no opening. Further examination shows a vestibular fistula and normally developed external genitalia. Which of the following statements about this condition is correct?

There is a failure of the rupture of the anal membrane (dorsal portion of the cloacal membrane).

Such abnormal anatomy is formed after week 12 of intrauterine development.

The presence of an associated perineal or vestibular fistula is more likely in females with trisomy 21.

There is a failure of the division of the embryonic cloaca into the urogenital sinus and rectoanal canal.

Other congenital abnormalities are extremely rare in patients with this condition.

A 28-year-old male presents to his primary care physician with complaints of intermittent abdominal pain and alternating bouts of constipation and diarrhea. His medical chart is not significant for any past medical problems or prior surgeries. He is not prescribed any current medications. Which of the following questions would be the most useful next question in eliciting further history from this patient?

"Can you tell me more about the symptoms you have been experiencing?"

"Does the diarrhea typically precede the constipation, or vice-versa?"

"Is the diarrhea foul-smelling?"

"Please rate your abdominal pain on a scale of 1-10, with 10 being the worst pain of your life"

"Are the symptoms worse in the morning or at night?"

A 45-year-old man is brought to the emergency department following a motor vehicle collision. He reports right hip pain and numbness along the right thigh. Physical examination shows decreased sensation to light touch over a small area of the proximal medial thigh. X-rays of the pelvis show a displaced pelvic ring fracture. Further evaluation of this patient is most likely to show which of the following findings?

Sensory deficit of the dorsal foot

Pelvic girdle and ligaments for USMLE Step 2 CK: High-Yield Anatomy Lessons

Pelvic Bones - The Bony Basin

Pelvic Girdle and Ligaments: Anterior View

The pelvic girdle is a basin-shaped ring of bones connecting the vertebral column to the femurs.
Composed of three main parts, which fuse at the acetabulum (hip socket):
- Ilium: Large, wing-like superior part; site of the iliac crest.
- Ischium: Posteroinferior part; features the ischial tuberosity ("sit bone").
- Pubis: Anterior part; joins at the pubic symphysis.

⭐ The sacroiliac (SI) joint, a synovial joint between the ilium and sacrum, is a frequent, yet often overlooked, source of chronic low back pain.

Pelvic Joints - Articulation Junctions

Lumbosacral Joint:
- Junction of the L5 vertebra and the sacrum.
- Stabilized by the strong iliolumbar ligament.
Sacroiliac (SI) Joints:
- Paired synovial joints linking the iliac bones to the sacrum.
- Transmit upper body weight to the appendicular skeleton.
- Minimal movement; reinforced by strong sacroiliac ligaments.
Pubic Symphysis:
- Anterior cartilaginous joint connecting the two pubic bones.
Sacrococcygeal Joint:
- A slightly movable joint between the sacrum and coccyx.

Pelvic girdle: anterior bony anatomy and posterior ligaments

⭐ During pregnancy, the hormone relaxin increases the laxity of the pubic symphysis and SI joints, which can cause pelvic girdle pain.

Pelvic Ligaments - Strong Stabilizers

Key ligaments providing robust stability to the bony pelvis. They resist weight-bearing forces and define critical neurovascular pathways.

Posterior Pelvic Ligaments, Foramina, and Nerves

Ligament	From	To	Key Function
Sacrospinous	Ischial spine	Lateral sacrum & coccyx	Converts greater sciatic notch into foramen.
Sacrotuberous	Ischial tuberosity	PSIS, sacrum, coccyx	Converts lesser sciatic notch into foramen.
Iliolumbar	L5 transverse process	Medial iliac crest	Strengthens lumbosacral joint.
Sacroiliac	Sacrum	Ilium	Anterior, posterior, & interosseous bands; main SI joint stabilizers.

Pelvic Variations - Sex, Types & Trauma

Sex Differences:
- Female (Gynecoid): Wider, shallower, with a circular/oval inlet and a subpubic angle > 80°. Optimized for childbirth.
- Male (Android): Narrower, deeper, with a heart-shaped inlet and a subpubic angle < 70°.

Male vs. Female Pelvis: Key Anatomical Differences

Caldwell-Moloy Pelvic Types:
- Gynecoid: Classic female type; most favorable for vaginal birth.
- Android: Typical male type; associated with difficult labor.
- Anthropoid: Long AP diameter.
- Platypelloid: Wide transverse diameter; poor prognosis for vaginal birth.
Pelvic Ring Fractures:
- AP Compression ("Open Book"): High risk of major hemorrhage.
- Lateral Compression: Most common type; risk of bladder/urethral injury.
- Vertical Shear: Highly unstable; severe hemorrhage risk.

⭐ Pelvic fractures are strongly associated with posterior urethral injuries in males (membranous portion).

High‑Yield Points - ⚡ Biggest Takeaways

The pelvic girdle consists of the two hip bones (ilium, ischium, pubis) and the sacrum.

The sacrospinous ligament forms the greater sciatic foramen, the exit for the sciatic nerve.

The sacrotuberous ligament forms the lesser sciatic foramen, passage for the pudendal nerve.

The ischial spine is the key palpable landmark for a pudendal nerve block.

Pelvic ring fractures carry a high risk of life-threatening hemorrhage and urogenital injury.

The gynecoid pelvis has a wider subpubic angle, favoring childbirth.

Continue reading on Oncourse

CONTINUE READING — FREE

or get the app

App Store|Google Play