OSTEOLOGY OF ABDOMEN AND PELVIS

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Q.1 How the sacrum is formed?

By the fusion of 5 sacral vertebrae.

Q.2 What is the anatomical position of the sacrum in the body?

• Pelvic surfaces downwards and forwards.
• The upper surface of the body of the first sacral vertebra slopes forward at an angle of about 30 degrees.
• The upper end of the sacral canal is directed upwards and slightly backward.
  
  

Q.3 What are the relations and attachments of the ala of sacrum?

• Smooth medial part:
  Related to
  – Sympathetic chain,
  – Median sacral vessels
  – Right and left sacral vessels
  – Superior rectal vessels and lumbosacral trunk
  
  All are covered by the psoas major muscle.

• Rough lateral part:
  – Origin to iliacus
  – Attachment to iliolumbar ligament

• Margins:
  Ventral sacroiliac ligament
  
  

Q.4 What are the relations of the pelvic surface of the sacrum?

• Median sacral vessels:
  In median plane
  
  
• Sympathetic trunk:
  The medial margin of pelvic foramina.
  
  
• Peritoneum:
  In front of the upper 3 pieces, interrupted obliquely by the medial limb of the sigmoid mesocolon.
  
  
• Rectum:
  In front of lower 3rd pieces, separated at S3 by bifurcation of the superior rectal artery.
  
  

Q.5 How ‘Sacral hiatus’ is formed?

By failure of fusion of laminae of S5 vertebrae posteriorly.

Q.6 Name the structures emerging at the sacral hiatus.

• 5th sacral nerve.
• Coccygeal nerves.
• Filum terminal.
  
  

Q.7 What is the origin of erector spinae?

It has a linear U-shaped origin from the dorsal aspect of the sacrum. The medial limb of the U is attached to the spinous tubercles and the lateral limb to the transverse tubercles.

Q.8 How will you identify the lumbar vertebra?

• The large size of body
• Absence of costal facets on the body
  
  

Q.9 Name the structures attached to the spine of the lumbar vertebra.

• The posterior layer of lumbar fascia Interspinous ligament
• Supraspinous ligament
• Erector spinae muscle
• Multifidus muscle
• Interspinalis muscle
  
  

Q.10 What is ‘Sacralisation of lumbar vertebra’?

Fusion of the L5 vertebra or its transverse process on one or both sides with the sacrum.

Q.11 What is ‘spina Bifida?

Failure of the posterior fusion of two halves of the neural arch with each other results in a bony gap. Through the gap, the meninges and spinal cord may herniate out in the mid-line.

Q.12 How will you differentiate between male and female sacrum?

	Male sacrum	Female sacrum
Length and breadth	Longer and narrower	Shorter and wider
Body and ala	Transverse diameter of the body of S1 is larger than that of ala	The transverse diameter of the body is of S1 equal to the width of the ala
Auricular surface	Dorsal concavity is less marked	Dorsal concavity is more marked.
Pelvic curve	Sacrum more uniformly curved, and concavity is shallower	Curvature is irregular, concavity is deeper.

BONY PELVIS

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Q.1 How the bony pelvis is placed in anatomical position?

• The pelvic surface of the pubic symphysis faces backward and upwards.
• The plane of the pelvic inlet faces forwards and upwards at an angle of 50°–60° with horizontally.
• The plane of the pelvic outlet makes an angle of 15° with horizontal.
• The upper end of the sacral canal is directed upwards.
  
  

Q.2 What are the parts of the pelvis?

The pelvis is divided by the pelvic brim (pelvic inlet) into two parts:

• Greater (false) pelvis: upper part and
• Lesser (true) pelvis: the lower part
  
  

Q.3 What are the boundaries of the pelvic inlet (superior pelvic aperture)?

Anteriorly: Upper margin of the pubic symphysis.

Posteriorly: Sacral promontory.

On each side:
Anterior margin of the ala of sacrum, and linea terminales which includes an arcuate line of the ilium, pectineal line of the pubis, and pubic crest.

Q.4 What are the boundaries of the inferior pelvic aperture?

Anteriorly: Pubic arch

Posteriorly: Lateral margin of sacrum and coccyx

On each side:
Ischial tuberosity, lesser sciatic notch, ischial spine, and greater sciatic notch.

The lateral margin is formed by the sacrotuberous ligament.

Q.5 What is the axis of the pelvis?

This is an imaginary line joining the central points of anteroposterior diameters of the pelvic outlet and inlet. It is J-shaped, directed first downwards and backward and then downwards and forwards.

Q.6 How will you differentiate between male and female pelvis?

	Male pelvis	Female pelvis
General Features	Heavier and stronger	Lighter and thinner
	Bony markings: More prominent	Less prominent.
Ilia	Less vertical	More vertical
	Greater in height	Lesser in height
Iliac fossae:	Deeper	Shallower
Intercristal diameter:	Greater	Smaller
Pelvic inlet	Smaller and heart-shaped.	Larger and more circular.
Body of S1 vertebra forms:	Pubic tubercles are nearer because the pubic crest is narrower.	Pubic tubercles are wider apart because the pubic crest is longer.
	More than the width of the lateral part	Equal to the width of the lateral part
Pelvic outlet	Smaller	Larger
Sub-pubic angle:	50-60°	80-85°
Ischial tuberosities:	Less everted	More everted
Coccyx:	Less vertical	More vertical
Sciatic notches
Greater sciatic notch:	Narrower	Wider
Ischial spines:	Closer and inturned	Wider apart
Pelvic walls
Concavity of sacrum:	Shallower	Deeper
Sacrum:	Long and narrow	Short and wide
Obturator foramen:	Larger and ovoid	Smaller and triangular
Acetabulum:	Larger and faces fewer forwards	Smaller and faces more forwards
Puboischial index:	< 90	> 90
Pelvic cavity	Longer and more conical	Shorter and cylindrical

 

Q.7 What is the diagonal conjugate of the pelvis?

The diagonal conjugate is an anteroposterior diameter between the sacral promontory and pubic symphysis. This is normally at least 11.5 cm.

Q.8 What is the normal shape of the female pelvis and what are the different variations in it?

• Gynaecoid:
  Normally pelvic inlet is oval and the transverse diameter is slightly larger than the anteroposterior (AP) diameter. Seen in 41 percent.
  
  
• Android:
  Resembles triangular male pelvis and transverse diameter is more posteriorly placed than in the female. Seen in 33 percent.
  
  
• Anthropoid:
  Long and narrow pelvis. AP diameter is more than the transverse diameter. Seen in 24 percent.
  
  
• Platypelloid:
  AP diameter is small but the transverse diameter of the inlet is normal, i.e. pelvis appears flattened.

 

JOINTS OF PELVIS

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Q.1 Name the joints of the pelvis

• Lumbosacral joint
• Sacrococcygeal joint
• Intercoccygeal joint
• Sacro-iliac joint
• Pubic symphysis
  
  

Q.2 Name the ligaments of the sacrococcygeal joint.

• Ventral
• Deep dorsal
• Superficial dorsal
• Sacrococcygeal ligament
• Lateral
• Intercornual ligament
  
  

Q.3 What variety of joint pubic symphysis is?

Secondary cartilaginous joint

Q.4 Name the ligaments of the sacroiliac joint.

• Ventral
• Dorsal sacroiliac ligament
• Interosseous
• Sacrotuberous ligament
• Sacrospinous ligament