Week 18 - Pelvic Osteology Flashcards
What are the characteristics of lumbar vertebrae?
• Bodies are thick and robust
• Transverse processes are thin and tapered
• Spinous processes are thick, blunt, and point posteriorly
• Vertebral foramina are triangular
• Superior and inferior articular facets directly medially
• Allows flexion and extension; rotation is prevented
Key features that distinguish lumbar vertebrae from other vertebrae.
How many vertebrae form the sacrum?
5 fused vertebrae
The sacrum shapes the posterior wall of the pelvis.
What is the location of the center of gravity in relation to the sacral promontory?
Approximately 1 cm posterior to the sacral promontory
This has implications for pelvic stability and balance.
What are the bony openings associated with the sacrum?
• Sacral foramina
• Ventral foramina
• Dorsal foramina
These foramina allow for the passage of nerves and blood vessels.
What is the coccyx commonly referred to as?
Tailbone
It is formed from 3 to 5 fused vertebrae.
What is the primary function of the pelvic girdle?
Connects the lower limbs to the axial skeleton and provides strong support for the vertebral column
It consists of two coxal bones.
What are the three parts of the coxal bone?
• Ilium
• Ischium
• Pubis
Each part has distinct landmarks and functions.
What are the major landmarks of the ilium?
• Iliac crest
• Greater sciatic notch
• Auricular surface
• Arcuate line
The ilium is the largest part of the coxal bone.
What are the key landmarks of the ischium?
• Body
• Ramus
• Ischial spine
• Lesser sciatic notch
• Ischial tuberosity
• Obturator foramen (posterior half)
The ischium serves as a major site for muscle and ligament attachments.
What is the pubic symphysis?
A cartilaginous joint where the two pubic bones articulate
It is located inferior to the pubic symphysis.
What does the anterior longitudinal ligament prevent?
Hyperflexion
It runs down the entire vertebral column.
What are the boundaries of the pelvic inlet?
• Sacral promontory
• Anterior margins of the sacral alae
• Arcuate line
• Pectineal line
• Pubic bone
• Pubic symphysis
The pelvic inlet is a bony ring.
True or False: The greater pelvis is superior to the pelvic brim.
True
It contains the urinary bladder when full and the uterus during pregnancy.
What are the boundaries of the lesser pelvis?
• Posterior: sacrum and coccyx
• Lateral: inferior portion of ilium and ischium
• Anterior: pubic bones
The lesser pelvis is located inferior to the pelvic brim.
What characterizes an anthropoid pelvis?
• Long, narrow, oval inlet
• Wide sacrosciatic notch
• Long, narrow sacrum
• Straight side walls
This pelvic type is often associated with certain anatomical variations.
What are the characteristics of a gynecoid pelvis?
• Round, slightly ovoid or elliptical inlet
• Adequate sacrosciatic notch
• Wide interspinous diameters (≥10cm)
This type is most favorable for childbirth.
Fill in the blank: The pelvic outlet is ______ shaped.
diamond
The pelvic outlet has specific boundaries.
What is the purpose of pelvic measurements?
To determine disproportion between the fetal head and the pelvis
These measurements are crucial in assessing birth readiness.
What happens during an AP compression injury?
• Pubic symphysis breaks
• Tearing of posterior ligamentous complex
• May rupture venous plexus/internal iliac artery
This injury is often a result of road traffic accidents.
What occurs in a lateral compression injury?
• Internal rotation of hemi-pelvis
• Fractures around pubis
• Genito-urinary system injury
This type of injury is more common, occurring in 60-70% of cases.
How does a shear force injury occur?
• Road traffic accident
• Falling from a height onto one limb
This mechanism causes major instability.
What is a combination injury in the pelvis?
Involves AP compression, lateral compression, and shear force injuries
Each type has its own risks and implications for treatment.
What are the two subdivisions of the pelvis?
Greater pelvis and lesser pelvis
The pelvis is divided into these two parts based on anatomical structures.
What surrounds the greater pelvis?
Superior pelvic girdle
The superior pelvic girdle provides structural support for the greater pelvis.
What does the greater pelvis protect?
Inferior abdominal viscera
The protection provided is similar to that of the superior abdominal viscera by the inferior thoracic cage.
What surrounds the lesser pelvis?
