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Bony Pelvis

 

  • Must know

    1. Bones forming bony pelvis

    2. Joints of bony pelvis

    3. Ligaments of bony pelvis

    4. Boundaries of pelvic inlet

    5. Boundaries of pelvic outlet

    6. Differences between male and female pelvis

    7. Types of female bony pelvis

    8. Important dimensions of pelvic inlet, pelvic cavity and pelvic outlet.

 

 

 

 

                                                              

 

Functions of the Pelvis

  • Transfers weight from  axial sketeton to the lower limb.

  • Provides attachment for  muscles and ligaments.

  • Contains and protects visera.

1a. Bones forming pelvis

  •  4 bones:

    1. 2 Hip / innominate bones

    2. 1 Sacrum: Formed from 5 sacral vertebrae which fuse. 

    3. 1 coccyx: Formed from 4 fused vertebrae.

 

 

 

 

 

 

                                                            

1b.HIP BONE

  • Is made up of three parts:

    • Ilium

    • Pubis

    • Ischium

  • The three parts fuse by 16 years of age

 

 

  2. Joints of Pelvis

         (All are Secondary  cartilaginous joints except sacroiliac)

  1. Lumbosacral joint:  secondary cartilaginous joint  between  5th lumbar vertebra and  sacrum.

  2. Sacrococcygeal joint:  secondary cartilaginous joint between  sacrum and coccyx. 

  3. Sacro-iliac joints : plane synovial articulations between auricular surfaces of the sacrum and ilium on each side ((transmit weight of body from vertebral column to pelvic girdle)

  4. Pubic symphysis: secondary cartilaginous joint between  bodies of the pubic bones in the median plane. The symphysial surfaces, each covered by hyaline cartilage, are united by an interpubic disc of fibrocartilage.                                               

3.  Ligaments 

  • Include  sacrotuberous, sacrospinous,  iliolumbar and sacroiliac (ventral, introsseous & dorsal) ligaments.

  • Sacrotuberous ligament (ST) : extends from  dorsal surface ofthe sacrum (as well as from the ilium and coccyx) to the ischial tuberosity.

  • Sacrospinous ligament(SS) : extends from  lateral margin of  sacrum (and coccyx) to the ischial spine.

 

The sacrotuberous and sacrospinous ligaments converts the sciatic notches into  

  • greater  sciatic foramen(GSF) and

  • lesser sciatic foramen(LSF) 

 

                                             

Greater (False) and Lesser(True)Pelvis

  • Pelvis is divided by an oblique plane passing through the sacral pomontary, ala of sacrum, arcuate and pectineal lines, pubic crest  and the upper margin of the symphysis pubis, into the greater (false) and the lesser (true) pelvis.

  • The circumference of this plane is termed  pelvic brim.

 

 

SP - Sacral promontary

AS - Ala of Sacrum

AL- Arcuate Line

PL- Pecineal Line

PC - Pubic Crest

PS - Pubic Symphysis

 

 

Greater (Pink) and Lesser (Blue) Pelvis

LESSER /TRUE PELVIS

Pelvic Outlet Boundaries

 

 

  • Anteriorly: pubic symphysis,

  • Anterolaterally: right and left ischiopubic rami.

  • Laterally:  ischial tuberosities,

  • Posterolaterallysacrotuberous ligaments

  • Posteriorly: tip of the coccyx.

 

 

                                                              

Pelvic Inlet Boundaries

 

  • Posteriorly: Sacral promontary and anterior margins of ala of sacrum.

  • Laterally: Arcuate and pectineal lines.

  • Anteriorly: Upper margin of pubic symphysis, pubic crest and pubic symphysis.                                                   

  • The lesser or true  pelvis has an

    • inlet,

    • a cavity, and

    • an outlet,

    • each of  the above has three main diameters:

      • anteroposterior (or conjugate) ,

      • oblique, and

      • transverse

 Important dimensions of plevic inlet, pelvic cavity and pelvic outlet

  Plevic inlet

 Pelvic outlet

Differences between male and female pelvis                                                              

   Types of Pelvis

 

The four basic types of pelvis are classified as follows:

 

1. Gynecoid (the classic female type)

2. Android (resembling the male pelvis)

3. Anthropoid (resembling the pelvis of anthropoid apes)

4. Platypelloid (the flat pelvis)

 

The gynecoid pelvis is the most common, with major gynecoid pelvic features present in 50% of all women. Anthropoid and android features are less common, and platypelloid pelvic features are the least common.

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