Anatomy of the Pelvis
The pelvic ring is a closed compartment of bones containing urogenital organs, rectum, vessels, and nerves, forming a structure optimized for load transfer from the upper body to the lower limbs while facilitating bipedal movement. 1, 2
Bony Structure
The pelvis consists of three main components:
- Pelvic Ring: Formed by the sacrum and two ossa coxae (hip bones) 1, 3
- Os Coxae: Each hip bone is formed by the fusion of three bones:
- Sacrum: Forms the posterior wall of the pelvis 3
The bony architecture follows optimal engineering principles, providing maximal strength with minimal material 3. This structure is crucial for both bipedal locomotion and obstetrics in humans 2.
Soft Tissue Components
Fascial Layers
- The muscles inside the pelvis are covered by a fascial layer
- This fascial layer is a continuation of the abdominal transversal fascia extending to the pelvic floor 3
Connective Tissue
- Connective tissue fibers around pelvic viscera interweave with:
- Pelvic floor tissues
- Lateral connective tissue around vessels and nerves 3
- Lateral ligaments are formed by transversely arranged connective tissue around neurovascular sheaths, supporting:
- Bladder
- Uterus/prostate
- Rectum 3
- Vertical connective tissue ligaments accompany:
- Superior rectal artery and hypogastric nerves
- Ureter and ovarian vessels 3
Vascular and Neural Components
Vascular Supply
- The pelvis contains significant vascular structures:
- 80% of pelvic bleeding in trauma comes from veins
- 20% of pelvic bleeding comes from arteries 1
- Internal iliac vessels and their branches supply the pelvic organs 3
Lymphatic Drainage
- Lymphatic fluid from pelvic organs drains to:
- Aortic lymph nodes
- Lateral pelvic wall along branches of internal iliac vessels 3
Neural Components
- The pelvis contains important neural structures that can be evaluated with MR neurography, especially relevant in cases of chronic pain 1
Clinical Significance
Trauma Implications
- Pelvic fractures can create instability of the ring and increase internal volume
- This volume increase, particularly in "open book" lesions, can reduce the tamponade effect and facilitate hemorrhage
- The pelvic ring can contain up to several liters of blood 1
- High-energy impacts (falls, traffic accidents) are the primary mechanisms of pelvic ring fractures 1
Imaging Evaluation
- MRI: Provides high soft-tissue contrast resolution for anatomic evaluation of pelvic organs, structures, and post-surgical changes 1
- Ultrasound approaches:
- Radiographic assessment: Standard views include anteroposterior, inlet, outlet, and Judet views 5
Sexual Dimorphism
The pelvis is one of the most sexually dimorphic bony elements of the human body due to its role in obstetrics, with females typically having a wider, shorter pelvis compared to males 2.
Developmental Considerations
- The pelvis develops from embryonic limb buds through a complex timeline:
- Initial blastemal structure forms from mesenchyme
- Chondrification leads to first recognizable elements
- Primary ossification centers initiate in utero
- Secondary ossification occurs post-natally at various locations
- Complete development is not achieved until adulthood 4
- Fetal activity can affect normal pelvic development 4
- Developmental abnormalities may involve the number of bone elements, rate of ossification, density, or size/shape 6
Understanding pelvic anatomy is essential for proper evaluation of pelvic disorders, trauma management, and surgical planning, as the complex intersection of structure and function makes this region uniquely important in human physiology.