Inferior pelvic girdle
The inferior pelvic girdle provides the skeletal framework for the pelvic cavity and perineum.
What are the compartments of the trunk separated by?
Musculofascial pelvic diaphragm
This diaphragm separates the pelvic cavity from the perineum.
Which areas externally cover the pelvis?
Inferior anterolateral abdominal wall, gluteal region, perineum
These regions overlap and protect the pelvis from external forces.
What does the term perineum refer to?
Area between the thighs and buttocks, shallow compartment deep to this area
The perineum extends from the coccyx to the pubis.
What structures are included in the perineum?
Anus, external genitalia (penis, scrotum, vulva)
The perineum encompasses both the anus and external genitalia in males and females.
Fill in the blank: The greater pelvis is occupied by _______.
Inferior abdominal viscera
This occupation is crucial for the protection of these organs.
What is the pelvic girdle?
A basin-shaped ring of bones connecting the vertebral column to the two femurs.
The pelvic girdle supports the weight of the upper body and facilitates locomotion.
What are the primary functions of the pelvic girdle?
- Bear the weight of the upper body when sitting and standing
- Transfer weight from the axial to the lower appendicular skeleton
- Provide attachment for powerful muscles of locomotion and posture
- Contain and protect pelvic and inferior abdominal viscera
- Support the abdominopelvic viscera and gravid uterus
- Provide attachment for erectile bodies of external genitalia
- Form the pelvic floor and fill gaps around it
How many bones form the pelvic girdle in mature individuals?
Three bones: right and left hip bones and sacrum.
The hip bones are formed from the fusion of ilium, ischium, and pubis.
What are the names of the three bones that fuse to form each hip bone?
- Ilium
- Ischium
- Pubis
What is the pubic symphysis?
A secondary cartilaginous joint where right and left hip bones are joined anteriorly.
This joint allows for slight movement and is important during childbirth.
What are the two divisions of the pelvis?
- Greater pelvis (false pelvis)
- Lesser pelvis (true pelvis)
What is the pelvic brim?
The bony edge surrounding and defining the pelvic inlet.
It is formed by the promontory and ala of the sacrum and the linea terminalis.
What defines the pelvic outlet?
- Pubic arch anteriorly
- Ischial tuberosities laterally
- Inferior margin of the sacrotuberous ligament posterolaterally
- Tip of the coccyx posteriorly
What is the difference between greater and lesser pelvis?
Greater pelvis is superior to the pelvic inlet and contains abdominal viscera; lesser pelvis is between the pelvic inlet and outlet and includes the true pelvic cavity.
The lesser pelvis is significant in obstetrics and gynecology.
What are the sexual differences in the pelvic girdle?
- Male pelvis: thick and heavy, narrow and deep lesser pelvis, heart-shaped pelvic inlet
- Female pelvis: thin and light, wide and shallow lesser pelvis, oval pelvic inlet
What are the primary joints of the pelvic girdle?
- Sacro-iliac joints
- Pubic symphysis
What is the role of the sacro-iliac joints?
They link the axial skeleton to the inferior appendicular skeleton and transmit weight from the body to the hip bones.
These joints allow limited mobility necessary for stability.
True or False: The pelvic girdle is more rigid than the pectoral girdle.
True
Fill in the blank: The __________ forms the floor of the true pelvic cavity.
musculofascial pelvic diaphragm
What is the shape of the pelvic inlet in males?
Heart-shaped and narrow.
What is the shape of the pelvic inlet in females?
Oval and rounded; wide.
What are the features of the ilium?
- Superior, fan-shaped part of the hip bone
- Iliac crest
- Iliac fossa
- Auricular surface
- Iliac tuberosity
What is the ischial tuberosity?
The large postero-inferior protuberance of the ischium.
It serves as a point of attachment for muscles and ligaments.
What determines the width of the subpubic angle?
The distance between the right and left ischial tuberosities.
What is the plural of ilium?
ilia
What ligaments attach the sacrum to the iliac bones?
posterior and interosseous sacro-iliac ligaments
What type of joint is the sacro-iliac joint?
synovial joint
What is the primary function of the interosseous sacro-iliac ligaments?
Transferring weight from the axial skeleton to the ilia
True or False: The anterior sacro-iliac ligaments are the posterior external continuation of fibrous tissue.
False
What do the iliolumbar ligaments serve as in the sacro-iliac joint mechanism?
Accessory ligaments
What ligament transforms the sciatic notch into a large sciatic foramen?
sacrotuberous ligament
What are the two foramina created by the sacrotuberous and sacrospinous ligaments?
greater and lesser sciatic foramina
What type of movements are allowed at the sacro-iliac joint?
Slight gliding and rotary movements
What happens to the sacrum during exceptional force transmission from the lumbar vertebrae?
The superior end of the sacrum is pushed inferiorly and anteriorly
What helps prevent the superior and posterior rotation of the sacrum?
sacrotuberous and sacrospinous ligaments
What does the pubic symphysis consist of?
A fibrocartilaginous interpubic disc and surrounding ligaments
What is the difference in the interpubic disc between men and women?
It is generally wider in women
What are the two ligaments associated with the pubic symphysis?
- Superior pubic ligament
- Inferior (arcuate) pubic ligament
How do the iliolumbar ligaments contribute to the lumbosacral joints?
They strengthen the joints by radiating from the transverse processes of L5 to the ilia
What type of joint is the sacrococcygeal joint?
secondary cartilaginous joint
What reinforces the sacrococcygeal joint?
Anterior and posterior sacrococcygeal ligaments
Fill in the blank: The _______ connects the superior aspects of the pubic bodies.
superior pubic ligament
What is the role of the interpubic disc in the pubic symphysis?
Unites the bodies of the pubic bones in the median plane
Fill in the blank: The inferior pubic ligament rounds off the _______ as it forms the apex of the pubic arch.
subpubic angle
What is the normal female pelvic type called?
Gynecoid pelvis
The gynecoid pelvis typically has a rounded oval shape and a wide transverse diameter.
What are the common types of pelvic shapes in males?
A and C
These shapes are most common in males according to the variations in pelvic types.
What is the narrowest fixed distance through which a baby’s head must pass during vaginal delivery?
True (obstetrical) conjugate
This is measured from the middle of the sacral promontory to the posterosuperior margin of the pubic symphysis.
How is the diagonal conjugate measured?
By palpating the sacral promontory and marking the level of the pubic symphysis
The distance between the tip of the index finger and the marked level estimates the true conjugate.
What is the interspinous distance in the pelvic canal?
The narrowest part of the pelvic canal
This distance is not fixed and can change during late pregnancy.
What type of trauma commonly produces fractures of the pubic rami?
Anteroposterior compression of the pelvis
This can occur during crush accidents.
Which areas of the pelvis are weak and prone to fractures?
- Pubic rami
- Acetabula
- Sacro-iliac joints
- Alae of the ilium
These are common sites for fractures due to their structural vulnerabilities.
What can pelvic fractures cause in terms of injury?
Injury to pelvic soft tissues, blood vessels, nerves, and organs
This includes potential ruptures or tears in the urinary bladder and urethra.
What happens to the pelvic ligaments during late pregnancy?
They relax due to increased levels of sex hormones and relaxin
This relaxation allows for increased movement at the pelvic joints.
What is spondylolysis?
A defect allowing part of a vertebral arch to be separated from its body
This condition specifically affects the vertebra L5.
What occurs in spondylolisthesis?
The body of L5 vertebra may slide anteriorly on the sacrum
This can reduce the AP diameter of the pelvic inlet and interfere with childbirth.
How do obstetricians test for spondylolisthesis?
By running fingers along the lumbar spinous processes
An abnormally prominent L5 process suggests anterior movement relative to the sacrum.
What is the primary focus of attention in forensic medicine regarding skeletal remains?
Diagnosis of sex through the pelvic girdle
Sexual differences in the pelvic girdle are usually clearly visible.
What can cause pelvic fractures aside from direct trauma?
Forces transmitted from the lower limbs during falls
This includes falls on the feet.
What anatomical changes occur to the interpubic disc during pregnancy?
It increases in size, contributing to increased flexibility of the pubic symphysis
This change facilitates the passage of the fetus.
What is the effect of relaxation of sacro-iliac ligaments during pregnancy?
Greater rotation of the pelvis and increased lordotic posture
This occurs due to the change in the center of gravity.
